Researcher Database

Researcher Profile and Settings

Master

Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Integrated Systems Engineering

Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Integrated Systems Engineering

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Motohisa
  • Name (Kana)

    Junichi
  • Name

    200901043991039324

Alternate Names

Achievement

Research Interests

  • 選択成長   有機金属気相成長   量子ドット   結晶成長   半導体   フォトニック結晶   表面超格子   フォトルミネセンス   ヘテロ構造   論理回路   半導体ナノワイヤ   有機金属気相成長法   再成長   マスクパターン   線欠陥・点欠陥導入構造   スーパーアトム   人工結晶   多段原子ステップ   光取り出し効率   原子ステップ   顕微フォトルミネセンス   ナノ構造周期配列構造   人工原子   フォトニックバンドギャップ   単一光子光源   加工基板   3角格子   時間領域差分(FDTD)法   電界効果トランジスタ   フォトニック結晶スラブ   半導体デバイス   半導体物性   半導体ナノ構造   半導体結晶成長   

Research Areas

  • Nanotechnology/Materials / Optical engineering and photonics
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering
  • Nanotechnology/Materials / Crystal engineering
  • Nanotechnology/Materials / Applied materials

Research Experience

  • 2020/04 - Today Hokkaido University Research Center for Integrated Quantum Electronics Director
  • 2006/04 - Today Hokkaido University
  • 2001/04 - 2006/03 Hokkaido University Research Center for Integrated Quantum Electronics
  • 1994/04 - 2001/03 Hokkaido University
  • 1993/04 - 1994/03 Hokkaido University

Published Papers

  • Masahiro Sasaki, Tomoya Akamatsu, Katsuhiro Tomioka, Junichi Motohisa
    Nanotechnology 35 (19) 195604 - 195604 0957-4484 2024/02/20 [Refereed]
     
    Abstract We carried out in situ annealing of InP nanowires (NWs) in a metal-organic vapor phase epitaxial (MOVPE) growth reactor to control and reduce the tip size of InP NWs. InP NWs were grown by selective-area (SA) MOVPE on partially masked (111)A InP substrates, and annealing was successively applied in tertiarybutylphosphine (TBP) ambient. Initially, the InP NWs had a hexagonal cross-section with $\{11\bar{2}\}$ facets vertical to the substrates; they became tapered, and the edges were rounded by annealing. By appropriately selecting the annealing temperature and initial NW diameter, the tip size of the NW was reduced and NWs with a tip size of 20 nm were successfully formed. Subsequently, a thin InAsP layer was grown on the annealed NWs and their photoluminescence was investigated at low temperatures. The characterization results indicated the formation of InAsP quantum dots (QDs) emitting in the telecom band. Our approach is useful for reducing the size of the NWs and for the controlled formation of InAsP QDs embedded in InP NWs in photonic devices compatible with telecom bands.
  • Junichi Motohisa, Akamatsu Tomoya, Okamoto Manami, Tomioka Katsuhiro
    Japanese Journal of Applied Physics 63 (3) 03SP08 - 03SP08 0021-4922 2024/02/08 [Refereed]
     
    Abstract We report the growth and characterization of InP/InAsP/InP nanowires (NWs) and NW LEDs (NW-LEDs), which emit light at telecom wavelengths. InP-based NWs were grown by selective-area metal-organic vapor-phase epitaxy, and a thin InAsP layer was embedded in the NWs. The NW exhibited emission lines in their low-temperature photoluminescence spectra, suggesting the formation of quantum dots (QDs) in the NW. NW-LED operation was demonstrated at both room and low temperatures in the telecom band, but it was found that the emission wavelength range and blueshift behavior induced by current injection differed considerably between room and low temperatures. Our results suggest that an efficient path for carrier injection into the active InAsP layer should be explored for NW-QD-based single-photon sources operating via current-injection.
  • Hironori Gamo, Chen Lian, Junichi Motohisa, Katsuhiro Tomioka
    ACS Nano 1936-0851 2023/08/24
  • Katsuhiro Tomioka, Kazuharu Sugita, Junichi Motohisa
    Advanced Photonics Research 4 (7) 2699-9293 2023/04/20 [Refereed][Not invited]
     
    Nanometer‐scaled light sources using III–V compound semiconductor nanowires (NWs) on Si are expected as building blocks for next‐generation Si photonics, bioimaging, on‐chip microscopy, and light detection and ranging (LiDAR) techniques. This is, however, limited in a few materials systems due to complexity in integration of the vertical III–V NWs on Si and device process flow. Suppressing optical loss in the NW materials beyond the optical diffraction remains difficult in enhancing light extraction. Herein, the effect of the vertical metal‐clad architectures for the vertical nano‐light‐emitting diodes (LEDs) using GaAs/GaAsP‐related core–multishell NWs heterogeneously integrated on Si is investigated. The grown core–multishell NW is composed of a radial n‐GaAs/n‐GaAsP/p‐GaAs/p‐GaAsP double heterostructure. The vertical metal‐clad NW‐LEDs show suppression of carrier overflow effect and rapid enhancement of electrical luminescence.
  • Taiga Kunimoto, Shizuka Obara, Shinjiro Hara, Junichi Motohisa
    Japanese Journal of Applied Physics 62 (SC) SC1072 - SC1072 0021-4922 2023/02/17 [Refereed][Not invited]
     
    Abstract We investigated the beam profiles and polarization states in the low-temperature photoluminescence from vertical GaAs/InGaAs/GaAs core-multishell nanowire (NW) under continuous-wave and pulsed excitations. In the beam profile under pulsed excitation, a doughnut-shaped intensity distribution was confirmed. The beam was shown to exhibit an axisymmetric distribution in the polarization. These observations indicate that cylindrical vector beams were generated from the NW. The observed polarization did not correspond to low-order vector beams but suggested the generation of higher-order beams.
  • Yuki Azuma, Shun Kimura, Hironori Gamo, Junichi Motohisa, Katsuhiro Tomioka
    Japanese Journal of Applied Physics 62 (SC) SC1011 - SC1011 0021-4922 2022/12/30 [Refereed][Not invited]
     
    Abstract We characterized the current injection and electroluminescence (EL) properties of wurtzite (WZ) InP nanowire (NW) light-emitting diodes (LEDs) with axial junctions. The EL spectra of two samples with the same LED junction structure exhibited two different behaviors. One showed a single EL peak originating from the zinc-blende (ZB)-InP bandgap. The other showed two EL peaks originating from the ZB and WZ phases. This difference in EL behavior is attributed to the difference in the contact position and to depletion layer spreading. Clarification of the origin of the different EL peaks is important for optimizing the NW-LED structure.
  • S. Kimura, H. Gamo, Y Katsumi, J. Motohisa, K. Tomioka
    Nanotechnology 33 (30) 305204  2022/05 [Refereed]
  • Akinobu Yoshida, Hironori Gamo, Junichi Motohisa, Katsuhiro Tomioka
    Scientific Reports 12 (1) 2022/01 
    AbstractHeteroepitaxy has inherent concerns regarding crystal defects originated from differences in lattice constant, thermal expansion coefficient, and crystal structure. The selection of III–V materials on group IV materials that can avoid these issues has however been limited for applications such as photonics, electronics, and photovoltaics. Here, we studied nanometer-scale direct integration of InGaAs nanowires (NWs) on Ge in terms of heterogenous integration and creation of functional materials with an as yet unexplored heterostructure. We revealed that changing the initial Ge into a (111)B-polar surce anabled vertical InGaAs NWs to be integrated for all In compositions examined. Moreover, the growth naturally formed a tunnel junction across the InGaAs/Ge interface that showed a rectification property with a huge current density of several kAcm−2 and negative differential resistance with a peak-to-valley current ratio of 2.8. The described approach expands the range of material combinations for high-performance transistors, tandem solar cells, and three-dimensional integrations.
  • Michihito Shimauchi, Kazuki Miwa, Masachika Toguchi, Taketomo SATO, Junichi Motohisa
    Applied Physics Express 1882-0778 2021/10/06 [Refereed][Not invited]
  • Katsuhiro Tomioka, Hironori Gamo, Junichi Motohisa, Takashi Fukui
    2020 IEEE International Electron Devices Meeting (IEDM) 2020/12/12 [Not refereed]
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    Scientific Reports 10 (1) 2020/12 [Refereed][Not invited]
  • Tomoya Akamatsu, Katsuhiro Tomioka, Junichi Motohisa
    Nanotechnology 31 (39) 394003 - 394003 0957-4484 2020/09/25 [Refereed][Not invited]
  • Yoshiki Tai, Hironori Gamo, Junichi Motohisa, Katsuhiro Tomioka
    ECS Transactions 98 (6) 149 - 153 2020/09/23 [Not refereed]
  • Katsuhiro Tomioka, Fumiya Ishizaka, Junichi Motohisa, Takashi Fukui
    Applied Physics Letters 117 (12) 123501 - 123501 0003-6951 2020/09/21 [Refereed][Not invited]
  • Junichi Motohisa, Jun OHTA, Kenichi KAWAGUCHI, Seiya KASAI
    Japanese Journal of Applied Physics 2020/04/28
  • Junichi Motohisa, Hiroki Kameda, Masahiro Sasaki, Katsuhiro Tomioka
    Nanotechnology 30 (13) 134002 - 134002 0957-4484 2019/03/29 [Refereed][Not invited]
  • Kohei Chiba, Akinobu Yoshida, Katsuhiro Tomioka, Junichi Motohisa
    ACS Photonics 6 (2) 260 - 264 2330-4022 2019/02/20 [Refereed]
  • K. Tomioka, H. Gamo, J. Motohisa
    ECS Transactions 92 (4) 71 - 78 1938-5862 2019 
    Millivolt switches based on non-thermionic transport mechanism must demonstrate a steep slope (small gate bias swing), moderate conductance, high efficiency, and rational integration scheme including high density with complementary operation toward low-power integrated circuits. Because these inherent requirements can be satisfied by a vertical III-V nanowire (NW) channel with a surrounding-gate structure and a heterojunction underneath the NWs. Here we report on vertical tunnel field-effect transistor (TFET) technologies using III-V nanowire/Si heterojunctions.
  • Yusuke Minami, Akinobu Yoshida, Junichi Motohisa, KatsuhiroTomioka
    Journal of Crystal Growth 506 135 - 139 2019/01 [Refereed][Not invited]
  • Kohei Chiba, Katsuhiro Tomioka, Akinobu Yoshida, Junichi Motohisa
    AIP ADVANCES 7 (12) 125304  2158-3226 2017/12 [Refereed][Not invited]
     
    Composition controllability of vertical InGaAs nanowires (NWs) on Si integrated by selective area growth was characterized for Si photonics in the optical telecommunication bands. The pitch of pre-patterned holes (NW sites) changed to an In/Ga alloy-composition in the solid phase during the NW growth. The In composition with a nanometer-scaled pitch differed completely from that with a mu m-scaled pitch. Accordingly, the growth morphologies of InGaAs NWs show different behavior with respect to the In/Ga ratio. (c) 2017 Author(s).
  • Akinobu Yoshida, Katsuhiro Tomioka, Fumiya Ishizaka, Junichi Motohisa
    JOURNAL OF CRYSTAL GROWTH 464 75 - 79 0022-0248 2017/04 [Refereed][Not invited]
     
    We report the growth of InGaAs nanowires (NWs) on Ge(111) substrates using selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) for novel InGaAs/Ge hybrid complementary metal-oxide-semiconductor (CMOS) applications. Ge(111) substrates with periodic arrays of mask opening were prepared, and InGaAs was selectively grown on the opening region of Ge(111). A uniform array of InGaAs NWs with a diameter around 100 nm was successfully grown using appropriate preparation of the initial surfaces with an AsH3 thermal treatment and flow-rate modulation epitaxy (FME). We found that optimizing partial pressure of AsH3 and the number of FME cycles improved the yield of vertical InGaAs NWs. Line-scan profile analysis of energy dispersive X-ray (EDX) spectrometry showed that the In composition in the InGaAs NW was almost constant from the bottom to the top. Transmission electron microscope (TEM) analysis revealed that the interface between InGaAs NW and Ge had misfit dislocations, but their distance was longer than that expected from the difference in their lattice constants.
  • Shougo Yanase, Hirotaka Sasakura, Shinjiro Hara, Junichi Motohisa
    JAPANESE JOURNAL OF APPLIED PHYSICS 56 (4) 04CP04  0021-4922 2017/04 [Refereed][Not invited]
     
    We attempted to control the density and size of InP-based nanowires (NWs) and nanowire quantum dots (NW-QDs) during selective-area metalorganic vapor phase epitaxy. InP nanowire arrays with a 5 mu m pitch and an average NW diameter d of 67nm were successfully grown by optimization of growth conditions. InAsP quantum dots were embedded in these density-controlled InP NW arrays, and clear single-photon emission and exciton-biexciton cascaded emission were confirmed by excitation-dependent photoluminescence and photon correlation measurements. (C) 2017 The Japan Society of Applied Physics
  • Fumiya Ishizaka, Yoshihiro Hiraya, Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    NANO LETTERS 17 (3) 1350 - 1355 1530-6984 2017/03 [Refereed][Not invited]
     
    We demonstrated the formation of all-wurtzite (WZ) InP/AlInP core-multishell (CMS) nanowires (NWs) by selective-area growth with the crystal structure transfer method. The CMS NWs consisting of an AlInP-based double heterostructure showed that the crystal structure of the multi shell succeeded to the WZ phase from the WZ InP NW by the crystal structure transfer method. Transmission electron microscopy revealed that the core shell interface had a few stacking faults due to lattice mismatch. In addition, lattice constants of WZ AlInP with a variation of Al content were determined by X-ray diffraction reciprocal space mappings, and the WZ AlInP shell had tensile strain along the c-axis. The WZ AlInP shells (Al content: 25-54%) showed cathode luminescence emissions at 1.6-2.1 eV, possibly related to In-rich domains due to composition fluctuation in the WZ AlInp shell.
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    Novel Compound Semiconductor Nanowires: Materials, Devices, and Applications 465 - 516 2017/01/01 
    III-V nanowires (NWs) are promising building blocks for future electronic and optical devices because they have the advantage of having a core-shell structure that can be used to build threedimensional (3D) devices not limited to being thin films. Position-and size-controlled NWs are very important for exploiting these benefits. In this chapter, we report on selective-area growth of III-V NWs and recent progress on NW-based transistor and photovoltaic devices.
  • Fumiya Ishizaka, Yoshihiro Hiraya, Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    Japanese Journal of Applied Physics 56 (1) 010311  1347-4065 2017/01/01 [Refereed][Not invited]
     
    We report on the selective-Area growth and characterization of wurtzite (WZ) InP/AlGaP core-multishell nanowires. Quantum well (QW) structures were fabricated in AlGaP multishells by changing the alloy composition. Transmission electron microscopy revealed that the AlGaP multishells were grown with a WZ structure on the side of the WZ InP core. The lattice constants of the WZ InP core and WZ AlGaP shell were determined by X-ray diffraction. Cathodoluminescence studies showed that the WZ AlGaP QW with an Al composition of 20% exhibited green emissions at 2.37 eV. These results open the possibility of fabricating green light-emitting diodes using WZ AlGaP-based materials.
  • Katsuhiro Tomioka, Fumiya Ishizaka, Junichi Motohisa, Takashi Fukui
    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016 [Refereed][Not invited]
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    2016 46TH EUROPEAN SOLID-STATE DEVICE RESEARCH CONFERENCE (ESSDERC) 397 - 402 1930-8876 2016 [Refereed][Not invited]
     
    Tunnel FETs (TFETs) with steep subthreshold slope have been attracting much attention as building blocks for future low-power integrated circuits and CMOS technology devices. Here we report on recent advances in vertical TFETs using III-V/Si heterojunctions. These heterojunctions, which are formed by direct integration of III-V nanowires (NWs) on Si, are promising tunnel junction for achieving steep subthreshold slope (SS). The III-V/Si heterojunction inherently forms abrupt junctions regardless of precise doping technique because the band discontinuity is determined by only the offset of III-V and Si, and depletion region can be controlled by the III-V MOS structure. Thus, good gate-electrostatic control with a large internal electrical field for modulation of tunnel transport can be achieved. Here we repot on recent advances in the vertical TFETs using the III-V NW/Si heterojunction with surrounding-gate architecture and demonstrate steep-SS behavior and very low parasitic leakage current.
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    SEMICONDUCTORS, DIELECTRICS, AND METALS FOR NANOELECTRONICS 14 75 (5) 127 - 134 1938-5862 2016 [Refereed][Not invited]
     
    Tunnel field-effect transistors (TFETs) with a steep subthreshold-slope (SS) are promising low-power switches for future large-scale integrated circuits (LSIs) with low power consumption and high performance. Recently, we demonstrated vertical TFETs with III-V/Si heterojunctions. This new sort of tunnel junction achieves a steep SS because of its unique figure-of-merit. Here, we report on recent progress on vertical TFETs using Si/III-V heterojunctions and means for boosting on-state current.
  • Naoto Tamaki, Akihito Sonoda, Aya Onodera, Junichi Motohisa
    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016 [Refereed][Not invited]
  • Akinobu Yoshida, Katsuhiro Tomioka, Fumiya Ishizaka, Kohei Chiba, Junichi Motohisa
    SEMICONDUCTORS, DIELECTRICS, AND METALS FOR NANOELECTRONICS 14 75 (5) 265 - 270 1938-5862 2016 [Refereed][Not invited]
     
    III-V compound semiconductors and Ge are promising future channel materials because of their high carrier mobility. For example the electron mobility of InAs is about 20 times faster than that of Si at room temperature and hole mobility of Ge is about 5 times faster than that of Si. In this paper, we report direct integration of InGaAs nanowires (NWs) on Ge(111) substrate by selective-area metal organic vapor phase epitaxy (SA-MOVPE) for realization of high carrier mobility InGaAs/Ge hybrid CMOS applications, and characterization of the composition and growth modes of InGaAs NWs by X-ray diffraction (XRD) measurement.
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    International Symposium on VLSI Technology, Systems, and Applications, Proceedings 2015- 1930-8868 2015/06/03 [Refereed][Not invited]
     
    MOSFETs using III-V channels with multi-gate architecture and tunnel junctions are promising alternative building blocks for highperformance and low power nanoelectronic circuits. CMOS. In this paper, we review recent advances in direct integration of vertical III-V nanowire (NW)-channel on Si and FET application such as vertical III-V NW surrounding-gate transistors (SGTs) and tunneling FET (TFETs) using III-V NW/Si heterojunctions.
  • Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    ECS Transactions 69 (10) 109 - 118 1938-5862 2015 [Refereed][Not invited]
     
    Tunnel field-effect transistors (TFETs) have been attracting much attention as building-blocks for future low-power integrated circuits. Here we report recent progress in TFETs with surrounding-gate architecture and III-V nanowire/Si heterojunctions. We also discuss guidelines or obtaining steep-slope turn-on behavior in these devices.
  • Daisuke Uchida, Masayuki Ikebe, Junichi Motohisa, Eiichi Sano
    Journal of Signal Processing 19 (6) 219 - 226 2015 [Refereed][Not invited]
  • Zhixin Cui, Rajagembu Perumal, Tomotsugu Ishikura, Keita Konishi, Kanji Yoh, Junichi Motohisa
    APPLIED PHYSICS EXPRESS 7 (8) 085001  1882-0778 2014/08 [Refereed][Not invited]
     
    InAs nanowire with < 110 > orientation is proposed for use as an electron spin transport channel for application to spintronics devices, particularly the Datta-Das spin transistor. Stable zinc blende crystal NWs were grown using a molecular beam epitaxy system. Subsequently, global back-gate NW field effect transistors were fabricated, and the superiority of the electrical transport properties within our resultant < 110 > NWs was demonstrated by comparing the field-effect mobility with a < 111 > NW control sample. Additionally, single NW Hall-bar devices were fabricated, which allowed us to obtain the transport properties accurately, and Hall effect measurements were successfully taken at different temperatures. (C) 2014 The Japan Society of Applied Physics
  • 自動しきい値補償型Dickson Charge Pumpによる整流特性の効率化
    謝侃, 池辺将之, 本久順一, 佐野栄一
    映情学技報 38 (26) 61 - 64 2014/07 [Not refereed][Not invited]
  • 間欠動作TDCを用いたシングルスロープADC構成の検討”
    染谷槙人, 内田大輔, 池辺将之, 本久順一, 佐野栄一
    映情学技報 38 (26) 51 - 54 2014/07 [Not refereed][Not invited]
  • Junichi Motohisa, Yoshinori Kohashi, Satoshi Maeda
    NANO LETTERS 14 (6) 3653 - 3660 1530-6984 2014/06 [Refereed][Not invited]
     
    We investigated far-field (FF) emission patterns of nanowire light-emitting diodes (NW-LEDs). NW-LEDs were fabricated using vertical InP-NW arrays with axial pn-junctions grown on InP (111)A substrates, and the emission intensity of NW-LEDs was measured as a function of view angle theta, where theta = 0 degrees indicates the direction normal to the substrate or that along the NWs. For NW arrays with pitch a of around 1 mu m, we found a clear dip in the emission intensity at theta = 0 degrees, which was explained by an analogy with dipole antenna, or a smaller contribution of the lowest order guided modes for emission as compared with higher order guided and free-space radiation modes. Results of the simulation of radiation patterns by the finite-difference time-domain method and near-field to far-field transformation are also described. They also confirm that the dip at 6 = 00 is specific to light emission from NWs. We also investigated the dependence of the FF pattern on the pitch of the NW array, and the observation was qualitatively explained by the relative contribution of the guided and free-space radiation modes.
  • Daisuke Uchida, Masayuki Ikebe, Junichi Motohisa, Eiichi Sano, Akira Kondou
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 (4) 04EE20  0021-4922 2014/04 [Refereed][Not invited]
     
    We propose an inductorless common-mode rejection filter with a gyrator-C network for common-mode-noise reduction. By adopting a gyrator-C network and ladder structure, high-order and small filter circuits with active transformer operation were fabricated. The filter was designed and fabricated in a Taiwan Semiconductor Manufacturing Company (TSMC) 0.18 mu m CMOS process. This filter exhibited a CMRR of 80 dB, output noise voltage of 103 nV/Hz(1/2), third-order input intercept point of 8.8 dBm at 1 MHz operation, and cutoff frequency of under 6 MHz. The total power consumption was 14.8 mW with a 2.5 V supply, and the chip area was 0.7 x 0.4 mm(2). (C) 2014 The Japan Society of Applied Physics
  • Y. Kohashi, S. Hara, J. Motohisa
    MATERIALS RESEARCH EXPRESS 1 (1) 015036  2053-1591 2014/03 [Refereed][Not invited]
     
    We grew gallium-rich (x > 0.50) and indium -rich (x < 0.50) Ini,GaxAs nano wires by catalyst free selective-area metal organic vapor-phase epitaxy (SAMOVPE), and compared their growth dynamics dependence on V/III ratio. It was found that the growth dynamics of In, GaxAs nanowires is clearly dependent on the alloy composition x. Specifically, for gallium rich nanowire growth, the axial growth rate of nanowires initially increased with decreasing V/III ratio, and then started to decrease when the V/III ratio continued to decrease below a critical value. On the other hand, axial growth rate of indium -rich nanowires monotonically decreased with decreasing V/III ratio. In addition, the alloy composition was strongly dependent on the V/III ratio for gallium -rich nanowire growth, while it was relatively independent of the V/III ratio for indium -rich nanowire growth. We discuss the origin of dissimilarity in the growth dynamics dependence on V/III ratio between gallium -rich and indium rich InGaAs nanowire growth, and conclude that it is due to the inherent dissimilarity between GaAs and InAs. Our finding provides important guidelines for achieving precise control of the diameter, height, and alloy composition of nanowires suitable for future nanowire-based electronics.
  • Daisuke Uchida, Masayuki Ikebe, Junichi Motohisa, Eiichi Sano
    2014 21ST IEEE INTERNATIONAL CONFERENCE ON ELECTRONICS, CIRCUITS AND SYSTEMS (ICECS) 770 - 773 2014 [Refereed][Not invited]
     
    We propose a single-slope ADC with an intermittent operational time-to-digital converter (TDC). Applying an n-bit TDC that uses a multi-phase-clock signal reduced the conversion time by a factor of 2(n), achieved timing consistency, and realized robust meta-stability. However, since a TDC needs to operate continuously, it required a large dissipation power. In this study, we focus on generating the PWM signal of a single-slope ADC and apply a scheme for limiting the TDC operation period in order to reduce TDC power dissipation. We designed and fabricated a 12-bit ADC, which consists of a 6-bit TDC and 6-bit-single-slope ADC, by using a 0.18-mu m CMOS process. The ADC, at 100 kS/s, consumes 5.5 mu W from a 1-V supply. Its INL and DNL were -1.9/ +1.9 LSB and -0.8/+0.5 LSB, respectively.
  • CMOS common-mode filter with gyrator-C network
    D. Uchida, M. Ikebe, J. Motohisa, E. Sano, A. Kondou
    Int'l Conf. Solid State Devices and Materials 886 - 887 2013/09 [Refereed][Not invited]
  • Yuta Kobayashi, Yoshinori Kohashi, Shinjiro Hara, Junichi Motohisa
    APPLIED PHYSICS EXPRESS 6 (4) 045001.1-045001.4  1882-0778 2013/04 [Refereed][Not invited]
     
    We attempted the selective-area metalorganic vapor-phase epitaxial (SA-MOVPE) growth of InAs nanowires (NWs) using a tungsten/dielectric composite mask and fabricated nanowire vertical surrounding-gate field-effect transistors (NW-VSG-FETs), where tungsten served as both the mask in SA-MOVPE growth and the bottom electrode of the FET. The growth of NWs with diameters as low as 100 nm was demonstrated using the composite mask. The fabricated NW-VSG-FET exhibited improved drain current density as compared with our previously reported NW-VSG-FETs, and a larger on/off ratio as compared with previously reported NW-VSG-FETs having similar electrodes at the bottoms of NWs. (C) 2013 The Japan Society of Applied Physics
  • Yoshinori Kohashi, Shinya Sakita, Shinjiroh Hara, Junichi Motohisa
    APPLIED PHYSICS EXPRESS 6 (2) 025502.1-025502.3  1882-0778 2013/02 [Refereed][Not invited]
     
    Control of the diameter and pitch of InGaAs nanowire arrays in selective-area metalorganic vapor-phase epitaxy was investigated. It was found that their nucleation was strongly dependent on the geometry of the mask, resulting in the difficulty of nucleation for a larger mask pitch, particularly for an opening diameter of less than 50 nm. Precise adjustment of the V/III ratio enabled us to control the nucleation independently of the mask pitch for smaller openings, and we successfully obtained 30-nm-diameter InGaAs nanowires independently of the mask pitch by the proposing V/III-ratio-controlled two-step growth method. (C) 2013 The Japan Society of Applied Physics
  • Yasuaki Masumoto, Ken Goto, Shinichi Tomimoto, Premila Mohan, Junichi Motohisa, Takashi Fukui
    JOURNAL OF LUMINESCENCE 133 135 - 137 0022-2313 2013/01 [Refereed][Not invited]
     
    Bimolecular interlayer scattering of electrons was observed in wurtzite InP/InAs/InP core-multishell nanowires by means of femtosecond up-conversion luminescence spectroscopy. Two-body Auger scattering took place in hexagonal InAs nanotubes constituting type-II quantum wires and wells. (c) 2011 Elsevier B.V. All rights reserved.
  • Junichi Motohisa, Yasufumi Fujiwara, Masakazu Sugiyama, Kiyoshi Yase, Seung Ki Joo, Jinho Ahn, Jeong Min Baik, Kyeong Jae Byeon, Sung Yoon Chung, Deok Kee Kim, Hyounwoo Kim, Ju Young Kim, Young Keun Kim, Ki Young Ko, Jung Hyuk Koh, Bon Heun Koo, Hee Chul Lee, Heon Lee, Jeong Hoon Lee, Sang Yeol Lee, Sunyoung Caroline Lee, Byungwoo Park, In Sung Park, Jeong Woong Park, Won Il Park, Wooyoung Yoon
    Japanese Journal of Applied Physics 52 (10 PART2) 0021-4922 2013 [Refereed][Not invited]
  • Junichi Motohisa
    2012 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM) 249 - 252 1092-8669 2013 [Refereed][Not invited]
     
    I describe our study on the growth of InP-based nanowires (NW) by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) and their optical properties. Vertically-aligned InP NWs were grown on InP (111) A oriented substrates, and they exhibited transition of crystal structures depending on the growth conditions. Laterally or vertically heterostructured NWs were also grown by SA-MOVPE based on InP NWs, and their optical properties were studied by using mu-PL measurement. InP NWs with a vertical pn-junction were also grown and was applied to NW light-emitting diodes (LEDs).
  • Junichi Motohisa, Kenji Hiruma
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 (11) 11PE07.1-11PE07.7  0021-4922 2012/11 [Refereed][Not invited]
     
    The light absorption of various types of semiconductor nanowire (NW) arrays for photovoltaic applications was calculated. The electromagnetic field in multilayer structures containing NW arrays was calculated by the scattering-matrix treatment developed by Whittaker and Culshaw [ Phys. Rev. B 60 (1999) 2610], and the absorptance spectra Ad (lambda) of the NW arrays were obtained from the transmittance and reflectivity of the structures. The ultimate efficiency eta and weighted average absorptance Aavr of the NW array solar cells were evaluated from Ad (lambda). A general tendency of the light absorption in NW arrays in relation to their structural parameters, such as the pitch a of an NW array and the size d of an NW, was identified, and the differences between the optimum structural parameters of NW arrays in terms of light absorption in the cases of InP, GaAs, Si, and Ge were determined. The maximum eta was obtained for a 375, 350, 700, and 400 nm, for InP, GaAs, Si, and Ge NW arrays with d= a 0: 5, respectively. Moreover, Aavr for multijunction structures consisting of GaAs and Ge NWs and GaAs NWs on a germaninum substrate was also calculated and showed that both of these structures exhibited good light trapping capabilities for photovoltaic applications. It is shown that the photogeneration profiles of carriers in two types of multijunction structures are different. (C) 2012 The Japan Society of Applied Physics
  • シングルスロープA/D変換器の高速化に向けたインターリーブ型ランプ波形発生器
    内田大輔, 池辺将之, 本久順一, 佐野栄一, 近藤亮
    映情学技報 36 (31) 45 - 48 2012/07 [Not refereed][Not invited]
  • インターリーブ動作による高速ランプ波形発生器
    内田大輔, 近藤 亮, 池辺将之, 本久順一, 佐野栄一
    LSIとシステムのワークショップ2012 228 - 229 2012/05 [Not refereed][Not invited]
  • Satoshi Maeda, Katsuhiro Tomioka, Shinjiroh Hara, Junichi Motohisa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 (2) 02BN03.1-02BN03.4  0021-4922 2012/02 [Refereed][Not invited]
     
    We fabricated nanowire light-emitting diodes (LEDs) using InP nanowires (NWs). Indium phosphide NWs with axial p-n junction were grown by selective-area metalorganic vapor phase epitaxy. The results of secondary-electron-microscopy (SEM) observation and photoluminescence measurement showed the formation of wurtzite InP NWs with some mixture of zincblende crystal phase, as expected from the used growth conditions. NW-LEDs were fabricated by sputtering indium tin oxide (ITO) after a planarization process for the top contact and AuZn evaporation for the backside contact. Current-voltage characterisitics showed clear rectifying characteristics with a small leakage current, and fairly linear current-light output characteristics were observed. By designing the pitch of the NW array, emission from individual NWs was confirmed, which opens the possibility for realizing a single NW-LED applicable to single-photon emitters. (C) 2012 The Japan Society of Applied Physics
  • Sasakura H., Dorenbos S. N., Akopian N., van Kouwen M. P., Motohisa J., Kobayashi Y., Kumano H., Kondo K., Tomioka K., Fukui T., Suemune I., Zwiller V.
    Phys. Rev. B American Physical Society 85 (7) 075324-1 - 075324-7 1098-0121 2012/02 [Refereed][Not invited]
     
    We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. Elongation of the transverse exciton-spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well explained by the motional narrowing mechanism induced by Gaussian fluctuations of environmental charges in the nanowire. The longitudinal exciton-spin relaxation time is evaluated by the degree of the random polarization of emission originating from exciton states confined in a single-nanowire quantum dot by using Mueller calculus based on Stokes parameters representation. The reduction in the random polarization component with decreasing excitation power is caused by suppression of the exchange interaction of electron and hole due to an optically induced internal electric field by the dipoles at the wurtzite and zinc-blende heterointerfaces in the InP nanowire.
  • Yoshinori Kohashi, Takuya Sato, Keitaro Ikejiri, Katsuhiro Tomioka, Shinjiroh Hara, Junichi Motohisa
    JOURNAL OF CRYSTAL GROWTH 338 (1) 47 - 51 0022-0248 2012/01 [Refereed][Not invited]
     
    Indium-rich InGaAs nanowires were grown on an InP (111)B substrate by catalyst-free selective-area metal-organic vapor phase epitaxy, and the growth-temperature dependence of growth rate and composition was studied. In particular, nanowire growth rate rapidly decreases as growth temperature increases. This tendency is opposite (for a similar temperature range) to that found in a previous study on selective-area growth of gallium-rich InGaAs nanowires. This difference between indium-rich and gallium-rich nanowires suggests that the influence of growth temperature on the growth of InGaAs nanowires is dependent on the group-III supply ratio. On the basis of previous experimental observations in InAs and GaAs nanowires, temperature dependence of nanowire growth rate and its dependence on group-III supply ratio are predicted. A guideline to determine the optimum growth conditions of InGaAs nanowires is also discussed. (C) 2011 Elsevier B.V. All rights reserved.
  • Kisu Kim, Masayuki Ikebe, Junichi Motohisa, Eiichi Sano
    2012 19th IEEE International Conference on Electronics, Circuits and Systems (ICECS) 512 - 515 2012 [Refereed][Not invited]
     
    We propose a multi-slope ADC with a Time to Digital Converter (TDC). In a single-slope ADC, when using a TDC that has resolution of n bits, the conversion time will be reduced by a factor of 2(n). Applying the TDC that uses the multi-phase-clock signal reduced the circuit areas of TDC by half, achieved timing consistency, and realized robust meta-stability. We also apply multi-slope scheme for reducing the ADC-operation cycles. We designed and fabricated an 11-bit ADC, by using a TSMC 0.18-mu m CMOS process. The ADC, at 100 kS/s, achieved SNDR of 59.6 dB (9.6 ENOB) and SFDR of 72.7 dB. Its INL and DNL were +1.32/-0.80LSB and +0.48/-0.37LSB, respectively. The entire ADC consumes 5.1 mu W from a 1-V supply.
  • A. Kondou, M. Ikebe, J. Motohisa, Y. Amemiya, E. Sano
    IEEE International Conference on Electronics, Circuits, and Systems 326 - 329 2011/12 [Refereed][Not invited]
  • Keitaro Ikejiri, Yusuke Kitauchi, Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui
    NANO LETTERS 11 (10) 4314 - 4318 1530-6984 2011/10 [Refereed][Not invited]
     
