Researcher Profile and Settings

Master

Affiliation (Master)

• Research Center for Integrated Quantum Electronics

Affiliation (Master)

• Research Center for Integrated Quantum Electronics

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Profile and Settings

Profile and Settings

• Name (Japanese)

  Sato

• Name (Kana)

  Taketomo

• Name

  200901007731172067

Alternate Names

http://hydrogen.rciqe.hokudai.ac.jp/~taketomo/home/index.html

Achievement

Research Interests

• Nitride Semiconductor   electron devices   wet etching   electrochemistry   porous structure   functionalization   photo-electric conversion   chemical sensor   

Research Areas

• Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment
• Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering

Research Experience

• 2004/04 - Today Hokkaido University Research Center for Integrated Quantum Electronics
• 2001/10 - 2004/03 Hokkaido University Graduate School of Engineering
• 2001/04 - 2001/09 Hokkaido University Research Center for Integrated Quantum Electronics

Education

• 1998/04 - 2001/03  Hokkaido University
• 1996/04 - 1998/03  Hokkaido University
• 1992/04 - 1996/03  Hokkaido University  School of Engineering

Committee Memberships

• 2021/11 - Today   SSDM Sub-Committee Area Vice Chair (Area4: Power / High‐speed Devices and Materials)

Awards

• 2000/11 応用物理学会 第61回秋期応用物理学会学術講演会『講演奨励賞』
   化合物半導体ナノショットキー界面の電気的特性とその制御 

  受賞者: 佐藤 威友
• 1997/12 電気関係学会北海道支部会 平成9年度『若手講演者賞』
   In situ 電気化学プロセスを用いたショットキー障壁の形成 

  受賞者: 佐藤 威友

Published Papers

• Reduction in Gap State Density near Valence Band Edge at Al2O3/p-type GaN Interface by Photoelectrochemical Etching and Subsequent SiO2 Cap Annealing

  Yining Jiao, Takahide Nukariya, Umi Takatsu, Tetsuo Narita, Tetsu Kachi, Taketomo Sato, Masamichi Akazawa

  Physica Status Solidi (B) Basic Research 0370-1972 2024 

  The process-dependent properties of Al2O3/p-type GaN (p-GaN) interfaces formed by atomic layer deposition at 300 °C after photoelectrochemical (PEC) etching are reported. For investigating the gap states at the Al2O3/p-GaN interface, metal-oxide-semiconductor (MOS) diodes are fabricated and examined by sub-bandgap-light-assisted and temperature-dependent capacitance–voltage (C–V) measurements. PEC etching prior to Al2O3/p-GaN interface formation is conducted with the etching depth varied in the range between 12.5 and 32.1 nm. The C–V characteristics of the MOS diodes without PEC etching indicate Fermi-level pinning due to the near-surface defect level in p-GaN at 0.7 eV above the valence band edge EV and a high density of gap states around the midgap. However, all samples with PEC etching exhibit C–V characteristics, indicating a reduction in the density of the defect states at EV + 0.7 eV and midgap states. Still, PEC etching after capless annealing at 800 °C for the activation of Mg acceptors cannot reduce the density of gap states near the valence band edge. On the other hand, annealing of a sample with a SiO2 cap layer at 800 °C after PEC etching can reduce the gap state density near the valence band edge.
• Investigation of dominance in near-surface region on electrical properties of AlGaN/GaN heterostructures using TLM, XPS, and PEC etching techniques

  Ryota Ochi, Takuya Togashi, Yoshito Osawa, Fumimasa Horikiri, Hajime Fujikura, Kazunari Fujikawa, Takashi Furuya, Ryota Isono, Masamichi Akazawa, Taketomo Sato

  Applied Physics Express IOP 16 (9) 091002-1 - 091002-2 2023/09 [Refereed][Not invited]
  
• Detection of defect levels in vicinity of Al2O3/ p-type GaN interface using sub-bandgaplight- assisted capacitance–voltage method

  Masamichi Akazawa, Yuya Tamamura, Takahide Nukariya, Kouta Kubo, Taketomo Sato, Tetsuo Narita, Tetsu Kachi

  Journal of Applied Physics 132 (19) 195302-1 - 195302-10 2022/11/16 [Refereed][Not invited]
  
• Fabrication of GaN nanowires containing n+-doped top layer by wet processes using electrodeless photo-assisted electrochemical etching and alkaline solution treatment

  Michihito Shimauchi, Kazuki Miwa, Masachika Toguchi, Taketomo SATO, Junichi Motohisa

  Applied Physics Express 1882-0778 2021/10/06 [Refereed][Not invited]
  
• Self-terminating contactless photo-electrochemical (CL-PEC) etching for fabricating highly uniform recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs)

  Masachika Toguchi, Kazuki Miwa, Fumimasa Horikiri, Noboru Fukuhara, Yoshinobu Narita, Osamu Ichikawa, Ryota Isono, Takeshi Tanaka, Taketomo Sato

  Journal of Applied Physics 130 (2) 024501 - 024501 0021-8979 2021/07/14 [Refereed][Not invited]
  
• HfSiOx-gate GaN MOS-HEMTs for RF power transistor

  Tamotsu Hashizume, Ryota Ochi, Erika Maeda, Toshihide Nabatame, Koji Shiozaki, Taketomo Sato

  Proceedings of SPIE - The International Society for Optical Engineering 11686 0277-786X 2021 

  We have investigated AlGaN/GaN high-electron mobility transistors (HEMTs) with a high κ gate dielectric using hafnium silicate (HfSiOx). The (HfO2)/(SiO2) laminate structure was deposited on the AlGaN surface by a plasma enhanced atomic layer deposition, followed by a post-deposition annealing at 800 °C. The HfSiOx-gate HEMT showed good transfer characteristics with a high transconductance expected from its κ value and a subthreshold swing of 71 mV/ decade. In addition, we observed excellent capacitance-voltage (C-V) characteristics with negligible frequency dispersion in the metal-oxide-semiconductor (MOS) HEMT diode. The detailed C-V analysis showed low state densities in the order of 1011 cm-2 eV-1 at the HfSiOx/AlGaN interface.
• Fabrication of Recessed-Gate AlGaN/GaN Hemts Utilizing Contactless Photo-Electrochemical (CL-PEC) Etching

  Masachika Toguchi, Kazuki Miwa, Fumimasa Horikiri, Noboru Fukuhara, Yoshinobu Narita, Osamu Ichikawa, Ryota Isono, Takeshi Tanaka, Taketomo Sato

  ECS Meeting Abstracts 68th 2020/11/23 [Not refereed][Not invited]
  
• (Invited) Photo-Electrochemical Etching and Porosification of III-Nitride Semiconductors

  Taketomo Sato, Masachika Toguchi

  ECS Meeting Abstracts 2020/11/23 [Not refereed][Invited]
  
• Depth profiling of surface damage in n-type GaN induced by inductively coupled plasma reactive ion etching using photo-electrochemical techniques

  Shinji Yamada, Kentaro Takeda, Masachika Toguchi, Hideki Sakurai, Toshiyuki Nakamura, Jun Suda, Tetsu Kachi, Taketomo Sato

  Applied Physics Express 13 (10) 106505 - 106505 1882-0778 2020/10/01 [Refereed]
  
• Gate controllability of HfSiOx/AlGaN/GaN MOS high-electron-mobility transistor

  Ryota Ochi, Erika Maeda, Toshihide Nabatame, Koji Shiozaki, Taketomo Sato, Tamotsu Hashizume

  AIP Advances 10 (6) 065215 - 065215 2020/06/01 [Refereed][Not invited]
  
• Thermal-assisted contactless photoelectrochemical etching for GaN

  Fumimasa Horikiri, Noboru Fukuhara, Hiroshi Ohta, Naomi Asai, Yoshinobu Narita, Takehiro Yoshida, Tomoyoshi Mishima, Masachika Toguchi, Kazuki Miwa, Hiroki Ogami, Taketomo Sato