    Indium phosphide (InP) nanowires, which have crystal phase mixing and transition from zinc blende (ZB) to wurtzite (WZ), are grown in intermediate growth conditions between ZB and WZ by using selective-area metalorganic vapor phase epitaxy (SA-MOVPE). The shape of InP nanowires is tapered unlike ZB or WZ nanowires. A growth model has been developed for the tapered nanowires, which is simply described as the relationship between tapered angle and the ratio of ZB and WZ segments. In addition, the peak energy shift in photoluminescence measurement was attributed to the quantum confinement effect of the quantum well of the ZB region located in the polytypic structure of ZB and WZ in nanowires.
  • Katsuhiro Tomioka, Keitaro Ikejiri, Tomotaka Tanaka, Junichi Motohisa, Shinjiroh Hara, Kenji Hiruma, Takashi Fukui
    JOURNAL OF MATERIALS RESEARCH 26 (17) 2127 - 2141 0884-2914 2011/09 [Refereed][Invited]
     
    We review the position-controlled growth of III-V nanowires (NWs) by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). This epitaxial technique enables the positioning of the vertical NWs on (111) oriented surfaces with lithographic techniques. Core-shell structures have also been achieved by controlling the growth mode during SA-MOVPE. The core-shell III-V NW-based devices such as light-emitting diodes, photovoltaic cells, and vertical surrounding-gate transistors are discussed in this article. Nanometer-scale growth also enabled the integration of III-V NWs on Si regardless of lattice mismatches. These demonstrated achievements should have broad applications in laser diodes, photodiodes, and high-electron mobility transistors with functionality on Si not made possible with conventional Si-CMOS techniques.
  • H. Sasakura, C. Hermannstädter, S. N. Dorenbos, N. Akopian, M. P. van Kouwen, J. Motohisa, Y. Kobayashi, H. Kumano, K. Kondo, K. Tomioka, T. Fukui, I. Suemune, V. Zwiller
    Physical Review B 85, 075324/1-7 (2012) American Physical Society 85 (7) 75324 - 75324 1098-0121 2011/09 [Refereed][Not invited]
     
    We have investigated the optical properties of a single InAsP quantum dot
    embedded in a standing InP nanowire. A regular array of nanowires was
    fabricated by epitaxial growth and electron-beam patterning. The elongation of
    transverse exciton spin relaxation time of the exciton state with decreasing
    excitation power was observed by first-order photon correlation measurements.
    This behavior is well explained by the motional narrowing mechanism induced by
    Gaussian fluctuations of environmental charges in the InP nanowire. The
    longitudinal exciton spin relaxation time was evaluated by the degree of the
    random polarization of emission originating from exciton state confined in a
    single nanowire quantum dots by using Mueller Calculus based on Stokes
    parameters representation.
  • A 12b low power multi-slope ADC with time to digital converter
    K. Kim, M. Ikebe, A. Kondou, J. Motohisa, Y. Amemiya, E. Sano
    2011 Int'l Conf. Solid State Devices and Materials 1069 - 1070 2011/09 [Refereed][Not invited]
  • ジャイレータ回路とマルチバンドレシーバーへの応用
    近藤亮, 池辺将之, 本久順一, 雨宮好仁, 佐野栄一
    映像情報メディア学会技術報告 35 (28) 125 - 130 2011/07 [Not refereed][Not invited]
  • Yasuaki Masumoto, Yuuki Hirata, Premila Mohan, Junichi Motohisa, Takashi Fukui
    APPLIED PHYSICS LETTERS 98 (21) 211902  0003-6951 2011/05 [Refereed][Not invited]
     
    The photoluminescence from single InP/InAs/InP core-multishell nanowires (CMNs) was highly linearly polarized in perpendicular to the nanowire long axis. Taking account of dielectric confinement of light field, we found the internal optical dipole squared perpendicular to the nanotube long axis d(0x)(2) is larger than that parallel to the axis d(0z)(2) by two orders of magnitude. With the increase in the thickness of InAs nanotubes, the ratio beta = d(0x)(2)/d(0z)(2) increases. This strong anisotropy in beta comes from nearly perfect wurtzite structure of InP/InAs/InP CMNs and small inclusion of p(z)-character into the Gamma(7)(B)-hole state. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3592855]
  • 容量分圧動作を用いたsingle-slope A/D変換器
    金基秀, 池辺将之, 本久順一, 佐野栄一
    LSIとシステムのワークショップ2011 201 - 203 2011/05 [Not refereed][Not invited]
  • Shota Fujisawa, Takuya Sato, Shinjiro Hara, Junichi Motohisa, Kenji Hiruma, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 (4) 04DH03.1-04DH03.6  0021-4922 2011/04 [Refereed][Not invited]
     
    We developed a growth method for forming a GaAs quantum well (QW) buried in GaAsP/GaAs heterostructure nanowires (NWs) by selective-area metal organic vapor phase epitaxy (SA-MOVPE). To determine the optimum growth conditions of GaAsP NWs, we varied the [(C4H9)PH2 + AsH3]/[(CH3)(3)Ga] ratio between 20 and 185. As a result, we could obtain NWs with good height uniformity when the ratio was 20. To form such NWs with a GaAs QW, we fabricated GaAs NWs of about 60 nm in diameter before the GaAsP growth. The NW uniformity was considerably improved by introducing GaAs growth. Photoluminescence (PL) measurements at 4.2 K indicated that the QW had a spectral peak about 150 meV higher than the acceptor-related recombination emission peak of GaAs, which is near 1.5 eV. The QW thickness estimated from the spectral peak energy of PL was 5.2 nm, which is in fair agreement with the value calculated from the GaAs growth rate. (C) 2011 The Japan Society of Applied Physics
  • Masayuki Ikebe, Junichi Motohisa
    INTERNATIONAL SYMPOSIUM ON PHOTOELECTRONIC DETECTION AND IMAGING 2011: ADVANCES IN IMAGING DETECTORS AND APPLICATIONS 8194 (Pt.1) 819402.1-819402.8  0277-786X 2011 [Not refereed][Not invited]
     
    We investigated a negative feedback method for adding functionality to a CMOS image sensor. Our sensor effectively uses the method to set any intermediate voltage into a photodiode capacitance while a pixel circuit is in motion. The negative feedback reset functions as a noise cancellation technique and can obtain intermediate image data during charge accumulation. As an above application, dynamic range compression is achieved by individually selecting pixels and by setting an intermediate processing and were able to output frame-difference images without frame buffers. The experimental results obtained with a chip fabricated using a 0.25-mu m CMOS process demonstrate that dynamic range compression and intra-frame motion detection are effective applications of negative feedback resetting.
  • Yukinobu Makihara, Masayuki Ikebe, Junichi Motohisa, Eiichi Sano
    IEEJ Transactions on Electronics, Information and Systems 電気学会 131 (3) 490 - 498 1348-8155 2011 [Refereed][Not invited]
     
    We proposed a new architecture for a phase-locked loop (PLL) obtained by comparing clock periods. We evaluated the use of a clock-period comparator (CPC) for the digitally controlled PLL we propose, where only the frequency should be locked. However, frequency control with the CPC resulted in the phase being locked. Thus, phase-lock operation was also achieved. The theoretical analysis of the phase-lock mechanism was confirmed through system simulations. We discussed about dead-zone problem caused by a time delay of circuits. We evaluated phase-shift direction detector to solve the dead zone problem. We designed the element blocks of the new PLL using a 0.25-μm CMOS process. We confirmed phase-lock operation through SPICE simulations of the MOSFET level. Moreover, we manufactured a trial circuit for the new PLL. We also confirmed phase-lock operation in the proposed PLL through measurements. © 2011 The Institute of Electrical Engineers of Japan.
  • Junichi Motohisa, Katsuhiro Tomioka, Bin Hua, Kumar S.K. Varadwaj, Shinjiroh Hara, Kenji Hiruma, Takashi Fukui
    Advances in III-V Semiconductor Nanowires and Nanodevices 145 - 157 2011 [Refereed][Not invited]
     
    We describe the growth and optical properties of III-V semiconductor nanowires and their application to nanoscale photonic devices such as Fabry-Perot cavity, waveguides, optically-pumped lasers, and lightemitting diodes. The nanowires were grown by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) on the (111) oriented substrates. Nanowires containing heterostructures in their radial direction, that is, core-shell heterostructures, have also been realized by controlling the growth mode during SA-MOVPE. The nanowires were characterized by micro-photoluminescence measurements and those detached from the grown substrate showed resonant peaks associated with Fabry-Perot cavity modes. It was simultaneously shown that core-shell hetereostructured nanowires exhibited stronger photoluminescence than bare nanowires due to reduced surface non-radiative recombination. Furthermore, core-shell nanowires exhibited lasing oscillation originating from the cavity formed by both end facets at pulsed-laser excitation. Meanwhile, electroluminescence from core-shell nanowires was also demonstrated. © 2011 Bentham Science Publishers Ltd. All rights reserved.
  • Sasakura H, Kumano H, Suemune I, Dorenbos S. N, Kouwen M, P. van, Zwiller V, Kabayashi Y, Motohisa J, Tomioka K, Fukui T, Herm, stadter C
    Meeting Abstracts of the Physical Society of Japan 一般社団法人 日本物理学会 66 (0) 1342-8349 2011 [Not refereed][Not invited]
  • Y. Takayama, K. Tomioka, S. Hara, T. Fukui, J. Motohisa
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 8 (2) 272 - 274 1862-6351 2011 [Refereed][Not invited]
     
    We report on the selective-area metalorganic vapor phase epitxial growth of GaSb on (111)-oriented GaAs substrates partially covered with a SiO2 mask layer. The mask pattern consisted of periodic circular openings with diameter ranging from 200 to 500 nm and pitch ranging from 500 nm to 3 mu m. Selective-area growth of GaSb was achieved on the (111) A substrates, while GaSb was grown in few parts of the mask openings on the (111) B substrate. In addition, exposure to an Sb-precursor prior to the growth significantly affected the coverage of GaSb of the mask opening region, and it increases (decreases) on the (111) A ((111) B) substrate as compared to AsH3 exposure. The results are explained based on a model of exchange of Sb-As at the initial stage of growth. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Masatoshi Yoshimura, Katsuhiro Tomioka, Kenji Hiruma, Shinjiro Hara, Junichi Motohisa, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 315 (1) 148 - 151 0022-0248 2011/01 [Refereed][Not invited]
     
    We grew on GaAs(1 1 1)B InGaAs nanowires with lattice-mismatched composition using catalyst-free selective-area metalorganic vapor phase epitaxy and analyzed the effect of lattice mismatch on crystal structure and quality. An energy dispersive X-ray microscopy analysis indicated that the atomic contents of group-III atoms, Ga and In, were constant with little dispersion along a 2 mu m-long nanowire. This indicates that a possible difference in migration length between In and Ga atoms on the sidewall facets has no effect on the compositional distribution along the nanowires with lengths of up to 2 mu m. Photoluminescence spectra for InGaAs planar layers grown on GaAs(1 0 0) and GaAs(1 1 1)B substrates showed no peak corresponding to the InGaAs band-edge emission, due to lattice mismatch between the layers and the substrate. However, the nanowires with a lattice mismatch of 2.1% showed a strong and sharp band-edge emission peak at 1.12 eV. This means that crystal quality of the InGaAs nanowires was better than that of the planar layers for a lattice-mismatched system. (C) 2010 Elsevier B.V. All rights reserved.
  • Kenji Hiruma, Katsuhiro Tomioka, Premila Mohan, Lin Yang, Jinichiro Noborisaka, Bin Hua, Atsushi Hayashida, Shota Fujisawa, Shinjiro Hara, Junichi Motohisa, Takashi Fukui
    J. Nanotechnology Vol. 2012 169284-1 - 169284-29 2011 [Refereed][Invited]
  • Atsushi Hayashida, Takuya Sato, Shinjiro Hara, Junichi Motohisa, Kenji Hiruma, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 312 (24) 3592 - 3598 0022-0248 2010/12 [Refereed][Not invited]
     
    We developed a growth method for forming a GaAs quantum well contained in an AlGaAs/GaAs heterostructure nanowire using selective-area metal organic vapor phase epitaxy To find the optimum growth condition of AlGaAs nanowires we changed the growth temperature between 800 and 850 C and found that best uniformity of the shape and the size was obtained near 800 C but lateral growth of AlGaAs became larger which resulted in a wide GaAs quantum well grown on the top (1 1 1)B facet of the AlGaAs nanowire To form the GaAs quantum well with a reduced lateral size atop the AlGaAs nanowire a GaAs core nanowire about 100 nm in diameter was grown before the AlGaAs growth which reduced the lateral size of AlGaAs to roughly half compared with that without the GaAs core Photoluminescence measurement at 42 K indicated spectral peaks of the GaAs quantum wells about 60 meV higher than the acceptor-related recombination emission peak of GaAs near 1 5 eV The photoluminescence peak energy showed a blue shift of about 15 meV from 1 546 to 1 560 eV as the growth time of the GaAs quantum well was decreased from 8 to 3 s Transmission electron microscopy and energy dispersive X-ray analysis of an AlGaAs/GaAs heterostructure nanowire indicated a GaAs quantum well with a thickness of 5-20 nm buried along the < 1 1 1 > direction between the AlGaAs shells showing a successful fabncation of the GaAs quantum well (C) 2010 Elsevier B V All rights reserved
  • M. Shin, M. Ikebe, J. Motohisa, E. Sano
    17th IEEE International Conference on Electronics, Circuits, and Systems 865 - 868 2010/12 [Refereed][Not invited]
  • S. N. Dorenbos, H. Sasakura, M. P. van Kouwen, N. Akopian, S. Adachi, N. Namekata, M. Jo, J. Motohisa, Y. Kobayashi, K. Tomioka, T. Fukui, S. Inoue, H. Kumano, C. M. Natarajan, R. H. Hadfield, T. Zijlstra, T. M. Klapwijk, V. Zwiller, I. Suemune
    APPLIED PHYSICS LETTERS 97 (17) 171106  0003-6951 2010/10 [Refereed][Not invited]
     
    We report the experimental demonstration of single-photon and cascaded photon pair emission in the infrared, originating from a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires is fabricated by epitaxial growth on an electron-beam patterned substrate. Photoluminescence spectra taken on single quantum dots show narrow emission lines. Superconducting single photon detectors, which have a higher sensitivity than avalanche photodiodes in the infrared, enable us to measure auto and cross correlations. Clear antibunching is observed [g((2))(0) = 0.12] and we show a biexciton-exciton cascade, which can be used to create entangled photon pairs. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506499]
  • Yasuaki Masumoto, Ken Goto, Bipul Pal, Premila Mohan, Junichi Motohisa, Takashi Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 42 (10) 2579 - 2582 1386-9477 2010/09 [Refereed][Not invited]
     
    Spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires (CMNs) was studied at 5K by means of time- and spectrally resolved photoluminescence. Up to 1.2 ns type-II excitons lose their energy slowly at the initial rate of 8 x 10(6) eV/s and at the later rate of 3 x 10(6) eV/s reflecting two-dimensional spectral diffusion in the quantum well region in CMNs. Acoustic-phonon-assisted migration of excitons to lower-energy-localized states leads to the spectral diffusion in two-dimension. Spectral diffusion of type-II excitons is discussed by extending the theory of spectral diffusion of type-I excitons. (C) 2009 Elsevier B.V. All rights reserved.
  • A 12b two-stage single-slope ADC with time to digital converter
    M. Shin, M. Ikebe, J. Motohisa, E. Sano
    2010 Int'l Conf. Solid State Devices and Materials 337 - 338 2010/09 [Refereed][Not invited]
  • Yasuaki Masumoto, Ken Goto, Seitaro Yoshida, Yoshiki Sakuma, Premila Mohan, Junichi Motohisa, Takashi Fukui
    PHYSICAL REVIEW B 82 (7) 075313.1-075313.5  1098-0121 2010/08 [Refereed][Not invited]
     
    Spectral diffusion of type-II excitons in InP/InAs/InP core-multishell nanowires (CMNs) and type-I excitons in an InAs/InP single quantum well (SQW) was studied by means of time-resolved and spectrally resolved photoluminescence. InP/InAs/InP CMNs in hexagonal symmetry are made of six facets and six edges which work as two-dimensional quantum wells and one-dimensional quantum wires, respectively. At 5 K type-II excitons lose their energy in two stages. In the first stage, two-dimensional spectral diffusion takes place in the type-II quantum well region in CMNs similar to spectral diffusion of type-I excitons in the InAs/InP SQW. In the second stage, slower one-dimensional spectral diffusion takes place in the quantum wire region in CMNs. Acoustic-phonon-mediated migration of excitons to lower-energy-localized states leads to the spectral diffusion in two dimensions and one dimension.
  • Katsuhiro Tomioka, Junichi Motohisa, Shinjiroh Hara, Kenji Hiruma, Takashi Fukui
    NANO LETTERS 10 (5) 1639 - 1644 1530-6984 2010/05 [Refereed][Not invited]
     
    We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.
  • Yusuke Kitauchi, Yasunori Kobayashi, Katsuhiro Tomioka, Shinjiro Hara, Kenji Hiruma, Takashi Fukui, Junichi Motohisa
    NANO LETTERS 10 (5) 1699 - 1703 1530-6984 2010/05 [Refereed][Not invited]
     
    We study the catalyst-free growth of InP nanowires using selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and show that they undergo transition of crystal structures depending on the growth conditions. InP nanowires were grown on InP substrates where the mask for the template of the growth was defined. The nanowires were grown only in the opening region of the mask. It was found that uniform array of InP nanowires with hexagonal cross section and with negligible tapering were grown under two distinctive growth conditions. The nanowires grown in two different growth conditions were found to exhibit different crystal structures. It was also found that the orientation and size of hexagon were different, suggesting that the difference of the growth behavior. A model for the transition of crystal structure is presented based on the atomic arrangements and termination of InP surfaces. Photoluminescence measurement revealed that the transition took place for nanowires with diameters up to 1 mu m.
  • Masaki Igarashi, Masayuki Ikebe, Sousuke Shimoyama, Kenta Yamano, Junichi Motohisa
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers 映像情報メディア学会 64 (3) 389 - 398 1342-6907 2010/03 [Refereed][Not invited]
     
    We propose a fast 2-D bilateral filtering method without kernel-size dependency. Focusing on weighted local histograms and the central limit theorem combined with applying line buffers of column histograms, enables us to reduce the number of necessary memory accesses and calculations. Numerical experiments demonstrated a reduction in both calculations and kernel-size independency. We used a dual core 2-GHz CPU with our method and were able to achieve one million pixels per 0.5 sec operation without the need for downsampling, Single Instruction/Multiple Data (SIMD) or multi-thread operation.
  • Tomotaka Tanaka, Katsuhiro Tomioka, Shinjiroh Hara, Junichi Motohisa, Eiichi Sano, Takashi Fukui
    APPLIED PHYSICS EXPRESS 3 (2) 025003.1-025003.3  1882-0778 2010 [Refereed][Not invited]
     
    We report on the fabrication and characterization of vertical InAs nanowire channel field effect transistors (FETs) with high-k/metal gate-all-around structures. Single InAs nanowires were grown on Si substrates by the selective-area metalorganic vapor phase epitaxy method. The resultant devices exhibited n-channel FET characteristics with a threshold voltage of around -0.1 V. The best device exhibited maximum drain current (I(DS, max)/w(G)), maximum transconductance (g(m, max)/w(G)), on-off ratio (I(ON/OFF)), subthreshold slope (SS) of 83 mu A/mu m, 83 mu S/mu m, 10(4), and 320 mV/decade, respectively, for a nanowire diameter of 100 nm. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/APEX.3.025003
  • Masatoshi Yoshimura, Katsuhiro Tomioka, Kenji Hiruma, Shinjiro Hara, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 (4) 04DH08.1-04DH08.5  0021-4922 2010 [Refereed][Not invited]
     
    We fabricated InGaAs nanowires (NWs) in SiO2 mask openings on a GaAs(111) B substrate at growth temperatures of 600-700 degrees C using catalyst-free selective-area metal organic vapor phase epitaxy. At a growth temperature of 600 degrees C, particle-like depositions occurred, but they decreased in number and density when the growth temperature was increased to 650 degrees C and disappeared above 675 degrees C. The heights and growth rates of the NWs increased when the growth temperature was increased and the mask opening diameter was decreased from 300 to 50 nm. Photoluminescence (PL) spectra measured for the NWs indicated a blue shift in the peak from 0.95 to 1.3 eV as the growth temperature was increased from 600 to 700 degrees C, indicating an increase in the Ga composition from 62 to 88% in the InGaAs NWs. (C) 2010 The Japan Society of Applied Physics
  • Masaki Igarashi, Masayuki Ikebe, Sohsuke Shimoyama, Kenta Yamano, Junichi Motohisa
    Proceedings of the International Conference on Image Processing(ICIP) 3301 - 3304 2010
  • Yasunori Kobayashi, Junichi Motohisa, Katsuhiro Tomioka, Shinjiro Hara, Kenji Hiruma, Takashi Fukui
    2010 22ND INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM) 1092-8669 2010 [Refereed][Not invited]
     
    We grew InAsP and InP/InAsP/InP heterostructure NWs (NWs) by selective-area MOVPE and carried out micro-photoluminescence (mu-PL) measurement. We investigated growth conditions for InAsP NWs and that embedded in InP NWs, and obtained exciton and biexciton emissions from InAsP QDs at optimized growth conditions. Negative binding energy of biexciton was observed due to the strong Coulomb interaction between the holes in the QDs.
  • J. Motohisa, K. S. K. Varadwaj, K. Tomioka, T. Fukui
    2010 15TH OPTOELECTRONICS AND COMMUNICATIONS CONFERENCE (OECC) 214 - + 2010 [Refereed][Not invited]
     
    We report on the optical properties of III-V semiconductor nanowires (NWs) grown by by selective-area matalorganic vapor phase epitaxy and its application to photonic devices. Results for NWs containing heterostructures are mainly discussed.
  • T. Fukui, K. Tomioka, S. Hara, K. Hiruma, J. Motohisa
    PROCEEDINGS OF 2010 CONFERENCE ON OPTOELECTRONIC AND MICROELECTRONIC MATERIALS AND DEVICES (COMMAND 2010) 209 - 210 1097-2137 2010 [Refereed][Not invited]
     
    We fabricated various kinds of III-V semiconductor nanowires and core-shell nanowires using selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (111) oriented substrates, such as GaAs, GaAs/AIGaAs, InP, InPllnAsllnP on III-V substrates, and InAs and GaAs on Si. As for device applications, we fabricated GaAs/GaAsP core-shell nanowire photo-excited lasers, and InP core-shell pn junction solar cells. We also demonstrate III-V semiconductor nano-wires grown on Si (111) substrates.
  • J. Motohisa, B. Hua, K. S. K. Varadwaj, S. Hara, K. Hiruma, T. Fukui
    2010 IEEE PHOTONICS SOCIETY WINTER TOPICALS MEETING SERIES 139 - + 2010 [Refereed][Not invited]
  • T. Fukui, K. Tomioka, S. Hara, K. Hiruma, J. Motohisa
    2010 22ND INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM) 1092-8669 2010 [Refereed][Not invited]
     
    We fabricated various kinds of III-V semiconductor nanowires and core-shell nanowires using selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (111) oriented substrates, such as GaAs, GaAs/AlGaAs, InP, InP/InAs/InP on III-V substrates, and InAs and GaAs on Si. As for device applications, we fabricated GaAs/GaAsP core-shell nanowire photo-excited lasers, and InP core-shell pn junction solar cells. I will also introduce III-V semiconductor nanowires grown on Si (111) substrates
  • Hiroatsu Yoshida, Keitaro Ikejiri, Takuya Sato, Shinjiroh Hara, Kenji Hiruma, Junichi Motohisa, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 312 (1) 52 - 57 0022-0248 2009/12 [Not refereed][Not invited]
     
    We analyzed twin defects in GaAs nanowires as thin as 100-400 nm and tetrahedral structures as small as 1.0 mu m, which were selectively grown by metal organic vapour-phase epitaxy (MOVPE) within a SiO(2) mask window fabricated on GaAs(1 1 1)B substrates. In particular, we focused on the correlation between the twins and GaAs(1 1 1)B surface reconstructions. We confirmed that the shape of GaAs cyrstals selectively grown on GaAs(1 1 1)B substrates changed from hexagonal nanowires to truncated tetrahedra when the size of the mask opening was increased from 100 to 1000 nm under the same growth conditions. The shape also changed from tetrahedral to hexagonal with decreasing growth temperature (T(g) : 600-800 degrees C) and with increasing arsine (AsH(3)) partial pressure (1.0 x10(-4) to 5.0 x 10(-4) atm). Rotational twins around the < 1 1 1 > axis were found in the tetrahedra by transmission electron microscopy (TEM) and scanning electron microscopy observations. In addition, the probability of twins developing in the tetrahedra increased with decreasing mask opening size, with decreasing T., and with increasing AsH(3) partial pressure. The TEM study also revealed the existence of a high density of rotational twins in the nanowires, and their density increased with decreasing nanowire diameter, suggesting a correlation between the twins and the shape/size of GaAs crystals. These findings were semi-quantitatively compared with a reported phase diagram for GaAs(1 1 1)B surface reconstruction. By analyzing the relationship between twin development and MOVPE conditions, we found that the shape change of GaAs crystals on GaAs(1 1 1)B and the formation of twins coincided well with the transition of GaAs surface reconstruction between the (2 x 2) and (root 19 x root 19) structures. (C) 2009 Elsevier B.V. All rights reserved.
  • Fabrication and electrical characterization of InAs tubular channel nanowire FETs
    T. Sato, J. Motohisa, S. Hara, E. Sano, T. Fukui
    Int'l Sympo. on Advanced Nanodevics and Nanotechnology 91 - 92 2009/12 [Refereed][Not invited]
  • Pal, Bipul, Goto, Ken, Ikezawa, Michio, Masumoto, Yasuaki, Mohan, Premila, Motohisa, Junichi, Fukui, Takashi
    JOURNAL OF LUMINESCENCE ELSEVIER SCIENCE BV 129 (12:::Sp. Iss. SI) 1941 - 1944 0022-2313 2009/12 [Refereed][Not invited]
  • Growth of tubular InAs nanowires for FET applications
    T. Sato, J. Motohisa, S. Hara, E. Sano, K. Hiruma, T. Fukui
    Proc. 4th Nanowire Growth Workshop NWG 2009 79  2009/10 [Refereed][Not invited]
  • Lin Yang, Junichi Motohisa, Takashi Fukui, Lian Xi Jia, Lei Zhang, Ming Min Geng, Pin Chen, Yu Liang Liu
    OPTICS EXPRESS 11 17 (11) 9337 - 9346 1094-4087 2009/05 [Refereed][Not invited]
     
    We report on the fabrication of the nanowires with InGaAs/GaAs heterostructures on the GaAs(111) B substrate using selective-area metal organic vapor phase epitaxy. Fabry-Perot microcavity modes were observed in the nanowires with perfect end facets dispersed onto the silicon substrate and not observed in the free-standing nanowires. We find that the calculated group refractive indices only considering the material dispersion do not agree with the experimentally determined values although this method was used by some researchers. The calculated group refractive indices considering both the material dispersion and the waveguide dispersion agree with the experimentally determined values well. We also find that Fabry-Perot microcavity modes are not observable in the nanowires with the width less than about 180 nm, which is mainly caused by their poor reflectivity at the end facets due to their weak confinement to the optical field. (C) 2009 Optical Society of America
  • Katsuhiro Tomioka, Yasunori Kobayashi, Junichi Motohisa, Shinjiroh Hara, Takashi Fukui
    NANOTECHNOLOGY 20 (14) 145302 (8 PP.)  0957-4484 2009/04 [Not refereed][Not invited]
     
    We report on selective-area growth of vertically aligned GaAs nanowires on Si(111) substrate. Modification of the initial Si(111) surface by pretreatment under an AsH(3) atmosphere and low-temperature growth of GaAs were important for controlling the growth orientations of the GaAs nanowire on the Si(111) surface. We also found that the size of openings strongly affected the growth morphology of GaAs nanowires on Si(111). Small diameter openings reduced the antiphase defects and improved the optical properties in the GaAs nanowires. Moreover, we realized coherent growth without misfit dislocation at the GaAs/Si interface. Finally, we demonstrated fabrication of a GaAs/AlGaAs core-shell nanowire array on a Si surface and revealed that the luminescence intensity was markedly enhanced by passivation effects. These results are promising for future III-V nanowire-based optoelectronic integration on Si platforms.
  • Ken Goto, Michio Ikezawa, Shinichi Tomimoto, Bipul Pal, Yasuaki Masumoto, Premila Mohan, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS 48 (4) 04C203.1-04C203.3  0021-4922 2009/04 [Not refereed][Not invited]
     
    We report on the photoluminescence and time-resolved photoluminescence spectroscopy of wurtzite InP/InAs/InP core-multishell nanowires. Multiple peaks appeared in the photoluminescence spectra owing to the monolayer variation of InAs layers. Each photoluminescence peak has a broad photoluminescence band coming from the inhomogeneous broadening in a core-multishell single nanowire. Inhomogeneous broadening caused time-dependent red shift (spectral diffusion) at a constant energy-loss rate. The long-time-span (similar to 10ns) time-resolved photoluminescence measurement clarified that spectral diffusion takes place in two stages (initially at a fast rate and later at a slow rate). The fast one is ascribed to spectral diffusion on the side of the nanowire and the slow one is ascribed to spectral diffusion at the corner of the nanowire. This suggests that photoexcited excitons in a core-multishell nanowire move from the side of the nanowire toward the corner of the nanowire. (C) 2009 The Japan Society of Applied Physics
  • SHIMOYAMA SOUSUKE, IGARASHI MASAKI, IKEBE MASAYUKI, MOTOHISA JUNICHI
    J Signal Process 〔信号処理学会〕 13 (2) 151 - 159 1342-6230 2009/03 [Not refereed][Not invited]
  • Hajime Goto, Katsutoshi Nosaki, Katsuhiro Tomioka, Shinjiro Hara, Kenji Hiruma, Junichi Motohisa, Takashi Fukui
    APPLIED PHYSICS EXPRESS 2 (3) 035004.1-035004.3  1882-0778 2009/03 [Not refereed][Not invited]
     
    We report on the formation of core-shell pn junction InP nanowires using a catalyst-free selective-area metalorganic vapor-phase epitaxy (SA-MOVPE) method. A periodically aligned dense core-shell InP nanowire array was fabricated and used in photovoltaic device applications. The device exhibited open-circuit voltage (V-OC), short-circuit current (I-SC) and fill factor (FF) levels of 0.43 V, 13.72 mA/cm(2) and 0.57, respectively, which indicated a solar power conversion efficiency of 3.37% under AM1.5G illumination. This study demonstrates that high quality core-shell structure nanowire fabrication is possible by SA-MOVPE and that the nanowire arrays can be used in integrated nanowire photovoltaic devices. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/APEX.2.035004
  • Bin Hua, Junichi Motohisa, Yasunori Kobayashi, Shinjiroh Hara, Takashi Fukui
    NANO LETTERS 9 (1) 112 - 116 1530-6984 2009/01 [Not refereed][Not invited]
     
    Highly uniform GaAs/GaAsP coaxial nanowires were prepared via selective-area metal organic vapor phase epitaxy. Photoluminescence spectra from a single nanowire indicate that the obtained heterostructures can produce near-infrared (NIR) lasing under pulsed light excitation. The end facets of a single nanowire form a natural mirror surface to create an axial cavity, which realizes resonance and give stimulated emission. This study is a considerable advance toward the realization of nanowire-based NIR light sources.
  • Sohsuke Shimoyama, Masaki Igarashi, Masayuki Ikebe, Junichi Motohisa
    Proceedings of the International Conference on Image Processing(ICIP) 3153 - 3156 2009
  • Bin Hua, Junichi Motohisa, Shinjiroh Hara, Takashi Fukui
    NANOWIRES - SYNTHESIS, PROPERTIES, ASSEMBLY AND APPLICATIONS 1144 103 - 108 0272-9172 2009 [Refereed][Not invited]
     
    Highly uniform GaAs/GaAsP coaxial nanowires were prepared via selective-area metal organic vapor phase epitaxy (SA-MOVPE). Photoluminescence (PL) spectra from a single nanowire indicate that the obtained heterostructures can produce near-infrared (NIR) lasing under pulsed light excitation. The end facets of a single nanowire form natural mirror surface to create an axial cavity, which realizes resonance and give stimulated emission. This study is a considerable advance towards the realization of nanowire-based NIR light sources.
  • Ken Goto, Shinichi Tomimoto, Bipul Pal, Yasuaki Masumotol, Premila Mohan, Junichi Motohisa, Takashi Fukui
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 1 6 (1) 205 - + 1862-6351 2009 [Refereed][Not invited]
     
    We report on the photoluminescence (PL) and time-resolved PL (TR-PL) Spectroscopy of wurtzite InP/InAs/InP core-multishell nanowires. Multiple peaks appeared in the PL spectra due to monolayer variation of InAs layers and each PL peak showed a blueshift with a cube-root dependence on the excitation power. This blueshift results from the band-bending in the type-II band configuration. Fast decay caused by the relaxation of the band-bending was observed at higher energy sides of the PL peaks in the TR-PL measurement. The blueshift calculated by a triangular quantum well approximation in type-II configuration was in good agreement with that observed in the experiment. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • H. Sasakura, H. Kumano, I. Suemune, J. Motohisa, Y. Kobayashi, M. van Kouwen, K. Tomioka, T. Fukui, N. Akopian, V. Zwiller
    16TH INTERNATIONAL CONFERENCE ON ELECTRON DYNAMICS IN SEMICONDUCTORS, OPTOELECTRONICS AND NANOSTRUCTURES (EDISON 16) 193 01232  1742-6588 2009 [Refereed][Not invited]
     
    We report optical properties of InP/InAsP/InP nanowire quantum dots and single-photon Fourier spectroscopy of an exciton in a single InAsP quantum dot embedded in an InP nanowire. The coherent length of the time-averaged emission originating from the single InAsP QD was measured by a Mach-Zehnder interferometer inserted in the photoluminescence path. Effects of fluctuations in surrounding excess charges trapped in the InP nanowire were investigated by excitation power and energy dependencies.
  • Frequency and phase lock operation using clock-period comparator
    Y. Makihara, M. Ikebe, J. Motohisa, E. Sano
    Proc. of Intl. Symposium on Multimedia and Communication Technology (ISMAC) 241 - 244 2009/01 [Refereed][Not invited]
  • TOMIOKA Katsuhiro, SATO Takuya, HARA Shinjiroh, MOTOHISA Junichi, FUKUI Takashi
    Journal of the Surface Science Society of Japan 日本表面科学会 29 (12) 726 - 730 0388-5321 2008/12/10 [Not refereed][Not invited]
     
    We report on the growth of III-V compound semiconductor nanowires by selective-area MOVPE. Position-controlled growth of GaAs nanowire, and InP/InAs/InP core-multi shell nanowires are reviewed. The nanowires are oriented to <111>B or <111>A directions and they have hexagonal cross-section surrounded with {1-10} vertical side facets and (111)B or A top surface. Also, we can control the growth direction to axial or radial by changing the growth parameters. InP/InAs/InP core-multi shell nanowires whose well thickness is of several monolayers are fabricated by using this method. We also review on the growth of vertical GaAs nanowires on Si substrate and fabrication of InGaAs nanowire-FETs.
  • A 0.18um 3GHz true single phase clocking divider-by-3 circuit
    M. Ikebe, J. Motohisa, E. Sano
    2008 WSEAS Intl. Conf. on Circuits, Systems, Electronics, Control & Signal Processing 110 - 113 2008/12 [Refereed][Not invited]
  • Takuya Sato, Yasunori Kobayashi, Junichi Motohisa, Shinjiro Hara, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 310 (23) 5111 - 5113 0022-0248 2008/11 [Refereed][Not invited]
     
    We studied the growth of InGaAs nanowires on InP(1 1 1)B substrates by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). We proposed a growth model of InGaAs nanowires based on the observation Of growth under various condition. We investigated the composition of InGaAs nanowires using micro-photoluminescence and confirmed the relation between composition of InGaAs nanowires and the growth rate. (C) 2008 Elsevier B.V. All rights reserved.
  • Katsuhiro Tomioka, Junichi Motohisa, Shinjiroh Hara, Takashi Fukui
    Nano Letters 8 (10) 3475 - 3480 1530-6984 2008/10 [Not refereed][Not invited]
     
    We report on control of growth directions of InAs nanowires on Si substrate. We achieved to integrate vertical InAs nanowires on Si by modifying initial Si(111) surface in selective-area metal-organic vapor phase epitaxy with flow-rate modulation mode at low temperature. Cross-sectional transmission electron microscope and Raman scattering showed that misfit dislocation with local strains were accommodated in the interface. © 2008 American Chemical Society.
  • V. Zwiller, N. Akopian, M. van Weert, M. van Kouwen, U. Perinetti, L. Kouwenhoven, R. Algra, J. Gomez Rivas, E. Bakkers, G. Patriarche, L. Liu, J. -C. Harmand, Y. Kobayashi, J. Motohisa
    COMPTES RENDUS PHYSIQUE 9 (8) 804 - 815 1631-0705 2008/10 [Refereed][Not invited]
     
    Semiconducting nanowire heterostructures represent a new class of nanostructures that offer unprecedented freedom in material design. The position, diameter, composition and doping can be controlled with precision and complex structures such as core-shell and branched wires have already been demonstrated. Here we show that heterostructures in nanowires can define quantum emitters and that single spins can be addressed optically. We also present results on electrically contacted nanowires. The operation of single nanowires as light emitting diode or photodetector is demonstrated. To cite this article: V Zwiller et al., C. R. Physique 9 (2008). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
  • 牧原幸伸, 池辺将之, 本久順一, 佐野栄一
    信学技報 一般社団法人電子情報通信学会 108 (253) 165 - 170 0913-5685 2008/10 [Not refereed][Not invited]
     
    本研究では,周期比較方式を用いた位相同期回路(Phase Locked Loop:PLL)の新規アーキテクチャを提案する.周期比較器を導入する事により,ループ・フィルタの特性に依存しない位相ロック動作を確認することができた.通常,周期比較のみでは位相ロック動作は得られない.提案型PLLは厳密な周期の大小比較により,符号の変わる微小な周期差が位相差を制御し位相ロック動作が得られる.提案型PLLを0.25μm CMOSプロセスで回路設計し,その動作をシミュレーションで確認した.回路設計の際導入した,デジタル制御発振器の特性改善も行った.また動作確認のため試作を行い,測定により位相同期を確認した.
  • Keitaro Ikejiri, Takuya Sato, Hiroatsu Yoshida, Kenji Hiruma, Junichi Motohisa, Shinjiroh Hara, Takashi Fukui
    NANOTECHNOLOGY 19 (26) 265604 (8 PP.)  0957-4484 2008/07 [Not refereed][Not invited]
     
    GaAs nanowires were selectively grown by metal-organic vapour-phase epitaxy within a SiO(2) mask window pattern fabricated on a GaAs( 111) B substrate surface. The nanowires were 100-3000 nm in height and 50-300 nm in diameter. The height decreased as the mask window diameter was increased or the growth temperature was increased from 700 to 800 degrees C. The dependence of the nanowire height on the mask window diameter was compared with a calculation, which indicated that the height was inversely proportional to the mask window diameter. This suggests that the migration of growth species on the nanowire side surface plays a major role. Tetrahedral GaAs grew at an early stage of nanowire growth but became hexagonal as the growth process continued. The calculated change in Gibbs free energy for nucleation growth of the crystals indicated that tetrahedra were energetically more favourable than hexagons. Transmission and scanning electron microscopy analyses of a GaAs nanowire showed that many twins developed along the [111] B direction, suggesting that twins had something to do with the evolution of the nanowire shape from tetrahedron to hexagon.
  • L. Yang, J. Motohisa, K. Tomioka, J. Takeda, T. Fukui, M. M. geng, L. X. Jia, L. Zhang, Y. L. Liu
    NANOTECHNOLOGY 19 (27) 0957-4484 2008/07 [Refereed][Not invited]
     
    Hexagonal nanopillars with a single InGaAs/GaAs quantum well (QW) were fabricated on a GaAs (111) B substrate by selective-area metal-organic vapor phase epitaxy. The standard deviations in diameter and height of the nanopillars are about 2% and 5%, respectively. Zincblende structure and rotation twins were identified in both the GaAs and the InGaAs layers by electron diffraction. The excitation-power-density-dependent micro-photoluminescence (mu-PL) of the nanopillars was measured at 4.2, 50, 100 and 150 K. It was shown that, with increasing excitation power density, the mu-PL peak's positions shift to a higher energy, and their intensity and width increase, which were rationalized using a model that includes the effects of piezoelectricity, photon-screening and band-filling. It was also revealed that the rotation twins significantly reduce the diffusion length of the carriers in the nanopillars, compared to that in the regular semiconductors.
  • Phase lock operation by clock-period comparison for all digital PLL
    Y. Makihara, M. Ikebe, J. Motohisa, E. Sano
    Intl. Symposium on Topical Problems of Nonlinear Wave Physics (NWP) 49 - 50 2008/07 [Refereed][Not invited]
  • Shinji Hashimoto, Junichiro Takeda, Akihiro Tarumi, Shinjiro Hara, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (5) 3354 - 3358 0021-4922 2008/05 [Not refereed][Not invited]
     
    We report on a promising approach for the formation of compound semiconductor two-dimensional photonic crystal slabs utilizing selective-area metal-organic vapor phase epitaxy (SA-MOVPE). The selective-area growth process for the submicron-sized air holes of InP-based semiconductors was investigated on InP(111)A and (111)B substrates with a periodic array of hexagonal SiO(2) masks. By optimizing growth conditions, a highly uniform array of hexagonal air holes in InP and InGaAs with a 500 nm pitch was formed on (111)B substrates. We also fabricated air-hole arrays with InP/InGaAs/InP double heterostructures on InP(111)B, and confirmed photoluminescence from an InGaAs quantum well at low temperatures. [DOI: 10.1143/JJAP.47.3354]
  • Hiroko Iguchi, Shinjiroh Hara, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 (4) 3253 - 3256 0021-4922 2008/04 [Not refereed][Not invited]
     
    The authors report that the formation of MnAs nanoclusters (NCs) on GaInAs (1 1 1)A surfaces strongly depends on metal-organic vapor phase epitaxial growth conditions. It was confirmed from the atomic force microscope observation that deep holes were formed on the surfaces under low V/Mn ratio and high growth temperature conditions, in addition to the formation of MnAs NCs. From the results of cross-sectional transmission electron microscope observation, these deep holes were formed on the underlying GaInAs layers, and MnAs NCs were embedded in the GaInAs (1 1 1)A layers. The formation of these embedded MnAs NCs was possibly caused by the phenomenon of "endotaxy". From the experimental results of thermal treatments of the samples, it was revealed that the deep holes were formed on the GaInAs (1 1 1)A surfaces even after the thermal annealing in the atmosphere of Mn source gas and hydrogen. Therefore, we concluded that high AsH(3) partial pressure (V/Mn ratio) conditions were required for the MnAs growth on GaInAs (1 1 1)A surfaces.
  • Takuya Sato, Junichi Motohisa, Jinichiro Noborisaka, Shinjiro Hara, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 310 (7-9) 2359 - 2364 0022-0248 2008/04 [Refereed][Not invited]
     
    We studied the growth of InGaAs nanowires on InP(1 1 1)B substrates by selective-area metal organic vapor phase epitaxy (SA-MOVPE). It was found that the initial growth rate of the nanowires depends on the supply ratio of source gas of Ga and In, and it is higher for increasing supply ratio of Ga. At the initial stage, the diameters of the nanowires were almost the same as those of the openings of the mask, indicating that the lateral growth was negligible, while the height of the nanowires increased superlinearly with time. For longer growth time, the diameter of nanowires as well as height increased linearly with time. A possible growth mechanism for such dependence on time and supply ratio of group III source gases is discussed. (C) 2007 Elsevier B.V. All rights reserved.
  • Yasunori Kobayashi, Masayasu Fukul, Junichi Motohisa, Takashi Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 40 (6) 2204 - 2206 1386-9477 2008/04 [Refereed][Not invited]
     
    We have investigated the optical properties of single InP nanowires (NWs) grown by selective-area metalorganic vapor phase epitaxy. Systematic measurements on several single NWs revealed that some of they exhibited good optical quality at low temperature. Band gap energy of InP NWs with wurtzite crystal structure was found to be larger by about 88meV than that of zincblende InP, in good agreement with theoretical prediction. (C) 2007 Elsevier B.V. All rights reserved.
  • Shinjiroh Hara, Daichi Kawamura, Hiroko Iguchi, Junichi Motohisa, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 310 (7-9) 2390 - 2394 0022-0248 2008/04 [Refereed][Not invited]
     
    The authors report on the self-assembly and the selective-area formation of ferromagnetic MnAs nanoclusters (NCs) on III-V compound semiconductors (1 1 1) B surfaces by metal-organic vapor-phase epitaxy (MOVPE). Hexagonal MnAs NCs with well-defined crystal facets and a high degree of uniformity are self-assembled on planar GaInAs surfaces grown on InP (1 1 1) B substrates. The lateral size and height of typical NCs are 100 and 47 nm, respectively. Lattice images taken by transmission electron microscopy (TEM) show that the top surfaces of the MnAs NCs are atomically flat, and that the interfaces between the NCs and the GaInAs layers are abrupt. We have, in addition, controlled the positions of the MnAs NCs by selective-area MOVPE on GaAs (I 1 1) B substrates partially masked with SiO2 thin films. The hexagonal MnAs NCs do not grow on the SiO2 surfaces, but grow successfully on the GaAs ones, under a relatively high growth temperature condition of 850 degrees C. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiruma Kenji, Ikejiri Keitaro, Yoshida Hiroatsu, Tomioka Katsuhiro, Motohisa Junichi, Hara Shinjiroh, Fukui Takashi
    Journal of the Japanese Association of Crystal Growth 日本結晶成長学会 34 (4) 224 - 232 0385-6275 2008/01/31 [Not refereed][Not invited]
     
    GaAs and InAs nanowires were selectively grown by using metal-organic vapor-phase epitaxy. The nanowires were as thin as several tens to several hundreds nanometers and as long as several micronmeters. Scanning electron microscope observations showed that the growth direction of nanowires was parallel to the <111> B crystallographic orientation. It was found by a transmission electron microscopy analysis that the crystal structure of the GaAs nanowire was zincblende with rotational twins around the <111> axis. For the GaAs nanowires, the density of twins along the <111> direction increased as the nanowire diameter decreased. The growth mechanism was understood based upon a model that the GaAs nanowire was composed of stacked thin-layers with interfaces containing rotational twins.
  • Masayuki Ikebe, Masaki Igarashit, Junichi Motohisa
    Kyokai Joho Imeji Zasshi/Journal of the Institute of Image Information and Television Engineers 一般社団法人映像情報メディア学会 62 (3) 376 - 383 1342-6907 2008 [Not refereed][Not invited]
     
    We investigated a negative feedback method for adding functionality to a CMOS image sensor, Our sensor effectively uses the method to set any intermediate voltage into a photodiode capacitance while a pixel circuit is in motion. The negative feedback reset functions as a noise cancellation technique and can obtain intermediate image data during charge accumulation. Using the above features, we achieved duplicated interlaced processing and were able to output framedifference images without frame buffers. The experimental results obtained with a chip fabricated using a 0.25-μm CMOS process demonstrate that intra-frame motion detection is an effective application of negative feedback resetting.
  • 比留間 健之, 原 真二郎, 本久 順一, 福井 孝志
    化学工学会 研究発表講演要旨集 公益社団法人 化学工学会 2008 805 - 806 2008
  • M. Fukui, Y. Kobayashi, J. Motohisa, T. Fukui
    Physica Status Solidi (C) Current Topics in Solid State Physics 5 (9) 2743 - 2745 1862-6351 2008 [Refereed][Not invited]
     
    We have performed micro-photoluminescence (μ-PL) spectroscopy and imaging of single GaAs/InGaAs/GaAs nano-wires (NWs) grown by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) on masked GaAs (111)B substrates. Strong emission was observed from both end of the NW dispersed on a Si substrate. Measurements of excitation power dependence and two types of spatially- and spectrally-resolved image revealed that those emissions, located around 1.40 and 1.44 eV, were from InGaAs quantum well embedded in the GaAs NW, and were suggested to be from different region. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
  • J. Noborisaka, T. Sato, J. Motohisa, K. Tomioka, S. Hara, T. Fukui
    Device Research Conference - Conference Digest, DRC 177 - 178 1548-3770 2008 [Refereed][Not invited]
  • M. Fukui, Y. Kobayashi, J. Motohisa, T. Fukui
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 9 5 (9) 2743 - 2745 1610-1634 2008 [Refereed][Not invited]
     
    We have performed micro-photoluminescence (mu-PL) spectroscopy and imaging of single GaAs/InGaAs/GaAs nanowires (NWs) grown by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) oil masked GaAs (111)B substrates. Strong emission was observed from both end of the NW dispersed on a Si substrate. Measurements of excitation power dependence and two types of spatially- and spectrally-resolved image revealed that those emissions, located around 1.40 and 1.44 eV, were front InGaAs quantum well embedded in the GaAs NW, and were suggested to be from different region. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • B. Hua, J. Motohisa, S. Hara, T. Fukui
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 9 5 (9) 2722 - + 1862-6351 2008 [Refereed][Not invited]
     
    We report the formation of Fabry Perot microcavity in single GaAs nanowire prepared by selective-area metalorganic vapor phase epitaxy. The fabricated nanowires with hexagonal cross section are highly uniform and vertically oriented. Microphotoluminescence measurements of single GaAs nanowire exhibit several periodic peaks in the intensity, which are suggestive of the longitudinal modes of a Fabry-Perot cavity. The cavity is formed along the length of the nanowire and the (111) facets of both ends act as reflecting mirrors in this case. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • NOBORISAKA Jinichiro, SATO Takuya, MOTOHISA Junichi, HARA Shinjiro, FUKUI Takashi
    IEICE technical report 一般社団法人電子情報通信学会 107 (473) 5 - 10 0913-5685 2008/01 [Refereed][Not invited]
     
    Semiconductor nanowires are attracting much attention as a new class of nanoscale materials. Particularly, vertical surrounding gate FETs, which is a one of the useful applications utilizing semiconductor nanowires, have been expected to show superior transconductance, high current on-off (I_) ratio and reduced short channel effects compared with conventional planar type FETs. In experiment, Silicon-doped n-InGaAs nanowires were grown by catalyst-free selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). The nanowire FETs with MIS back-gate and 80% coverage MES top-gate on SiO_2-coated Si substrates were fabricated and characterized by defining metal contacts at both ends of the nanowires and the Al top-gate between contacts.
  • The design of high frequency true single phase clocking divider-by-3 circuit
    M. Ikebe, Y. Takada, M. Ohuchi, J. Motohisa, E. Sano
    Int. J. Circuits, Systems and Signal processing 2 (3) 219 - 228 2008 [Refereed][Not invited]
  • Ying Ding, Junichi Motohisa, Bin Hua, Shinjiroh Hara, Takashi Fukui
    NANO LETTERS 7 (12) 3598 - 3602 1530-6984 2007/12 [Not refereed][Not invited]
     
    Hexagonal cylindrical InP nanowires with a wurtzite structure were fabricated by selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). The microcavity modes and waveguides in InP nanowires were investigated by photoluminesence (PL) spectra. Optical mode analysis for InP nanowires with different lengths reveals the axial Fabry-Perot cavity in InP nanowires, which were formed between the two end facets of nanowires. In addition, T-branch subwavelength guiding and optical coupling in InP nanowires were observed.
  • Katsuhiro Tomioka, Junichi Motohisa, Shinjiroh Hara, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 (45-49) L1102 - L1104 0021-4922 2007/12 [Not refereed][Not invited]
     
    Crystallographic structure of InAs nanowires, which were grown by selective-area metalorganic vapor phase epitaxy on (111)B-oriented substrates, was investigated by transmission electron microscopy (TEM). The TEM images showed that the nanowires had many stacking faults along the growth direction. Statistical analysis of the atomic-layer stacking showed that InAs nanowires contained both zincblende and wurtzite crystal phases, whose transition took place in every one to three monolayers. This specific crystal phase transition resulted in peculiar electron diffraction patterns. The stacking of the atomic layers had no distinct correlation with the diameter of the nanowires.
  • Jinichiro Noborisaka, Takuya Sato, Junichi Motohisa, Shinjiro Hara, Katsuhiro Tomioka, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (11) 7562 - 7568 0021-4922 2007/11 [Not refereed][Not invited]
     
    Single InGaAs nanowire-top-gate metal-semiconductor field-effect transistors (MESFETs) were fabricated and characterized. Silicon-doped n-InGaAs nanowires (with a typical diameter of 100nm) were grown by catalyst-free selective-area metalorganic vapor-phase epitaxy (SA-MOVPE). The FETs of single nanowires on SiO2-coated Si substrates were fabricated by defining metal contacts at both ends of the nanowires and the metal top gate between contacts. According to the measurements of drain current-voltage and gate transfer characteristics, the top-gate MESFETs exhibited significant enhancements in device performance characteristics compared with FETs under back-gate operation; that is, a peak transconductance of 33 mS/mm and a current on-off ratio of 10(3) were obtained. A possibility for further improvements in FET characteristics was also considered.
  • 本久 順一
    Solid state physics アグネ技術センタ- 42 (10) 661 - 666 0454-4544 2007/10 [Not refereed][Not invited]
  • IGUCHI Hiroko, HARA Shinjiroh, MOTOHISA Junichi, FUKUI Takashi
    Extended abstracts of the ... Conference on Solid State Devices and Materials 2007 66 - 67 2007/09/19 [Not refereed][Not invited]
  • Bin Hua, Junichi Motohisa, Ying Ding, Shinjiroh Hara, Takashi Fukui
    APPLIED PHYSICS LETTERS 91 (13) 131112-131112-3  0003-6951 2007/09 [Not refereed][Not invited]
     
    The authors present the formation of Fabry-Perot cavity in single GaAs nanowire prepared by selective-area metal organic vapor phase epitaxy. The grown nanowires with hexagonal cross section are highly uniform and vertically oriented. Microphotoluminescence measurements of single GaAs nanowire exhibit periodic peaks in the intensity, which are suggestive of the longitudinal modes of a Fabry-Perot cavity. The cavity is formed along the length of the nanowire and the (111) facets of both ends act as reflecting mirrors. Additionally, optical waveguides in GaAs nanowires were also observed. (C) 2007 American Institute of Physics.
  • Noboru Ooike, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (7A) 4344 - 4350 0021-4922 2007/07 [Not refereed][Not invited]
     
    We studied the states working in the memory operation of GaAs narrow-wire field-effect transistors (FETs) with embedded InAs quantum dots (QDs). The GaAs narrow-wire FETs with a few InAs QDs above the channel were fabricated by selective-area metal organic vapor-phase epitaxy (SA-MOVPE). The drain current, measured by sweeping the gate voltage forward and backward, exhibited clear clockwise hysteresis due to the charging of electrons into the states induced by InAs QDs with a threshold voltage Shift (Delta V-th) of 30 mV at 20 K. To better understand the mechanism of this memory operation, we studied the traps concerning the InAs QDs by drain-current deep-level transient spectroscopy (DLTS). Peaks representing three kinds of electron traps concerning InAs QDs were observed in the DLTS spectra. These peaks exhibited different dependences on the applied gate pulsed voltage during the DLTS measurement. In comparison with the temperature dependence Of Delta V-th, we found that our memory operation was attributed to one localized state introduced by InAs QDs.
  • Optical evidence for Aharonov-Bohm effect in quantum tubes
    S. Nomura, K. Tsumura, P. Mohan, J. Motohisa, T. Fukui
    The 17th International Conference on Electronic Properties of Two-dimensional Systems 2007/07 [Refereed][Not invited]
  • Kohei Tsumura, Shintaro Nomura, Pamela Mohan, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 (17-19) L440 - L443 0021-4922 2007/05 [Not refereed][Not invited]
     
    The oscillation of photoluminescence peak energies is observed in InAs quantum tubes depending on the magnetic flux through the tube. The oscillation is shown to be due to the Aharonov-Bohm effect of a charged exciton in a quantum tube. No quadratic shift in photoluminescence peak energies is observed, which is a characteristic feature of a thin quantum tube with a single channel surrounding the magnetic flux through the tube.
  • Kohei Tsumura, Shintaro Nomura, Pamela Mohan, Junichi Motohisa, Takashi Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 (17-19) L440 - L443 0021-4922 2007/05 [Not refereed][Not invited]
     
    The oscillation of photoluminescence peak energies is observed in InAs quantum tubes depending on the magnetic flux through the tube. The oscillation is shown to be due to the Aharonov-Bohm effect of a charged exciton in a quantum tube. No quadratic shift in photoluminescence peak energies is observed, which is a characteristic feature of a thin quantum tube with a single channel surrounding the magnetic flux through the tube.
  • Lin Yang, Junichi Motohisa, Junichiro Takeda, Katsuhiro Tomioka, Takashi Fukui
    NANOTECHNOLOGY 18 (10) 0957-4484 2007/03 [Refereed][Not invited]
     
    We report on the fabrication of highly uniform hexagonal nanopillars with single InGaAs/GaAs quantum wells (QW) on GaAs( 111) B substrate by selective-area metal-organic vapour phase epitaxy. The standard size deviation of the fabricated nanopillars with single InGaAs/GaAs QW is about 2% and the standard deviation in their height about 5%. With a decrease in temperature, the peak position shifts to shorter wavelength, the peak intensity increases and the peak width decreases. The calculated well width based on the finite square potential well model taking account of the strain effect and the piezoelectric effect is smaller than the value determined from the growth rate and the growth time, which is mainly due to indium segregation and its incorporation into the subsequent GaAs layer grown at the higher temperature.
  • L. Yang, J. Motohisa, J. Takeda, T. Fukui
    SENSORS AND ACTUATORS A-PHYSICAL 133 (2) 288 - 293 0924-4247 2007/02 [Refereed][Not invited]
     
    It is shown that the photonic crystal slab (PCS) with hexagonal air holes has band gaps in the guided mode spectrum, which can be compared to that of the PCS with circular air holes, thus it is also a good candidate to be used for the PC devices. The PC with hexagonal air holes and a = 0.5 mu m and r = 0.15 mu m was fabricated successfully by selective area metal organic vapor phase epitaxy (SA-MOVPE). The vertical and smooth sidewalls are formed and the uniformity is very good. The same process was also used to fabricate a hexagonal air hole array with the width of 0.1 km successfully. The air-bridge PCS with hexagonal air holes and a = 0. 3 mu m and r = 0.09 mu m was also fabricated successfully by SA-MOVPE. Further optimization of the growth conditions for the sacrificial layer and the selective etching of the GaAs cap layer is also needed. Our experimental results indicate that SA-MOVPE is a promising method for fabricating PC devices and photonic nanostructures. (c) 2006 Elsevier B.V. All rights reserved.
  • B. Pal, K. Goto, M. Ikezawa, Y. Masumoto, P. Mohan, J. Motohisa, T. Fukui
    2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), VOLS 1-5 2490 - + 2007 [Not refereed][Not invited]
     
    Time- and spectrally-resolved PL from a periodic array of InP/InAs/InP core-multishell nanowires is presented. InAs layer shows multipeak PL spectra. PL decay is nonexponential and very slow, with decay rate depending on energy. (C) 2007 Optical Society of America
  • Lin Yang, Junichi Motohisa, Takashi Fukui
    2007 7TH IEEE CONFERENCE ON NANOTECHNOLOGY, VOL 1-3 668 - + 2007 [Refereed][Not invited]
     
    We report on the fabrication of the highly uniform hexagonal nanopillars with single InGaAs/GaAs quantum well (QW) on the GaAs (111)B substrate by selective-area metal organic vapor phase epitaxy. The standard size deviation of the fabricated nanopillars with single InGaAs/GaAs QW is about 2% and the standard deviation in their height about 5%. The excitation-power-density-dependent micro-photoluminescence (mu-PL) from the selective-area-grown hexagonal nanopillars with single InGaAs/GaAs QW on the GaAs (111)B substrate was measured at 4.2 k, 50 k, 100 k and 150 k. With an increase in the excitation power density, the PL peak position shifts to the higher energy. A model considering the piezoelectric effect, the photon-screening effect and the band-filling effect was used to calculate the PL peak positions. The agreement between the experimental results and the calculation results is good. We also find that the diffusion length of the carriers in the nanopillars with single InGaAs/GaAs QW reduces greatly compared to the general value in semiconductors, which is mainly due to the existence of rotation twins. With an increase in the excitation power density, the PL intensity increases and the PL peak width increases, which also can be explained qualitatively with the above model.
  • Ying Ding, Junichi Motohisa, Takashi Fukui
    2007 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 443 - + 1092-8669 2007 [Refereed][Not invited]
  • Noboru Ooike, Junichi Motohisa, Takashi Fukui
    2007 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 567 - 570 1092-8669 2007 [Refereed][Not invited]
     
    We studied emission process of electrons in InAs quantum dot (QD) memory devices by means of drain-current deep level transient spectroscopy (DLTS). The GaAs narrow-wire field effect transistors with a few InAs QDs above the channel were fabricated by selective-area metal organic vapor-phase epitaxy. The drain current, measured by sweeping the gate voltage forward and backward, exhibited clear clock-wise hysteresis due to charging of electrons into the states induced by InAs QDs with a threshold voltage shift (A Vth) of 30 mV at 20 K. Peaks representing three kinds of electron traps concerning InAs QDs were observed in the DLTS spectra. These peaks exhibited different dependences on the applied gate pulsed voltage during the DLTS measurement. In comparison with the temperature dependence of Delta Vth, we found that our memory operation was attributed to one localized state introduced by InAs QDs.
  • Takashi Fukui, Premila Mohan, Junichi Motohisa
    2007 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 384 - 387 1092-8669 2007 [Refereed][Not invited]
     
    We report the growth and characteristics of InP nanowires and InP/InAs/InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. InP hexagonal nanowires with (110) sidewall facets were successfully formed on (111)B InP substrates. The core-multishell nanowires were also formed composed of InAs tube-like layer buried in a higher bandgap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all the three layers were epitaxially grown without the assistance of any catalyst. The periodically aligned nanowires and core-multishell nanowires were highly uniform, and Wulzaite structures. 4K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the PL peaks were in good agreement with calculated values.
  • Shinjiroh Hara, Junichi Motohisa, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 298 612 - 615 0022-0248 2007/01 [Refereed][Not invited]
     
    We demonstrate the successful formation of ferromagnetic MnAs nanoclusters, self-assembled on GaInAs (I 1 1) B surfaces by metalorganic vapor phase epitaxy (MOVPE). The hexagonal MnAs nanoclusters show strong ferromagnetic coupling at room temperature when the external magnetic fields are applied in a direction parallel to the InP (I 1 1) B wafer planes. We have found that, on GaInAs/InP (I 1 1) B layers, the size and density of the MnAs nanoclusters strongly depend on the MOVPE growth conditions. The averaged height of the nanoclusters is decreased from 250 to 61 nm with increasing V/Mn ratios in a supply gas from 60 to 750, whereas their density is increased from 10(7) to 10(8) cm(-2). It is increased from 66 to 319 nm with increasing growth temperatures from 550 to 700 degrees C, whereas the density is decreased from 10(8) to 10(7) cm(-2). The size and density of the MnAs nanoclusters are controllable by optimizing MOVPE growth conditions, such as growth temperatures, V/Mn ratios and growth time. (c) 2006 Elsevier B.V. All rights reserved.
  • K. Tomioka, P. Mohan, J. Noborisaka, S. Hara, J. Motohisa, T. Fukui
    JOURNAL OF CRYSTAL GROWTH 298 644 - 647 0022-0248 2007/01 [Refereed][Not invited]
     
    We report on size, shape, and position-controlled growth of high-density InAs nanowire array on InAs (I I I)B substrates by selective-area metalorganic vapor phase epitaxy (SA-MOVPE). In the optimized growth condition, uniform array of vertically aligned nanowires were formed. Growth carried under different growth temperatures, T-G, indicated that the lateral growth along the <(1) over bar 10 > directions was suppressed for T-G >= 540 degrees C to uniform array of thin InAs nanowires. This behavior is thought to be due to decreased number of bonds available for binding In atoms at step sites via desorption of As adatoms as growth temperature increased. Average height of the InAs nanowires found to depend significantly on the diameter of nanowires. (c) 2006 Elsevier B.V. All rights reserved.
  • Keitaro Ikejiri, Jinichiro Noborisaka, Shinjiroh Hara, Junichi Motohisa, Takashi Fukui
    JOURNAL OF CRYSTAL GROWTH 298 616 - 619 0022-0248 2007/01 [Not refereed][Not invited]
     
    We studied the growth mechanism of GaAs nanowires in selective-area metalorganic vapor phase epitaxy (MOVPE) by investigating the dependences on substrate orientations and growth conditions. The nanowire structures were formed only on GaAs (I I l)B substrate under high temperature (750 degrees C) and low arsine partial pressure conditions. Structures selectively grown on substrates with various orientations always exhibited specific low-index facets such as { 110}, {111}A, and {111}B. It was also found that the appearance of these facets depended strongly on the growth conditions. Furthermore, we have observed a considerable lateral growth on the sidewalls of the nanowires when the growth temperature was lowered and arsine partial pressure was increased, indicating that the growth mode could be changed by the growth conditions. These results demonstrate that the growth mechanism of GaAs nanowires by SA-MOVPE is neither catalyst nor oxide assisted but by the formation of facets during growth. (c) 2006 Elsevier B.V. All rights reserved.
  • Aharonov-Bohm oscillation of a charged exciton in a quantum tube
    S. Nomura, K. Tsumura, J. Motohisa, T. Fukui
    12th Advanced Heterostructure Workshop 2006/12 [Refereed][Not invited]
  • L. Yang, J. Motohisa, J. Takeda, K. Tomioka, T. Fukui
    APPLIED PHYSICS LETTERS 89 (20) 0003-6951 2006/11 [Refereed][Not invited]
     
    The authors report the fabrication of the nanopillars with single InGaAs/GaAs quantum well by selective-area metal organic vapor phase epitaxy. The standard diameter deviation of the nanopillars is about 8% and the standard deviation in their height about 5%. Their photoluminescence peak positions shift to the longer wavelength with an increase in the diameter of the nanopillars, which is not due to the quantum confinement effect in the radial or axial direction but due to the stoichiometry difference of the indium content in the nanopillars with different diameters. (c) 2006 American Institute of Physics.
  • MOTOHISA Junichi, FUKUI Takashi
    應用物理 応用物理学会 75 (3) 296 - 302 0369-8009 2006/03/10 [Not refereed][Not invited]
  • P Mohan, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 88 (13) 0003-6951 2006/03 [Refereed][Not invited]
     
    We report the growth of InP/InAs/InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4 K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values. (c) 2006 American Institute of Physics.
  • Y. Natsui, Y. Miyoshi, N. Ooike, J. Motohisa, T. Fukui
    e-Journal of Surface Science and Nanotechnology 4 180 - 183 1348-0391 2006/02/10 [Refereed][Not invited]
     
    We propose and fabricate a 1-bit adder circuit having only two single electron transistors (SETs) for AND and XOR logic operations by using SA-MOVPE. Two SETs have two common input gates and different Coulomb oscillation periods. The logic operation can be achieved on the basis of a binary decision diagram (BDD) architecture using Coulomb blockade (CB) in GaAs dots. We also demonstrate Coulomb oscillations caused by input gate voltages for a SET. Oscillation features of two input gates are the same and their phases can be shifted by the control gate. © 2006 The Surface Science Society of Japan.
  • Junichi Motohisa, Takashi Fukui
    NANOMATERIAL SYNTHESIS AND INTEGRATION FOR SENSORS, ELECTRONICS, PHOTONICS, AND ELECTRO-OPTICS 6370 63700B.1-63700B.11  0277-786X 2006 [Not refereed][Not invited]
     
    We describe our recent results on the formation of catalyst-free III-V semiconductor nanowires and related nanostructures utilizing selective-area metalorganic vapor phase epitaxial (SA-MOVPE) growth. Array of vertically aligned nanowires are grown on partially masked GaAs and InP substrate along the [111]B or [111]A directions, respectively. The alignment and size of the nanowires are controlled by the mask patterning as well as growth conditions. Nanowires containing heterostructures in their radial direction have also been realized by controlling the growth mode during SA-MOVPE. Their optical and transport properties are also investigated and described.
  • P Mohan, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 88 (1) 013110-013110-3  0003-6951 2006/01 [Not refereed][Not invited]
     
    We report the realization of ordered arrays of single-crystalline InAs nanotubes by a simple pure-eptiaxial approach. The process involved the fabrication of lattice-mismatched InP/InAs core-shell nanowires using selective area metalorganic vapor phase epitaxy on InP (111)A substrates. The subsequent removal of the InP core resulted in vertically aligned InAs nanotubes which were highly uniform with well-defined features and controllable dimensions. Transmission electron microscopy studies confirmed that the nanotubes were single-crystalline with wurtzite crystal structure and temperature-dependent transport measurements revealed that they were conductive without any intentional doping. The realization of such conductive InAs nanotubes opens up new possibilities for both fundamental studies and future device applications. (c) 2006 American Institute of Physics.
  • Magneto-optical properties of electron-hole states in GaAs quantum wires
    H. Tamura, S. Nomura, M. Yamaguchi, T. Akazaki, H. Takayanagi, P. Mohan, J. Motohisa, T. Fukui
    J. Phys. 38 130  2006/01 [Refereed][Not invited]
  • P Mohan, J Motohisa, T Fukui
    NANOTECHNOLOGY 16 (12) 2903 - 2907 0957-4484 2005/12 [Refereed][Not invited]
     
    We report on the systematically controlled growth of InP nanowire arrays by catalyst-free selective area metalorganic vapour phase epitaxy on partially masked InP(1 I 1)A substrates. The length, diameter, shape and position of the nanowires were precisely controlled by careful choice of the growth conditions and mask patterning. Manipulation of the growth conditions also enabled us to deliberately define the nanowire growth along either the axial or the radial direction, which has significant potential for the realization of novel nanostructures. Transmission electron microscopy studies revealed that the InP nanowires grown were single-crystalline with wurtzite crystal structure and the photoluminescence studies carried out at 4 K on InP nanowire arrays revealed a single intense emission peak with a significant blueshift. The controlled fabrication thus enabled the nanowires to be realized in a highly uniform manner as reproducibly identical structures and with perfect positioning in predetermined configurations, making them highly suitable for practical integration into nanodevices.
  • J Takeda, M Akabori, J Motohisa, R Notzel, T Fukui
    NANOTECHNOLOGY 16 (12) 2954 - 2957 0957-4484 2005/12 [Refereed][Not invited]
     