  Applied Physics Express 13 (4) 1882-0778 2020/04/01 

  Advanced contactless photoelectrochemical etching for GaN was conducted under the condition that the sulfate radicals (SO4•-) as the oxidizing agent were mainly produced from the S2O82- ions by heat. The generation rate of SO4•- was determined from the titration curve of the pH in the mixed solutions between KOH (aq.) and K2S2O8 (aq.); it clearly increased with an increase in the S2O82- ion concentration. The highest etching rate of >25 nm min-1 was obtained in the "alkali-free" electrolyte of 0.25 mol dm-3 (NH4)2S2O8 (aq.) at 80 °C, which was approximately 10 times higher than that reported by previous studies.
• Self-termination of contactless photo-electrochemical (PEC) etching on aluminum gallium nitride/gallium nitride heterostructures

  Kazuki Miwa, Yuto Komatsu, Masachika Toguchi, Fumimasa Horikiri, Noboru Fukuhara, Yoshinobu Narita, Osamu Ichikawa, Ryota Isono, Takeshi Tanaka, Taketomo Sato

  Applied Physics Express 13 (2) 026508 - 026508 1882-0778 2020/02/01 [Refereed]
  
• Fabrication of recessed structures for GaN HEMTs by a simple wet etching process

  Fumimasa Horikiri, Noboru Fukuhara, Masachika Toguchi, Kazuki Miwa, Yoshinobu Narita, Osamu Ichikawa, Ryota Isono, Takeshi Tanaka, Taketomo Sato

  CS MANTECH 2020 - 2020 International Conference on Compound Semiconductor Manufacturing Technology, Digest of Papers 127 - 130 2020 

  Photoelectrochemical (PEC) etching is a promising technology for fabricating GaN devices with low damage. In the simple contactless PEC (CL-PEC) etching process that includes K2S2O8 in the electrolyte as an oxidizing agent, a sample is dipped into the electrolyte under UV irradiation. In this study, we applied CL-PEC to the gate-recess process of GaN HEMTs on an SiC substrate. The etching depth of the recess showed considerable reproducibility by the self-termination feature, and the residual AlGaN layer thickness was approximately 5 nm. The Schottky gate HEMTs with a recessed structure showed the normally off characteristics, and the Vthvalue was +0.4 V with a standard deviation of ±3.8 mV.
• Photoelectrochemical Etching Technology for Gallium Nitride Power and RF Devices

  Fumimasa Horikiri, Noboru Fukuhara, Hiroshi Ohta, Naomi Asai, Yoshinobu Narita, Takehiro Yoshida, Tomoyoshi Mishima, Masachika Toguchi, Kazuki Miwa, Taketomo Sato

  IEEE Transactions on Semiconductor Manufacturing 32 (4) 489 - 495 2019/10 [Refereed][Not invited]
  
• Low-Damage Etching for AlGaN/GaN HEMTs Using Photo-Electrochemical Reactions

  Taketomo Sato, Masachika Toguchi, Yuto Komatsu, Keisuke Uemura

  IEEE Transactions on Semiconductor Manufacturing 32 (4) 483 - 488 2019/08 [Refereed][Not invited]
  
• Anisotropic Electrochemical Etching of Porous Gallium Nitride by Sub-Bandgap Absorption Due to Franz-Keldysh Effect

  Masachika Toguchi, Kazuki Miwa, Taketomo Sato

  Journal of The Electrochemical Society 166 (12) H510 - H512 2019/07 [Refereed][Not invited]
  
• Electrodeless photo-assisted electrochemical etching of GaN using a H3PO4-based solution containing S2O82– ions

  Masachika Toguchi, Kazuki Miwa, Fumimasa Horikiri, Noboru Fukuhara, Yoshinobu Narita, Takehiro Yoshida, Taketomo Sato

  Applied Physics Express 12 066504-1 - 066504-4 2019/05 [Refereed][Not invited]
  
• Effect of photoelectrochemical etching and post-metallization annealing on gate controllability of AlGaN/GaN high electron mobility transistors

  Keisuke Uemura, Manato Deki, Yoshio Honda, Hiroshi Amano, Taketomo Sato

  Japanese Journal of Applied Physics 58 (SC) SCCD20-1 - SCCD20-6 2019/05 [Refereed][Not invited]
  
• Simple wet-etching technology for GaN using an electrodeless photo-assisted electrochemical reaction with a luminous array film as the UV source

  Horikiri Fumimasa, Fukuhara Noboru, Ohta Hiroshi, Asai Naomi, Narita Yoshinobu, Yoshida Takehiro, Mishima Tomoyoshi, Toguchi Masachika, Miwa Kazuki, Sato Taketomo

  APPLIED PHYSICS EXPRESS 12 (3) 1882-0778 2019/03/01 [Refereed][Not invited]
  
• Effects of a photo-assisted electrochemical etching process removing dry-etching damage in GaN

  Matsumoto Satoru, Toguchi Masachika, Takeda Kentaro, Narita Tetsuo, Kachi Tetsu, Sato Taketomo

  JAPANESE JOURNAL OF APPLIED PHYSICS 57 (12) 0021-4922 2018/12 [Refereed][Not invited]
  
• 新規製造現場での基盤技術 光電気化学反応を利用した半導体の低損傷加工と高精度エッチング技術

  佐藤威友

  ケミカルエンジニヤリング 63 (6) 399‐405  0387-1037 2018/06 [Not refereed][Invited]
  
• Low-damage etching of nitride semiconductors utilizing photo-electrochemical reactions for electron devices

  植村圭佑, 松本悟, 渡久地政周, 伊藤圭亮, 佐藤威友, 佐藤威友

  電子情報通信学会技術研究報告 電子情報通信学会 117 (331(ED2017 49-71)) 23‐26 - 26 0913-5685 2017/11/23 [Not refereed][Not invited]
  
• Precise thickness control in recess etching of AlGaN/GaN hetero-structure using photocarrier-regulated electrochemical process

  Yusuke Kumazaki, Keisuke Uemura, Taketomo Sato, Tamotsu Hashizume

  JOURNAL OF APPLIED PHYSICS 121 (18) 0021-8979 2017/05 [Refereed][Not invited]
   

  The photocarrier-regulated electrochemical (PREC) process was developed for fabricating recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) for normally off operation. The PREC process is based on photo-assisted electrochemical etching using low-energy chemical reactions. The fundamental photo-electrochemical measurements on AlGaN/GaN heterostructures revealed that the photo-carriers generated in the top AlGaN layer caused homogeneous etching of AlGaN with a smooth surface, but those generated in the GaN layer underneath caused inhomogeneous etching that roughens the surface. The concept of the PREC process is to supply the photo-carriers generated only in the AlGaN layer by selecting proper conditions on light wavelength and voltage. The phenomenon of self-termination etching has been observed during the PREC process, where the etching depth was controlled by light intensity. The recessed-gate AlGaN/GaN HEMT fabricated with the PREC process showed positive threshold voltage and improvement in transconductance compared to planar-gate AlGaN/GaN HEMTs. Published by AIP Publishing.
• Precise Structural Control of GaN Porous Nanostructures Utilizing Anisotropic Electrochemical and Chemical Etching for the Optical and Photoelectrochemical Applications

  Yusuke Kumazaki, Satoru Matsumoto, Taketomo Sato

  JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164 (7) II477 - II483 0013-4651 2017 [Refereed][Not invited]
   

  A low-damaged wet process utilizing electrochemical (EC) etching and subsequent chemical etching has been developed for the fabrication of GaN porous structures. Superior controllability in depth and diameter could be obtained by achieving anisotropic nature of the vertical direction to the substrate by EC etching and horizontal direction by tetramethylammonium hydroxide (TMAH) etching, respectively. The optical and photoelectrochemical properties of GaN porous structures were very sensitive to the structural properties. Photoreflectance measurement revealed that porous sample had an effective refractive index that could be controlled by TMAH etching time. In photoelectrochemical measurement, the incident-photon-to-current conversion efficiency (IPCE) was dramatically enhanced to as high as 91% by the formation of porous structures. A series of experimental results were consistently explained by the change of thickness of pore wall and width of space charge region. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.
• Low-damage Recess Etching of AlGaN/GaN Hetero-structure by Electrochemical Process

  熊崎祐介, 植村圭佑, 佐藤威友

  電子情報通信学会技術研究報告 116 (357(CPM2016 90-112)) 45‐50  0913-5685 2016/12/05 [Not refereed][Not invited]
  