    GaAs hexagonal air-hole arrays fabricated by selective-area metal-organic vapour phase epitaxy (SA-MOVPE) on patterned GaAs(I I I)B substrates are promising for applications to hexagonal air-hole-type two-dimensional photonic crystal (2D-PhC) slabs, because the grown structures exhibit smooth flat surfaces surrounded by crystal facets. In this paper, we describe SA-MOVPE carried out under various gas-flow sequences in order to reduce the growth temperature, and to obtain uniform air-hole arrays without lateral over-growth (LOG). We found that the growth rate in the pattern region and LOG were closely related to the effective As coverage and the desorption rate of the source materials. By optimizing SA-MOVPE, we obtained uniform hexagonal air-hole arrays with almost no LOG for arrays with 500-400 nm periodicity using alternate supply of the source materials (flow-rate modulation epitaxy mode). Finally, we successfully fabricated air-bridge-type hole arrays using selective etching of a sacrificial layer for vertical confinement of light in 2D-PhCs.
  • L Yang, J Motohisa, J Takeda, T Fukui
    OPTICS EXPRESS 13 (26) 10823 - 10832 1094-4087 2005/12 [Refereed][Not invited]
     
    The photonic band diagrams of the photonic crystal slabs (PCSs) with various structural air holes were calculated by plane wave expansion method with super cell method. The calculated results indicate that the PCSs with hexagonal or triangular air holes have enough large photonic band gaps in the guided mode spectrum, hence they are good candidates to be used for the PC devices. The PCs with hexagonal or triangular air holes were fabricated successfully on n-type GaAs (111) B substrate by selective-area metal organic vapor phase epitaxy (SA-MOVPE). Vertical and smooth facets are formed and the uniformities are very good. The same process was also used to fabricate hexagonal air hole arrays with the width of 100 nm successfully. A procedure was proposed and utilized to fabricate the air-bridge PCS with normal hexagonal air holes. The fabricated hexagonal air holes are very uniform and the sidewalls are smooth and vertical. Our experimental results indicate that SA- MOVPE growth is a promising low-damage fabrication method for PC devices and photonic nano-strucutres. (c) 2005 Optical Society of America.
  • D Nataraj, N Ooike, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 87 (19) 193103.1-193103.3  0003-6951 2005/11 [Not refereed][Not invited]
     
    Narrow wirelike openings were defined on SiO2-masked GaAs (001) substrates by electron-beam lithography and wet chemical etching methods. A one-dimensional GaAs channel-coupled InAs quantum dot memory device was fabricated in this opened area by the selective-area metal-organic vapor phase epitaxy. Drain current measurement by sweeping the gate voltage forward and backward showed clear hysteresis up to 180 K due to electrons charging into the quantum dots with a threshold voltage difference (Delta V-th) of 165 mV at 20 K and 29 mV at 180 K. Comparison of experimental Delta V-th values with the theoretically calculated ones showed that around 300 and 50 electrons were responsible for the memory operation at 20 and 180 K, respectively. Real time measurements showed that the write/erase states of the memory device were discriminated for more than 5 min at 20 K and about 100 s at 77 K. (C) 2005 American Institute of Physics.
  • J Noborisaka, J Motohisa, S Hara, T Fukui
    APPLIED PHYSICS LETTERS 87 (9) 0003-6951 2005/08 [Refereed][Not invited]
     
    We fabricated GaAs/AlGaAs core-shell nanowires by using selective-area metalorganic vapor phase epitaxy. First, GaAs nanowires were selectively grown on partially masked GaAs (111)B substrates; then AlGaAs was grown to form freestanding heterostructured nanowires. Investigation of nanowire diameter as a function of AlGaAs growth time suggested that the AlGaAs was grown on the sidewalls of the GaAs nanowires, forming GaAs/AlGaAs core-shell structures. Microphotoluminescence measurements of GaAs and GaAs/AlGaAs core-shell nanowires reveal an enhancement of photoluminescence intensity in GaAs/AlGaAs core-shell structures. Based on these core-shell nanowires, AlGaAs nanotubes were formed by using anisotropic dry etching and wet chemical preferential etching to confirm the formation of a core-shell structure and to explore a new class of materials. (c) 2005 American Institute of Physics.
  • L Yang, J Motohisa, T Fukui
    OPTICAL ENGINEERING 44 (7) 078002.1-078002.7  0091-3286 2005/07 [Not refereed][Not invited]
     
    A procedure for the use of the effective-index method (EIM) for high-index-contrast photonic crystal slabs (PCSs) is proposed and discussed. For such a structure, the unperturbed slab supports more than one guided mode in the vertical direction. If the EIM considering the fundamental mode only is used to deal with such a structure, large calculation errors will be introduced into the results. By comparing the gap map in the guided-mode spectrum of the hole-type PCS with those of hole-type two-dimensional photonic crystals (2-D PCs) with different refractive indices, we find that if the refractive index is selected appropriately, the agreement between these two gap maps is very good. The dispersion curves of the effective 2-D line-defect hole-type PC waveguide also agree very well with those of the line-defect hole-type PCS waveguide. However, for the pillar-type PCS, we cannot use the EIM to reduce the required calculation time and computer memory. We think that the main reason for this is the different guiding mechanisms of the optical field in these two types of PCSs. (c) 2005 Society of Photo-Optical Instrumentation Engineers.
  • Y Miyoshi, F Nakajima, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 87 (3) 033501.1-033501.3  0003-6951 2005/07 [Not refereed][Not invited]
     
    We demonstrate single-electron operation of a 1 bit adder circuit using GaAs single-electron tunneling transistors (SETs). GaAs dot and wire coupled structures for the fabrication of SETs were grown by a selective-area metalorganic vapor-phase epitaxy technique. The logic circuit was realized based on a binary decision diagram architecture using Coulomb blockade (CB) in GaAs dots and switching operations were achieved in a single-electron mode because of the CB effects. Through this architecture, a 1 bit adder circuit was realized with three SETs, two of which were for AND logic and one with two input gates for exclusive OR (XOR). Both AND and XOR operations were demonstrated at 1.9 K, which indicated successful fabrication of the 1 bit adder. (c) 2005 American Institute of Physics.
  • Magneto-optics of GaAs quantum wire lattices grown by selective-area MOVPE
    M. Yamaguchi, S. Nomura, T. Akazaki, H. Tamura, H. Takayanagi, P. Mohan, J. Motohisa, T. Fukui
    The 15th International Conference on the Electronic Properties of Two-Dimensional Systems, 2005/07 [Refereed][Not invited]
  • J Noborisaka, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 86 (21) 213102.1-213102.3  0003-6951 2005/05 [Not refereed][Not invited]
     
    We report on the fabrication of GaAs hexagonal nanowires surrounded by {110} vertical facets on a GaAs (111) B substrate using selective-area (SA) metalorganic vapor-phase epitaxial (MOVPE) growth. The substrate for SA growth was partially covered with thin SiO2, and a circular mask opening with a diameter d(0) of 50-200 nm was defined. After SA-MOVPE, GaAs nanowires with a typical diameter d ranging from 50 to 200 nm and a height from 2 to 9 μ m were formed vertically on the substrate without any catalysts. The size of the nanowire depends on the growth conditions and the opening size of the masked substrate. A possible growth mechanism is also discussed. © 2005 American Institute of Physics.
  • L Yang, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 (4B) 2531 - 2536 0021-4922 2005/04 [Not refereed][Not invited]
     
    The standard plane wave expansion (PWE) method with the supercell method was used to calculate the band diagrams of photonic crystal slabs (PCSs) with hexagonal optical atoms. A hole-type PCS with hexagonal optical atoms has almost the same width of first band gap for the TE-like mode as its two-dimensional (2D) counterpart. However, the first band gap of a pillar-type PCS with hexagonal optical atoms shrinks considerably compared with that of its 2D counterpart. The hole-type PCS with normal hexagonal optical atoms has a slightly wider first band gap for TE-like modes than does that with orthogonal hexagonal optical atoms. PCSs with normal and orthogonal hexagonal optical atoms have band gaps that can be compared to those of PCSs with circular optical atoms. Hence they are appropriate structures for fabricating PC devices. The dispersion curves of line-defect PC waveguides were also calculated by the PWE method with the supercell method and several potential methods for modulating their dispersion curves were also discussed. Modulating the width of the line defect and the size of the optical atoms along the line defect were proved to be effective ways for obtaining a single-mode line-defect PC waveguide with a large bandwidth.
  • S Hara, J Motohisa, J Noborisaka, J Takeda, T Fukui
    COMPOUND SEMICONDUCTORS 2004, PROCEEDINGS 184 393 - 398 0951-3248 2005 [Refereed][Not invited]
     
    We demonstrate formation of nano-wires with GaInAs/GaAs double hetero-structures using selective area metal-organic vapor phase epitaxy (SA-MOVPE) on SiO2 masked GaAs (111) B Substrates with periodic circular openings. Hexagonal nano-wires with six vertical {101} sidewall facets and a lateral size of around 70 to 260 nm are successfully fabricated on the masked GaAs (111) B substrates. Using microscopic area photoluminescence (mu-PL) measurements, PL emission from single GaInAs/GaAs double hetero-structure nano-wires is clearly identified at energy of around 1.28 eV. Full width at half maximum (FWHM) of the PL emission spectra from nano-wires is as narrow as around 10 meV.
  • L Yang, J Motohisa, J Takeda, T Fukui
    2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS 527 - 529 2005 [Refereed][Not invited]
     
    The gap maps in the guided mode spectrum of the photonic crystals slabs with hexagonal optical atoms were calculated by the plane wave expansion method and such structures were also fabricated by SA-MOVPE successfully.
  • J Motohisa, F Noborisaka, S Hara, M Inari, T Fukui
    Physics of Semiconductors, Pts A and B 772 877 - 878 0094-243X 2005 [Refereed][Not invited]
     
    We report on a novel catalyst-free approach to form GaAs, AlGaAs and InGaAs nanowires and their arrays by selective area metalorganic vapor phase epitaxy (SA-MOVPE). At optimized growth conditions, extremely uniform array of GaAs or InGaAs nanowires with diameter d of 100 nm to 200 nm were grown on GaAs and InP substrates, respectively. It was found the the shape (height h and size d) depends strongly on the growth conditions as well as the size do and pitch a of the mask opening. In particular, the height h of the pillar becomes higher as d is reduced. On the other hand, h decreases as a is increased. Based on these results, we obtained hexagonal nanowires with much smaller d (similar to 50 nm) and longer h (> 6 mu m) by doing SA-MOVPE on masked substrates with smaller d(0).
  • N Ooike, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 272 (1-4) 175 - 179 0022-0248 2004/12 [Refereed][Not invited]
     
    We have fabricated GaAs/AlGaAs nano-wire field effect transistors (FET's) having novel self-aligned tungsten (W) gate electrode by using selective-area metal organic vapor-phase epitaxy (SA-MOVPE). Stacked film Of SiO2/W was used as a mask for SA-MOVPE, where W is to form self-aligned gate on the side of the nano-wire structure, while SiO2 deposited on W is used to prevent lateral growth over the mask. With an appropriate design for the wire width, W, the distance, H, between the channel and the gate, FET action with good pinch-off and transfer characteristics was demonstrated at room temperature. Maximum transconductance g(m), of 600 muS/mum was achieved with a nanowire FET with channel width (W = 80 nm). (C) 2004 Elsevier B.V. All rights reserved.
  • J Motohisa, J Noborisaka, J Takeda, M Inari, T Fukui
    JOURNAL OF CRYSTAL GROWTH 272 (1-4) 180 - 185 0022-0248 2004/12 [Refereed][Not invited]
     
    We report on a catalyst-free approach for the growth of semiconductor nanowires which is attracting interest as building blocks for nanoscale electronics and circuits. Our approach is based on selective-area MOVPE and nanowires are grown from small circular openings of SiO2, mask defined on (I I I)B-oriented substrates. At optimized conditions, extremely uniform array of GaAs and InGaAs nanowires with diameter of about 200 nm was grown on GaAs and trip substrates, respectively. The nanowires have hexagonal cross-section and are perpendicular to the substrates, indicating that they are surrounded by I I 10) facet sidewalls. By reducing the mask opening size, nanowires with diameter down to 50 nm and length more than 5 mum were successfully formed. Photoluminescence and transmission electron microscopy characterization was also carried out. (C) 2004 Elsevier B.V. All rights reserved.
  • J Takeda, M Inari, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 272 (1-4) 570 - 575 0022-0248 2004/12 [Refereed][Not invited]
     
    We report on the selective-area metal-organic vapor-phase epitaxial (SA-MOVPE) growth of GaAs-based periodic air-hole arrays on partially masked GaAs (I I])A substrates for application to two-dimensional photonic crystals (2D PhCs). We obtained uniform I-pin-pitch GaAs 2D air-hole arrays on GaAs (I I I)A substrates with vertical side walls under high AsH3 partial pressure and low-growth-rate conditions. However, under these growth conditions, lateral over-growth (LOG) occurs at three corners of hexagonal air-hole, and the hole shape change to triangle. We clarified the mechanism of selective area growth on a GaAs (I I I)A substrates. We also tried shorter pitch (400nm) GaAs air-hole arrays and AlGaAs SA-MOVPE on GaAs (I I])A. (C) 2004 Elsevier B.V. All rights reserved.
  • N Ooike, J Motohisa, T Fukui
    THIN SOLID FILMS 464 220 - 224 0040-6090 2004/10 [Refereed][Not invited]
     
    We propose and demonstrate a novel self-aligning process for fabricating the tungsten (W) gate electrode of GaAs nanowire FETs by using selective-area metalorganic vapor phase epitaxy (SA-MOVPE) where SiO2/W composite films are used to mask the substrates. First, to study the growth process and its dependence on mask materials, GaAs wire structures were grown on masked substrates partially covered with a single W layer or SiO2/W Composite films. We found that lateral growth over the masked regions could be suppressed when a wire along the [110] direction and a SiO2/W composite mask were used. Using this composite mask, we fabricated GaAs narrow channel FETs using W as a Schottky gate electrode, and we were able to observe FET characteristics at room temperature. (C) 2004 Elsevier B.V. All rights reserved.
  • J Motohisa, J Takeda, M Inari, J Noborisaka, T Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 23 (3-4) 298 - 304 1386-9477 2004/07 [Refereed][Not invited]
     
    We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar structures using selective area (SA) metalorganic vapor phase epitaxy (MOVPE). By performing growth on SiO2-masked (111)B GaAs substrates with circular or hexagonal hole openings, extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting (101) vertical facets with their diameter of order of 100 nm were obtained. Unexpectedly, strong intense light emission was observed for the room temperature photoluminescence measurement of the pillar arrays in triangular lattice, which is promising for the application to the photonic crystals to enhance the light extraction efficiency from the materials with high refractive index. Furthermore, it was also found that hexagonal pillars with size 60 nm and large aspect ratio (> 100) by reducing the size of initial hole size of mask, opening a possibility to grow nanowires using epitaxial growth. (C) 2004 Elsevier B.V. All rights reserved.
  • FUKUI Takashi, MOTOHISA Junichi
    應用物理 応用物理学会 73 (5) 593 - 598 0369-8009 2004/05/10 [Not refereed][Not invited]
  • P Mohan, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 84 (14) 2664 - 2666 0003-6951 2004/04 [Not refereed][Not invited]
     
    The experimental realization of two-dimensional semiconductor artificial lattice based on InAs quantum wires is reported here. Artificial Kagome lattice fabricated using InAs quantum wires of unit cell size 0.7 mum has been theoretically proved to show ferromagnetism. Fabrication of such a structure with InAs quantum wires was attempted by selective area metalorganic vapor phase epitaxy using GaAs (111)A substrates. Temperature-dependent growth mode change was observed and Volmer-Weber growth mode at high temperature inhibited the formation of uniform structure. Low temperature and low AsH3 partial pressure resulted in the successful fabrication of 0.7 mum period InAs-based Kagome lattice structure. (C) 2004 American Institute of Physics.
  • L Besombes, JJ Baumberg, J Motohisa
    SEMICONDUCTOR SCIENCE AND TECHNOLOGY 19 (4) S148 - S151 0268-1242 2004/04 [Refereed][Not invited]
     
    Measurements of optical Rabi oscillations in the excited states of individual InGaAs are presented. Under pulsed resonant excitation we observe Rabi oscillations with increasing pulse area, which are damped after the first maximum and minimum. We show that the observed damping comes from an additional non-resonant generation of carriers in the quantum dot. The observation of Rabi oscillations provides an efficient way of directly measuring the excitonic transitions' dipole moments. A polarization anisotropy of the dipole moment is resolved in some of the quantum dots.
  • HJ Kim, J Motohisa, T Fukui
    NANOTECHNOLOGY 15 (3) 292 - 296 0957-4484 2004/03 [Refereed][Not invited]
     
    We investigated In0.8Ga0.2As self-assembled quantum dots (SAQDs) and their underlying GaAs wire structures grown by metalorganic vapour phase epitaxy on SiO2-patterned exact and vicinal (001) GaAs substrates. The directions of the misorientation of the vicinal (001) GaAs substrate and the patterned wire SiO2 mask were [110]. During the growth of the GaAs layer on SiO2-patterned vicinal (001) GaAs substrates, {110}, {111}A, and {113}A facets were evolved by the opening layer width of the masks and the misorientation angles of the substrates. The ratio of the growth rate on the {111}A sidewalls to that on the neighbouring facets, (G({111}A)), was increased by using the vicinal substrate having the higher misorientation angle, hence the surface migration of Ga adatoms from the {111}A sidewalls to the top region (MS,T) decreased. In0.8Ga0.2As SAQDs having regular periodicity on a narrow (001) top terrace were formed on a SiO2-patterned 5degrees-off (001) GaAs substrate.
  • M Inari, J Takeda, J Motohisa, T Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 (2-4) 620 - 624 1386-9477 2004/03 [Refereed][Not invited]
     
    Fabrication of high-quality photonic crystals (PCs) is an important issue for precise control of photon propagation. In particular, high aspect ratio, smooth surface, and high uniformity are required to achieve two-dimensional PCs (2DPCs). We report on the fabrication of InP and InGaAs pillar structures on InP substrates by using selective area metal-organic vapor-phase epitaxy (SA-MOVPE) for application to InP-based 2DPCs. This method is very promising as a way to form semiconductor 2DPCs because it makes it possible to obtain PC structures without process-induced damage. To form uniform pillar arrays, we investigated the properties of SA-MOVPE growth on InP (111)A and (111)B substrates. We found that pillar shapes strongly depended on the TBP pressure and growth temperature, and on the optimum growth conditions of uniform pillar structures having {110} vertical side facets. (C) 2003 Elsevier B.V. All rights reserved.
  • J Motohisa, J Takeda, M Inari, T Fukui
    ENGINEERED POROSITY FOR MICROPHOTONICS AND PLASMONICS 797 103 - 108 0272-9172 2004 [Refereed][Not invited]
     
    We report on the growth of GaAs and GaAs/AlGaAs heterostructured hexagonal pillar arrays using selective area (SA) metalorganic vapor phase epitaxy (MOVPE) for the application of two-dimensional photonic crystals (2D-PhCs). SA-MOVPE was carried out on SiO2 masked (111)B GaAs substrates with circular or hexagonal hole openings. Extremely uniform array of hexagonal GaAs/AlGaAs pillars consisting {110} vertical facets with their diameter of order of 200 nm were obtained. Unexpectingly strong intense light emission was observed for the room temperature photoluminescence measurement, which suggests low surface nonradiative recombination and enhancement of the light extraction efficiency of the pillar arrays.
  • J Noborisaka, J Motohisa, J Takeda, M Inari, Y Miyoshi, N Ooike, T Fukui
    2004 International Conference on Indium Phosphide and Related Materials, Conference Proceedings 647 - 650 1092-8669 2004 [Refereed][Not invited]
     
    We report on the fabrication of GaAs and InGaAs hexagonal nanowires surrounded by {110} vertical facets on GaAs (111)B and InP (111)B substrates using selective area (SA) MOVPE growth. The substrate for SA-growth was partially covered with thin SiO2 and circular mask opening with diameter d(0) of 50-200 nm was defined. After SA-MOVPE, GaAs or InGaAs nanowires with the typical diameter d ranging from 50 nm to 200 nm and height 2 mu m to 9 mu m was formed vertically on the substrates, depending on the growth conditions and the pattern geometry. Possible growth mechanism is also discussed.
  • M Akabori, J Takeda, J Motohisa, T Fukui
    NANOTECHNOLOGY 14 (10) 1071 - 1074 0957-4484 2003/10 [Refereed][Not invited]
     
    We report on the selective area metal-organic vapour phase epitaxial growth of an InGaAs nano-pillar array on a partially masked TnP(1 1 1)B substrate. This technique is very promising as a way to form semiconductor two-dimensional photonic crystals (2DPCs) suitable for infrared optical fibre communication. We successfully formed uniform hexagonal 2DPCs having vertical (110) facet sidewalls on 400 nm-pitch masked substrates. We observed vertical growth enhancement as well as the lateral overgrowth suppression for high aspect ratio InGaAs nano-pillar array formation under high growth-rate, long growth-time, and narrow window-opening conditions. We verified infrared emission from the InGaAs nano-pillar array by low-temperature photoluminescence measurement.
  • F Nakajima, Y Miyoshi, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 83 (13) 2680 - 2682 0003-6951 2003/09 [Refereed][Not invited]
     
    We experimentally demonstrated single-electron operations of an AND/NAND logic circuit based on a self-organized GaAs quantum-dot (QD) network fabricated by applying a selective-area metalorganic vapor-phase epitaxy technique. Single-electron logic operations using four cooperating single-electron tunneling (SET) transistors has been tested. This logic circuit has an architecture based on a binary decision diagram (BDD) using a Coulomb blockade (CB) in GaAs QDs, which is a representation of digital logic functions using directed graphs. BDD node devices consisting of two SET transistors achieved a two-way path switching operation in single-electron mode due to the CB effects which appeared complementarily in the two SET transistors at 1.9 K. We also demonstrated an AND/NAND operation in a logic circuit by integrating two BDD nodes. (C) 2003 American Institute of Physics.
  • P Mohan, F Nakajima, M Akabori, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 83 (4) 689 - 691 0003-6951 2003/07 [Not refereed][Not invited]
     
    Artificial two-dimensional semiconductor Kagome lattice structures formed by quantum wires can show ferromagnetism when the flatband is half filled, even though it does not have any magnetic elements. Experimental realization of such a Kagome lattice structure is reported. The structure, with different pattern periods, was formed with GaAs quantum wires by selective area metalorganic vapor phase epitaxy on GaAs (111)B substrates. To overcome the lateral overgrowth and to improve the shape of smaller period pattern, flow rate modulation epitaxy was employed and a GaAs Kagome lattice structure with 1 mum period was effectively grown. (C) 2003 American Institute of Physics.
  • H Takahashi, Y Miyoshi, E Nakajima, P Mohan, J Motohisa, T Fukui
    APPLIED SURFACE SCIENCE 216 (1-4) 402 - 406 0169-4332 2003/06 [Refereed][Not invited]
     
    We fabricated quantum wires (QWRs) with sub-micron wire width using GaAs/AlGaAs selectively doped structures grown by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (001) masked GaAs substrates partially covered by SiON. From the measurement of a two-terminal conductance as a function of geometrical wire width, QWRs with effective channel width <100 nm are formed without application of any gate bias. The magnetoresistance measurement at 1.7 K also suggests the formation of narrow QWRs, although it also indicates a presence of potential fluctuation along the QWRs. The effective channel width of present QWRs are much narrower than the previously reported values (similar to300 nm) of those formed by SA-MOVPE. (C) 2003 Published by Elsevier Science B.V.
  • L Besombes, JJ Baumberg, J Motohisa
    PHYSICAL REVIEW LETTERS 90 (25) 0031-9007 2003/06 [Refereed][Not invited]
     
    The excited states of neutral and charged single InGaAs/GaAs quantum dots are studied using a confocal microspectroscopy technique. Because of their different Coulomb energy shifts, the charged and neutral states of the same quantum dot can be selectively excited. The charge of the quantum dot is controlled by a photo-depletion mechanism. Time-resolved coherent spectroscopy shows that the dephasing time of the excited states is longer when the quantum dot is charged. Rabi oscillation of the excited state of a singly charged quantum dot is demonstrated.
  • Hyo Jin Kim, Junichi Motohisa, Takashi Fukui
    Digest of Papers - Microprocesses and Nanotechnology 2003 - 2003 International Microprocesses and Nanotechnology Conference, MNC 2003 28 - 29 2003 [Refereed][Not invited]
     
    While In0.8G80.2As SAQDs formed on Si02-pattemed exact (001) GaAs substrate had only ground state emissions on (001) top surface, those had ground and excited state emissions on Si02-patterned 5°-off (001) GaAs substrate. The intensities of excited states was increased by the enhanced W(001). As the excitation power of laser increased, the intensities of ground state emissions were saturated and the intensities of the excited state emissions became larger. These results suggest that discrete nature of the density of states in SAQDs was successfully improved by using SiO2-pattemed 5°-off (001) GaAs substrate.
  • HJ Kim, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 81 (27) 5147 - 5149 0003-6951 2002/12 [Refereed][Not invited]
     
    We investigated the formation of In0.8Ga0.2As self-assembled quantum dots (SAQDs) grown on SiO2-patterned 1degrees 2degrees, and 5degrees-off (001) GaAs substrates by selective area metalorganic vapor phase. epitaxy technique. The SiO2 patterns were filled with various stripe opening windows along the misorientation direction of the substrates. During the growth of the GaAs buffer layer on the opening regions, the steps on the (001) top facet was affected by the widths of the (001) top facet and the misorientation angles of the substrates. Single- or double-row aligned In0.8Ga0.2As SAQDs having definite interval were successfully fabricated on the (001) top facet With optimized top width and periodicity of step bunching. These results indicate that the selective growth technique of SAQDs by utilizing SiO2-patterned vicinal substrates is promising for nanoelectronic device applications such as single-electron memory devices. (C) 2002 American Institute of Physics. [DOI: 10.1063/1.1534385].
  • J Motohisa, F Nakajima, T Fukui
    APPLIED SURFACE SCIENCE 190 (1-4) 184 - 190 0169-4332 2002/05 [Refereed][Not invited]
     
    We describe fabrication methods of GaAs and InAs quantum dot (QD) structures and related semiconductor nanostructures having nanoscale heterointerfaces grown by the selective area metalorganic vapor-phase epitaxial (SA-MOVPE) method on partially masked GaAs substrates. GaAs QD arrays and wire-dot coupled structures having strong lateral confinement were fabricated on appropriately designed masked substrates. InAs QDs were also formed on various kinds of GaAs pyramidal and wire structures, where site-selective formation is demonstrated by the combination of self-assembling growth mode and selective area growth. The application of QDs to single-electron transistors using SA-MOVPE is also described. (C) 2002 Elsevier Science B.V. All rights reserved.
  • J Takeda, M Akabori, J Motohisa, T Fukui
    APPLIED SURFACE SCIENCE 190 (1-4) 236 - 241 0169-4332 2002/05 [Refereed][Not invited]
     
    A two-dimensional (2D) periodic array having air/semiconductor interfaces can be applied to photonic crystals (PCs), which are expected to control spontaneous emission and optical transports in the next-generation devices. In this paper, we report on the selective area metal-organic vapor phase epitaxial (SA-MOVPE) growth of a AlxGa1-xAs 2D periodic array on a GaAs (I I 1)B substrate for application to 2DPCs having GaAs/AlGaAs heterostructures. AlxGa1-xAs (x = 0, 0.25 and 0.50) growth was carried out on triangular lattice array of hexagonal GaAs openings and hexagonal SiNx masks. A uniform Al0.50Ga0.50As X hexagonal pillar array and a GaAs hexagonal air-hole array with a 1 mum-period were successfully obtained. The important growth parameter for uniform 2DPC structure formation by SA-MOVPE was clarified. Furthermore, we describe the successful demonstration of a 400 nm-period pillar array and an air-hole array, which corresponds to the optical communication wavelength lambda = 1.3-1.55 mum. The results indicate that SA-MOVPE method is very promising for the formation of uniform semiconductor 2DPCs without the occurrence of process-induced damages. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Kusuhara, F Nakajima, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 (4B) 2508 - 2512 0021-4922 2002/04 [Not refereed][Not invited]
     
    We investigate the formation of InAs quantum dots (QDs) on the top of AlGaAs ridge wire structures along the [(1) over bar 10] direction by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and study their size distribution. It is found that the size distribution of QDs depends on the top width W of AlGaAs wires and growth amount theta of InAs. InAs dot size across the AlGaAs wires are limited by W and it becomes uniform for narrower W. In contrast, the size along the wire exhibits nonuniformity, particularly for narrower W and large theta. In addition, the shapes of InAs dot change depending on W. The results are discussed based on the diffusion of In from facets and masked area and the coalescence of QDs.
  • T Ishihara, S Lee, M Akabori, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 237 1476 - 1480 0022-0248 2002/04 [Refereed][Not invited]
     
    We fabricated self-organized InxGa1-xAs quantum dots on GaAs(0 0 1) vicinal surfaces having multiatomic steps by using metalorganic vapor phase epitaxy. The dots preferentially grew along the GaAs multiatomic step edges. We investigated the density and uniformity of the dots as a function of the substrate misorientation angle, the layer thickness, the In content, and the growth temperature. Observation of grown surfaces by atomic force microscopy showed that the dot formation depended strongly on the In content and layer thickness. In general, for lower In contents and/or thinner layers, no dot formation was observed because the interface stresses were insufficient for three-dimensional island growth. For higher In content and/or thicker layers, high-density dots formed on the GaAs multiatomic steps. However, these dots were not always uniform: they included small dots (similar to 40 nm) and large islands (> 100 nm). Under optimum growth conditions, that is, 3.2-monolayer In0.8Ga0.2As growth, we obtained high-density (6.2 x 10(10)/cm(2)) and highly uniform (10-25 nm) small quantum dots along the GaAs multiatomic step edges. (C) 2002 Published by Elsevier Science B.V.
  • WG van der Wiel, S De Franceschi, JM Elzerman, S Tarucha, LP Kouwenhoven, J Motohisa, F Nakajima, T Fukui
    PHYSICAL REVIEW LETTERS 88 (12) 0031-9007 2002/03 [Not refereed][Not invited]
     
    We report a strong Kondo effect (Kondo temperature similar to4 K) at high magnetic field in a selective area growth semiconductor quantum dot. The Kondo effect is ascribed to a singlet-triplet transition in the ground state of the dot. At the transition, the low-temperature conductance approaches the unitary limit. Away from the transition, for low bias voltages and temperatures, the conductance is sharply reduced. The observed behavior is compared to predictions for a two-stage Kondo effect in quantum dots coupled to single-channel leads.
  • F Nakajima, Y Ogasawara, J Motohisa, T Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 13 (2-4) 703 - 707 1386-9477 2002/03 [Refereed][Not invited]
     
    We fabricated a two-way current switch by selective area metalorganic vapor phase epitaxy and showed their characteristics as path switch based on a Coulomb blockade phenomena, Two-way current switch was realized by integrating two quantum dot (QD) devices having two types (control/main) of gate electrodes. Coulomb oscillation were observed as a function of both control and main gate voltage in each QD-devices (QDDs). It was also found that the phase of the Coulomb oscillations for the main gate could be controlled by tuning the control gate voltage. We demonstrated the switching between two current paths at appropriate bias conditions where Coulomb oscillation of two QDDs was complementary. (C) 2002 Elsevier Science B.V. All rights reserved.
  • J Motohisa, WG van der Wiel, JM Elzerman, S De Franceschi, F Nakajima, Y Ogasawara, T Fukui, LP Kouwenhoven
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 13 (2-4) 687 - 690 1386-9477 2002/03 [Refereed][Not invited]
     
    We describe transport measurements in a novel dual-gated single electron transistor based on a quantum dot (QD) fabricated by selective area growth of metalorganic vapor phase epitaxy. We observed, for the first time, clear Coulomb oscillations fabricated in combination with direct growth and lithographically defined metal gates, and achieved nearly independent control of the QD potential and the tunneling barrier height. We also were able to observe a signature of Kondo resonance when the coupling between leads and a quantum dot was sufficiently strong. (C) 2002 Elsevier Science B.V. All rights reserved.
  • M Akabori, J Takeda, J Motohisa, T Fukui
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 13 (2-4) 446 - 450 1386-9477 2002/03 [Refereed][Not invited]
     
    We describe a novel fabrication method of two-dimensional photonic crystals (2DPCs) by using selective area metal-organic vapor-phase epitaxial (SA-MOVPE) growth on (111)B masked substrates and its application to air-bridge-type structures with selective wet-chemical etching. This method is very promising as a way to form semiconductor 2DPCs because a PC membrane without process-induced damages can be obtained. To form uniform PC membranes having an air-hole array, we investigated the properties of SA-MOVPE regrowth on sub-micron-pitch masked substrates, We found that the optimum growth conditions strongly depend on the width of the GaAs opening as well as the pitch of the 2DPCs. An air-bridge structure having 250-nm-pitch 2DPC was also demonstrated by using a combination of SA-MOVPE regrowth and selective wet-chemical undercut etching. (C) 2002 Elsevier Science B.V. All rights reserved.
  • F Nakajima, Y Ogasawara, J Motohisa, T Fukui
    JOURNAL OF APPLIED PHYSICS 90 (5) 2606 - 2611 0021-8979 2001/09 [Not refereed][Not invited]
     
    We describe a method for fabricating GaAs dot arrays and dot-wire coupled structures having periodic nanofacets which uses selective area metalorganic vapor phase epitaxy. First, a thin GaAs buffer layer and an AlGaAs layer are grown on a masked substrate having wirelike openings with periodic width modulation. The width of AlGaAs wirelike structure is naturally squeezed by the periodic combination of nanofacets, and its top (001) surface is partially isolated by a self-limited region. Next, an AlGaAs/GaAs quantum well structure is fabricated on the substrate to form dots on the narrower top terraces, wires on the wider terraces, and ridge wires in the self-limited region. Cathodoluminescence images clearly showed dot arrays and dot-wire coupled structures were formed using this method. A single electron transistor with the same structure was also fabricated, and clear Coulomb blockade oscillation was observed. We also describe single electron tunneling devices with these dot arrays and dot-wire coupled structures. (C) 2001 American Institute of Physics.
  • Sangyoru Lee, Masashi Akabori, Takahiro Shirahata, Kenji Takada, Junichi Motohisa, Takashi Fukui
    Journal of Crystal Growth Vol. 231No. 1-2pp. 75-81 75 - 81 0022-0248 2001/09/01 [Not refereed][Not invited]
     
    We investigate the formation of self-organized InGaAs quantum wires (QWRs) on coherent multiatomic-stepped GaAs that had been grown on GaAs vicinal substrates by metal-organic vapor phase epitaxy. The key issues in the formation of InGaAs QWRs are the uniformity of the multiatomic steps and the large modulation in the lateral thickness of InGaAs on multiatomic-stepped GaAs structures. We use images obtained by atomic force microscopy and cross-sectional images of InGaAs layers obtained by transmission electron microscopy to investigate the surface morphology of InGaAs layers on multiatomic-stepped GaAs structures. As a result, we found that in the initial stages of InGaAs growth, Ga and In atoms preferentially attach themselves to the bottom edges of the multiatomic steps, and multiatomic-stepped structures with their own characteristic period and then reappear. These results suggest that the Schwoebel barrier, which causes the step bunching, may be decreased by the change of surface reconstruction after the introduction of small amount of In atoms to GaAs surfaces in the initial stage of growth. Furthermore, multiatomic-stepped structures formed during the growth of InGaAs layers have different periods from those on the underlying GaAs layer. The difference between the multiatomic-stepped structures on GaAs and InGaAs is thought to be caused by the difference of Schwoebel barriers between these two stepped surfaces. © 2001 Elsevier Science B.V. All rights reserved.
  • HY An, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 40 (4A) 2312 - 2316 0021-4922 2001/04 [Refereed][Not invited]
     