• Formation of GaN porous structures with improved structural controllability by photoassisted electrochemical etching

  Yusuke Kumazaki, Zenji Yatabe, Taketomo Sato

  JAPANESE JOURNAL OF APPLIED PHYSICS 55 (4) 04EJ12  0021-4922 2016/04 [Refereed][Not invited]
   

  We aimed to develop a photoassisted electrochemical etching process for the formation of GaN porous structures. Pore linearity and depth controllability were strongly affected by the anode voltage. In addition, the use of light with an energy below the band gap played an important role in controlling the pore diameter. Spectro-electrochemical measurements revealed that the high electric field induced at the GaN/electrolyte interface caused a redshift of the photoabsorption edge. This specific phenomenon can be explained by a theoretical calculation based on the Franz-Keldysh effect. On the basis of the results of our experimental and theoretical analyze, we propose a formation model for GaN porous structures. We also note that the application of the Franz-Keldysh effect is useful in controlling the structural properties of GaN porous structures. (C) 2016 The Japan Society of Applied Physics
• Electrochemical Formation of N-type GaN and N-type InP Porous Structures for Chemical Sensor Applications

  Taketomo Sato, Xiaoyi Zhang, Keisuke Ito, Satoru Matsumoto, Yusuke Kumazaki

  2016 IEEE SENSORS 1930-0395 2016 [Refereed][Not invited]
   

  The feasibility of liquid-phase sensors based on n-type GaN and n-type InP porous structures was investigated. The response currents to the addition of H2O2 increased on the porous electrodes. The source-drain currents of ion-sensitive field-effect transistors having a porous channel changed with good response to the pH values. The sensitivities of two kinds of chemical sensors to ions were drastically enhanced by the implementation of the porous structures having large surface areas with good conductivity.
• Interface control technologies for high-power GaN transistors - Self-stopping etching of p-GaN layers utilizing electrochemical reactions

  Taketomo Sato, Yusuke Kumazaki, Masaaki Edamoto, Masamichi Akazawa, Tamotsu Hashizume

  GALLIUM NITRIDE MATERIALS AND DEVICES XI 9748 97480Y  0277-786X 2016 [Refereed][Invited]
   

  The selective and low-damaged etching of p-type GaN or AlGaN layer is inevitable process for AlGaN/GaN high-power transistors. We have investigated an electrochemical etching of p-GaN layer grown on AlGaN/GaN heterostructures, consisting of an anodic oxidation of p-GaN surface and a subsequent dissolution of the resulting oxide. The p- GaN layer was electrochemically etched by following the pattern of the SiO2 film that acted as an etching mask. Etching depth was linearly controlled by cycle number of triangular waveform at a rate of 25 nm/cycle. The AFM, TEM and mu-AES results showed that the top p- GaN layer was completely removed after 5 cycles applied, and the etching reaction was automatically sopped on the AlGaN surface. I-V and C-V measurements revealed that no significant damages were induced in the AlGaN/GaN heterostructures.
• Large photocurrents in GaN porous structures with a redshift of the photoabsorption edge

  Taketomo Sato, Yusuke Kumazaki, Hirofumi Kida, Akio Watanabe, Zenji Yatabe, Soichiro Matsuda

  SEMICONDUCTOR SCIENCE AND TECHNOLOGY 31 (1) 0268-1242 2016/01 [Refereed][Not invited]
   

  Photoresponse and photoabsorption properties of GaN porous structures were investigated by measuring photocurrent and spectroscopic photoabsorption under monochromatic light with various wavelengths. The measured photocurrents on the porous GaN electrodes were larger than those on the planar electrodes due to the unique features of the former electrode, such as large surface area and low photoreflectance properties. Moreover, the photocurrents were observed even under illumination with wavelength of 380 nm, corresponding to photon energy of 3.26 eV, which is 130 meV lower than the bandgap energy of bulk GaN. A potential simulation revealed that a high-electric field was induced at the pore tips due to modification of the potential in the porous structures. The observed redshift of the photoabsorption edge can be qualitatively explained by the Franz-Keldysh effect.
• Electrochemical formation and UV photoresponse properties of GaN porous structures

  Hirofumi Kida, Yusuke Kumazaki, Zenji Yatabe, Taketomo Sato

  IEICE technical report. Electron devices 電子情報通信学会 115 (170) 51 - 54 0913-5685 2015/07 [Not refereed][Not invited]
  
• Spectro-electrochemical characterization of GaN/electrolyte interface and its application to the nanostructure formation

  Yusuke Kumazaki, Akio Watanabe, Zenji Yatabe, Taketomo Sato

  IEICE technical report. Electron devices 電子情報通信学会 115 (63) 63 - 66 0913-5685 2015/05 [Not refereed][Not invited]
  
• Interface trap states in Al2O3/AlGaN/GaN structure induced by inductively coupled plasma etching of AlGaN surfaces

  Zenji Yatabe, Joel T. Asubar, Taketomo Sato, Tamotsu Hashizume

  PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 212 (5) 1075 - 1080 1862-6300 2015/05 [Refereed][Not invited]
   

  We have investigated the effects of the inductively coupled plasma (ICP) etching of AlGaN surface on the resulting interface properties of the Al2O3/AlGaN/GaN structures. The experimentally measured capacitance-voltage (C-V) characteristics were compared with those calculated taking into account the interface states density at the Al2O3/AlGaN interface. As a complementary method, photoassisted C-V method utilizing photons with energies less than the bandgap of GaN was also used to probe the interface state density located near AlGaN midgap. It was found that the ICP etching of the AlGaN surface significantly increased the interface state density at the Al2O3/AlGaN interface. It is likely that ICP etching induced the interface roughness, disorder of chemical bonds and formation of various type of defect complexes including nitrogen-vacancy-related defects at the AlGaN surface, leading to poor C-V curve due to higher interface state density at the Al2O3/AlGaN interface.
• Formation of GaN-Porous Structures Using Photo-Assisted Electrochemical Process in Back-Side Illumination Mode

  Akio Watanabe, Yusuke Kumazaki, Zenji Yatabe, Taketomo Sato

  ECS ELECTROCHEMISTRY LETTERS 4 (5) H11 - H13 2162-8726 2015 [Refereed][Not invited]
   

  We investigated the structural features of gallium-nitride-porous structures formed using the photo-assisted electrochemical process in the back-side illumination (BSI) mode. The pore diameter and depth were strongly affected by the direction of illumination, where higher controllability was achieved compared with front-side illumination. The spectroscopic measurements revealed that illumination with photon energy below the bulk bandgap plays an important role in pore formation. We propose a formation model by considering the Franz-Keldysh effect that can consistently explain the obtained experimental data in which anodic etching occurs only at the pore tips under the high electric field induced in the depletion region. (C) 2015 The Electrochemical Society. All rights reserved.
• Bias-dependent photoabsorption properties of gan porous structures under back-side illumination

  Taketomo Sato, Hirofumi Kida, Yusuke Kumazaki, Zenji Yatabe

  ECS Transactions 69 (2) 161 - 166 1938-6737 2015 [Refereed][Not invited]
   

  Photoabsorption properties of GaN porous structures were investigated by measuring photocurrent and light transmittance under monochromatic light with various wavelengths. The measured photocurrents on the porous GaN electrode were larger than those on the planar electrodes, and those were observed even under illumination with lower photon energy than the bandgap energy of bulk GaN. Moreover, the light transmittance that was measured in the back-side illumination (BSI) mode depended strongly on the applied voltage to the porous electrode with change of the photocurrents. The observed photoabsorption properties can be qualitatively explained by the Franz-Keldysh effect namely, the high electric field induced in the GaN porous structure easily causes a redshift of the photoabsorption edge.
• Characterization of electronic states at insulator/(Al)GaN interfaces for improved insulated gate and surface passivation structures of GaN-based transistors

  Zenji Yatabe, Yujin Hori, Wan-Cheng Ma, Joel T. Asubar, Masamichi Akazawa, Taketomo Sato, Tamotsu Hashizume

  Japanese Journal of Applied Physics Institute of Physics 53 (10) 100213-1 - 10 0021-4922 2014/10 [Refereed][Not invited]
   

  <b>38^th JSAP Paper Award</b>
  
  <b>Spotlights 2014</b>
  
  <b>Selected Topics in Applied Physics, "Progresses and Future Prospects in Nitride Semiconductors"</b>
  
  This paper presents a systematic characterization of electronic states at insulators/(Al)GaN interfaces, particularly focusing on insulator/AlGaN/GaN structures. First, we review important results reported for GaN metal–insulator–semiconductor (MIS) structures. SiO₂ is an attractive material for MIS transistor applications due to its large bandgap and high chemical stability. In-situ SiNx is effective for improving the operation stability of high electron mobility transistors (HEMTs). Meanwhile, Al₂O₃/GaN structures have high band offsets and low interface state densities, which are also desirable for insulated gate applications. We have proposed a calculation method for describing capacitance–voltage (<i>C</i>–<i>V</i>) characteristics of HEMT MIS structures for evaluating electronic state properties at the insulator/AlGaN interfaces. To evaluate near-midgap states at insulator/AlGaN interfaces, a photo-assisted <i>C</i>–<i>V</i> technique using photon energies less than the bandgap of GaN has been developed. Using the calculation in conjunction with the photo-assisted <i>C</i>–<i>V</i> technique, we estimate interface state density distributions at the Al₂O₃/AlGaN interfaces.
• Correlation between Structural and Photoelectrochemical Properties of GaN Porous Nanostructures Formed by Photo-Assisted Electrochemical Etching

  Yusuke Kumazaki, Akio Watanabe, Zenji Yatabe, Taketomo Sato

  Journal of The Electrochemical Society The Electrochemical Society 161 (10) 705 - 709 0013-4651 2014/08 [Refereed][Not invited]
   

  We investigated the correlation between structural and photoelectrochemical properties of GaN porous nanostructures formed by photo-assisted electrochemical etching. The porous nanostructures were formed during light irradiation of the top-surface of homo-epitaxial layers grown on freestanding GaN substrates. The pore depth, wall thickness, and surface morphology of porous nanostructures were strongly influenced by the way holes generated by the light irradiation were supplied. Such structural features influenced the optical properties of GaN porous nanostructures. The photoluminescence peaks measured on GaN porous nanostructures were shifted to higher energies because of the quantum confinement in the thin GaN walls between pores. Formation of porous nanostructure decreased the photoreflectance of the GaN surface, and the smallest reflectance was obtained from the porous sample having large pores on its surface after the ultrathin layer with small pores had been removed by surface-etching. The photoelectrochemical response measured on GaN porous nanostructures in a NaCl electrolyte were drastically enhanced by the unique features of those structures, such as low photoreflectance and large surface area. The largest photocurrents were obtained from the sample from which H₃PO₄ treatment had removed the ultrathin layer without thinning the pore walls.
• III‐V族化合物半導体多孔質構造の形成と機能素子への応用

  佐藤威友, 熊崎祐介, 渡部晃生

  表面技術協会講演大会講演要旨集 129th 295 - 297 0917-2947 2014/03 [Not refereed][Invited]
  
• GaNパワー素子のための絶縁膜界面制御

  橋詰 保, 谷田部 然治, 佐藤 威友

  電気学会研究会資料. EDD, 電子デバイス研究会 EDD-14 (39-49) 13 - 16 2014/03 [Not refereed][Invited]
  
• Interface Characterization and Control of GaN-based Heterostructures

  HASHIZUME TAMOTSU, YATABE ZENJI, SATO TAKETOMO

  表面科学 The Surface Science Society of Japan 35 (2) 96-101 (J-STAGE) - 101 0388-5321 2014 [Not refereed][Invited]
   

  Interface properties of GaN-based heterostructures have been characterized. Schottky contacts on dry-etched n-GaN layers showed leaky I-V characteristics. An anneal process at 400°C was effective in recovering the rectifying characteristics. To characterize interface properties of Al₂O₃ insulated gates on AlGaN/GaN structures with and without the inductively coupled plasma (ICP) etching of AlGaN, we have developed a C-V calculation method taking into account electronic state charges at the Al₂O₃/AlGaN interface and a photoassisted C-V technique utilizing photons with energies less than the bandgap of AlGaN. It was found that the ICP etching caused the monolayer-level interface roughness, disorder of the chemical bonds and formation of various types of defect complexes at the AlGaN surface, resulting in poor C-V characteristics due to high-density interface states at the Al₂O₃/AlGaN interface.
• Photoelectrode properties of GaN porous structures formed by photo-assisted electrochemical process

  KUMAZAKI YUSUKE, WATANABE AKIO, YATABE ZENJI, SATO TAKETOMO

  電子情報通信学会技術研究報告 113 (329(ED2013 64-89)) 113 - 116 0913-5685 2013/11 [Not refereed][Not invited]
  
• Investigation on optical absorption properties of electrochemically formed porous InP using photoelectric conversion devices

  Yusuke Kumazaki, Tomohito Kudo, Zenji Yatabe, Taketomo Sato

  Applied Surface Science 279 116 - 120 0169-4332 2013/08/15 [Refereed][Not invited]
   

  We investigated the optical absorption properties of InP porous structures formed by the electrochemical process using photoelectric conversion (PC) devices formed on p-n junction substrates. The photocurrent measurements revealed that the current from PC devices changed in response to the incident light power and the thickness of the top layer on the p-n interface. Since the photocarriers contributing to the observed photocurrents are excited by the photons reaching the p-n interface through the top layer, the photocurrents give us information on the optical absorption properties of the top layer. The photocurrents observed on a porous device with a porous structure in the top layer were lower than that of a non-porous device, indicating that the absorption properties of InP were enhanced after the formation of porous structures. This phenomenon can be explained in terms of absorption coefficient, α, increased by the light scattering and the sub-bandgap absorption in the porous layer. © 2013 Published by Elsevier B.V.
• Photoabsorption and Photoelectric Conversion Properties of InP Porous Structures Formed by the Electrochemical process

  KUMAZAKI Yusuke, JINBO Ryohei, YATABE Zenji, SATO Taketomo

  電子情報通信学会技術研究報告 113 (39(ED2013-27)) 61 - 64 2013/05 [Not refereed][Not invited]
  
• 電気化学的手法によるInP多孔質構造の光吸収特性と光電変換

  熊崎 祐介, 神保 亮平, 谷田部 然治, 佐藤 威友

  電子情報通信学会技術研究報告 113 (39(ED2013-27)) 61 - 64 2013/05 [Not refereed][Not invited]
  
• Formation and Photoelectrical Measurements of Pt Schottky Interfaces on InP Porous Structures

  Ryohei Jinbo, Yusuke Kumazaki, Zenji Yatabe, Taketomo Sato

  ECS Transactions 50 (37) 247 - 252 1938-5862 2013/03 [Refereed][Not invited]
   

  Schottky interfaces were formed on InP porous structures by the electrodeposition of Pt films. The coverage of the Pt film and its optical reflectance depended largely on the surface morphology of the porous structure. Removal of the irregular top layer formed at the initial stage of the pore formation effectively improved the coverage of the Pt film inside pores. According to <i>I</i>-<i>V</i> measurements, the Pt/porous InP showed higher photocurrents with lower dark currents than those of a reference planar sample.
• Control of Insulated Gate Interfaces on AlGaN/GaN Heterostructures for Power Devices

  Yujin Hori, Taketomo Sato, Tamotsu Hashizume

  2013 1ST IEEE WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS (WIPDA) 143 - 146 2013 [Refereed][Not invited]
   

  Interface properties of Al2O3 insulated gates on AlGaN/GaN structures prepared by atomic layer deposition have been characterized, focusing on the interface state density distribution at the Al2O3/AlGaN interface. We have developed a C-V calculation method taking into account electronic states charges at the Al2O3/AlGaN interface and a photoassisted C-V technique utilizing photons with energies less than the bandgap of AlGaN. These techniques were then applied to investigate the effect of the ICP etching of AlGaN on the interface properties.
• Large photocurrent-response observed at Pt/InP Schottky interface formed on anodic porous structure