    In this paper, we present the results of polarization-dependent micro-photoluminescence (mu -PL) measurements of InAs quantum dots (QDs) selectively formed on GaAs pyramidal structures by selective area metalorganic vapor phase epitaxy. Under nonresonant excitation, strong optical anisotropy is observed in the PL spectra of the InAs QDs. Under near-resonant excitation, where the excitation energy is close to the wetting layer luminescence, the linear polarization degree of InAs QD is larger than that observed under nonresonant excitation. When excited and detected li-hts have the same polarization along two [110] directions, the PL is intense. However, in the cross polarization configurations, the PL intensities are very weak. The observed strong optical anisotropy in InAs QDs formed on GaAs pyramids under nonresonant excitation can be attributed mainly to the asymmetry of the QD potential which results from the anisotropic strain relaxation and shape of QDs, while that under the near-resonant excitation is explained by the hot photoluminescence effect.
  • T Terasawa, F Nakajima, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 223 (4) 523 - 527 0022-0248 2001/03 [Refereed][Not invited]
     
    We investigated the lateral thickness modulation of InGaAs layers grown on width-modulated GaAs wire structures in selective area metalorganic vapor phase epitaxy (SA-MOVPE). The InGaAs layer was formed for various GaAs buffer layer thicknesses and growth conditions. Growth of the InGaAs layer was enhanced, which is caused by the atom migration of group III atom from sidewall facets. The result indicates that the lateral thickness modulation along the [1 1 0] direction becomes more abrupt if one suppresses the diffusion on the top (0 0 1) terrace surface and the supply of growth species from sidewall facets in the transition region. (C) 2001 Elsevier Science B.V. All rights reserved.
  • M Akabori, J Motohisa, T Fukui
    PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II 87 779 - 780 0930-8989 2001 [Refereed][Not invited]
     
    We study magneto-transport properties of a 70 nm-period lateral surface superlattice (LSSL) utilizing self-organized GaAs multiatomic steps formed on GaAs (001) vicinal substrates. We measure four-terminal magnetoresistance (MR) and Hall resistance (HR) for current flow perpendicular and parallel to the multiatomic steps. Unique MR characteristics such as positive MR, amplitude modulation, phase inversion are clearly observed in high magnetic fields in spite of less anisotropy in HR. The results are clearly explained by the predicted theories based on the spectra of Landau subbands.
  • J Motohisa, T Fukui
    PHYSICS AND APPLICATIONS OF SEMICONDUCTOR QUANTUM STRUCTURES 13 - 64 2001 [Refereed][Not invited]
     
    We describe the fabrication of quantum wire (QWR) and quantum dot (QD) structures by metal-organic vapour phase epitaxial (MOVPE) growth, their characterization of optical and electronic properties and their application to quantum devices. Firstly, multiatomic steps formed during MOVPE growth on vicinal (001) GaAs surfaces were used to introduce lateral confinement potential and to realize QWRs. Based on the understanding of the formation process of GaAs and InGaAs multiatomic steps on vicinal (001) GaAs surfaces, InGaAs/GaAs QWRs were successfully fabricated on multiatomic steps and their one-dimensional nature was verified by comprehensive study of their optical properties. Application of QWRs to lasers was also demonstrated. Next, GaAs and InAs quantum dot and related nanostructures were fabricated by selective area (SA)-MOVPE growth. Zero-dimensional character of QDs formed by SA-MOVPE was demonstrated by the ultra-narrow PL peak from InAs QDs. Quantum dots connecting with GaAs quantum wires were also fabricated and they were applied to GaAs single electron transistors (SETs) and resistance-load single electron inverter circuit. Clear Coulomb blockade type conductance oscillations were observed near the pinch-off voltage of SETs at low temperatures. The inverter operation of a circuit using this SET together with load resistance was also demonstrated.
  • J Motohisa, T Terasawa, T Kusuhara, F Nakajima, T Fukui
    2001 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 370 - 373 1092-8669 2001 [Refereed][Not invited]
     
    We describe formation of self-assembling InAs quantum dots (QDs) combined with selective area metalorganic vapor phase epitaxy (SA-MOVPE) on masked (001) GaAs substrates. It was found that formation of QDs in SA-MOVPE was depended on the direction and top width of the GaAs mesa and wire structures. In particular, surface steps, which are mainly formed at the edge of (001) top surface, affects the formation of QDs on (001) surface. Such step-induced islanding is utilized to form a position controlled single InAs QD at the bend of the wires in two directions. We also discuss a possibility application of QDs for single electron memories where position-controlled QDs are used in combination with ridge quantum wires realized by the SA-MOVPE technology.
  • J Motohisa, HY An
    PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II 87 1211 - 1212 0930-8989 2001 [Refereed][Not invited]
     
    We report the investigation of optical properties and carrier relaxation in InAs QDs selectively formed on the top of GaAs pyramidal structures with low temperature micro- photoluminescence (mu -PL) and micro-photoluminescence excitation (mu -PLE) measurements. The power dependent mu -PL spectra show well-defined ground and excited states. We have also observed relative strong PLE peaks which are ascribed to the multiple LO phonon resonance. Excited states and carrier relaxation of InAs QDs formed on GaAs pyramids are also discussed.
  • T Harada, Y Oda, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 39 (12B) 7090 - 7092 0021-4922 2000/12 [Not refereed][Not invited]
     
    We describe periodic nano-faceting structures formed naturally on patterned vicinal (110) GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Periodic trenches are formed along the [1-10] direction on initial surfaces with pattern periods of 2 mum. 1 mum, 800 nm, and 600 nm. Periodic nano-faceting structures consisting of (110) and (111)B surfaces are clearly formed on the GaAs grown surfaces, and the periods are almost exactly equal to the pattern periods. The growth modes are observed from cross-sectional scanning electron microscope (SEM) images of GaAs/AlGaAs multilayer growth. The growth rate of the (111)B sidewall facets is higher than that of the (110) terraces, which indicates that quantum wire (QWR) structures can be formed naturally at step edges. Quantum well (QW) structures of GaAs/In0.18Ga0.82As/GaAs are also grown on patterned vicinal substrates. A photoluminescence (PL) spectrum at 4 K shows two sharp emission peaks from QWs on the (111)B sidewall facets at a lower energy and on the (110) terraces at a higher energy. These results suggest that it is possible to fabricate QWR arrays with high uniformity on (111)B sidewall facets.
  • CK Hahn, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 221 599 - 604 0022-0248 2000/12 [Refereed][Not invited]
     
    Position-controlled InAs single/double self-assembled quantum dots (SAQDs) were formed by selective area (SA) metalorganic vapor-phase epitaxy (MOVPE). Narrow GaAs (001)-areas, in the range of 70-200 nm in width/length. were constructed by SA-MOVPE on partially SiNx masked substrates. The number of InAs SAQDs formed on the width-controlled GaAs (001)-facet strongly depends on the width of the top facet. It is also found out that the two-dimensional (2D)-to-3D growth mode transition of InAs in selective MOVPE growth is determined not only by the growth conditions but also by the pattern itself. Different vapor-phase diffusions of source materials depending on the pattern together with dissimilar interfacet surface migration of adatoms are thought to be the origin. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Y Nakamura, T Noda, J Motohisa, H Sakaki
    PHYSICA E 8 (3) 219 - 222 1386-9477 2000/09 [Refereed][Not invited]
     
    Laterally modulated two-dimensional electron systems with 15 nm periodicity have been formed at n-AlGaAs/GaAs heterojunctions by making use of multi-atomic steps formed on vicinal (1 1 1)B GaAs epilayers. Highly anisotropic electron mobilities have been observed, where mobility mu(parallel to) parallel to the steps increases monotonically up to 280 000 cm(2)/V s with carrier density Ns at 4.2 K while mobility mu(perpendicular to) perpendicular to the steps decreases remarkably to 32 000 cm(2)/V s at high N-s. By comparing this experimental result with theory, we have found that a periodic component of the in-plane potential is important for the anisotropy. (C) 2000 Elsevier Science B.V. All rights reserved.
  • F Nakajima, J Motohisa, T Fukui
    APPLIED SURFACE SCIENCE 162 650 - 654 0169-4332 2000/08 [Refereed][Not invited]
     
    Novel quantum nano-structures which consist of quantum dots connected with quantum wires through tunneling barriers have successfully been fabricated using selective area metalorganic vapor phase epitaxy (SA-MOVPE) and have been applied to form single electron devices. GaAs/AlGaAs modulation doped heterostructures are grown on a GaAs (001) substrate partially masked with SiNx. A quasi-1 dimensional electron gas (Q-1DEG) is formed in a narrow wire-like opening, which has two prominences and a dent to modulate the channel width. From the transport properties, we confirm that a quantum dot and quantum wires connected through tunneling barriers, that is, a single electron transistor structure, is naturally formed in the part of the channel with modulated width. We will discuss the mechanism by which the dot and tunnel barriers are formed by SA-MOVPE. (C) 2000 Elsevier Science B.V. All rights reserved.
  • HY An, J Motohisa
    APPLIED PHYSICS LETTERS 77 (3) 385 - 387 0003-6951 2000/07 [Refereed][Not invited]
     
    Optical properties of InAs quantum dots on GaAs pyramidal structures formed by selective area metal organic vapor phase epitaxy have been studied with low-temperature excitation powerdependent microphotoluminescence (mu-PL) and microphotoluminescence excitation (mu-PLE) spectroscopy. The power-dependent mu-PL spectra show well-defined ground and excited states whose interlevel energy spacings are estimated to be about 21 meV. These experimental results demonstrate the discrete nature of zero-dimensional density of states in position and number controlled InAs quantum dots (QDs) selectively grown on GaAs pyramids. We have also observed relative strong PLE peaks which are ascribed to the multiple longitudinal optical phonon resonance. Excited states and carrier relaxation of InAs QDs formed on GaAs pyramids are discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)02229-4].
  • CK Hahn, J Motohisa, T Fukui
    APPLIED PHYSICS LETTERS 76 (26) 3947 - 3949 0003-6951 2000/06 [Refereed][Not invited]
     
    Position- and number-controlled InAs self-organized quantum dots (SOQDs) were formed by selective-area-metal-organic chemical vapor phase epitaxy on the partially SiNx patterned GaAs (001) substrate. The mask layer was patterned along the [110] direction, and somewhat wider rectangular openings were also attached to the line. As a result of GaAs SA growth, a pyramidal shaped structure was formed on the rectangular region of the pattern. The top area of the pyramidal structure is a very narrow hexagonal-shaped (001) facet which is surrounded by two-{111}B and four-{124} facets. The SOQD was preferentially formed on the top (001) facet because the growth rate on the (001) facet is far much higher than on the surrounding sidewalls. It is found that the number of SOQDs formed is strongly dependent on the width of the top (001)-facet so that control of single, double, and multiple SOQD(s) is possible. (C) 2000 American Institute of Physics. [S0003-6951(00)05526-1].
  • M Akabori, J Motohisa, T Fukui
    2001 IEEE INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS 191 - 196 2000 [Refereed][Not invited]
     
    We report on a novel fabrication method of air-hole-type semiconductor two-dimensional photonic crystals (2D PCs) by selective area metal-organic vapor phase epitaxy (SA-MOVPE). The PC structures are formed on GaAs (111)B substrates with a triangular lattice an-ay of hexagonally shaped silicon-nitride (SiNx) masks. The periods of triangular lattice are 10 mum, 2 mum, 1 mum and 0.5 mum. GaAs growth is carried out by conventional MOVPE and flow-rate modulation epitaxy (FME) with trimethylgallium (TMGa) and arsine (AsH3). By optimizing growth conditions, we can obtain uniform hexagonal network structures with a 0.5 pm-period and a 0.28 mum-height under low As coverage and low Ga supply i.e. low growth rate. Therefore, the results indicate that the formation of hexagonal network structures by SA-MOVPE is very useful to realize air-hole-type semiconductor 2D PCs.
  • T Ogawa, M Akabori, J Motohisa, T Fukui
    JOURNAL OF APPLIED PHYSICS 87 (2) 745 - 749 0021-8979 2000/01 [Refereed][Not invited]
     
    We studied the effect of growth interruption time and growth temperature on the natural formation of InGaAs/AlGaAs quantum disk structures grown on high-index GaAs (311)B substrates by metalorganic vapor phase epitaxy at about 800 degrees C. The InGaAs/AlGaAs quantum disks were uniformly grown only with growth interruption time of 0 s. With increasing growth interruption time, the self-organized growth mode disappeared with the growth interruption time of 20 s. During growth interruption, strain for the natural formation of quantum disks was released by intermixing between In and Al. With decreasing growth temperature, the quantum disk did not show a hexagonal shape with clear facets. The quantum disks were formed at temperature range between 700 and 830 degrees C. The self-organization appeared through strain-driven mass transport. The strain-driven mass transport seems to have two characteristic lengths such as the amplitude and the periodicity determined by In composition and the InGaAs layer thickness from electron-beam induced mass transport phenomena. (C) 2000 American Institute of Physics. [S0021-8979(00)04802-7].
  • T Harada, Y Oda, J Motohisa, T Fukui
    MICROPROCESSES AND NANOTECHNOLOGY 2000, DIGEST OF PAPERS 246 - 247 2000 [Refereed][Not invited]
  • J Motohisa, C Tazaki, T Irisawa, M Akabori, T Fukui
    JOURNAL OF ELECTRONIC MATERIALS 29 (1) 140 - 145 0361-5235 2000/01 [Refereed][Not invited]
     
    We investigated the delta-doping (delta-doping) of Si using SiH(4) on MOVPE-grown GaAs (001) vicinal surfaces to explore the possibility of selective incorporation of Si along atomic steps, and to demonstrate doping quantum wires by the combination of multiatomic steps and wire-like doping. It was found that the doping density on vicinal surfaces was enhanced as the misorientation angle was increased, which suggested the enhanced decomposition of SiH(4) and the selective incorporation of Si at step edges. It was also found that this selective incorporation could be enhanced by annealing the surface prior to the delta-doping, which resulted from the reduced incorporation of Si at the terrace regions. Anisotropic electron transport properties which are expected from the wire-like incorporation along step edges are also discussed.
  • M Akabori, K Yamatani, J Motohisa, T Fukui
    COMPOUND SEMICONDUCTORS 1999 (166) 215 - 218 0951-3248 2000 [Refereed][Not invited]
     
    We report on the transport properties of quasi one-dimensional electron gas (Q1DEG) with periodic potential modulation. The potential modulation is realized by self-organized GaAs multiatomic steps formed on GaAs (001) vicinal substrates during metalorganic vapor phase epitaxy (MOVPE), and a split gate (SPG) or a wrap gate (WPG) structure is utilized to form narrow Q1DEG channels. We have found that the SPG structure shows quantized conductance plateaus, which indicates 1D ballistic transport In contrast to above, the WPG structure shows Coulomb blockade type oscillations in the conductance-gate voltage characteristics near the pinch-off. We consider that these results originate from the difference of electrostatics coupling of gate and channel in each structure.
  • Junichi Motohisa, Chiharu Tazaki, Masashi Akabori, Takashi Fukui
    Journal of Crystal Growth Vol. 221pp. 47-52 47 - 52 0022-0248 2000/01/01 [Not refereed][Not invited]
     
    We report on properties of delta-doping (δ-doping) of Si using SiH4 on GaAs singular and vicinal (0 0 1) surfaces in metalorganic vapor-phase epitaxy (MOVPE). The δ-doping was carried out on GaAs surfaces with different types of surface morphology to investigate the incorporation mechanism of Si and clarify the importance of atomic steps and kinks. It is found that the doping density is larger in vicinal substrates than singular substrates, and that it increased with misorientation angle. We also have found that catalytic decomposition of SiH4 at step and kink sites play a role for the incorporation of Si.
  • Masashi Akabori, Junichi Motohisa, Takashi Fukui
    Physica E: Low-Dimensional Systems and Nanostructures Vol. 7pp. 766-771 766 - 771 1386-9477 2000/01/01 [Not refereed][Not invited]
     
    We study magneto-transport properties of two-dimensional electron gas (2DEG) subjected to a periodic potential with a period of 60-70 nm, where the potential modulation is realized by periodically corrugated InGaAs channel layer formed on self-organized GaAs multiatomic steps. We find a large positive magnetoresistance (MR) when the current is perpendicular to the potential modulation, while such positive resistance is not observed for the current parallel to the potential modulation. It is also found that the amplitude of MR oscillation for current perpendicular to the potential modulation is extremely large over 3.5 T, and is modulated in 2-3.5 T. In addition, we also find the anisotropy in electron mobility. The results can be explained by the large potential modulation in the lateral surface superlattice (LSSL) and associating modulation of Landau subbands in LSSL.
  • T Fukui, F Nakajima, K Kumakura, J Motohisa
    BULLETIN OF MATERIALS SCIENCE 22 (3) 531 - 535 0250-4707 1999/05 [Refereed][Not invited]
     
    A novel method of formation of uniform GaAs quantum dot (QD) structures, using selective area metalorganic vapour phase epitaxy (SA-MOVPE), and their application to single electron transistors (SETs) are demonstrated. The SiNx-coated substrates having a wire-like opening with three prominences are used. The wire-like opening is aligned in the [110] direction, which corresponds to channel region of SET. AlGaAs/GaAs modulation-doped heterostructures are grown on these substrates. Due to three prominences on the wire, the quasi-one-dimensional electron gas (Q-1DEG) channel, having a periodic variation in its width, are naturally formed. This leads to the formation of a quantum dot near the central prominence and two tunneling barriers beside the dot, which are connected to quantum wires. I-D-V-G characteristics under constant source-drain bias condition show clear conductance oscillations near the pinch-off, and oscillations are observed up to 65 K. I-D-V-DS characteristics measured at 2.1 K show clear Coulomb blockade. The results indicate the formation of SET by SA-MOVPE. Using similar method, resistance-load single electron inverter circuit is also fabricated.
  • K Yamatani, N Akabori, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (4B) 2562 - 2565 0021-4922 1999/04 [Not refereed][Not invited]
     
    We investigated the potential modulation in a novel lateral surface superlattice (LSSL) structure which was realized by utilizing multiatomic steps. The structure was grown by metalorganic vapor-phase epitaxy (MOVPE) on vicinal GaAs substrates to introduce periodic thickness modulation to the channel GaAs layer with spontaneously formed multiatomic steps. Devices having split gates were fabricated on the epitaxially grown LSSL structure. The potential modulation was investigated by a potential sweeping technique, where different bias voltages were applied to the split gates to change the minima of the potential across the multiatomic steps. We observed plateaus and oscillations of conductance as a function of the gate voltage. Systematic shifts of these positions were also observed when offset voltages between the two gates were applied and changed. These features are assumed to originate from the potential modulation induced by multiatomic steps.
  • T Ogawa, M Akabori, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (2B) 1040 - 1043 0021-4922 1999/02 [Not refereed][Not invited]
     
    We have studied surface deformation due to electron-beam irradiation in strained InGaAs/AlGaAs layers grown on GaAs (100) and (311)B planes in a horizontal low-pressure metalorganic vapor phase epitaxy system at about 800 degrees C. The surface deformation was observed in real time using a high-resolution scanning electron microscope at a magnification of 300,000. The surface deformation occurred from the inside of InGaAs/AlGaAs grown layer under the electron-beam irradiated area with the accelerating voltage of 30 kV and the scanning time ranging from 60 to 120 s. The surface deformation was not consist of amorphous-carbon contamination. The mass transport seems to be caused by the residual strain relaxation due to electron-beam irradiation.
  • F Nakajima, K Kumakura, J Motohisa, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (1B) 415 - 417 0021-4922 1999/01 [Not refereed][Not invited]
     
    GaAs single electron transistors (SETs) are successfully fabricated using selectively grown GaAs/AlGaAs modulation doped structures by metalorganic vapor phase epitaxy (MOVPE) on (001) GaAs masked substrates. SET shows clear Coulomb oscillations and Coulomb gaps modulated by gate voltage. GaAs single electron tunneling inverter circuits having a SET and a variable load resistance are also formed. The operation of a resistance-load inverter circuit is confirmed at 1.9K from the transport properties of this SET and input-output characteristics.
  • K Hayakawa, K Kumakura, J Motohisa, T Fukui
    COMPOUND SEMICONDUCTORS 1998 (162) 415 - 419 0951-3248 1999 [Refereed][Not invited]
     
    We report on the fabrication of nanometer scale AlGaAs network structures on GaAs (001) masked substrates by selective area metaloganic voper phase epitaxy (SA-MOVPE). The SiNx masks are periodically etched off with 250nm width to the both [110] and [(1) over bar 10] directions and with the periodicity ranging from 600nm to 2100nm. It is found that AlGaAs network structures are formed with extreme selectivity. We also find that the wire regions of the mesh structures consist {111}A and {111}B facet sidewalls and their widths are controlled by the growth conditions. Next, we grow InAs on AlGaAs network structures. The results show that InAs dots can be grown at the crossing points of AlGaAs network structures under the appropriate conditions. These results indicate that ridge quantum wires, pyramidal quantum dots and InAs dots can easily be fabricated on these structures with excellent controllability in their size, position and alignment.
  • Y Aritsuka, T Umeda, J Motohisa, T Fukui
    EPITAXIAL GROWTH-PRINCIPLES AND APPLICATIONS 570 97 - 104 0272-9172 1999 [Refereed][Not invited]
     
    We investigate the growth mode and the growth mechanisms of selectively grown GaAs nanometer wire structures by metalorganic vapor phase epitaxy (MOVPE). The nanometer wire structures with (111)A or(111)B facet sidewalls are grown on SiNx masked (001) GaAs with line and space pattern openings. As the growth proceeds, the growth rates increase because Ga atoms migrate from SiNx mask surface and (111) facet sidewalls. After the wire formation with triangular cross section is complete, no further growth occurs on the top of the wires, which is called self-limited growth mode. The shape and width of the top area are observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM), and the mechanism of self-limited growth is discussed. We also simulate the growth rate during selective area growth. From the comparison with the experimental results and the simulation, we estimate the amounts of Ga atom migration from SiNx mask area and(lll) facet sidewalls to the wire areas. Finally, we form InAs quantum dots on these GaAs wires, and observe photoluminescence spectra from QDs.
  • T. Ogawa, M. Akabori, J. Motohisa, T. Fukui
    Microelectronic Engineering 47 231 - 233 0167-9317 1999/01/01 [Not refereed][Not invited]
     
    We have studied the self organization of InGaAs/AlGaAs quantum disks grown on GaAs (311)B surface in MOVPE system. The change of the surface morphology due to the change of growth interruption time and growth temperature was investigated.
  • T. Ogawa, M. Akabori, J. Motohisa, T. Fukui
    Physica B: Condensed Matter 270 313 - 317 0921-4526 1999/01/01 [Not refereed][Not invited]
     
    The strained InGaAs/AlGaAs layer structures have been grown on GaAs (100) and (311)B substrates in a horizontal low-pressure metalorganic vapor-phase epitaxy system at a temperature of 800°C. In the surface observation using a high-resolution scanning electron microscope, we have found that surface deformation phenomena induced by electron-beam irradiation in strained In0.36Ga0.64As,/Al0.3Ga0.7As layers on GaAs (100) and (311)B substrates. The change of the surface morphology was observed in real time on the display of SEM with the accelerating voltage of 30 kV and the irradiated time of 60-120 s. The surface deformation through mass transport seems to be the cause of the residual strain relaxation due to electron-beam irradiation.
  • M Akabori, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 195 (1-4) 579 - 585 0022-0248 1998/12 [Refereed][Not invited]
     
    We used multiatomic steps spontaneously formed on vicinal surfaces during metalorganic vapor phase epitaxial (MOVPE) growth to introduce lateral potential modulation into two-dimensional electron gas (2DEG) and to realize a novel lateral surface superlattice (LSSL) with period of around 70 nm. Their electron transport properties were investigated at low temperatures and large anisotropies in the mobility and transconductance characteristics were found for the current parallel and perpendicular to the multiatomic steps. The potential modulation was further applied to form multiple quantum dots and tunnel junctions in combination with the squeezing of the width of the channel defined across the multiatomic steps. The Coulomb blockade type conductance oscillations were observed at low temperature transport measurement. (C) 1998 Elsevier Science B.V. All rights reserved.
  • K Kumakura, J Motohisa, T Fukui
    PHYSICA E 2 (1-4) 809 - 814 1386-9477 1998/07 [Refereed][Not invited]
     
    GaAs wire transistors and single electron transistors (SETs) were successfully fabricated using GaAs/AlGaAs modulation doped structures grown by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (001) masked GaAs substrates. The results of magnetoresistance of wire transistors applying the negative gate bias show the one-dimensional transport. In SETs, near the pinch-off voltage, Coulomb blockade type conductance oscillations were observed up to 65 K. Coulomb gap and total capacitance CZ were estimated to be 12 mV and 13 aF, respectively. Fabrication process and transport properties of the devices were described. (C) 1998 Elsevier Science B.V. All rights reserved.
  • J Motohisa, JJ Baumberg, AP Heberle, J Allam
    SOLID-STATE ELECTRONICS 42 (7-8) 1335 - 1339 0038-1101 1998/07 [Refereed][Not invited]
     
    We have studied photoluminescence (PL) from single InAs self-assembled quantum dots (QDs) by micro-PL measurements and, in particular, studied the excitation intensity dependence. We have found strong quenching in both the peak and integrated intensity of narrow PL lines when the excitation power was increased. This suggests that the present behavior is mainly due to the change of carrier screening and relaxation between the InAs wetting layer and InAs QDs. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • T Umeda, K Kumakura, J Motohisa, T Fukui
    PHYSICA E 2 (1-4) 714 - 719 1386-9477 1998/07 [Refereed][Not invited]
     
    We demonstrate InAs growth on the top of GaAs pyramidal structures formed by selective area MOVPE; and show a successful achievement of the position controlled self-organized InAs quantum dots. First, GaAs pyramidal structures are selectively grown on GaAs (001)substrates with SiNx masks which have circular opening patterns in 150 nm diameter, and in 160-500 nm periodicity. Next, InAs layer is grown on GaAs pyramids. In this case, InAs dots are preferentially formed on the top portion of the pyramids. Finally, GaAs capping layer is overgrown on InAs dots. Photoluminescence (PL) spectrum shows strong emission from InAs quantum dots formed on the top portions of the pyramids. (C) 1998 Elsevier Science B.V. All rights reserved.
  • S Hara, J Motohisa, T Fukui
    SOLID-STATE ELECTRONICS 42 (7-8) 1233 - 1238 0038-1101 1998/07 [Refereed][Not invited]
     
    We have been demonstrating natural formation and characterization of InGaAs strained quantum wire (QWR) structures on coherent GaAs multiatomic steps grown by metalorganic vapor phase epitaxy (MOVPE). In this paper, we report on the optical properties of InGaAs QWRs. First, photoluminescence (PL) and photoluminescence excitation (PLE) spectra were taken at 77 K. PLE spectra showed the polarization anisotropy for excitation light with electric field parallel or perpendicular to the QWRs. Next, we measured the PL of InGaAs QWRs on GaAs multiatomic steps at 4.2 K, in magnetic fields, to examine the lateral confinement. It was found that the diamagnetic coefficient is 16 mu eV/T-2 and is much smaller than that of quantum well (QWL) on singular (001) GaAs substrates (45 mu eV/T-2), which suggests the presence of lateral confinement. We also succeeded for the first time in the pulsed laser operation of InGaAs QWRs on GaAs multiatomic steps at 77 K by current injection. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • S Hara, J Motohisa, T Fukui
    ELECTRONICS LETTERS 34 (9) 894 - 895 0013-5194 1998/04 [Refereed][Not invited]
     
    The authors report the first successful demonstration of self-organied InGaAs quantum wire (QWR) laser diodes (LDs) utilising GaAs multi-atomic steps at 77K by pulsed current injections. The lasing wavelength of InGaAs QWR-LDs is consistent with the peak position of photoluminescence spectra at 77K. When a cavity direction is perpendicular to the QWR's array direction, the threshold current density of InGaAs QWR-LDs is smaller than that of quantum well LDs.
  • T Irisawa, J Motohisa, M Akabori, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 37 (3B) 1514 - 1517 0021-4922 1998/03 [Not refereed][Not invited]
     
    We have investigated the delta-doping of Si on GaAs vicinal surfaces on which self-organized multiatomic steps are formed during metalorganic vapor phase epitaxy (MOVPE) and the possibility of its wire-like selective incorporation into step edges to form doping quantum wires (DQWRs). We evaluated the electrical characteristics of delta-doped layers by Hall and C-V measurements and investigated their dependence on misorientation angles of GaAs vicinal substrates and doping time. The incorporation of Si is enhanced by steps. This effect is particularly important at the initial stage of delta-doping when the surface coverage of Si is not high. Our results also suggest that the doping density at multiatomic step regions is higher than at terrace regions. Therefore, it is expected that the selective wire-like incorporation of Si takes place at the step edges, and DQWRs can be realized under suitable growth conditions.
  • T Ogawa, M Kawase, M Akabori, J Motohisa, T Fukui
    1998 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS - CONFERENCE PROCEEDINGS 607 - 610 1092-8669 1998 [Refereed][Not invited]
     
    We have found that mass transport phenomena were induced by electron-beam irradiation in strained In0.36Ga0.64As/Al0.3Ga0.7As layers on GaAs (100) and (311)B substrates. The strained InGaAs/AlGaAs layer structures have been grown on GaAs (100) and (311)B substrates in a horizontal low-pressure metaloganic vapor phase epitaxy system at a temperature of 800 degrees C and 830 degrees C. In the surface observation using high-resolution scanning electron microscope, the surface morphology was changed into a deformed structure by electron beam with the accelerating voltage of 30kV and the scanning time of 60 similar to 120 sec. The surface deformation phenomena were observed in real time on the display of SEM, the deformation was not amorphous-carbon contamination. The mass transport seems to be caused by the residual strain relaxation due to electron-beam irradiation.
  • T. Irisawa, J. Motohisa, M. Akabori, T. Fukui
    Digest of Papers - Microprocesses and Nanotechnology 1998: 1998 International Microprocesses and Nanotechnology Conference 1998-July 301 - 302 1998/01/01 [Not refereed][Not invited]
  • Fukui T, Ishizaki J, Hara S, Kumakura K, Motohisa J
    Journal of the Japanese Association of Crystal Growth 日本結晶成長学会 24 (2) 196 - 198 0385-6275 1997/07/01 [Not refereed][Not invited]
     
    GaAs self-organized quantum nano-structures were fabricated by metalorganic chemical vapor deposition on vicinal and patterned GaAs substrates. Using step bunching phenomena during GaAs growth on vicinal GaAs substrate, high density quantumwire array was formed. GaAs quantum dots were also fabricated on GaAs pyramidal structures grown SiNx masked(001)GaAs with square opening.
  • M Akabori, J Motohisa, T Irisawa, S Hara, J Ishizaki, T Fukui
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 36 (3B) 1966 - 1971 0021-4922 1997/03 [Refereed][Not invited]
     
    We have studied the transport properties of novel lateral surface superlattice electron wave interference devices in which multiatomic steps are utilized to introduce periodic potentials into two dimensional electron systems. The device structure was fabricated by metalorganic vapor phase epitaxy (MOVPE) on vicinal GaAs surfaces, and spontaneously formed multiatomic steps were periodically embedded at the heterojunction of n-AlGaAs/GaAs. Oscillations of the transconductance as a function of gate voltage were found in three different devices. Our simple analysis suggests that the oscillations found in two devices result from the periodic potentials induced by the multiatomic steps and coherent electron wave interference, whereas those in the other one arise from random interference. Our results imply the effect of height and randomness in the periodic potential on the characteristics of electron wave interference devices.
  • K Kumakura, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 170 (1-4) 700 - 704 0022-0248 1997/01 [Refereed][Not invited]
     
    We have demonstrated novel GaAs quantum dot arrays coupled to quantum wire networks, that is, coupled quantum dots (CQDs) formed by selective area metalorganic vapor phase epitaxy (SA-MOVPE). First, GaAs buffer layers are grown on GaAs(001) substrates with SiNx square masks in 400 nm periodicity to [100] and [010] directions. GaAs cross-wire structures with pyramids at the corners are obtained. Next, GaAs/AlGaAs quantum wells are overgrown on top of these structures. Quantum dots (QDs) and quantum wires (QWRs) are formed at the top portions of the pyramids and at the ridges of wires, respectively. The cathodoluminescence (CL) image shows strong emission from the top portions of the pyramids, which suggests that high-quality CQD structures are formed by SA-MOVPE.
  • S Hara, J Motohisa, T Fukui
    JOURNAL OF CRYSTAL GROWTH 170 (1-4) 579 - 584 0022-0248 1997/01 [Refereed][Not invited]
     
    We investigate the formation of self-organized InGaAs quantum wires (QWRs) on coherent GaAs multiatomic steps grown on vicinal GaAs substrates. In our previous study, GaAs QWRs were formed at the edge of AlAs multiatomic steps grown by metalorganic vapor phase epitaxy (MOVPE). We also found that coherent multiatomic steps formed on GaAs tend to be disturbed during AlAs growth. In the present investigation, we clarify that a thin InGaAs layer with less than 0.15 In content grows in step flow growth mode from the edge of GaAs multiatomic steps, while that with more than 0.2 In content grows in three-dimensional nucleation and growth mode at the edge of multiatomic steps due to the strain effect. Next, we fabricate InGaAs/GaAs strained QWRs at the edge of coherent GaAs multiatomic steps. Locally thick InGaAs QWR structures are observed by a transmission electron microscope. Photoluminescence (PL) measurements reveal that the PL spectra of InGaAs QWR samples show lower energy shift (red-shift) by about 30 meV compared to those of quantum well ones due to the formation of InGaAs QWRs at the edge of coherent GaAs multiatomic steps.
  • M Sakuma, T Fukui, K Kumakura, J Motohisa
    CONTROL OF SEMICONDUCTOR SURFACES AND INTERFACES 448 259 - 263 0886-7860 1997 [Refereed][Not invited]
     
    We propose and demonstrate a new mask material of AlGaAs native oxide for selective area metalorganic vapor phase epitaxy (MOVPE) which has several advantages over conventional SiNx or SiO2 masks. GaAs selective area growth occurs on masked substrate of AlGaAs native oxide whose Al composition is 0.4, and the wire structures with trapezoidal cross section are formed along [100] direction on (001) GaAs substrates with line & space mask pattern. Furthermore, after annealing the selectively grown GaAs wire samples, GaAs layers can be regrown with atomically smooth surface, in which GaAs wires are perfectly buried. The results show that this novel selective area MOVPE technique using AlGaAs native oxide masks are promising for quantum nano-structure device fabrication.
  • D Dixon, LP Kouwenhoven, PL McEuen, Y Nagamune, J Motohisa, H Sakaki
    PHYSICAL REVIEW B 53 (19) 12625 - 12628 1098-0121 1996/05 [Refereed][Not invited]
     
    We have measured the nonlinear transport properties of two GaAs/AlxGa1-xAs quantum dots connected in series. At high source-drain bias the Coulomb oscillations develop a sharp overstructure. The behavior of this overstructure is studied as a function of the electrostatic potentials of the dots. The structure is shown to arise from the modulation of interdot tunneling that occurs as the quantum levels in the two dots are aligned and dealigned.
  • T Fukui, K Kumakura, K Nakakoshi, J Motohisa
    SOLID-STATE ELECTRONICS 40 (1-8) 799 - 802 0038-1101 1996 [Refereed][Not invited]
     