  Ryohei Jinbo, Tomohito Kudo, Zenji Yatabe, Taketomo Sato

  THIN SOLID FILMS 520 (17) 5710 - 5714 0040-6090 2012/06 [Refereed][Not invited]
   

  A photoelectric-conversion device-based on an InP porous structure utilizing the large surface area inside pores and the low reflectance on the porous surface-is proposed. The InP walls inside the pores are covered with thin platinum films that form a Schottky barrier yielding an electric field that separates photo carriers generated under illumination. The coverage of the platinum film and its optical reflectance depended largely on the surface morphology of the porous structure. Removal of the irregular top layer formed at the initial stage of the pore formation effectively improved the coverage of the platinum film, which showed a very low optical reflectance (i.e., below 3.2%). According to current-voltage measurements under illumination, the platinum/porous InP showed larger photocurrents and higher responsivity than those of a reference planar sample. (C) 2012 Elsevier B.V. All rights reserved.
• Electrochemical formation of InP porous structures for their application to photoelectric conversion devices(Session 2B : Graphene and III-Vs)

  OKAZAKI Hiroyuki, SATO Taketomo, HASHIZUME Tamotsu

  Technical report of IEICE. SDM 一般社団法人電子情報通信学会 110 (110) 85 - 89 0913-5685 2010/06/23 [Not refereed][Not invited]
   

  We report the electrochemical formation of porous structures on n-type epitaxial layers grown on p-type InP substrates in view of the application to the photoelectric conversion devices. We successfully formed the arrays of regular-sized pores whose diameter and depth could be changed by the doping density and anodic conditions, respectively. From the photo I-V measurements, we confirmed the optical absorption process in the porous layers whose photovoltaic response strongly depended on the structural properties.
• Realization of an extremely low reflectance surface based on InP porous nanostructures for application to photoelectrochemical solar cells

  Taketomo Sato, Naoki Yoshizawa, Tamotsu Hashizume

  THIN SOLID FILMS 518 (15) 4399 - 4402 0040-6090 2010/05 [Refereed][Not invited]
   

  Extremely low reflectance was obtained from InP porous nanostructures in UV, visible, and near-infrared ranges. Porous samples were electrochemically prepared on which 130-nm-diameter nanopores were formed in a straight, vertical direction and were laterally separated by 50-nm-thick InP nanowalls. The reflectance strongly depended on the surface morphology. The lowest reflectance of 0.1% in the visible light range was obtained after the irregular top layer had been completely removed. Superior photoelectrochemical properties were obtained on the InP porous structures clue to two unique features: the large surface area inside pores, and the large photon absorption enhanced on the low reflectance surface. (C) 2010 Elsevier B.V. All rights reserved.
• Low Reflectance Surface Observed on InP Porous Structures after Photoelectrochemical Etching

  T. Sato, N. Yoshizawa, H. Okazaki, T. Hashizume

  SEMICONDUCTOR ELECTROLYTE INTERFACE AND PHOTOELECTROCHEMISTRY 25 (42) 83 - 88 1938-5862 2010 [Refereed][Not invited]
   

  Extremely low reflectance was obtained from InP porous nanostructures in UV, visible, and near-infrared light ranges. The reflectance strongly depended on the surface morphology of the porous structures prepared by the electrochemical process, and the lowest reflectance of 0.1% in the visible light range was obtained from a sample after the irregular top layer was completely removed. Large anodic photocurrents were obtained on the InP porous structures that had low reflectance surfaces with deeper pores.
• Electrochemical Functionalization of InP Porous Nanostructures with a GOD Membrane for Amperometric Glucose Sensors

  Taketomo Sato, Akinori Mizohata, Tamotsu Hashizume

  JOURNAL OF THE ELECTROCHEMICAL SOCIETY 157 (2) H165 - H169 0013-4651 2010 [Refereed][Not invited]
   

  The electrochemical functionalization of n-type InP porous nanostructures and their feasibility for biochemical sensor applications were investigated. The porous structures have extremely large surface areas, i.e., over 10 m(2)/cm(3), and superior electrical properties with conductive semiconductor substrates. As a first attempt at electrochemical functionalization, we successfully deposited a glucose oxidase (GOD) membrane onto an InP surface under an applied anodic bias of 1.2 V. With the addition of glucose, the response currents on the porous electrodes increased compared to those on planar InP electrodes due to their enlarged surface area. The sensitivity curves of the porous electrodes we used showed good linearity between the response currents and concentrations in a range from 0 to 5 mM.
• Electrochemical Formation of InP Porous Structures and Their Application to High-Sensitive Chemical Sensors

  SATO Taketomo, YOSHIZAWA Naoki, OKAZAKI Hiroyuki, HASHIZUME Tamotsu

  電子情報通信学会技術研究報告. ED, 電子デバイス 一般社団法人電子情報通信学会 ED2010 (35) 11 - 15 0913-5685 2010 [Not refereed][Not invited]
   

  We proposed a novel ion-sensitive field-effect transistor (ISFET) having a porous-gate structure. Porous structures were formed in n-type InP layers, working as channel layers, grown on p-type (001) substrates. The porous-gate ISFETs could detect the potential changes at the inner pores with a current signal whose value can be controlled by the back gate bias applied to the p-type substrate. Our proposed ISFETs demonstrated good performance for detecting pH values in the electrolyte, showing promise for high-sensitive chemical sensors.
• OPTICAL AND ELECTRICAL PROPERTIES OF InP POROUS STRUCTURES FORMED ON P-N SUBSTRATES

  Hiroyuki Okazaki, Taketomo Sato, Naoki Yoshizawa, Tamotsu Hashizume

  2010 22ND INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM) 1092-8669 2010 [Refereed][Not invited]
   

  We demonstrated to form InP porous structures on n-type epitaxial layers grown on p-type (001) substrates. The high-density array of straight pores with 150nm diameter and 5000nm depth was formed by the electrochemical anodization process, where the pore depth could be controlled by the anodization time in the n-type layer. The present p-n InP porous structures show the low optical reflectance in UV-, visible-and near-infrared region. The current transport properties clearly show the rectifying behavior. These features are very promising for practical application to high-efficiency photo-sensitive devices.
• Fundamental Study of InP-Based Open-Gate Field-Effect Transistors for Application to Liquid-Phase Chemical Sensors

  Naoki Yoshizawa, Taketomo Sato, Tamotsu Hashizume

  JAPANESE JOURNAL OF APPLIED PHYSICS 48 (9) 91102  0021-4922 2009/09 [Refereed][Not invited]
   

  We prove with this paper that InP-based open-gate field-effect transistors (FETs) work well as liquid-phase chemical sensors. The open-gate FET clearly exhibited current saturation and a pinch-off behavior in the electrolyte, resulting in a rapid response to the gate bias applied via the electrolyte. A series of sensing measurements showed that the surface potential of the InP linearly changed with the pH values of the electrolytes in a pH range from 3.0 to 12.0. The pH sensitivity of the open-gate FETs depended on the ion species contained in the electrolyte. A Si3N4 layer was useful as an ion selective membrane for the InP open-gate FETs to improve the selectivity of H+ ions. (C) 2009 The Japan Society of Applied Physics
• Report on "The 2008 Workshop for Refreshing Science in Sapporo (Hokkaido Univ.)"

  ARITA Masashi, SUGAWARA Yo, UEMURA Tetsuya, ADACHI Satoshi, SUGAWARA Hirotake, KASAI Seiya, MATSUDA Ken-ichi, SATO Taketomo, TAKAHASHI Yasuo, FUKUI Takashi

  応用物理教育 33 (1) 25 - 30 1346-4434 2009/07/31 [Not refereed][Not invited]
  
• Integration of Zn-Cd-Te-Se Semiconductors on Si Platforms via Structurally Designed Cubic Templates Based on Group IV Elements

  John Tolle, Radek Roucka, Brandon Forrest, Andrew V. G. Chizmeshya, John Kouvetakis, Vijay R. D'Costa, Christian D. Poweleit, Michael Groenert, Taketomo Sato, Jose Menendez

  CHEMISTRY OF MATERIALS 21 (14) 3143 - 3152 0897-4756 2009/07 [Refereed][Not invited]
   

  This work describes the development and application of a new class of highly versatile Ge-Sn/Si (100) hybrid substrate systems for the integration of a broad range of technologically important II-VI optical materials on silicon platforms. GeSn buffer layers were grown directly on Si(100), via introduction of Lomer edge dislocations at the interface, and exhibited low densities of threading defects, atomically flat surfaces, and strain-free microstructures. Specialized cleaning protocols were first developed to obtain GeSn surfaces possessing superior chemical purity and single-crystalline, long-range orientation for subsequent heteroepitaxy. The quality of the resulting platforms was then validated using proof-of-concept fabrication of prototype AlGaAs/GaAs/AlGaAs quantum well structures, which exhibited optical properties comparable to those of analogs grown via homoepitaxy on bulk GaAs substrates. The application of these platforms in CMOS-compatible integration of the II-VI materials was explored using a progressive strategy based on the systematic epitaxial fabrication of simple binaries within Zn-Cd-Te-Se class. This culminated in the Formation of fully lattice matched ZnSc/'GeSn/Si(100) structures for the first time, as well as highly mismatched CdTe and CdTe/ZnTe systems directly on silicon. These successful depositions represent an important milestone en route to the ultimate integration of ZnSe, CdTe, Zn(1-)zCd(z)Te and Hg(1-x)Cd(x)Te with Si for applications in high-performance IR photodetectors, imaging technologies, and high-efficiency, low-cost solar cells.
• Formation and application of InP porous structures on p-n substrates

  SATO Taketomo, YOSHIZAWA Naoki, OKAZAKI Hiroyuki, HASHIZUME Tamotsu

  IEICE technical report. Electron devices 一般社団法人電子情報通信学会 109 (97) 117 - 120 0913-5685 2009/06/17 [Not refereed][Not invited]
   

  We demonstrated to form InP porous structures on n-type epitaxial layers grown on p-type (001) substrates. The high-density array of straight pores with 150nm diameter and 5000nm depth was formed by the electrochemical anodization process, where the pore depth could be controlled by the anodization time in the n-type layer. The present p-n InP porous structures show the low optical reflectance in UV-, visible- and near-infrared region. The current transport properties clearly show the rectifying behavior. These features are very promising for practical application to high-efficiency photo-s...
• Formation and application of InP porous structures on p-n substrates

  SATO Taketomo, YOSHIZAWA Naoki, OKAZAKI Hiroyuki, HASHIZUME Tamotsu

  Technical report of IEICE. SDM 一般社団法人電子情報通信学会 109 (98) 117 - 120 0913-5685 2009/06/17 [Not refereed][Not invited]
   

  We demonstrated to form InP porous structures on n-type epitaxial layers grown on p-type (001) substrates. The high-density array of straight pores with 150nm diameter and 5000nm depth was formed by the electrochemical anodization process, where the pore depth could be controlled by the anodization time in the n-type layer. The present p-n InP porous structures show the low optical reflectance in UV-, visible- and near-infrared region. The current transport properties clearly show the rectifying behavior. These features are very promising for practical application to high-efficiency photo-s...
• Electrochemical formation and functionalization of InP porous nanostructures and their application to chemical sensors(Session8B: High-Frequency, Photonic and Sensing Devices)

  MIZOHATA Akinori, YOSHIZAWA Naoki, SATO Taketomo, HASHIZUME Tamotsu

  Technical report of IEICE. SDM 一般社団法人電子情報通信学会 108 (122) 327 - 330 0913-5685 2008/07/02 [Not refereed][Not invited]
   

  We investigated the electrocatalytic activity of n-type InP porous nanostructures and the feasibility of their functionalization for the biochemical sensor applications. The porous structures have extremely large surface areas over 10m^2/cm^3 and superior electrical properties with conductive semiconductor substrates. The response currents to the addition of H_2O_2 increased on the porous electrodes due to their enlarged surface area, and its sensitivity had good linearity with H_20_2 concentration. As a first attempt of the electrochemical functionalization, glucose oxidase membrane was su...
• Electrochemical formation and functionalization of InP porous nanostructures and their application to chemical sensors(Session8B: High-Frequency, Photonic and Sensing Devices)

  MIZOHATA Akinori, YOSHIZAWA Naoki, SATO Taketomo, HASHIZUME Tamotsu

  IEICE technical report. Electron devices 一般社団法人電子情報通信学会 108 (121) 327 - 330 0913-5685 2008/07/02 [Not refereed][Not invited]
   

  We investigated the electrocatalytic activity of n-type InP porous nanostructures and the feasibility of their functionalization for the biochemical sensor applications. The porous structures have extremely large surface areas over 10m^2/cm^3 and superior electrical properties with conductive semiconductor substrates. The response currents to the addition of H_2O_2 increased on the porous electrodes due to their enlarged surface area, and its sensitivity had good linearity with H_20_2 concentration. As a first attempt of the electrochemical functionalization, glucose oxidase membrane was su...
• Amperometric detection of hydrogen peroxide using InP porous nanostructures

  Taketomo Sato, Akinori Mizohata, Naoki Yoshizawa, Tamotsu Hashizume

  APPLIED PHYSICS EXPRESS 1 (5) 51202  1882-0778 2008/05 [Refereed][Not invited]
   

  The electrocatalytic activity of n-type InP porous nanostructures was investigated in terms of their application to amperometric biochemical sensors. The current sensitivities for H(2)O(2) detection were strongly dependent on the structural properties of these porous nanostructures. A sample with deeper pores responsed more sensitively because of the enlarged surface area inside the nanopores. The removal of an irregular top layer also effectively improved the current sensitivity. The conductive porous nanostructures presented here were very promising for the direct amperometric detection of H(2)O(2). (c) 2008 The Japan Society of Applied Physics.
• Photoelectrochemical etching and removal of the irregular top layer formed on InP porous nanostructures

  Taketomo Sato, Akinori Mizohata

  ELECTROCHEMICAL AND SOLID STATE LETTERS 11 (5) H111 - H113 1099-0062 2008 [Refereed][Not invited]
   

  A photoelectrochemical (PEC) process was developed to remove the irregular top layer from InP porous nanostructures. After anodic formation of a nanopore array, the PEC process repeated in the same electrolyte under illumination. The etching rate of the pore surfaces was strongly associated with their structural properties, being greater in the irregular top layer. The irregular top layer was completely removed by monitoring and controlling the anodic photocurrents in the ramped bias mode. (c) 2008 The Electrochemical Society.
• Electrochemical formation of InP porous nanostructures and its application to amperometric chemical sensors

  Taketomo Sato, Akinori Mizohata, Toshiyuki Fujino, Tamotsu Hashizume

  PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 11 2008 5 (11) 3475 - 3478 1610-1634 2008 [Refereed][Not invited]
   

  In this paper, we report the electrochemical formation of the InP porous nanostructures and their feasibility for the application to the amprometric chemical sensors. Our two step electrochemical process consists of the pore formation on a (001) n-type InP substrate and the subsequent etching of pore walls caused by changing the polarity of the InP electrode in A HCL based electrolyte. By applying the anodic bras to the Inp electrode, the high density array of uniform nanopores was formed on the surface Next, the cathodic bias was applied to the porous sample to reduce the wait thickness by cathodic decomposition of InP, where the thickness of InP nanowall decreased uniformly along the entire depth of the porous layer. From the amperometric measurements of the porous electrode, it was found that the electrocatalytic, activity was much higher than that of the planar electrode. Furthermore, the current sensitivity for the H(2)O(2) detection was much enhanced after the cathodic decomposition process. The InP porous nanostructure formed by the present process is one of the promising structures for the application to the semiconductor based bio/chemical sensors. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
• Complete removal of irregular top layer for sensor applications of InP porous nanostructures

  Taketomo Sato, Akinori Mizohata, Naoki Yoshizawa, Tamotsu Hashizume

  ECS Transactions 16 (3) 405 - 410 1938-5862 2008 [Refereed][Not invited]
   

  The photo-electrochemical (PEC) process was developed to remove the irregular top layer of InP porous nanostructures for the application to amperometric chemical sensors. The PEC etching rate of the pore surface was associated with their structural properties, resulting in the complete removal of the irregular layer by monitoring and controlling the anodic photo-currents. The porous electrode prepared by PEC process gave higher sensitivity for detecting H2O2 due to the enlarged openings of all pores with complete removal of irregular top layer. ©The Electrochemical Society.
• Electrochemical formation of InP porous nanostructures and its application to amperometric chemical sensors