    We have fabricated AlGaAs/GaAs quantum dot structures using selective area metalorganic vapor phase epitaxy (MOVPE). First, GaAs pyramidal structures with four-fold symmetric {011} facet side walls are formed on SINx masked (001) GaAs with square openings. After the pyramidal structures were completely formed, no growth occurs on the top or side walls of the pyramids. Furthermore, the shape and width of the top area observed by a scanning electron microscope (SEM) and an atomic force microscope (AFM) is shown to be highly uniform. This indicates that self-limited growth occurs. Next, using these uniform pyramids, GaAs quantum dots are overgrown on top of the pyramids using different growth conditions. Sharp photoluminescence (PL) spectra are observed from uniform quantum dots.
  • LP Kouwenhoven, NC vanderVaart, YV Nazarov, S Jauhar, D Dixon, K McCormick, J Orenstein, PL McEuen, Y Nagamune, J Motohisa, H Sakaki
    SURFACE SCIENCE 361 (1-3) 591 - 594 0039-6028 1996 [Refereed][Not invited]
     
    We have measured DC transport through a GaAs/AlGaAs quantum dot in the presence of a microwave signal of frequency f. We find features related to the photon energy hf whose positions in gate voltage are independent of the microwave power but vary linearly with frequency. The measurements demonstrate photon-assisted tunneling in the mesoscopic regime.
  • D Dixon, LP Kouwenhoven, PL McEuen, Y Nagamune, J Motohisa, H Sakaki
    SURFACE SCIENCE 361 (1-3) 636 - 639 0039-6028 1996 [Refereed][Not invited]
     
    We have measured linear and non-linear transport through a double quantum-dot system fabricated from the two-dimensional electron gas (2DEG) formed by a GaAs/AlGaAs heterostructure. At small source-drain bias, we observe Coulomb oscillations when the gate voltages of the two dots are tuned so that both dots conduct, in agreement with classical models of the two-dot system. At higher source-drain bias these Coulomb oscillations develop sharp overstructure, which arises from the alignment and de-alignment of quantized energy levels of the two dots.
  • T Fukui, S Hara, J Ishizaki, K Ohkuri, J Motohisa
    COMPOUND SEMICONDUCTORS 1995 145 919 - 924 0951-3248 1996 [Refereed][Not invited]
     
    Coherent multiatomic steps on vicinal (001) GaAs surfaces during metalorganic vapor phase epitaxial (MOVPE) growth are investigated by atomic force microscopy (AFM). AFM images show coherent multiatomic steps with extremely straight edges over a several micron scale. The average spacing of multiatomic steps depends on growth temperature, growth rate and AsH3 partial pressure. Similar multiatomic steps also appear on GaAs substrate surfaces after thermal treatment under AsH3/H-2 atmosphere at temperatures higher than 700 degrees C. Furthermore, we fabricate GaAs quantum well wires (QWWs) on these coherent multiatomic steps. Locally thick GaAs, that is, QWWs are formed at corners of multiatomic steps. Photoluminescence spectra of QWWs show energy shift caused by the QWWs formation. These results suggest that self-organized QWWs can be formed uniformly on coherent multiatomic steps.
  • AKABORI Masashi, MOTOHISA Junichi, IRISAWA Tomoki, HARA Shinjiroh, ISHIZAKI Jun-ya, FUKUI Takashi
    IEICE technical report. Electron devices 一般社団法人電子情報通信学会 96 (352) 53 - 58 1996 [Refereed][Not invited]
     
    We have studied the transport properties of a novel lateral surface superlattice type of electron wave interference devices in which multiatomic steps are utilized to introduce periodic potentials into two dimensional electron system. The device structure was fabricated by metalorganic vapor phase epitaxial growth on vicinal GaAs surfaces and spontaneously formed multiatomic steps were periodically embedded at the heterojunction of n-AlGaAs/GaAs. Oscillations of the transconductance as a function of gate voltage were found in three different devices. Our simple analysis suggests that the oscillations found in two devices results from the periodic potentials induced by the multiatomic steps and coherent electron wave interference, whereas in the rest one from the random interference. Our results imply the effect of the height and the randomness in the periodic potential on the characteristics of the electron wave interference devices.
  • J. Motohisa, M. Akabori, S. Hara, J. Ishizaki, K. Ohkuri, T. Fukui
    Physica B: Condensed Matter 227 295 - 298 0921-4526 1996/01/01 [Not refereed][Not invited]
     
    We propose a new, lateral surface superlattice (LSSL) type of electron interference devices, where the period of LSSL is typically 60 nm, by utilizing multiatomic steps on a vicinal GaAs (001) surface. Conductivity of the device is theoretically studied by taking the effect of randomness in the LSSL into account. We also investigate its drain and transconductance characteristics experimentally at low temperatures, and found clear oscillations in gm - VG characteristics, which were ascribed to the electron interference effect.
  • S HARA, J MOTOHISA, T FUKUI, H HASEGAWA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 34 (8B) 4401 - 4404 0021-4922 1995/08 [Not refereed][Not invited]
     
    Coherent multiatomic steps with extremely straight edges are naturally formed on vicinal (001) GaAs surfaces during metalorganic vapor phase epitaxial growth. GaAs quantum well wires (QWWs) are formed on these self-organized multiatomic steps. In our previous study, a thin AlGaAs layer was grown on GaAs with multiatomic steps as a lower barrier of QWWs. However, the height and spacing of the steps slightly fluctuate on AlGaAs layer surfaces. Therefore, in this experiment, AlAs layer instead of AlGaAs layer was used as a lower barrier layer to improve the uniformity of the height and spacing of the steps. Atomic force microscopy observations and photoluminescence (PL) measurements at 20 K revealed that the underlying coherent GaAs multiatomic steps were well traced by the AlAs barrier layer rather than the AlGaAs barrier layer. Furthermore, we measured the polarization anisotropy of the PL spectra from the QWWs with AlAs. These results suggest that uniform QWWs are successfully formed using multiatomic steps on vicinal (001) GaAs surfaces.
  • K KUMAKURA, K NAKAKOSHI, J MOTOHISA, T FUKUI, H HASEGAWA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 34 (8B) 4387 - 4389 0021-4922 1995/08 [Not refereed][Not invited]
     
    We have fabricated AlGaAs/GaAs quantum dot structures using selective area metalorganic vapor phase epitaxy (MOVPE). First, GaAs pyramidal structures with fourfold symmetric (011) facet sidewalls are formed on SiNx-masked (001) GaAs with square openings. Once the pyramidal structures were completely formed, no growth occurs on the top or sidewalls of the pyramids. Furthermore, the shape and width of the top area observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM) is shown to be highly uniform. This indicates that self-limited growth occurs. Next, using these uniform pyramids, GaAs quantum dots are overgrown on top of the pyramids under different growth conditions. Sharp photoluminescence (PL) spectra are observed from uniform quantum dots.
  • J MOTOHISA, K KUMAKURA, M KISHIDA, T YAMAZAKI, T FUKUI, H HASEGAWA, K WADA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 34 (2B) 1098 - 1101 0021-4922 1995/02 [Not refereed][Not invited]
     
    We report on a growth process on patterned GaAs (001) substrate during metalorganic vapor-phase epitaxy (MOVPE) and a novel approach for the fabrication of AlGaAs/GaAs quantum dot (QD) structures. The patterned substrate has an array of holes on the surface and those holes are partially filled with GaAs by MOVPE growth, followed by GaAs/AlGaAs quantum well structures. Detailed investigation on the growth process on such patterned substrates revealed the presence of complicated two-dimensional duffusion of Ga and Al between two different surfaces. Formation of GaAs dots was directly confirmed by spatially resolved cathodoluminescence measurements.
  • L. P. Kouwenhoven, S. Jauhar, J. Orenstein, P. L. McEuen, Y. Nagamune, J. Motohisa, H. Sakaki
    Physical Review Letters 73 (25) 3443 - 3446 0031-9007 1994/12/19
  • K KUMAKURA, K NAKAKOSHI, M KISHIDA, J MOTOHISA, T FUKUI, H HASEGAWA
    JOURNAL OF CRYSTAL GROWTH 145 (1-4) 308 - 313 0022-0248 1994/12 [Refereed][Not invited]
     
    We have studied the dynamics of selective area metalorganic vapor phase epitaxial (MOVPE) growth for the fabrication of high-quality GaAs/AlGaAs micro-pyramids on masked (001) GaAs substrates. The growth rates are estimated from the cross-sectional observation of micro-pyramidal structures with a scanning electron microscope (SEM), and photoluminescence (PL) spectra of quantum wells (QWs) fabricated near the top of the pyramids. It is found that the growth rate during the formation of the pyramidal structures depends strongly on the effective area of the surface on which growth takes place preferentially. Our results indicate that it is important to investigate this detailed behavior during selective growth and, in a phenomenological sense, growth behavior in the macroscopic regime can be utilized for the precise control of the nano-structure fabrication.
  • S HARA, J ISHIZAKI, J MOTOHISA, T FUKUI, H HASEGAWA
    JOURNAL OF CRYSTAL GROWTH 145 (1-4) 692 - 697 0022-0248 1994/12 [Refereed][Not invited]
     
    GaAs/AlGaAs quantum well wires (QWWs) were successfully fabricated using multiatomic steps on GaAs vicinal substrates by metalorganic vapor phase epitaxy (MWE). Coherent multiatomic steps with extremely straight step edges were observed on GaAs and AlGaAs epitadally grown layers on vicinal substrates over a wide observation area by atomic force microscopy (AFM). Formation of QWW structures is due to the fact that the GaAs growth rate on AlGaAs with multiatomic steps is much larger at the corners of steps than on the terraces. GaAs QWWs at the corners of steps accompanied by quantum wells (QWs) on the terraces were observed in cross-sectional transmission electron microscope (TEM) images. Photoluminescence (PL) of QWWs was measured at 20 K. The PL peak energy of the QWW structures grown on 5.0 degrees-misoriented substrates was 23 meV smaller than that of a reference QW structure on an exactly oriented substrate. Since the total amount of the grown material is basically the same for both structures, this peak energy shift indicates the formation of quantum-wire-like structures at the corners of multiatomic steps. Furthermore, this observed red shift is in good agreement with a simple theoretical estimate of the QWW structures observed by TEM. These results suggest that the present novel fabrication method of QWWs is very promising for the formation of uniform nano-meter size quantum wires without any processing damage.
  • Y NAGAMUNE, H SAKAKI, LP KOUWENHOVEN, LC MUR, CJPM HARMANS, J MOTOHISA, H NOGE
    APPLIED PHYSICS LETTERS 64 (18) 2379 - 2381 0003-6951 1994/05 [Refereed][Not invited]
     
    We report on single electron transport via a novel quantum dot structure fabricated by a combination of mesa etching and gate formation. In this device electrons are confined in an etched submicron wire and squeezed further by two barrier gates. The resulting dot is of a very small size, and the number of confined electrons can be tuned down to the few electron limit. This novel structure has a large charging energy and an improved current quantization during turnstile operation. In small dots, containing only a few electrons, we found Coulomb oscillations with an unexplained multiple peak structure.
  • J MOTOHISA, H SAKAKI
    APPLIED PHYSICS LETTERS 63 (13) 1786 - 1788 0003-6951 1993/09 [Refereed][Not invited]
     
    We have succeeded in the formation of a quasi-one-dimensional electron gas on an edge surface of an A]GaAs/GaAs multiple quantum well (MQW) structure with well width of 100 nm. The sample was prepared by the exposure of a cleaved surface of an MQW substrate and subsequent overgrowth of a doped AlGaAs layer on the edge. The existence of electrons on the edge surface and their one dimensionality are, respectively, evidenced by the angular dependence of magnetoresistance and the magnetic depopulation effect.
  • J MOTOHISA, H SAKAKI
    SUPERLATTICES AND MICROSTRUCTURES 13 (2) 255 - 258 0749-6036 1993 [Refereed][Not invited]
  • J MOTOHISA, H SAKAKI
    APPLIED PHYSICS LETTERS 60 (11) 1315 - 1317 0003-6951 1992/03 [Refereed][Not invited]
     
    We have theoretically investigated the influence of interface roughness on the scattering and mobility of electrons in very thin quantum wires, where all the electrons are in the lowest subband. In particular, the magnitude and electron concentration dependence of mobility are studied and shown to depend sensitively on the correlation length-LAMBDA and amplitude-DELTA of roughness. It is found that interface roughness scattering is drastically suppressed as the electron concentration increases, as in the case of impurity scattering when a realistic set of roughness parameters is chosen for edge quantum wire structures. General criteria to achieve ultra-high mobility in various quantum wire structures are also discussed.
  • N IKARASHI, A SAKAI, T BABA, K ISHIDA, J MOTOHISA, H SAKAKI
    APPLIED PHYSICS LETTERS 57 (19) 1983 - 1985 0003-6951 1990/11 [Refereed][Not invited]
  • N IKARASHI, A SAKAI, T BABA, K ISHIDA, J MOTOHISA, H SAKAKI
    HIGH RESOLUTION ELECTRON MICROSCOPY OF DEFECTS IN MATERIALS 183 187 - 192 1990 [Refereed][Not invited]
  • M TANAKA, J MOTOHISA, H SAKAKI
    QUANTUM-WELL AND SUPERLATTICE PHYSICS III 1283 254 - 260 1990 [Refereed][Not invited]

MISC

  • 小原康, 島内道人, 佐藤威友, 本久順一  応用物理学会北海道支部/日本光学会北海道支部合同学術講演会講演予稿集  55th-16th-  2020
  • Photoluminescence of Zn-Doped InP Nanowires: Mixing of Crystal Structures, Donor-Acceptor Pair Recombination, and Surface Effects
    J. Motohisa, H. Kameda, M. Sasaki, S. Hara, K. Tomioka  Collected Abstract of the 29th International Conference on Defects in Semiconductors (ICDS 2017), Matsue, Japan, July 31-August 4, 2017, TuP-33  1  -2  2017/08  [Refereed][Not invited]
  • Density Control of InP-based Nanowires and Nanowire Quanutm Dots
    S. Yanase, H. Sasakura, S. Hara, J. Motohisa  Collected Abstract of the 35th Electronic Materials Symposium (EMS-35), Moriyama, Japan, July 6-8, 2016, Th3-2  1  -2  2016/07  [Refereed][Not invited]
  • Growth and Characterization of Vertical Nanocavity Using Core-Multishell Nanowires
    T. Wada, S. Hara, J. Motohisa  Collected Abstract of the 2015 International Conference on Solid State Devices and Materials (SSDM 2015), Sapporo, Japan, September 27-30, 2015, D-4-3  1  -2  2015/09  [Refereed][Not invited]
  • 木下 康大, 池辺 将之, 本久 順一  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (124)  33  -36  2015/07/02
  • 木下 康大, 池辺 将之, 本久 順一  映像情報メディア学会技術報告 = ITE technical report  39-  (22)  33  -36  2015/07
  • Photoluminescence Study of Doping-Induced Crystal Structure Transition in Indium Phosphide Nanowires
    H. Kameda, S. Yanase, K. Tomioka, S. Hara, J. Motohisa  Collected Abstract of the 17th International Conference on Modulated Semiconductor Structures (MSS-17), Sendai, Japan, July 26-31, 2015, Mo-PM-33  1  -1  2015/07  [Refereed][Not invited]
  • Uchida Daisuke, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2015-  27  -27  2015/02/24
  • Tomioka Katsuhiro, Motohisa Junichi, Fukui Takashi  Proceedings of the IEICE General Conference  2015-  (2)  "SS  -94"-"SS-95"  2015/02/24
  • Design and Growth of Nanowire Nanocavity
    T. Wada, S. Hara, J. Motohisa  Collected Abstract of the 2014 International Conference on Solid State Devices and Materials (SSDM 2014), Tsukuba, Japan, September 8-11, 2014, PS-13-12  1  -2  2014/09  [Refereed][Not invited]
  • KAN Xie, 池辺将之, 本久順一, 佐野栄一  電子情報通信学会技術研究報告  114-  (120(ICD2014 19-30))  2014
  • 染谷槙人, 内田大輔, 池辺将之, 本久順一, 佐野栄一  電子情報通信学会技術研究報告  114-  (120(ICD2014 19-30))  2014
  • 本久順一, 原真二郎  岩谷直治記念財団研究報告書  36-  101  -103  2013/08/01  [Not refereed][Not invited]
  • Kim Kisu, Uchida Daisuke, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2013-  14  -14  2013/03/05
  • 内田大輔, 染谷槙人, 池辺将之, 本久順一, 佐野栄一  電子情報通信学会技術研究報告  113-  (112(ICD2013 24-46))  2013
  • Composition-Dependent Growth Dynamics of InGaAs Nanowires in Selective-Area Metal-Organic Vapor Phase Epitaxy
    Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 2013 International Symposium on Advanced Nanodevices and Nanotechnology (ISANN 2013), Poipu Beach, Kauai, Hawaii, USA, December 8-13, 2013, Thu2-5  1  -1  2013  [Refereed][Not invited]
  • Study on the Lateral Growth on GaAs Nanowires
    T. Wada, Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 32nd Electronic Materials Symposium (EMS-32), Moriyama, Japan, July 10-12, 2013, Fr1-12  1  -2  2013  [Not refereed][Not invited]
  • Influence of V/III Ration on the Growth of InGaAs Nanowires in Selective-Area MOVPE
    Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 40th International Sympsium on Compound Semiconductors (ISCS 2013), Kobe, Japan, May 19-23, 2013, WeB2-2  1  -2  2013  [Refereed][Not invited]
  • 内田大輔, 池辺将之, 本久順一, 佐野栄一, 近藤亮  電子情報通信学会技術研究報告  112-  (159)  45  -48  2012/07/26  [Not refereed][Not invited]
  • MIZUNO Akira, IKEBE Masayuki, IGARASHI Masaki, MOTOHISA Junichi  ITE Technical Report  36-  (20)  9  -12  2012/05/21  [Not refereed][Not invited]
     
    We propose a fast single image dehazing method that uses the local statistics of the dark channel. In single image dehazing, a haze-free image is created from a single hazed image by calculating the transmission map of the haze. There is a high computational cost to this process because it requires a complex matrix operation. We have therefore focused on the local histogram of the dark channel in order to refine the transmission map more quickly. In the proposed method, edges of the regions and objects in the transmission map are recovered using the local histogram of the dark channel. We achieved an operation time dozens of times faster than the conventional method, thereby successfully reducing the memory consumption.
  • 加藤 直人, 池辺 将之, 本久 順一, 下山 荘介  研究報告コンピュータビジョンとイメージメディア(CVIM)  2012-  (18)  1  -6  2012/05/16  
    本稿では局所ヒストグラム平坦化を基にしたダイナミックレンジ圧縮技術の自動制御手法を提案する.局所ヒストグラム平坦化ではフィルタカーネル毎のヒストグラムを用いて補正関数を生成する.フィルタカーネル内の輝度値に偏りが大きい場合,補正関数の勾配が急になり不自然なコントラスト強調を招く.我々は今までに,補正関数の変動域に対して上限値と下限値を設定し,変動域を制限する手法を提案してきた.本研究は,画像の情報を利用して上限値と下限値を自動的に決定することを目的とする.特に今回の報告では,夜景画像を対象とし,その補正において影響が大きい上限値を決定した.夜景画像の補正指針として,主に,暗い領域を良好に認識できるように補正すること,光源等の比較的明るい領域を適切な明るさに補正することを考慮した.指針を基に上限値を手動で決定したところ,画像のヒストグラムとエッジ量が上限値の決定に寄与しているという知見を得た.提案手法では,この知見に基づいて上限値の自動化を行なった.主観評価を行ったところ,提案手法は既存手法に比べ,画像補正が適切であるいう結果が得られた.In this paper, we propose an automatic control method of parameters for local adaptive tone mapping based on Local Histogram Equalization (LHE). The tone mapping function is generated by a cumulative histogram in LHE. When luminance in the filter kernel has a large bias, gradient of mapping function is steep and the mapped image has unnatural artifacts. By setting upper and lower limits of fluctuation range of tone mapping function, our conventional method controls spatial contrast of the image. Our goal is setting upper and lower limits automatically. In this study, we focus on nightscape image and propose automatic control with upper limits. We have two main considerations about enhancement of nightscape image: remedying obscure regions, and adjusting bright regions like lights appropriately. Based on the considerations, we found knowledge that edge and histogram of the image have a relationship with upper limits. In subjective evaluation of the image quality, we confirmed that our method is better than conventional one.
  • Kim Kisu, Ikebe Masayuki, Motohisa Junichi, Amemiya Yoshihito, Sano Eiichi  Proceedings of the IEICE General Conference  2012-  2  -2  2012/03/06
  • Kondou Akira, Ikebe Masayuki, Motohisa Junichi, Amemiya Yoshihito, Sano Eiichi  Proceedings of the IEICE General Conference  2012-  (2)  139  -139  2012/03/06  [Not refereed][Not invited]
  • Keitaro Ikejiri, Yusuke Kitauchi, Katsuhiro Tomioka, Junichi Motohisa, Takashi Fukui  NANO LETTERS  12-  (1)  524  -525  2012/01  [Not refereed][Not invited]
  • Selective-Area Growth of Highly Uniform and Thin InGaAs Nanowires by Two-Step growth Method
    Y. Kohashi, S. Sakita, S. Hara, J. Motohisa  Collected Abstract of the 2012 Material Research Society (MRS) Fall Meeting, Boston, Massachusetts, USA, November 25-30, 2012, FF9.01  1  -1  2012  [Refereed][Not invited]
  • Control of Diameter and Pitch of InGaAs Nanowire Arrays in Selective-Area Metal-Organic Vapor-Phase Epitaxy
    Y. Kohashi, S. Sakita, S. Hara, J. Motohisa  Collected Abstract of the 2012 International Conference on Solid State Devices and Materials (SSDM 2012), Kyoto, Japan, September 25-27, 2012, C-2-3  1  -2  2012  [Refereed][Not invited]
  • Fabrication of Highly Uniform InGaAs Nanowires in 30 nm-Diameter Openings with Lower Density in Selective-Area Metal-Organic Vapor-Phase Epitaxy
    Y. Kohashi, Y. Kobayashi, M. Yatago, S. Hara, J. Motohisa  Collected Abstract of the 31st Electronic Materials Symposium (EMS-31), Izu, Japan, July 11-13, 2012, Th5-2  1  -2  2012  [Not refereed][Not invited]
  • IGARASHI MASAKI, IKEBE MASAYUKI, SHIMOYAMA SOHSUKE, MOTOHISA JUNICHI  Nonlinear Theory Its Appl IEICE (Web)  3-  (2)  222-232 (J-STAGE)  -232  2012  [Not refereed][Not invited]
     
    We propose a constant-time algorithm for a bilateral filter. Bilateral filter can be converted into the operation of three-dimensional (3D) convolution. By using recursive moving sum, we can reduce the number of calculations needed to construct a pseudo-Gaussian filter. Applying one-dimensional Gaussian filter to the 3D convolution, we achieved a constant-time bilateral filter. We used a 3-GHz CPU without SIMD instructions, or multi-thread operations. We confirmed our proposed bilateral filter to be processed in constant time. In practical conditions, high PSNR values over 40 dB are obtained.
  • Shimoyama Sousuke, Ikebe Masayuki, Igarashi Masaki, Mizuno Akira, Motohisa Junichi  ITE Technical Report  35-  (47)  9  -12  2011/11/11  [Not refereed][Not invited]
     
    Local Histogram Equalization (LHE), which is efficient for High Dynamic Range (HDR) compression, requires a large amount of calculation and induces unnatural image quality. Using checker-wise histogram acquisition and line buffer, memory accessing for local histograms is processed in O(1) time. For improving image quality, we proposed approximation of LHE by compositing gamma functions. Moreover the weighting of local histogram is developed by introducing mean values of bins for the suppression and control of halo effect. We set the range of parameters for controlling halo effect by sensitivity evaluation.
  • Kim Kisu, Ikebe Masayuki, Motohisa Junichi, Amemiya Yoshihito, Sano Eiichi  Proceedings of the Society Conference of IEICE  2011-  37  -37  2011/08/30
  • Kondou Akira, Ikebe Masayuki, Motohisa Junichi, Amemiya Yoshihito, Sano Eiichi  Proceedings of the Society Conference of IEICE  2011-  24  -24  2011/08/30  [Not refereed][Not invited]
  • Shimoyama Sohsuke, Ikebe Masayuki, Igarashi Masaki, Mizuno Akira, Motohisa Junichi  Proceedings of the Society Conference of IEICE  2011-  101  -101  2011/08/30  [Not refereed][Not invited]
  • Masumoto Y., Hirata Y., Mohan P., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  66-  (2)  777  -777  2011/08/24
  • Shimoyama Sousuke, Ikebe Masayuki, Igarashi Masaki, Mizuno Akira, Motohisa Junichi  ITE Technical Report  35-  (19)  13  -16  2011/05/20  [Not refereed][Not invited]
     
    Local Histogram Equalization (LHE), which is efficient for High Dynamic Range (HDR) compression, requires a large amount of calculation and induces unnatural image quality. Using checker-wise histogram acquisition and line buffer, memory accessing for local histograms is processed in O(1) time. For improving image quality, we proposed approximation of LHE by compositing gamma functions. Moreover the control of local histogram is developed by introducing mean values of bins for suppression of stripe artifacts arising from small number of bins and halo effect. Using C++, we achieved two million pixels per 0.45sec operation.
  • Kondou Akira, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2011-  (1)  70  -70  2011/02/28  [Not refereed][Not invited]
  • Makihara Yukinobu, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2011-  34  -34  2011/02/28  [Not refereed][Not invited]
  • Igarashi Masaki, Ikebe Masayuki, Shimoyama Sohsuke, Motohisa Junichi  Proceedings of the IEICE General Conference  2011-  (2)  66  -66  2011/02/28  [Not refereed][Not invited]
  • Shimoyama Sohsuke, Ikebe Masayuki, Igarashi Masaki, Yamano Kenta, Motohisa Junichi  Proceedings of the IEICE General Conference  2011-  (2)  67  -67  2011/02/28  [Not refereed][Not invited]
  • Mizuno Akira, Ikebe Masayuki, Motohisa Junichi  Proceedings of the IEICE General Conference  2011-  (2)  92  -92  2011/02/28  [Not refereed][Not invited]
  • 池辺将之, 下山荘介, 本久順一  応用物理学関係連合講演会講演予稿集(CD-ROM)  58th-  2011
  • InP Nanowire Light Emitting Diodes
    S. Maeda, K. Tomioka, S. Hara, J. Motohisa  Collected Abstract of the 2011 Material Research Society (MRS) Fall Meeting, Boston, Massachusetts, USA, November 28-December 2, 2011, BB20.48  1  -1  2011  [Refereed][Not invited]
  • Effect of Growth Temperature on the Growth of InGaAs Nanowires in Selective-Area MOVPE
    Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 2011 International Symposium on Advanced Nanodevices and Nanotechnology (ISANN 2011), Kaanapali, Maui, Hawaii, USA, December 4-9, 2011, P1-  1  -1  2011  [Refereed][Not invited]
  • Fabrication of III-V Nanowire-Based Surrounding-Gate Transistors on Si Substrate
    K. Tomioka, J. Motohisa, S. Hara, T. Fukui  Collected Abstract of the 220th ECS Meeting and Electrochemical Energy Summit, Boston, Massachusetts, USA, October 9-14, 2011, #1885  1  -1  2011  [Refereed][Not invited]
  • Fabrication and Characterization of InAs Nanowire Vertical Surrounding-Gate FETs
    Y. Kobayashi, Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 2011 International Workshop on Quantum Nanostructures and Nanoelectronics (QNN 2011), Tokyo, Japan, October 3-4, 2011, P-5  1  -1  2011  [Refereed][Not invited]
  • Study on the Growth of In-Rich InGaAs Nanowires by Selective-Area Metal-Organic Vapor-Phase Epitaxy
    Y. Kohashi, S. Hara, J. Motohisa  Collected Abstract of the 2011 International Conference on Solid State Devices and Materials (SSDM 2011), Nagoya, Japan, September 28-30, 2011, KM-5-4  1  -2  2011  [Refereed][Not invited]
  • Composition-Dependent Growth Dynamics of InGaAs Nanowires in Selective-Area MOVPE
    Y. Kohashi, T. Sato, S. Hara, T. Fukui, J. Motohisa  Collected Abstract of the 38th International Sympsium on Compound Semiconductors (ISCS 2011), Berlin, Germany, May 22-26, 2011, Tu-4A.4  1  -2  2011  [Refereed][Not invited]
  • 松田 一成, 江馬 一弘, 野田 武司, 早瀬 潤子, 本久 順一, 渡部 平司  應用物理  79-  (8)  690  -690  2010/08/10  [Not refereed][Not invited]
  • MAKIHARA Yukinobu, SHIN Mhun, IKEBE Masayuki, MOTOHISA Junichi, SANO Eiichi  ITE Technical Report  34-  (29)  89  -93  2010/07/22  [Not refereed][Not invited]
     
    We have proposed the method of re-measuring quantizing error of Single-Slope ADC for CMOS imager with TDC (Time-to-Digital Converter). Using n-bits TDC, the proposed ADC performed 2^n time faster operation. This method requires high-speed Ramp wave generation. Therefore, in this paper, we evaluated speed up with interleave operation and output summing of DACs. Although multiple DACs are used, there is no increase of quantization unit devices. In the interleaved DAC with 2^<n-m> of m-bits DACunits, it can perform as a Delta DAC (-2^1≦ΔVout≦2^<m-1>). We designed the current-controlled DAC circuits using 0.25um CMOS process. At 200-MHz-clock operation, we confirmed 800-MHz 12-bit operations with four of 10-bits DACunits.
  • IGARASHI Masaki, IKEBE Masayuki, SHIMOYAMA Sousuke, YAMANO Kenta, MOTOHISA Junichi  ITE Technical Report  34-  (19)  17  -20  2010/05/31  [Not refereed][Not invited]
     
    We propose a O(1) algorithm for bilateral filter using center-weighted spatial filter. We show that a bilateral filter can be converted into weighted histogram operation. Applying line buffers of column histograms, we can reduce the number of calculation needed to construct recursive center-weighted local histogram. We used a 2-GHz CPU with our method and confirmed that processing time is independent of filter radius. Also, we achieved high PSNR over 40dB.
  • 本久 順一, 早瀬 潤子, 永津 雅章, 納冨 昭宏  應用物理  79-  (3)  190  -190  2010/03/10  [Not refereed][Not invited]
  • Motohisa Junichi, Tanaka Tomotaka, Tomioka Katsuhiro, Fukui Takashi  Proceedings of the IEICE General Conference  2010-  (2)  "SS  -45"  2010/03/02
  • Kondou Akira, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2010-  (1)  62  -62  2010/03/02  [Not refereed][Not invited]
  • Shin Muung, Ikebe Masayuki, Makihara Yukinobu, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2010-  13  -13  2010/03/02  [Not refereed][Not invited]
  • Makihara Yukinobu, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2010-  14  -14  2010/03/02  [Not refereed][Not invited]
  • Shimoyama Sohsuke, Ikebe Masayuki, Igarashi Masaki, Yamano Kennta, Motohisa Junichi  Proceedings of the IEICE General Conference  2010-  (2)  39  -39  2010/03/02  [Not refereed][Not invited]
  • 井上理樹, 佐藤拓也, 池辺将之, 原真二郎, 福井孝志, 本久順一  応用物理学関係連合講演会講演予稿集(CD-ROM)  57th-  2010
  • 牧原幸伸, SHIN Mhun, 池辺将之, 本久順一, 佐野栄一  電子情報通信学会技術研究報告  110-  (140(ICD2010 21-38))  2010
  • Growth Mechanism of III-V Semiconductor Nanowires in Selective-Area Metal-Organic Vapor Phase Epitaxy
    J. Motohisa, H. Yoshida, K. Ikejiri, Y. Kitauchi, K. Tomioka, S. Hara, K. Hiruma, T. Fukui  Collected Abstract of the 2010 International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2010), Honolulu, Hawaii, USA, December 15-20, 2010  1  -1  2010  [Refereed][Not invited]
  • Integration of III-V NW-Based Vertical FETs on Si and Device Concept for Tunnel FET Using III-V/Si Heterojunctions
    K. Tomioka, J. Motohisa, S. Hara, K. Hiruma, T. Tanaka, T. Fukui  Collected Abstract of the 2010 Material Research Society (MRS) Fall Meeting, Boston, Massachusetts, USA, November 29-December 3, 2010, W5.5  1  -1  2010  [Refereed][Not invited]
  • Free-Standing GaAs/AlGaAs Heterostructure Nanowires with a Quantum Well Formed by Selective-Area Metal-Organic Vapor-Phase Epitaxy
    K. Hiruma, A. Hayashida, T. Sato, S. Hara, J. Motohisa, T. Fukui  Collected Abstract of the 16th International Conference on Crystal Growth (ICCG-16), Beijing, China, August 8-13, 2010  2010  [Refereed][Not invited]
  • Selective-Area Growth of InGaAs Nanowires on Si Substrate
    K. Tomioka, J. Motohisa, S. Hara, K. Hiruma, T. Fukui  Collected Abstract of the Nano Science + Engineering Symposia, the SPIE Optics + Photonics Conferences 2010, San Diego, California, USA, August 1-5, 2010, 7768-8  1  -1  2010  [Refereed][Not invited]
  • Electrical Characterization of InGaAs Nanowire MISFETs Fabricated by Dielectric-First Process
    Y. Kohashi, T. Sato, K. Tomioka, S. Hara, T. Fukui, J. Motohisa  Collected Abstract of the 29th Electronic Materials Symposium (EMS-29), Izu, Japan, July 14-16, 2010  1  -2  2010  [Not refereed][Not invited]
  • Selective-Area MOVPE Growth Using Masked Substrates Prepared by Nanoimprint Lithography
    M. Inoue, T. Sato, M. Ikebe, S. Hara, T. Fukui, J. Motohisa  Collected Abstract of the 29th Electronic Materials Symposium (EMS-29), Izu, Japan, July 14-16, 2010  1  -2  2010  [Not refereed][Not invited]
  • Lattice-Mismatched Growth of InGaAs Nanowires Formed on GaAs (111)B by Selective-Area MOVPE
    M. Yoshimura, K. Tomioka, K. Hiruma, S. Hara, J. Motohisa, T. Fukui  Collected Abstract of the 29th Electronic Materials Symposium (EMS-29), Izu, Japan, July 14-16, 2010  1  -2  2010  [Not refereed][Not invited]
  • Fabrication of GaAs/InAs Axial Nanowires on Si by Selective-Area MOVPE with Regrowth Method
    K. Tomioka, J. Motohisa, S. Hara, K. Hiruma, T. Fukui  Collected Abstract of the 37th International Symposium on Compound Semiconductors (ISCS-37), Kagawa, Japan, May 31-June 4, 2010, p. 328  328  -328  2010  [Refereed][Not invited]
  • Fabrication and Characterization of InAs Tubular Channel FETs using Core-Shell Nanowires Grown by SA-MOVPE
    T. Sato, J. Motohisa, E. Sano, S. Hara, T. Fukui  Collected Abstract of the 15th International Conference on Metal-Organic Vapor Phase Epitaxy (ICMOVPE-XV), Incline Village, Nevada, USA, May 23-28, 2010, p. 31  31  -31  2010  [Refereed][Not invited]
  • Heteroepitaxial growth of InGaAs nanowires formed on GaAs(111)B by Selective-Area MOVPE
    M. Yoshimura, K. Tomioka, K. Hiruma, S. Hara, J. Motohisa, T. Fukui  Collected Abstract of the 15th International Conference on Metal-Organic Vapor Phase Epitaxy (ICMOVPE-XV), Incline Village, Nevada, USA, May 23-28, 2010, p. 19  19  -19  2010  [Refereed][Not invited]
  • Selective-Area Growth of InGaAs Nanowires on Si Substrate
    K. Tomioka, M. Yoshimura, J. Motohisa, S. Hara, K. Hiruma, T. Fukui  Collected Abstract of the 15th International Conference on Metal-Organic Vapor Phase Epitaxy (ICMOVPE-XV), Incline Village, Nevada, USA, May 23-28, 2010, p. 19  19  -19  2010  [Refereed][Not invited]
  • Shimoyama Sousuke, Ikebe Masayuki, Igarashi Masaki, Motohisa Junichi  ITE Technical Report  33-  (56)  5  -8  2009/12/10  [Not refereed][Not invited]
     