  Taketomo Sato, Akinori Mizohata, Toshiyuki Fujino, Tamotsu Hashizume

  Physica Status Solidi (C) Current Topics in Solid State Physics 5 (11) 3475 - 3478 1862-6351 2008 [Refereed][Not invited]
   

  In this paper, we report the electrochemical formation of the InP porous nanostructures and their feasibility for the application to the amperometric chemical sensors. Our two step electrochemical process consists of the pore formation on a (001) n-type InP substrate and the subsequent etching of pore walls caused by changing the polarity of the InP electrode in a HCl-based electrolyte. By applying the anodic bias to the InP electrode, the high-density array of uniform nanopores was formed on the surface. Next, the cathodic bias was applied to the porous sample to reduce the wall thickness by cathodic decomposition of InP, where the thickness of InP nanowall decreased uniformly along the entire depth of the porous layer. From the amperometric measurements of the porous electrode, it was found that the electrocatalytic activity was much higher than that of the planar electrode. Furthermore, the current sensitivity for the H2O2 detection was much enhanced after the cathodic decomposition process. The InP porous nanostructure formed by the present process is one of the promising structures for the application to the semiconductor-based bio/chemical sensors. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
• Liquid-phase chemical sensors using InP-based open-gate FETs

  Naoki Yoshizawa, Taketomo Sato, Akinori Mizohata

  Proceedings of IEEE Sensors 1305 - 1308 2008 [Refereed][Not invited]
   

  In this paper, we demonstrated that the InP-based open-gate FET worked well as a liquid-phase chemical sensor in acid electrolytes. The open-gate FET clearly exhibited current saturation and pinch-off behavior in the electrolyte, resulted in a rapid response to the gate bias applied via the electrolyte. A series of sensing measurements showed that the surface potential of the InP linearly changed with the pH values of the electrolytes, and their sensitivity was strongly dependent on ion species contained in the electrolyte. © 2008 IEEE.
• 化合物半導体ナノ構造の自己組織化形成と高感度化学センサへの応用

  佐藤威友

  村田学術振興財団年報 (21) 222 - 229 0919-3383 2007/12 [Not refereed][Not invited]
  
• 陽極酸化によりn‐GaN上に形成された酸化膜の評価と応用

  塩崎奈々子, 石川史太郎, TRAMPERT A, GRAHN H. T, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集 68th (3) 1431  2007/09/04 [Not refereed][Not invited]
  
• Size-controlled porous nanostructures formed on InP(001) substrates by two-step electrochemical process

  Toshiyuki Fujino, Taketomo Sato, Tamotsu Hashizume

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (7A) 4375 - 4380 0021-4922 2007/07 [Refereed][Not invited]
   

  A high-densjty array of size-controlled porous nanostructures was formed on InP(001) substrates by a two-step electrochemical process using anodic and cathodic reactions. After the formation of InP porous structures by anodization, we subsequently applied cathodic decomposition to the reduction of the lateral thickness of the InP pore wall. The etching rate of the pore wall was extremely low and strongly dependent on the cathodic bias and crystal orientations of the wall surface. The thickness of InP walls could be precisely controlled in the range of 15-30nm by changing cathodic bias and cathodic decomposition time. From the PL measurement at room temperature, the porous structures showed strong blue-shifted emissions due to quantum confinement in thinner InP nanowalls.
• Formation of thin native oxide layer on n-GaN by electrochemical process in mixed solution with glycol and water

  Nanako Shiozaki, Taketomo Sato, Tamotsu Hashizume

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 (4A) 1471 - 1473 0021-4922 2007/04 [Refereed][Not invited]
   

  In this paper, we report on the feasibility of oxidizing n-GaN by an electrochemical process in a mixture containing an aqueous solution of tartaric a id and propylene glycol. Photons generated by UV illumination were supplied at the electrolyte-GaN interface during the oxidation process. In the constant-voltage mode, X-ray photoelectron spectroscopy analysis revealed that relatively thick Ga oxide layer formed on the n-GaN surface. However, the oxide surface was very rough. In addition, we found metallic Ga components in the oxide layer or at the oxide-GaN interface for longer oxidation times. On the other hand, a thin Ga2O3 layer with a smooth surface was grown by a constant-current process.
• Electrochemical formation of size-controlled InP nanostructures using anodic and cathodic reactions

  Taketomo Sato, Toshiyuki Fujino, Tamotsu Hashizume

  ELECTROCHEMICAL AND SOLID STATE LETTERS 10 (5) H153 - H155 1099-0062 2007 [Refereed][Not invited]
   

  A two-step electrochemical process using anodic and cathodic reactions was developed to form size-controlled nanostructures on InP(001) substrates. After anodic formation of a nanopore array, the cathodic decomposition process was applied to reduce the thickness of InP nanowalls. The etching rate of the nanowalls was extremely small and strongly dependent on the cathodic bias and crystal orientations of the wall surface. Wall thickness could be controlled in the range of 10-30 nm by changing the cathodic bias and processing time. (c) 2007 The Electrochemical Society.
• Performance of open-gate AlGaN/GaN HFET in various kinds of liquids

  KOKAWA Takuya, SATO Taketomo, HASHIZUME Tamotsu

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2006 326 - 327 2006/09/13 [Not refereed][Not invited]
  
• Optical Properties of Size-Controlled Porous Nanostructures Formed on n-InP (001) Substrates by Electrochemical Process

  FUJINO Toshiyuki, SATO Taketomo, HASHIZUME Tamotsu

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2006 728 - 729 2006/09/13 [Not refereed][Not invited]
  
• Selective molecular beam epitaxy growth of size- and position-controlled GaN/AlGaN nanowires on nonplanar (0001) substrates and its growth mechanism

  Sato Taketomo, Oikawa Takeshi, Hasegawa Hideki, Hashizume Tamotsu

  Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 24 (4) 2087 - 2092 0734-211X 2006/07/26 [Refereed][Not invited]
   

  Fundamental growth properties were investigated for the size-controlled selective MBE growth of AlGaN/GaN nanowires on the GaN (0001) prepatterned substrates both experimentally and theoretically. The lateral size of the present GaN nanowire was determined by two facet boundaries formed within AlGaN barrier layers. From the series of wire growth experiments, the growth selectivity and the measured angle of the facet boundary strongly depended on the Al composition and the initial crystalline facets of the mesa patterned templates. The experimental evolution of the cross-sectional structures...
• Liquid-phase sensors using open-gate AlGaN/GaN high electron mobility transistor structure

  Takuya Kokawa, Taketomo Sato, Hideki Hasegawa, Tamotsu Hashizume

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 24 (4) 1972 - 1976 1071-1023 2006/07 [Refereed][Not invited]
   

  Liquid-phase sensing characteristics of open-gate AlGaN/GaN high electron mobility transistor (HEMT) structures were investigated in aqueous solutions and polar liquids. In de-ionized water, the open-gate HEMT clearly showed good drain I-V characteristics with current saturation and pinch-off behavior, very similar to I-V characteristics of typical Schottky-gate HEMTs. We observed a fine parallel shift in the transfer curves according to change in the pH value in a solution, indicating the corresponding potential change at the AlGaN surface. The sensitivity for the potential change was 57.5 mV/pH, very close to the theoretical value of 58.9 mV/pH at 24 degrees C for the Nernstian response to, H+ ions. In the low drain bias region, the drain current linearly decreased with the pH value. This also indicated a systematic potential change at the AlGaN surface due to pH change. The present open-gate device showed a fast response to the pH change and a stable operation at fixed pH values. A possible mechanism for the pH response of the AlGaN surface is discussed in terms of equilibrium reactions of hydroxyls at the AlGaN surface with H+ in a solution. It was also found that the device was quite sensitive to changes in the electrostatic boundary conditions of the open-gate area by exposure to polar liquids. The drain current linearly decreased with increasing normalized liquid dipole moment. (c) 2006 American Vacuum Society.
• Future of heterostructure microelectronics and roles of materials research for its progress