    Local Histogram Equalization (LHE), which is efficient for High Dynamic Range (HDR) compression, requires a large amount of calculation and induces unnatural image quality. Using checker-wise histogram acquisition and line buffer, memory accessing for local histograms is processed in O(1) time. Moreover, for improving image quality, we proposed approximation of LHE by compositing gamma functions. Setting parameters to each luminance tone, image quality is regulated adaptively. Using C++, we achieved two million pixels per 0.3sec operation and real-time VGA movie processing.
  • 高村 禅, 沼田 秀昭, 野田 武司, 本久 順一  應用物理  78-  (12)  1102  -1102  2009/12/10  [Not refereed][Not invited]
  • Shin Mhun, IKEBE Masayuki, MOTOHISA Junichi, SANO Eiichi  ITE Technical Report  33-  (39)  75  -80  2009/10/01  [Not refereed][Not invited]
     
    We have proposed the method of re-measuring quantizing error of Single-Slope ADC for CMOS imager with TDC (Time-to-Digital Converter). Here, we examined adding TDC by D-FF with multi-phase clock, vis-a-vis Delay-line TDC with CMOS inverters. For the operation at 200MHz using 0.25um process, we verified to compensate the process variation of process within 8%, and to operate TDC in DNL: ±0.25LSB, INL: ±0.4LSB by simulation. In addition, utilizing deformation thermo-code, we reduced D-FFs of TDC. For 12bit A/D Converter, when the first stage 9bit ADC and the second stage 3bit TDC are considered, we can design the proposed ADC with only 13 of D-FFs. The linearity of A/D Converter due to the jitter of PLL or DLL and the process variation.
  • SHIN Mhun, IKEBE Masayuki, MOTOHISA Junichi, SANO Eiichi  IEICE technical report  109-  (214)  75  -80  2009/09/24  
    We have proposed the method of re-measuring quantizing error of Single-Slope ADC for CMOS imager with TDC (Time-to-Digital Converter). Here, we examined adding TDC by D-FF with multi-phase clock, vis-a-vis Delay-line TDC with CMOS inverters. For the operation at 200MHz using 0.25um process, we verified to compensate the process variation of process within 8%, and to operate TDC in DNL: ±0.25LSB, INL: ±0.4LSB by simulation. In addition, utilizing deformation thermo-code, we reduced D-FFs of TDC. For 12bit A/D Converter, when the first stage 9bit ADC and the second stage 3bit TDC are considered, we can design the proposed ADC with only 13 of D-FFs. The linearity of A/D Converter due to the jitter of PLL or DLL and the process variation.
  • Shin Muung, Ikebe Masayuki, Makihara Yukinobu, Motohisa Junichi, Sano Eiichi  Proceedings of the Society Conference of IEICE  2009-  25  -25  2009/09/01  [Not refereed][Not invited]
  • Oono Masaki, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2009-  (1)  60  -60  2009/03/04  [Not refereed][Not invited]
  • Takada Yusuke, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2009-  (1)  57  -57  2009/03/04  [Not refereed][Not invited]
  • Makihara Yukinobu, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2009-  (2)  135  -135  2009/03/04  [Not refereed][Not invited]
  • Shimoyama Sohsuke, Igarashi Masaki, Ikebe Masayuki, Motohisa Junichi  Proceedings of the IEICE General Conference  2009-  (2)  89  -89  2009/03/04  [Not refereed][Not invited]
  • Yamamoto Takurou, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2009-  50  -50  2009/03/04  [Not refereed][Not invited]
  • KITAUCHI Yusuke, MOTOHISA Junichi, KOBAYASHI Yasunori, FUKUI Takashi  IEICE technical report  108-  (437)  19  -22  2009/02/19  
    Recently, semiconductor nanowires have attracted much interest because of their unique properties. However, most of the nanowires have rotational twins or stacking faults, which might degrade their quality. In addition, they could exhibit crystal structures which are different from those in the bulk phase. Thus, it is important to clarify the formation mechanisms of defects and to control crystal structures. In this report, we describe the growth of InP nanowires by selective-area metalorganic vapor phase epitaxy (SA-MOVPE) and show that they shows both zincblende and wurtzite structure depending on the growth conditions.
  • 本久 順一  應用物理  78-  (1)  77  -78  2009/01/10
  • 井上理樹, 佐藤拓也, 池辺将之, 福井孝志, 本久順一  応用物理学会北海道支部・日本光学会北海道地区合同学術講演会講演予稿集  44th-5th-  2009
  • 牧原 幸伸, 池辺 将之, 本久 順一, 佐野 栄一  映像情報メディア学会技術報告  32-  (45)  165  -170  2008/10/22  [Not refereed][Not invited]
     
    本研究では,周期比較方式を用いた位相同期回路(Phase Locked Loop: PLL)の新規アーキテクチャを提案する.周期比較器を導入する事により,ループ・フィルタの特性に依存しない位相ロック動作を確認することができた.通常,周期比較のみでは位相ロック動作は得られない.提案型PLLは厳密な周期の大小比較により,符号の変わる微小な周期差が位相差を制御し位相ロック動作が得られる.提案型PLLを0.25μm CMOSプロセスで回路設計し,その動作をシミュレーションで確認した.回路設計の際導入した,デジタル制御発振器の特性改善も行った.また動作確認のため試作を行い,測定により位相同期を確認した.
  • Lin Yang, Junichi Motohisa, Junichiro Takeda, Katsuhiro Tomioka, Takashi Fukui  NANOTECHNOLOGY  19-  (40)  2008/10  [Not refereed][Not invited]
  • Takada Yusuke, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the Society Conference of IEICE  2008-  (1)  28  -28  2008/09/02  [Not refereed][Not invited]
  • FUKUI Takashi, HARA Shinjiro, HIRUMA Kenji, MOTOHISA Junichi  Technical report of IEICE. SDM  108-  (122)  1  -1  2008/07/02  
    III-V semiconductor nanowires were grown by selective area metalorganic vapor phase epitaxy on (111) oriented substrate. Here, we discus uniform growth of nanowire array and their optical transport device applications.
  • Makihara Yukinobu, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2008-  (2)  102  -102  2008/03/05  [Not refereed][Not invited]
  • Yamamoto Takurou, Ikebe Masayuki, Motohisa Junichi, Sano Eiichi  Proceedings of the IEICE General Conference  2008-  4  -4  2008/03/05  [Not refereed][Not invited]
  • Shimoyama Sohsuke, Igarashi Masaki, Ikebe Masayuki, Motohisa Junichi  Proceedings of the IEICE General Conference  2008-  (2)  24  -24  2008/03/05  [Not refereed][Not invited]
  • Goto K., Tomimoto S., Pal B., Masumoto Y., Mohan P., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  63-  (1)  683  -683  2008/02/29
  • L. Yang, J. Motohisa, J. Takeda, K. Tomioka, T. Fukui  APPLIED PHYSICS LETTERS  92-  (5)  2008/02  [Not refereed][Not invited]
  • 山本拓良, 池辺将之, 本久順一, 佐野栄一  電子情報通信学会大会講演論文集  2008-  2008
  • Pal B., Goto K., Ikezawa M., Masumoto Y., Mohan P., Motohisa J., Fukui T.  Applied Physics Letters  93-  (7)  073105  -73105  2008  [Not refereed][Not invited]
     
    We study optical transitions from a periodic array of InP/InAs/InP core-multishell nanowires (CMNs) having a wurtzite crystal structure by using photoluminescence (PL) and PL excitation (PLE) spectroscopy. Observing a large Stokes shift between PL and PLE spectra, a blueshift of the PL peak with a cube-root dependence on the excitation power and a slow and nonexponential decay of PL with an effective decay time of 16 ns suggest a type-II band alignment. Band-offset calculation based on the "model-solid theory" of Van de Walle [Phys. Rev. B 39, 1871 (1989)] supports type-II band lineup if the InAs layer in the wurtzite CMNs is assumed to sustain compressive strain in all directions.
  • FUKUI Takashi, HARA Shinjiro, MOTOHISA Junichi  Extended abstracts of the ... Conference on Solid State Devices and Materials  2007-  810  -811  2007/09/19
  • Goto K., Pal B., Masumoto Y., Mohan P., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  62-  (2)  681  -681  2007/08/21
  • Goto K., Pal B., Masumoto Y., Mohan P., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  62-  (1)  661  -661  2007/02/28
  • 池辺将之, 櫻谷直史, 五十嵐正樹, 本久順一  映像情報メディア学会技術報告  31-  (50(IST2007 86-93))  2007
  • Tsumura K., Nomura S., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  61-  (2)  536  -536  2006/08/18
  • Goto K., Pal B., Masumoto Y., Mohan P., Motohisa J., Fukui T.  Meeting abstracts of the Physical Society of Japan  61-  (2)  537  -537  2006/08/18
  • MOTOHISA Junichi, FUKUI Takashi  IEICE technical report  106-  (137)  63  -68  2006/07/03  
    We describe our recent results on the formation of III-V semiconductor nanowires and related nanostructures utilizing selective-area metalorganic vapor phase epitaxial (SA-MOVPE) growth. Array of vertically aligned nanowires are grown on partially masked GaAs and InP substrate along the [111]B or [111]A directions, respectively. The alignment and size of the nanowires are controlled by the mask patterning as well as growth conditions. Nanowires containing heterostructures in their radial direction have also been realized by controlling the growth mode during SA-MOVPE. Their optical and transport properties are also investigated and described.
  • NATARAJ Devaraj, OOIKE Noboru, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  2005-  154  -155  2005/09/13
  • HASHIMOTO S., TAKEDA J., TARUMI A., HARA S., MOTOHISA J., FUKUI T.  Extended abstracts of the ... Conference on Solid State Devices and Materials  2005-  762  -763  2005/09/13
  • TARUMI Akihiro, TAKEDA Junichiro, HASHIMOTO Shinji, MOTOHISA Junichi, FUKUI Takashi  IEICE technical report. Electron devices  104-  (623)  1  -4  2005/01/28  
    Photonic Crystals (PhCs), which have periodically modulated dielectric structures near light wavelength, can control spontaneous emission of light utilizing photonic band gap, so they have received much attention as a new optical devices. In this paper, we report on the fabrication of InP and InGaAs air-hole type 2D PhCs structures on InP substrates by using selective area metal organic vapor phase epitaxy (SA-MOVPE) for application to InP-based air-hole type 2D PhCs.
  • OOIKE N., MOTOHISA J., FUKUI T.  IEICE technical report. Electron devices  104-  (622)  1  -6  2005/01/20  
    We have fabricated GaAs/AlGaAs Field Effect Transistor (FETs) having a narrow wire channel and a self-aligned tungsten (W) gate electrode by using Selective-Area Metal Organic Vapor Epitaxy (SA-MOVPE). Stacked film of SiO_2/W was used as a mask for SA-MOVPE. In case that the structure in cross-section fabricated by SA-MOVPE is mesa-shape, the distance between bottom W-gate electrode on the substrate and channel layer become far, as the channel layer forms at a higher position of the mesa structure. So that, we fabricated wire structures with different structural parameters, for example channel-gate distance or channel width, and demonstrated relation of gate-control and their structural parameters. As a result, we obtained that the gate-control depended only on channel width. From these results, we will discuss operation mode of the narrow wire-transistor having self-aligned W gate.
  • YANG Lin, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  2004-  558  -559  2004/09/15
  • HARA Shinjiroh, MOTOHISA Junichi, TAKEDA Junichiro, NOBORISAKA Jinichiro, FUKUI Takashi  Journal of the Japanese Association of Crystal Growth  31-  (3)  167  -167  2004/08/25  
    We demonstrated formation of hexagonal nano-wires with GaInAs/GaAs double hetero-structures using SA-MOVPE growth on SiO_2 masked (111)B GaAs substrates with periodic round openings. Using μ-PL measurements, PL emission from single GaInAs/GaAs hexagonal nano-wire was successfully identified. These results indicated that GaInAs/GaAs hexagonal nano-wires had good crystal qualities.
  • MOTOHISA Junichi, FUKUI Takashi  Journal of the Japanese Association of Crystal Growth  31-  (3)  243  -243  2004/08/25  
    We report on the fabrication of periodic structures of InGaAs and InP on InP (111)A- or (111)B-oriented substrates by using selective-area (SA) MOVPE for the application of photonic crystals (PhCs). Array of hexagonal InGaAs and InP pillars are formed on masked substrates with circular mask openings at appropriate growth conditions. Air-hole arrays with InGaAs are also grown on substrates with periodic array of hexagonal masks.
  • INARI Masaru, TAKEDA Junichiro, MOTOHISA Junichi, FUKUI Takashi  Technical report of IEICE. SDM  103-  (631)  47  -50  2004/01/23  
    Photonic crystals (PCs) have received much attention as a new class of optical materials. PCs are modulated dielectric structures whose period is near the light wavelength, enabling us to control spontaneous emission and propagation of lightwaves using photonic band gaps. In particular, high aspect ratio, smooth surface, and high uniformity are required to achieve two-dimensional PCs (2DPCs). In this paper, we report on the fabrication of InP pillar structures on InP substrates by using selective area metal organic vapor phase epitaxy (SA-MOVPE) for application to InP-based 2DPCs.
  • J Motohisa, F Nakajima, T Fukui, WG van der Wiel, JM Elzerman, S De Franceschi, LP Kouwenhoven  APPLIED PHYSICS LETTERS  80-  (15)  2797  -2799  2002/04  [Not refereed][Not invited]
     
    We report on the fabrication of a dual-gated single-electron transistor (SET) based on a quantum dot (QD) formed by selective area growth of metalorganic vapor-phase epitaxy, and its low-temperature transport properties. We observe clear Coulomb oscillations in a SET fabricated in combination with direct growth of nanostructures and lithographically defined metal gates. The magnetic field dependence of the Coulomb oscillations as well as the Coulomb diamonds suggest strong carrier confinement in our QD. (C) 2002 American Institute of Physics.
  • ISHIHARA T., AKABORI M., MOTOHISA J., FUKUI T.  IEICE technical report. Electron devices  101-  (617)  29  -34  2002/01/21  
    The uniform and self-aligned S-K mode InGaAs quantum dots were formed on GaAs multiatomic steps on (001) vicinal surface by MOVPE. Under optimum In content (x=O.8) and InGaAs layer thickness (3.2ML) condition highly uniform InGaAs quantum dots were obtained. The size distribution of InGaAs dots depends on GaAs multiatomic step width strongly. The misorientation angle dependence on the formation of InGaAs quantum dots on GaAs multiatomic steps were also observed by AFM and PL. The results of PL measurement agreed well with AFM results.
  • MOTOHISA Junichi, NAKAJIMA Fumito, AKABORI Masashi, FUKUI Takashi  IEICE technical report. Electron devices  101-  (617)  1  -8  2002/01/21  
    We report on the formation of quantum nanostructures and their arrays by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on masked substrates and their application to quantum devices and circuits. With appropriately designed masked substrates, various kinds of nanostructures, such as quantum dot-quantum wire coupled structure arrays are realized. When SA-MOVPE is carried out on (111) B substrates, triangular lattice arrays of hexagonal air holes or pillars consisting of {110} facet sidewalls can be formed, which can be used for photonic crystals. For device application of such nanostructures, we fabricate single electron transistors in combination with lithographically defined dual gated structures, in which clear Coulomb oscillations and Coulomb diamonds are observed. Applications to logic circuits using single electron transistors are also described.
  • KUSUHARA Toyonori, NAKAJIMA Fumito, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  2001-  330  -331  2001/09/25
  • ODA Yasuhiro, HARADA Toshifumi, MOTOHISA Junichi, FUKUI Takashi  IEICE technical report. Electron devices  100-  (641)  9  -16  2001/02/21  
    We developed a method to fabricate various kind of semiconductor nano-structures using self-organized method in MOVPE crystal growth on patterned GaAs(001) vicinal substrates Periodic mutiatomic step structures are formed on the patterned vicinal substrate misoriented towards the [-110] direction with a line & space pattern along the [11] direction. In A crossed line & space pattern, square scale structures can be formed with crossed multiatomic steps. We found that growth rate was different between step edges and terrace regions on the surface of these structures. These results demonstrated that it is possible to fabricate various kind of quantum structures with controllability of periodicity.
  • LEE Sangyoru, AKABORI Masashi, SHIRAHATA Takahiro, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  2000-  512  -513  2000/08/28
  • TERASAWA T., NAKAJIMA F., MOTOHISA J., FUKUI T.  Extended abstracts of the ... Conference on Solid State Devices and Materials  2000-  504  -505  2000/08/28
  • NAKAJIMA F., MOTOHISA J., FUKUI T.  Technical report of IEICE. SDM  99-  (617)  1  -6  2000/02/09  
    We fabricated single electron devices by using selective area MOVPE and investigated their transport properties. GaAs/AlGaAs modulation doped heterostructures are grown on a GaAs (001) substrate partially masked with SiNx and narrow channel surrounded by facet sidewalls are formed near the top. The width of the channel is modulated by an appropriate patterning of the mask. By applying negative biases to a gate, a quantum dot connected with quantum wires through tunnel barriers are formed near the pinch-off voltage, as a result of the expansion of depletion layers. We successfully observed clear Coulomb blockade oscillations at low temperatures. We also fabricate logic circuits with an SET and a variable load resistance, and confirmed inverter operations.
  • TAZAKI Chiharu, AKABORI Masashi, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  1999-  546  -547  1999/09/20
  • YAMATANI Kazuki, AKABORI Masashi, MOTOHISA Junichi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  1998-  330  -331  1998/09/07
  • K Kumakura, J Motohisa, T Fukui  SOLID-STATE ELECTRONICS  42-  (7-8)  1227  -1231  1998/07  [Not refereed][Not invited]
     
    We fabricated novel quantum nanostructures where the quantum dots are connected with quantum wires using metalorganic vapor phase epitaxy (MOVPE) on (001) GaAs masked substrates. In particular a GaAs single electron transistor was successfully fabricated and its transport properties were investigated. We prepared two devices which have artificially designed two- or three-prominences in the channel region. These prominences produced a quantum clot connecting with quantum wires in applying the gate voltage. By comparing the electrical properties of the two devices, we discussed a model for formation of quantum dot and tunneling barriers in the channel. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • IRISAWA Tomoki, MOTOHISA Junichi, AKABORI Masashi, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  1997-  326  -327  1997/09/16
  • IRISAWA T., MOTOHISA J., AKABORI M., FUKUI T.  Journal of the Japanese Association of Crystal Growth  24-  (2)  234  -234  1997/07/01  
    We have investigated the possibility of selcctive incorporation of Si into step edges of GaAs vicinal surfaces to form doping quantum wircs. It has shown that the selective incorporation actually take place particularly at the initial stage of the doping.
  • Fukui T, Ishizaki J., Hara S, Kumakura K., Motohisa J.  Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1996-  (2)  145  -146  1996/09/13
  • AKABORI Masashi, MOTOHISA Junichi, IRISAWA Tomoki, HARA Shinjiroh, ISHIZAKI Jun-ya, OHKURI Kazunobu, FUKUI Takashi  Extended abstracts of the ... Conference on Solid State Devices and Materials  1996-  706  -708  1996/08/26
  • 中越 一彰, 熊倉 一英, 佐久間 誠, 本久 順一, 福井 孝志  電気学会研究会資料. EFM, 電子材料研究会  1995-  (1)  85  -93  1995/11/13
  • T FUKUI, J ISHIZAKI, S HARA, J MOTOHISA, H HASEGAWA  JOURNAL OF CRYSTAL GROWTH  146-  (1-4)  183  -187  1995/01  [Not refereed][Not invited]
     
    The multiatomic steps formed on GaAs vicinal surfaces by metalorganic vapor phase epitaxy (MOVPE) are by atomic force microscopy (AFM). An AFM image of an epitaxially grown GaAs surface showed coherent multiatomic steps with extremely straight edges over a wide area. The average height and spacing of the multiatomic steps are 1.2-8 and 30-110 nm, respectively. These terrace widths change with the growth conditions. Narrower terrace widths are obtained at higher growth rates, and under higher AsH3 partial pressures and higher impurity doping conditions. The results suggest that the migration distance of a Ga atom on the terrace and the sticking coefficient at the step sites depend on these growth conditions. Using multiatomic steps, GaAs/AlGaAs quantum well wires (QWWs) were grown on a GaAs vicinal surface. Cross-sectional transmission electron microscopy and photoluminescence show the successful fabrication of QWWs.
  • 岸田 基也, 熊倉 一英, 中越 一彰, 山崎 高宏, 本久 順一, 福井 孝志, 長谷川 英機  Bulletin of the Faculty of Engineering,Hokkaido University  (170)  p27  -33  1994/07  [Not refereed][Not invited]
  • Y NAKAMURA, M TSUCHIYA, J MOTOHISA, H NOGE, S KOSHIBA, H SAKAKI  SOLID-STATE ELECTRONICS  37-  (4-6)  571  -573  1994/04  [Refereed][Not invited]
     
    An edge quantum wire (EQWI) structure with a feature width of 120 nm was successfully prepared on (111)B micro facets; the structure was fabricated by an ensembles of several growth modes in molecular beam epitaxy (MBE) on a patterned (001) substrate without resorting to any advanced lithographic technique. A clear deviation from the linear relationship is observed in a Landau plot of magnetoresistance at low magnetic fields, providing the first evidence of magnetic depopulation of one-dimensional subbands in a facets EQWI. The sheet electron concentration measured is 5.4 x 10(11) cm-2, which corresponds to the linear concentration of 4.8 x 10(6) cm-1, and the mobility is 3 x 10(4) cm2 V-1 s-1 or higher. These values indicate a high crystal quality of the facet EQWI thus prepared.
  • H SAKAKI, T NODA, M TANAKA, J MOTOHISA, Y KADOYA, N IKARASHI  SEMICONDUCTOR INTERFACES AT THE SUB-NANOMETER SCALE  243-  217  -230  1993  [Not refereed][Not invited]
  • H SAKAKI, H SUGAWARA, J MOTOHISA, T NODA  INTERSUBBAND TRANSITIONS IN QUANTUM WELLS  288-  65  -72  1992  [Not refereed][Not invited]
  • M TANAKA, J MOTOHISA, H SAKAKI  SURFACE SCIENCE  228-  (1-3)  408  -411  1990/04  [Not refereed][Not invited]
  • J MOTOHISA, M TANAKA, H SAKAKI  APPLIED PHYSICS LETTERS  55-  (12)  1214  -1216  1989/09  [Not refereed][Not invited]

Books etc

Presentations

Research Projects

  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2022/04 -2026/03 
    Author : 冨岡 克広, 池辺 将之, 本久 順一
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/04 -2025/03 
    Author : 深田 直樹, J. Wipakorn, 宮崎 剛, 本久 順一, 冨岡 克広, 松村 亮
     
    現行の平面型金属・酸化膜・半導体電界効果型トランジスタ(MOSFET)では、微細化した回路素子からのリーク電流による発熱が大きくなるため、従来のスケール則に従った微細化だけでは素子の性能向上に限界が指摘されている。本研究では、IV族半導体Si、Ge、新規高移動度材料として注目されているGeSnから形成される特殊なコアシェルヘテロ接合により高電子移動度型トランジスタ(HEMT)構造を1次元ナノワイヤ内部に形成することで、次世代トランジスタの微細化限界・低消費電力化の課題を解決し、ナノ構造でも不純物散乱のない高移動度デバイスを実現する。 初年度はサイズ・配列制御可能で、大面積での繰り返しパターン形成が容易で時間短縮できるナノインプリント法と反応性イオンエッチング(RIE)法を適用し、i(intrinsic)-Ge/p-Si、逆構造であるp-Si/i-Geおよびp-Si/i-Ge1-xSnxコアシェルナノワイヤ中のコア領域のp-Siおよびi-Geナノワイヤアレイの形成を行った。RIEの条件をSiとGeで最適化することで、直径150nmのi-Geおよびp-Siナノワイヤアレイのサイズ・配列制御に成功した。RIEではナノワイヤ表面にダメージが導入される。そこで、表面ダメージ層を低温オゾン酸化とエッチングで除去し、ナノワイヤ径を高速チャネルのサイズとして利用できる50nmまで縮小化することに成功した。ナノワイヤFET形成のためのプロセスおよび大規模第一原理計算によるコアシェルナノワイヤモデルの構築を行った。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2023/03 
    Author : 本久 順一, 冨岡 克広
     
    令和3年度は、有機金属気相選択成長法により作製したGaAs/InGaAs/GaAs コアマルチシェル構造ナノワイヤの発光特性について前年度に引き続いて評価を行った。特に発光により得られたビームの形状、およびその偏光状態の詳細評価を行い、ナノワイヤがレーザ発振した場合に、ベクトル光波が放出されていることを確認した。具体的には、まず、試料を低温でパルス光励起した場合、半値幅の狭い発光ピークが複数観測され、そしてその強度が励起光強度とともに非線形的に増大することが明らかとなった。これによりナノワイヤのレーザ発振の兆候が確認されたが、この時得られた発光像を観測したところ、中心部の強度が弱い、ドーナツ形状となっていることが確認された。そして、そのピーク近傍のスペクトルをバンドパスフィルターで切り出し、その偏光状態を解析したところ、ビームの広がりの範囲内で、軸対称の偏光分布となっていることを確認した。これらの結果より、観測されたナノワイヤから放射されたビームは、中心に特異点を含むベクトル光波となっており、ナノワイヤが期待どおりWGM型のベクトル光波源として機能することが示された。また、得られた実験結果をさらに詳細に検討したところ、低次のベクトル光波であるTEモードやTMモードを反映した偏光分布ではなく、高次のベクトル光波が得られている可能性が示唆された。そして、このような明瞭な軸対称の偏光分布、特に特異点はナノワイヤがレーザ発振している場合にのみ得られ、連続光励起の時に観測されていたナノワイヤの共振モードに起因する発光ピークに対しては得られていないことから、連続光およびパルス光励起の元で得られる発光ピークの起源となるモードは異なること、および基本モードではナノワイヤはレーザ発振していないと判断される。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : Tomioka Katsuhiro
     
    In this research, we developed and explored heterogeneous integration of III-V nanowires heterogeneous for high-speed, low-power, and high-efficiency three-dimensional (3D) circuits application. a nanowire 3D-architecture revolutionized the existing planar integration paradigm, and created a new trend in next-generation electronics. We have created an ultra-efficient tunnel transistors driven by nanowatts based on a new Si/III-V nanowire junction and tunneling transport mechanism. These results would provided new design guidelines for three-dimensional circuit structures based on nanowire TFETs.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2021/03 
    Author : 本久 順一
     
    (1) 前年度実施したコンタクトレス光支援電気化学エッチング(PEC)およびアルカリ溶液処理によるGaNナノワイヤの形成法についてさらなる検討を行った。PECエッチング時間に対するエッチング深さの変化を評価したところ、エッチング時間が増えると、エッチング時間とエッチング深さの関係に線形性が失なわれるとともに、表面平坦性が劣化することが明らかとなった。さらに、その後のアルカリ溶液処理によりGaNナノワイヤの微細化および側面ラフネスの除去は可能であるが、現在の処理条件では長時間のPECエッチングよって発生したエッチング表面の非平坦性は改善しないという結果が得られた。 (2) 古典的1次元ナノワイヤMOSFETのモデルおよび1次元の弾道的輸送モデルにもとづき、InAsおよびGaNナノワイヤトランジスタの性能予測を行った。ナノワイヤ一周の寸法により規格化したオフ電流の密度が一定という条件のもとナノワイヤ寸法によるトランジスタの特性を比較したところ、いずれのモデルにおいても、オン電流密度がナノワイヤ直径の微細化ともに増大するという結果が得られた。これにより、ナノワイヤのような微細構造を有するトランジスタであっても、ナノワイヤ寸法を適切に制御し、またナノワイヤ密度を十分高くすることができれば(例えばナノワイヤの占有面積25%以上)ならば、大電流を制御する上では通常の縦型トランジスタよりも優位となる可能性のあること、よって、ナノワイヤの特徴である短チャネル効果耐性も考慮し、ナノワイヤ縦型トランジスタがパワーエレクトロニクス応用にも十分耐えられる可能性を示した。 (3) RF支援分子線エピタキシャル(RF-MBE)法を用いた選択成長法によるGaNナノワイヤの形成を確認した。高さ約0.3 μm、断面寸法120 nmのGaNナノワイヤアレイを得ることができた。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Sato Taketomo
     
    The photo-electrochemical (PEC) process was developed for fabricating recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). The photo-carriers generated in the top AlGaN layer caused homogeneous etching of AlGaN with a smooth surface. Self-termination phenomena observed under optimal PEC condition were useful for precisely controlling the etching depth in the AlGaN layer. Two types of HEMTs, i.e., Schottky-gate and metal-insulator-semiconductor (MIS)-gate, were fabricated. A recessed-gate AlGaN/GaN structure fabricated with PEC etching showed positive threshold voltage, and its variation was very small. A recessed-gate structure with PEC etching showed better current transport controllability with a small subthreshold-slope than that of planar-gate and dry-etched-gate AlGaN/GaN structures.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Motohisa Junichi
     
    We attempted the growth of InGaAs nanowires (NWs) on Si substrates by selective-area metalorganic vapor-phase epitaxy. By controlling the supply ratio of source materials of group III atoms, emission from InGaAs NW arrays in the telecommunication bands were successfully confirmed by the low-temperature photoluminescence measurement. InGaAs NW arrays with a vertical pn junction are also fabricated and photocurrent spectroscopy reveals that fabricated NW array exhibited optical bandgap in the telecommunication bands. Emission mechanism of InP-based light-emitting diode (LED) was investigated and radiative tunneling was the dominant emission mechanism in the NW-LEDs. Control of the emission wavelength and size of InAsP quantum dots embedded in InP NWs were attempted and emission from the telecommunication band was demonstrated. NW-LEDs utilizing InAsP/InP heterostructure NWs were also fabricated and confirmed the light emission in the near-infrared regions originating from InAsP layer.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Hara Shinjiro
     
    The purpose of this study is to create and integrate vertical nanowire-spin-transistors, in which vertical semiconductor nanowires (NWs) are used with magnetic tunnel junction (MTJ) electrodes, on semiconducting substrates, e.g., Si. Such vertical NW-spin-transistors are realized using free-standing NWs with a high aspect ratio fabricated by our bottom-up-type formation method in a reproducible manner in terms of a location and size of NWs on substrates. We succeeded in obtaining some experimental results mainly relating to quasi-one-dimensional mesoscopic phenomena of electron scattering and magnetotransport in NWs, control of magnetization switching in patterned CoFe nanolayers of CoFe/MgO-MTJ electrodes by external magnetic fields, selective-area growth of Si and Ge NWs based on a vapor-solid-liquid method, and magnetotransport properties of a nanowire with ferromagnetic Ni electrodes after carrying out the established device fabrication processes for burying and exposing NWs.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2019/03 
    Author : 本久 順一
     
    (1) 前年に引き続き、RF支援分子線エピタキシャル成長(RF-MBE)法を用いて、縦型トランジスタ応用に適したGaNナノワイヤの形成を試みた。特に、前年度不十分であったナノワイヤ長さについて改善を試みた。特に、成長初期は低N2流量、その後高N2流量とした2段階成長を導入することによって、断面寸法150~240nmの範囲で長さ420nm程度のGaNナノワイヤを得ることに成功した。これによりRF-MBE成長により形成したGaNナノワイヤを縦型FETへと応用する見通しを得た。 (2)成長したGaNナノワイヤをSOGで埋めこんだ後、SOGをエッチングしてナノワイヤ頂上部を露出させた後、上部ならびに基板に電極を形成することによって2端子素子を作製し、その電気伝導特性を評価した。アニール前後の特性を比較したところ、高バイアス領域での微分抵抗が変化しないことから、その値がナノワイヤの固有抵抗であると考えた。そして、その微分抵抗および測定に用いたナノワイヤ2端子素子の総電極面積よりRF-MBEにより形成したGaNナノワイヤの抵抗率を求め、0.25~1.5 ohm・cmの範囲にあることを示した。これらの値は、予想されるGaNナノワイヤの移動度を考慮するとキャリア密度が10^18 cm^-3オーダであることを示唆しており、FET動作をさせる上でも支障のない範囲の値なっていることを確認した。 (3) FET応用に適したGaNナノワイヤの形成手法として、光支援電気化学エッチングによって微細加工する方法を検討した。適切なマスクの設計により、GaNが光支援化学エッチングにより、光照射した部分を選択的にエッチングできることを確認した。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2018/03 
    Author : Junichi Motohisa
     
    We have developed novel phohtodetectors utilizing InGaAs nanowires (NWs) grown on Si substrates. InGaAs NWs with axial pn-junction was grown on p-type Si substrates partially covered with SiO2 mask by using selective-area metalorganic vapror phase epitaxy (SA-MOVPE). The controllability of the vertical InGaAs NWs, particularly of their In composition, was verified by detail investigation using SEM, XRD, and low-temperature photoluminescence (PL) measurements. Two-terminal devices fabricated using pin InGaAs NWs showed clear photoresponse at room temperature under photo irradiation of 635nm, and the sensitivity measured 0.13 A/W. The photoresponse at around 1.55 micron was also confirmed. Furthermore, the sensitivity of the device was improved by introducing higly-doped contact layers at the top and bottom of the NWs. Core-shell heterostructure was also introduced and photoresponse at 1.55 micron was improved by factor 20 due to the passivation effect of InP shell layers.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2018/03 
    Author : Taketomo Sato
     
    GaN-based photocatalyst electrodes utilizing electrochemically-formed porous structures have been developed. The precise control of pore diameter and depth has been achieved by optimizing the condition of electrochemical etching and subsequent wet-chemical etching. The decrease of photo reflectance and increase of the effective surface area of GaN porous structures lead to the improvement of the photo-electrochemical conversion efficiency. The functionalization utilizing NiO and Cu2O on n-GaN electrodes was very effective respectively for the improvement of corrosion resistance and the photoelectrochemical conversion in visible light region (400-600nm).
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2016/03 
    Author : SATO Taketomo, HASHIZUME Tamotsu, MOTOHISA Junichi, YATABE Zenji
     
    Towards the higher sensitivity of ion-sensitive field-effect transistors (ISFETs) on nitride semiconductors, the porous-gate ISFETs has been proposed and its basic technology was established. The porous structures with a high-aspect ratio having a several 10 nm-diameter were successfully formed in a controlled fashion utilizing the electrochemical oxidation and etching process. It was found that the unique features of porous structures such as a large surface area and a modified potential involved with a high-electric field are very effective to detect the photo-electrochemical reactions with high-sensitivity. The correlation between the ion-diffusion in the pores and charging and discharging to the double layer were discussed on the basis of the experimental and theoretical results, leading to the new finding for the high-speed and high-sensitive chemical sensors.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : MOTOHISA Junichi, SASAKURA Hirotaka
     
    To realize nanowire-based light-emitting devices, we grew III-V semiconductor nanowires by selective-area metalorganic vapor-epitaxy (SA-MOVPE) and carried out characterization of their optical properties. Main results are summarized as follows. (1) The far-field emission pattern of nanowire-based light-emitting diode was investigated experimentally and theoretically. Peculiar emission patterns for nanowires were clrarified. (2) Density-controled InP nanowire arrays were realized by SA-MOVPE. The InAsP quantum dots (QDs) were embedded in the low-density InP nanowire arrays, and emission from a single QD in a single nanowire was confirmed. (3) Mode structure of the nanowire-based optical cavity was investigated by numerical simulation and its design principle was established. GaAs/InGaAs/GaAs core-multishell heterostructure nanowires were grown following the established design and cavity mode resonance was clearly identified by temperature-dependent photoluminescence study.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : IGARASHI Hajime, WATANABE Kota, IKEBE Masayuki, MOTOHISA Junichi
     
    Batteryless wireless sensors are very effective for safety surveillance of infrastructures such as bridges, tunnels and steel towers of the power-transmission lines. In this study, vibration generators which power the wireless sensors have been developed. These vibration generators, which harvest energy from minute vibration of the structures, allow us to realize autonomous operation of the wireless sensors. Although the structures usually have wide vibration spectra, the conventional vibration generators, which have linear vibration modes, cannot harvest sufficient energy at nonresonant frequencies. In this study, it has been found that it is possible to generate chaotic vibration by introducing new design to the vibration generator and this leads to energy harvesting in wider vibration spectra.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2014/03 
    Author : MOTOHISA Junichi, SATO Taketomo
     
    To explore novel materials for photochemical water splitting, we attempted the fabrication of GaN-based nanostructuers and their characterization of electrochemical properties. Growth of GaN and InGaN nanostructures were attempted by selective-area growth using RF-plasma-assisted molecular beam epitaxy. Hexagonal pyramidal structures of GaN were successfully fabricated and a use of alternate mask material for selective-area growth was suggested to be important to realized nanowires which is suitable for water splitting. We also investigated the photo-electrochemical properties of GaN by measureing current-voltage characteristics of GaN in electroryte with and without light irradiation. Furthermore, their characteristics was compared with porous structures, which were fabricated by photo-assisted chemial etching and had high-denstiy nanometer-sized pores on the surface, and it was found that porous structures allowed much lager photocurrent as compared to planar structures.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011/04 -2014/03 
    Author : HARA Shinjiro, MOTOHISA Junichi, KLAR Peter Jens, ELM Matthias Thomas, KRUG VON NIDDA Hans-albrecht
     
    We realized vertical free-standing semiconducting nanowires (NW) hybridized with ferromagnetic MnAs nanoclusters (NC), which enables us to confine carriers one-dimensionally and control carrier spins, by utilizing our unique selective-area growth method. The dependences of MnAs NC formation on various NW templates were investigated. We observed that MnAs layers were grown on the top {111}B surface of InAs NWs with a diameter of about 80 nm, and into the host NWs from the side walls to form MnAs/InAs hetero-junctions, which enable us to realize spin-carrier injection to NWs, and in which most of the c-axes of hexagonal NiAs-type MnAs layers were approximately parallel to the <111>B directions of InAs NWs. We developed two-terminal device processes to realize spin-polarized light-emitting diodes. I-V characteristics of the prototype MnAs/GaAs hybrid NWs showed p-type conductivity possibly owing to thermal diffusion of Mn atoms into the host GaAs NW surfaces during the MnAs NC formation.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2009 -2010 
    Author : 佐藤 威友, 橋詰 保, 本久 順一, 古賀 裕明
     
    平成22年度は、n形インジウムリン(InP)ポーラス(多孔質)構造の内壁に白金(Pt)薄膜を形成する手法を開発し、InP配列ナノ構造を基盤とするPt/InPショットキー型光電変換素子の試作を行った。 1.n形InP多孔質構造の孔内壁表面にPt薄膜を電解析出により形成する手法を開発した。真空蒸着法と比較してPt薄膜による孔内壁表面の被覆率が高く、Pt薄膜の厚さは時間により制御可能であることを明らかにした。特に電解析出電圧をパルス波形で印加することにより、膜厚の緻密な制御が可能であり、孔径600nmで深さ4μmからなる多孔質構造の内壁に厚さ20nmの均一なPt薄膜の形成に成功した。 2.作製したPt/InP多孔質構造の光反射率特性を明らかにした。入射光200nm-1100nmの波長領域における光反射率は5%以下であり、平坦なInP基板と比較して表面反射が10分の1に低減されていることを明らかにした。 3.作製したPt/InP多孔質構造の電気的特性を明らかにした。上部(Pt側)と下部(InP側)に電極を形成して測定した電流・電圧特性が整流性を示すことを明らかにし、Pt/InP多孔質構造の界面にショットキー障壁が形成されていることを確認した。また、光照射下では、光強度に応じて逆方向電流が増大することを明らかにした。この増加電流は、比較用に作製したPt/プレーナInP接合と比べて2~3桁大きい。これらの結果により、微細孔が周期的に配列した半導体多孔質構造は、内壁表面に適切な電位障壁を形成することで光キャリアを効率的に分離することが可能であり、太陽電池をはじめとする高効率光電変換素子への応用に有望であることが示された。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2010 
    Author : FUKUI Takashi, AMEMIYA Yoshihito, MOTOHISA Junichi, KASAI Seiya, HARA Shinjiro
     
    A selective growth method for semiconductor nanowires by using electron beam lithography and metal organic vapor phase epitaxy has been established. The crystal structure and optical properties of GaAs and InP nanowires grown were characterized by electron microscopy and photoluminescence. Transistors, light emitting diodes and solar cells using heterostructure/p-n junction nanowires were fabricated to investigate the device characteristics, which showed promise for application to future nano-electronics.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2007 -2009 
    Author : MOTOHISA Junichi, IKEBE Masayuki
     
    We developed a formation method of high-density and highly uniform array of semiconductor nanowires to realize quantum integrated hardwares. In particular, fabrication and characterization of nanowire field-effect transistors (FETs) were charried out, and vertical nanowire FETs on Si substrates were demonstrated. We also proposed vertically-integrated logic circuits based on vertical FETs and investigated a method to laterally align nanowires for their high-density integration.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2006 -2007 
    Author : 福井 孝志, 本久 順一, 原 真二郎
     
    有機金属気相(MOVPE)選択成長技術とナノ構造の自然形成技術の組み合わせにより作製した量子ドット構造を用いた「単一電子メモリ」の実現を目的とし、本年度は、これまで作製を行ってきた、GaAs細線とInAs量子ドット構造を有する量子ドットメモリのトランスファ特性において生じるヒステリシスについて、その機構に関する詳細な評価・検討を行った。今回、電流ICTS法と呼ばれる評価手法を用い、トラップの準位、及び捕獲断面積を評価し、ヒステリシス機構について検討した。評価にはMOVPE選択成長技術を用いて作製した、InAs量子ドットを有する細線FET構造を用いた。電流ICTS法とは、Vdsを一定に保つと同時に、ゲート電極にパルス的に電圧を印加することでIdsに生じるトランジェントから、活性化エネルギ、捕獲断面積、及びトラップの密度を評価する手法である。得られたICTS信号(t・dI/dt)の温度依存性曲線では、ピークの位置が時定数を示す。温度低下に伴いピークが長時間側にシフトする傾向が確認された。時定数のアレニウスプロットにより、今回の測定結果からは典型的に2つの活性化エネルギを見積もることができ、それぞれ0.33eV、0.18evである。またそれらの捕獲断面積は1.6×10^<-15> cm^2、3.8×10^<-19> cm^2であった。捕獲断面積のオーダを考慮するとこれらの準位は量子ドット自体によるものでなく、量子ドットに起因して形成された欠陥の準位であると考えられるが、詳細なデータ解析は現在行っている最中である。またその他、量子ドットに注入するキャリアソースとして、半導体薄膜上の強磁性体ナノ構造の自己形成技術についても結晶成長実験を行った。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2005 -2006 
    Author : 原 真二郎, 本久 順一, 福井 孝志
     
    化合物半導体への強磁性MnAsナノ構造のエピタキシャル成長技術確立を目的とし、本年度は主にプレーナGalnAs{111}面上の有機金属気相成長に関して、結晶面方位依存性や、供給ガス比率(V/Mn比)・成長時間等の成長条件依存性を評価し、ナノクラスタ形成制御の観点から詳細なデータ取得を行った。これまで断面格子像観察・電子線回折による構造評価及び、磁気異方性評価から.、(111)B面上のMnAs成長では、六方晶のNiAs型MnAsナノクラスタが立方晶の閃亜鉛鉱型GaInAs表面に形成され、MnAsのc軸がGalnAsの[111]B方向と平行であるとの知見を得た。今回矩形ナノクラスタが形成される(001)面上及び、よりサイズの小さい六角形ナノクラスタが高密度に形成される(111)A面上で詳細な構造評価を行った結果、いずれの結晶面方位においてもNiAs型ナノクラスタが形成するものの、(111)B面上とは異なりナノクラスタの結晶軸が下地GaInAsの[111]方向から僅かに傾く、あるいはばらつきを持つ傾向にあった。これはV族(As)原子に覆われた(111)B表面と異なり、特に完全なIII族面である(111)A面では、 GaInAs層に埋め込まれたMnAsナノクラスタが形成されやすいことに起因すると考えられる。ただ(111)A面上においてもV/Mn比を60から1125と大幅に増加させることにより、微小ナノクラスタがより高密度に形成され、周囲の結晶表面の平坦性も向上する。今回の結果は、MnAsの結晶成長では従来のIII-V族化合物半導体に比べ著しく高いV族分圧が必要であることを示唆しており、半導体・強磁性体複合構造形成のための有用な知見となった。またより格子不整合度の小さいGaAs(111)B面上のMnAs成長では、10μm^2以上の広範囲に渡って平坦に薄膜状成長する傾向にあった。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2005 -2006 
    Author : 本久 順一, 原 真二郎, 福井 孝志
     
    平成18年度は前年度の成果を基盤として、有機金属気相選択成長法により作製されたナノワイヤの光学特性評価を目的として、以下のような研究を行った。 まず、InGaAs/GaAsナノワイヤに対し、顕微フォトルミネセンス(PL)法によりその発光特性の評価を行った。特に光学測定系の改善により、空間分解能約1μm程度でナノワイヤからの発光の空間像をを観察したところ、ナノワイヤ内部に局在するInGaAs層から実際に発光していることが明確に示された。また、同様の空間像から、直径約200nm、長さ2.6μm程度のナノワイヤにおいて、その両端から強い発光が得られていることが確認された。これはナノワイヤ内部で発生した光がナノワイヤに添って伝搬している、すなわちナノワイヤが光導波路として機能しているためであると考えられ、微小光素子や高効率の単一格子光源応用に向けての重要な知見を得た。 次に、InPナノワイヤに対し、顕微PLおよびラマン散乱測定により評価を行った。その結果、 InPナノワイヤでは平均的に10^<17>cm^<-3>程度あるいはそれ以下の電子がバックグラウンドに存在していることが確認された。そしてこれらのナノワイヤのうち、発光効率が高く不純物密度が少ないと考えられる単一のナノワイヤを詳細に評価した結果、ウルツ鉱形構造を有するInPナノワイヤではそのバンドギャップエネルギーカミ約1.50eVであり、InPバルクより80meV程度広いことが明らかとなった。 さらにInPナノワイヤに対して不純物ドーピングと伝導形の制御を試みた。シランをドーピングガスとしてナノワイヤ成長時に供給した場合、参照用のプレーナ基板と比べ密度が1桁程度少ないものの、期待通りシリコンがn形の不純物として取り込まれていることが明らかとなった。また、ジエチルジンクをドーピングガスとして用いた場合には、ラマン散乱の測定結果より、亜鉛がナノワイヤ中に取り込まれ、p形不純物として働いていることが確認された。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : MOTOHISA Junichi, FUKUI Takashi, SANO Eiichi, YANG Lin, SATO Taketomo
     
    We have established a method to fabricate two-dimensional crystals (2D-PhCs) and 2D-PhC slabs (2D-PhCs) by utilizing selective area metalorganic vapor phase epitaxial (SA-MOVPE) and investigated their optical properties. By doing SA-MOVPE growth on GaAs (111)B or InP(111)B substrates partially covered with periodic array of hexagonal masks, we have fabricated air-hole array of GaAs- and InP-based semiconductors. If the SA-MOVPE is carried out on sacrificial AIGaAs layer, For GaAs-based 2D-PhCs, we have succeeded in the fabrication of air-bridge-type 2D-PhCs and 2D-PhCs with line-defect and point-defect structures. We also have succeeded in the formation of GaAs/AlGaAs quantum wells with periodic air-holes and confirmed their photoluminescence (PL). InP- based 2D-PhCs with period of 400-500nm were also successfully formed after optimization of growth conditions. Emission from InP/InGaAs quantum well structures embedded in 2D-PhC was also fabricated and their optical properties were investigated PL, demonstrated that this structure is promising for the application of photonic devices operating in the optical-fiber communication wavelength. In addition, GaAs- and InP- based 2D-PhCs constructed from periodic array of hexagonal pillar arrays were also fabricated by SA-MOVPE on (111)B GaAs and (111)A InP substrates, respectively, where array of circular mask opening are defined. In particular, for GaAs-based pillar-type 2D-PhCs, it was found that the light emission from GaAs/AIGaAs quantum wells formed on the top of the pillars is found to dependent on the pitch of the pillar arrays and is enhanced by factor of 10 as compared to the reference planar structure. This phenomenon is qualitatively understood by the enhancement of light-extraction efficiency originating from the formation of photonic bandstructure by the introduction of the periodic structure on the top of high-index slabs. The optical properties 2D-PhCs and 2D-PhCSs, such as photonic bandstructures, dispersion of line-defect waveguides, transmittance and reflectivity, are also investigated theoretically using finite-difference-time-domain method, plane-wave expansion method, and scattering matrix method to understand the optical properties of 2D-PhCs and 2D-PhCSs, including a proposal of modified effective index method applicable to 2D-PhCs with high index contrasts.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2001 -2005 
    Author : 福井 孝志, 長谷川 英機, 雨宮 好仁, 本久 順一, 橋詰 保, 葛西 誠也
     
    平成17年度は、有機金属気相成長(MOVPE)選択成長法による量子ナノ構造を利用した単電子素子・単電子回路の実現と、高密度量子ナノ構造の周期配列の形成技術の確立を目的として、以下の研究を行った。 1.前年度に続き、単電子トランジスタの論理回路応用を目的に集積化を進めた。2分決定グラフ論理による1ビット加算器に関して、論文公表することが出来た。また、選択成長により作製したリッジ型量子細線と、自己形成InAs量子ドットを組み合わせた、フローティングゲート型の単電子メモリーの試作とその動作特性解析を進めた。試作した素子を温度20Kで評価した結果、ドレイン電流に、ゲート電圧に対する明瞭な時計回りのヒステリシスが観測された。印加するゲート電圧の最大値を変化させる実験、あるいはヒステリシスの幅やしきい値のシフト量およびその温度依存性、さらにゲート電圧を変化させた後の時間応答などの実験結果により、このヒステリシスが、ゲート側から注入された電子が量子ドットに保持されることに起因することが示された。 2.単電子素子の高温動作化を目的として、選択成長を用い、新しい種類のナノ構造の作製を試みた。具体的には、円形あるいは6角形のマスク開口部を有するGaAs(111)B基板に対して選択成長を行うことにより、直径50nm、長さは9μmにもおよぶ、GaAsナノワイヤ構造の作製に成功した。そして、このナノワイヤを単電子素子へと応用するプロセス手法を考案した。同様な構造はInP(111)A基板上にも作製した。まずInPナノワイヤ、横方向成長を利用したInP/InAsコアシェル構造、さらにInP/InAs/InP横方向ヘテロ構造からなるInAs量子リングを作製し、その光学的特性から、量子閉じ込め構造を確認した。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2002 -2004 
    Author : HASHIZUME Tamotsu, MOTOHISA Junichi, KASAI Seiya, AKAZAWA Masamichi
     
    The purpose of this research was to characterize and control surface/interface properties of GaN-based material systems such as AlGaN/GaN hetrostrcutures for the stability improvement of high-frequency and high-power transistors. The main results obtained are listed below : (1)Serious deterioration such as stoichiometry disorder and nitrogen deficiency (N deficiency) was found at the processed AlGaN surfaces. This resulted in formation of a localized deep donor level related to N vacancy (V_N), causing excess leakage currents at the AlGaN Schottky interface and serious drain current collapse in AlGaN/GaN heterostructure field effect transistors. (2)An Al_2O_3-based surface passivation scheme including the N_2-plasma surface treatment was proposed and applied to an insulated-gate type HFET. A large conduction-band offset of 2.1 eV was achieved at the Al_2O_3/Al_<0.3>Ga_<0.7>N interface. No current collapse was observed in the fabricated Al_2O_3 insulated-gate HFETs under both drain stress and gate stress. (3)From the detailed temperature-dependent current-voltage (I-V-T) measurements, we discussed the mechanism of leakage currents through GaN and AlGaN Schottky interfaces. The experiments were compared to the calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation results indicates that the barrier thinning caused by unintentional surface-defect donors enhances the funneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2002 -2003 
    Author : 本久 順一, 須田 善行, 葛西 誠也
     
    平成15年度は、フラットバンド強磁性が実験的に確認できるという理論的予測がされている、周期0.7μmのInAsによるKagome格子を有機金属気相成長(MOVPE)選択成長法により作製するするため、以下のような実験を行った。 まず、SiO_2膜堆積を堆積したGaAs(111)A基板に対して、電子線リソグラフィ、およびウエットエッチングにより、MOVPE選択成長用のマスク基板を作製した。マスクのパターンは昨年度のものと同様、6角形あるいは3角形のマスクを周期的に配列させたものであるが、今回は、(111)B基板ではなく、(111)A基板を用いている。その後、窓明け部分へ、GaAsおよびInAsを、MOVPE選択成長を行った。 まず、(111)Aプレーナ面では平坦な表面が得られる、温度500Cにおいて格子周期が1〜3μmのマスクパターンに対して、選択成長を行った場合、細線の交点部分にのみ、3次元的にInAsが成長するが、成長温度を下げると、3次元成長モードから2次元成長へと転移することが明らかとなった。この成長モードの転移は、成長温度の低下に伴う表面拡散長の減少によって説明でき、またGaAsとInAsの格子定数の差による歪みは、その成長界面で発生したミスフィット転移により緩和されていると考えられる。この結果、ピットを含み、表面平坦性には問題があるが、垂直{110}ファセットを側壁として有する細線の交差構造である、InAsによるKagome格子が、そのマスクパターンを踏襲して形成可能であることが示された。さらに、表面平坦性を改善するため、アルシン(AsH_3)分圧に対する依存性について調べた。その結果、AsH_3分圧を下げた場合に、表面平坦性に優れ、また横方向成長が抑制され、マスクパターンを踏襲したKagome格子構造が形成されることがわかった。 以上に述べた成長条件の最適化の結果、温度400C・低AsH_3分圧という成長条件で、MOVPE選択成長により、周期0.7μmのInAs Kagome格子の形成に成功した。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2000 -2002 
    Author : MOTOHISA Junichi, SATO Taketomo, HASHIZUME Tamotsu
     
    We have developed a technique to form two-dimensional periodic array of hexagonal pillars and air-hole structures for the application of two-dimensional crystals (2DPCs) by selective area metalorganic vapor phase epitaxial (SA-MOVPE) growth. Firstly, SA-MOVPE of GaAs and AlGaAs was carried out on (111)B GaAs substrates partially covered with SiO_2 masks. Array of circular or hexagonal openings of the mask pattern was arranged to realize triangular lattice with periodicity of about 0.5μm. By optimizing the growth conditions, uniform array of hexagonal pillar structures consisting of vertical {110} facets was successfully grown on the masked substrates, which can be used as 2DPC. Similar array of hexagonal InGaAs pillars was also grown on (111)B InP masked substrates, and was found to exhibit high optical qualify suitable for 2DPCs using InP-based materials. In addition, by growing a masked substrate with hexagonal SiO_2 masks arranged to form triangular lattice, we succeeded in the growth of GaAs 2DPC structures with hexagonal air-hole arrays when the growth conditions were optimized to suppress lateral overgrowth. Furthermore, by growing air-hole type 2DPCs on AlGaAs (111)B surfaces and selective undercut etching of AlGaAs, 2DPC slab was also successfully fabricated. Finally, Photonic bands of 2DPCs consisting of hexagonal air-hole arrays or hexagonal dielectric rods were also calculated by using plane-wave expansion method, and they were compared with those consisting of conventional circular air-holes or circular rods. Although the overall features of the photonic bands quite looked alike, the discrepancy originating from the shape of air-holes and rods were found. Especially in hexagonal air-hole arrays in orthogonal-type triangular lattice, the enhancement of overlap between TM and TE gap demonstrated, which is effective to realize 2D full photonic bandgap.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2001 -2001 
    Author : 福井 孝志, 本久 順一
     
    平成13年度は、有機金属気相成長(MOVPE)選択成長法により高密度量子ナノ構造の形成技術を確立すること、それを利用した単電子トランジスタの基本的特性や物理を解明すること、および、それらを回路へと応用することを目的として、以下の研究を行った。 1.MOVPE選択成長のマスクパターンを適切に設計することにより、高密度GaAs量子ドットアレイや、高密度の量子ドット-量子細線結合構造アレイの形成を試みた。作製された構造のカソードルミネセンス測定から、量子ナノ構造が設計通りに形成されていることが確認された。 2.上記の形成技術を基盤として、量子ドットによる単電子トランジスタを形成し、その伝導特性を極低温において詳細に測定した。明瞭なクーロン振動・クーロンダイアモンドが確認されるとともに、ある条件下では、非常に強い量子ドットにおける近藤効果が観測された。特に、強磁場中で観測された近藤効果においては、その微分コンダクタンス特性の零バイアス付近に特異なディップ構造を観測し、それが2段階近藤効果に起因していることを明らかにした。 3.相補型インバーター回路への応用を目的として、上記の単電子トランジスタを、2個同一基板上に集積化し、直列接続した回路を試作した。2つの単電子トランジスタの相補的動作を確認し、相補型単電子インバーター回路実現への見通しを得た。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2001 
    Author : HASHIZUME Tamotsu, TAKEYAMA Mayumi, KANESHIRO Chinami, MOTOHISA Junichi, FUJIKURA Hajime
     
    For the application to high-power/high-frequency electronic devices, we have investigated the formation processes of insulated structures on GaN and their interface properties. The main results obtained are listed below : (1) Chemistry and electronic properties of GaN surfaces after various kinds of surface treatments were characterized by x-ray photoelectron spectroscopy (XPS). Strong upward band bending of 1.4 eV was found at the air-exposed GaN surface. This is due to the high density of surface states. The surface treatment in the NH_40H solution and the ECR-excited N_2 plasma significantly decreased the surface band bending to 0.5 eV, indicating the reduction of the Fermi level pinning. (2) We have successfully fabricated the SiN_χ gate structure on the treated n-GaN surface by the ECR-CVD process. The SiN_χ/n-GaN structure showed the type-I band lineup and a low interface state density distribution in the range of 10^<11> cm^<-2> eV^<-1>. The surface passivation utilizing the ECR-CVD SiNx film enhanced the drain saturation current and improved the stability in the GaN/AlGaN heterostructure field effect transistors. (3) Electrical characterization of AlN/GaN interfaces was carried out by the C-V technique in samples grown by metal organic chemical vapor deposition. A low value of interface state density D_ of < 1x 10^<11> cm^<-2> eV^<-1> was achieved around the energy position of Ec-0.8eV. This indicates that the AlN/GaN structures have good interface properties with low interface state density, and are very promising for advanced MIS devices. (3) A novel surface passivation process for AIGaN/GaN heterostructures utilizing an ultrathin Al_20_3 layer (〜1 nm) was proposed. The reverse leakage current for the Schottky gate contact on the Al_20_3-passivated heterostructure surface was reduced by three orders of magnitude than that for the conventional Schottky gate structure. C-V results showed good gate controllability of two-dimensional electron gas (2DEG) by the novel gate structure.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1999 -2001 
    Author : HASHIZUME Tamotsu, KASAI Seiya, KANESHIRO Chinami, MOTOHISA Junichi, SEKI Shouhei, TAKEYAMA Mayumi
     
    The purpose of this research was to develop the formation processes of a stable Schottky contact and a ohmic contact with a low resistivity to GaN, based on the systematic characterization of the GaN surfaces and metal-GaN interfaces. The main results obtained are listed below: (1) Chemistry and electronic properties of GaN surfaces after various kinds of surface treatments were characterized by x-ray photoelectron spectroscopy (XPS). Strong upward band bending of 1.4 eV was found at the air-exposed GaN surface. This is due to the high density of surface state. The surface treatment in the NH_4OH solution and the ECR-excited N_2 plasma significantly decreased the surface band bending to 0.5 eV, indicating the reduction of the Fermi level pinning. (2) We investigated the leakage mechanism through metal/n-GaN interfaces by detailed current-voltage-temperature (I-V-T) measurements. A large deviation from the thermionic emission (TE) transport was observed in the reverse I-V curves with a large excess leakage. A novel barrier- modified thermionic-field emission (TFE) model based on presence of near-surface fixed changes or surface states was proposed to explain the observed large reverse leakage currents. (3) A novel surface passivation process for AlGaN/GaN heterostructures utilizing an ultrathin Al_2O_3 layer (〜 1 nm) was proposed. The reverse leakage current for the Schottky gate contact on the Al_2O_3-passivated heterostructure surface was reduced by three orders of magnitude than that for the conventional Schottky gate structure. C-V results showed good gate controllability two-dimensional electron gas (2DEG) by the novel gate structure. (4) Mg-doped GaN surfaces were characterized by XPS. The surface accumulation of Mg at the Mg-doped GaN seems to cause the formation of the disordered surface layer including a tenacionus oxide layer, leading to the large downward band-bending of 1.3-1.4 eV at the surface. The surface treatment in ECR-N_2 plasma was very effective in removing such a disordered layer.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -2000 
    Author : FUKUI Takashi, MOTOHISA Junichi
     
    We have developed a technique to form position-and size-controlled quantum wires (QWRs) and quantum dots (QDs) by selective area metalorganic vapor phase epitaxial (SA-MOVPE) growth. The technique is applied for the direct fabrication of single electron transistors and circuits using QD-QWR coupled structures. Main results of the project are summarized below. (1) We investigated the mechanism of SA-MOVPE for the fabrication of high-density QD arrays with extreme uniformity. We have found and clarified the self-limited mechanism in SA-MOVPE where the top size and shape of the GaAs pyramidal structures and ridge structures are maintained after the formation of such 3-dimensional structures. This self-limited growth mode is utilized to achieve size uniformity in QDs. We also have clarified that the top size of the GaAs pyramid is determined by the balance between the adsorption and desorption of adatoms at the step edges and can be controled by the growth conditions. (2) Based on the fabrication technique of QD arrays, we have proposed and succes sfully fabricated a two-dimensional coupled array of QDs and QWRs by SA-MOVPE.The optical characterization has confirmed the formation of network-like array of QDs and QWRs. The results indicate that our proposed fabrication method is effective to realize high-density integration of quantum devices, such as single electron transistors, for future electronics. (3) Single electron transistors have successfully been fabricated by the combination of coupled structures of QWR-QD-QWR formed by SA-MOVPE technique and Schottky gate technology. We have succeeded in the demonstration of the circuit operation of single electron inverters, which integrates quantum wire transistor and single electron transistors fabricated by one-step growth on designed masked substrate for SA-MOVPE.Our quantum dot devices also have shown to exhibit strong lateral confinement that are beneficial to explore the physics of nanostructures, such as Kondo effect in QDs.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -1998 
    Author : HASEGAWA Hideki, WU Nan-jan, FUJIKURA Hajime, MOTOHISA Jyunichi, HASHIZUME Tamotsu
     
    The purpose of this study is to realize the "Schottky limit" for various metal-compound semiconductor (M-S) interfaces by removing Fermi-level pinning using an in-situ electrochemical process and to apply this process to various devices. The main results obtained are listed below : 1) A novel in-situ electrochemical process enables us to produce Schottky contacts with strongly metal-workfunction dependent Schottky barrier heights (SBHs) for InP, GaAs and GaN.Particularly, SBHs higher than 0.86 and 0.92eV were achieved for Pt/n-InP and Pt/n-GaAs contacts, respectively. These values are close to those in the Schottky limit. 2) The M-S interfaces prepared by the in-situ electrochemical process were found to possess no oxide interlayers, no interface stress as well as no process-induced defect levels. 3) Detailed AFM measurements revealed that the electrochemical deposition was initiated by formation of nm-sized metal particles. Further deposition did not increase the particle size but increased density of particle. The SBH values exhibited a strong correlation with the particle distribution. The most uniform distribution of the smallest particles gave highest SBH values for Pt/n-InP contact. An I-V measurements using AFM system with conductive tip revealed that such high SBHs were realized in single Pt particles on InP and GaAs. 4) The above results can be explained as follows : Under optimized conditions, the low-energy electrochemical process forms fine metal nano particles without causing a large degree of disorder on the semiconductor surface. The interface is free from oxide interlayers, interface stress and process-induced defects. This leads to removal of the Fermi-level pinning and to strongly metal-workfunction dependent SBH values. 5) The in-situ electrochemical process was successfully applied to formation of sub-micron T-shaped
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1996 -1997 
    Author : 齊藤 俊也, 本久 順一, 藤倉 序章, 本久 順一, 齊藤 俊也
     
    平成9年度は、人工原子″スーパーアトム″の作製に関する基礎検討として、分子線エピタキシャル成長方を用いた微細構造形成の検討、また、そのネットワーク化に向けた検討を行うとともに、自己形成量子ドットの作製および光学的評価を行ない、以下のような結論を得た。 (1)InP基板表面に正方形のメサ(台地状の構造)に線状のメサが結合した構造を加工により形成し、この上に分子線エピタキシ(MBE)法によりInAlAs/InGaAs/InAlAs構造の成長を行った。詳細な構造観察の結果、適切な成長条件下で、正方形メサ上にInGaAs量子ドットが、線状メサ上にInGaAs量子細線が形成され、InAlAs/InGaAs系の材料を用いた選択成長が人工原子構造の作製、およびその多数個連結した素子の作製に関して今後有用であることが示唆された。 (2)詳細な光学的測定によって、上記のInGaAs量子細線・量子ドットの結合部分には高さ100meV程度のポテンシャル障壁が存在することが明らかとなった。また、初期加工基板形状・成長条件等を様々に変えて形成した細線・ドット結合構造の構造観察から、ドット・細線・ポテンシャル障壁のサイズが、初期基板形状・成長条件により精密に制御可能であることが明らかとなり、InAlAsを核とする人工原子およびネットワークの形成手法に関する重要な知見を得た。 (3)また、格子不整合系の人工原子作製の可能性に関する基礎検討として、GaAs/InAs自己形成量子ドットの形成、および光学的評価を行い、ウェット層とドットのクーロン相互作用が光学的特性に影響を及ぼすことが判明した。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1995 -1996 
    Author : HASEGAWA Hideki, AKAZAWA Masamichi, MOTOHISA Junichi, HASHIZUME Tamotsu
     
    The purpose of this study is to investigate the interaction mechanism between surface states and confined levels in III-V compound semiconductor quantum structures and to control the surface properties by use of ultrathin silicon interface control layr (SiICL) for fabrication of novel optical devices. The main results obtained are listed below : (1) It was found that the photoluminescence (PL) intensity from the near-surface quantum well (OW) with the surface-to-well distance of 5nm, was reduced by a factor of 1000 as compared with that from the reference QW located deeply inside. We revealed that this phenomenon is caused by strong interaction between the quantized states in near-surface QW and surface states. Acomplete recovery of PL intensity was achieved by use of Si-ICL based passivation technique. (2) X-ray photoelectron spectroscopy analysis revealed that there were no oxidized and nitrided phase of semiconductor surface at the passivation film/semiconductor interfaces. (3) By applying the Si-ICL passivation method, a nearly complete recovery of PL intensity was achieved with an observed maximum recovery factor of 400 for the InGaAs quantum wires. The quantum wires passivated with SiICL showed strong PL intensity even at room temperature. (4) The Si-ICL passivation technique was successfully applied to passivation of side walls of InGaAs quantum wires fabricated by wet etching process. (5) Detailed computer simulation pointed out that a clear passivation effects can be explained by substantial reduction of surface states by Si-ICL based passivation technique
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1994 -1995 
    Author : MOTOHISA Junichi, SAITOH Toshiya, SAWADA Takayuki
     
    The objective of the present research is to realize semiconductor quantum nanostructures with controlled interfaces by utilizing the self-organized nature of the crystal growth. In particular, various types of quantum nanostructures were fabricated by metal-organic vapor phase epitaxial growth (MOVPE) growth on patterned substrates or on vicinal substrates. The main results are listed below. (1) We studied on a growth process on patterned GaAs (001) substrate during metal-organic vapor phase epitaxy (MOVPE) and a novel approach for the fabrication of AlGaAs/GaAs quantum dot (QD) structures. The patterned substrate have an array of holes on the surface and those holes are partially filled with GaAs by MOVPE growth, followed by GaAs/AlGaAs quantum well structures. Detailed investigation on growth process on such patterned substrates revealed the presence of complicated two-dimensional migration of Ga and Al between different facets. Formation of GaAs dots was directly confirmed by spatially resolved cathodoluminescence measurements. (2) We propose a new, lateral surface superlattice (LSSL) type of electron interference devices, where the period of LSSL is typically 60nm, by utilizing multiatomic steps on a vicinal GaAs (001) surface. Conductivity of the device is theoretically studied by taking the effect of randomness in the LSSL into account. We also investigate its drain and transconductance characteristics experimentally at low temperatures, and found clear oscillations in gm-V_G characteristics, which were ascribed to the electron interference effect.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1994 -1995 
    Author : FUKUI Takashi, MOTOHISA Junichi, HASEGAWA Hideki
     
    We have fabricated AlGaAs/GaAs quantum dot structures using selective area metalorganic vapor phase epitaxy (MOVPE). First, GaAs pyramidal structures with four-fold symmetric {011} facet side walls are formed on SiN_x masked (001) GaAs with square openings. Once the pyramidal structures were completely formed, no growth occurs on the top and side walls of the pyramids. Furthermore, the shape and width of the top area observed by a scanning electron microscope (SEM) and an atomic force microscope (AFM) shows to be highly uniform. This indicates that self-limited growth mode occurs. Next, using these uniform pyramids, GaAs quantum dots are overgrown on the top of pyramids using different growth conditions. Sharp photoluminescence (PL) spectra are observed from uniform quantum dots.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1992 -1993 
    Author : FUKUI Takashi, AKAZAWA Masamichi, MOTOHISA Jun-ich, HASEGAWA Hideki
     
    GaAs and AlGaAs micro-Pyramidal Structures having four-fold symetry facets (011) were fabricated using selective area MOVPE on (001) GaAs substrates partlally masked with a SiO_2. In order to study accurate growth rate, wider mask-patterned substrates were used. Low pressure horizontal MOVPE reactor was used. Source materials were TMGa, TEAI, quality of micro-pyramidal structures were characterized by cleaved cross section image of scanning electron microscope (SEM) and photoluminescence (PL) from quantum well. The main results are as follows : The growth rate enhances in selective are growth, compared to a planer GaAs layr. The growth rate enhancement is small under high AsH_3 partical pressure. From these results, growth mechanisms were discussed.
  • 半導体ナノ構造の形成、評価とデバイス、回路応用

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