  Hideki Hasegawa, Seiya Kasai, Taketomo Sato, Tamotsu Hashizume

  IEICE TRANSACTIONS ON ELECTRONICS E89C (7) 874 - 882 0916-8524 2006/07 [Refereed][Invited]
   

  With advent of the ubiquitous network era and due to recent progress of III-V nanotechnology, the present III-V heterostructure microelectronics will turn into what one might call III-V heterostructure nanoelectronics, and may open up a new future in much wider application areas than today, combining information technology, nanotechnology and biotechnology. Instead of the traditional top-down approach, new III-V heterostructure nanoelectronics will be formed on nanostructure networks formed by combination of top-down and bottom-up approaches. In addition to communication devices, emerging devices include high speed digital LSIs, various sensors, various smart-chips, quantum LSIs and quantum computation devices covering varieties of application areas. Ultra-low power quantum LSIs may become brains of smart chips and other nanospace systems. Achievements of new functions and higher performances and their on chip integration are key issues. Key processing issue remains to be understanding and control of nanostructure surfaces and interfaces in atomic scale.
• Future of heterostructure microelectronics and roles of materials research for its progress

  Hideki Hasegawa, Seiya Kasai, Taketomo Sato, Tamotsu Hashizume

  IEICE TRANSACTIONS ON ELECTRONICS E89C (7) 874 - 882 0916-8524 2006/07 [Refereed][Invited]
   

  With advent of the ubiquitous network era and due to recent progress of III-V nanotechnology, the present III-V heterostructure microelectronics will turn into what one might call III-V heterostructure nanoelectronics, and may open up a new future in much wider application areas than today, combining information technology, nanotechnology and biotechnology. Instead of the traditional top-down approach, new III-V heterostructure nanoelectronics will be formed on nanostructure networks formed by combination of top-down and bottom-up approaches. In addition to communication devices, emerging devices include high speed digital LSIs, various sensors, various smart-chips, quantum LSIs and quantum computation devices covering varieties of application areas. Ultra-low power quantum LSIs may become brains of smart chips and other nanospace systems. Achievements of new functions and higher performances and their on chip integration are key issues. Key processing issue remains to be understanding and control of nanostructure surfaces and interfaces in atomic scale.
• Selective molecular beam epitaxy growth of size- and position-controlled GaN/AlGaN nanowires on nonplanar (0001) substrates and its growth mechanism

  Taketomo Sato, Takeshi Oikawa, Hideki Hasegawa, Tamotsu Hashizume

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 24 (4) 2087 - 2092 1071-1023 2006/07 [Refereed][Not invited]
   

  Fundamental growth properties were investigated for the size-controlled selective MBE growth of AlGaN/GaN nanowires on the GaN (0001) prepatterned substrates both experimentally and theoretically. The lateral size of the present GaN nanowire was determined by two facet boundaries formed within AlGaN barrier layers. From the series of wire growth experiments, the growth selectivity and the measured angle of the facet boundary strongly depended on the Al composition and the initial crystalline facets of the mesa patterned templates. The experimental evolution of the cross-sectional structures was well reproduced by a computer simulation based on the phenomenological growth model where the slope angle dependence of lifetime of adatoms was taken into account. The lateral width of present nanowires could be kinetically controlled by the growth conditions and the supply thickness of AlGaN layers. (c) 2006 American Vacuum Society.
• Self-assembled formation of uniform InP nanopore arrays by electrochemical anodization in HCl based electrolyte

  Taketomo Sato, Toshiyuki Fujino, Hideki Hasegawa

  APPLIED SURFACE SCIENCE 252 (15) 5457 - 5461 0169-4332 2006/05 [Refereed][Not invited]
   

  Attempts were made to optimize the electrochemical anodization process for the formation of high-density, regular and straight nanopore arrays on InP. The structure, shape and size of the pores were very sensitive to substrate orientations, electrolyte concentrations and anodization voltages. Among (1 1 1)A, (1 1 1)B and (0 0 1) substrate orientations, the most uniform and most straight nanopore arrays were obtained on (0 0 1) substrates at anodization voltages of 5-7 V by using 1.0-1.5 M HCl electrolyte containing HNO3. The pore depth could be controlled up to 80 mu m by the anodization time. (c) 2005 Elsevier B.V. All rights reserved.
• Sensing mechanism of InP hydrogen sensors using Pt Schottky diodes formed by electrochemical process

  T Kimura, H Hasegawa, T Sato, T Hashizume

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (4B) 3414 - 3422 0021-4922 2006/04 [Refereed][Not invited]
   

  Hydrogen sensing characteristics of Pt/InP Schottky diodes fabricated by electro-deposition were investigated. Such diodes gave high Schottky barrier heights (SBHs) of 650-810 meV. Upon exposure to hydrogen in air, the diodes exhibited a remarkable increase in forward and reverse currents. The saturation current on a log scale and the transient speed changed in proportion to the square root of the hydrogen pressure, P-H2. Upon exposure to hydrogen in vacuum or in nitrogen, a much larger and much faster increase in current took place. However, the saturation Current was almost independent Of P-H2, and the current increase remained almost the same after the hydrogen was removed. The sensing mechanism is explained in terms of changes in SBH caused by interface dipoles formed at Pt/InP interfaces due to adsorbed atomic hydrogen. Transient waveforms and dependence of saturation current and transient time constant on P-H2 were explained quantitatively by a simple theory where processes including atomic hydrogen generation, transport; storage, adsorption, desorption, and reaction with oxygen are effectively included.
• Embedded nanowire network growth and node device fabrication for GaAs-based high-density hexagonal binary decision diagram quantum circuits

  T Tamura, Tamai, I, S Kasai, T Sato, H Hasegawa, T Hashizume

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 (4B) 3614 - 3620 0021-4922 2006/04 [Refereed][Not invited]
   

  The basic feasibility of constructing hexagonal binary decision diagram (BDD) quantum circuits on GaAs-based selectively grown (SG) nanowires was investigated front viewpoints of electrical connections through embedded nanowires and electrical-uniformity of devices formed on nanowires. For this, <(1) over bar 10 >- and < 510 >-oriented nanowires and hexagonal network structures combining these nanowires were formed on (001) GaAs substrates by selective molecular beam epitaxy (MBE) growth. The width and vertical position of the nanowires could be controlled by growth conditions for both <(1) over bar 10 >- and < 510 >-directions. By current-voltage (I-V) measurements, good electrical connection was confirmed at the node point where vertical alignment of embedded GaAs nanowire pieces was found to be important. SG quantum wire (QWR) switches formed on the nanowires showed good gate control over a wide temperature range with clear conductance quantization at low temperatures. Good device uniformities were obtained on the test chips, providing a good prospect for future integration. BDD node devices using SG QWR switches showed clear path switching characteristics. Estimated power-delay product values were very small, confirming the feasibility of ultra low-power operation of future circuits.
• Precisely controlled anodic etching for processing of GaAs-based quantum nanostructures and devices

  N Shiozaki, T Sato, M Akazawa, H Hasegawa

  JOURNAL DE PHYSIQUE IV 132 249 - 253 1155-4339 2006/03 [Refereed][Not invited]
   

  For controlled low-damage etching of AlGaAs/GaAs nanostructures. fundamental properties of an etching process consisting of anodic oxidation and subsequent oxide dissolution are investigated both theoretically and experimentally. Anodic oxides formed on GaAs (001) and (111)B surfaces have the same composition and the same anodization parameters according to XPS, SEM and AFM measurements. The same applies to those formed on Al(0.3)Gi(0.7)As (001) and (111)B surfaces. The etching depth can be precisely controlled in nanometer scale by the anodization voltage. Selective etching was realized, using the lithography patterns. The surface morphology is much better than that in the standard wet chemical etching.
• Precisely controlled anodic etching for processing of GaAs-based quantum nanostructures and devices

  N Shiozaki, T Sato, M Akazawa, H Hasegawa

  JOURNAL DE PHYSIQUE IV 132 249 - 253 1155-4339 2006/03 [Refereed][Not invited]
   

  For controlled low-damage etching of AlGaAs/GaAs nanostructures. fundamental properties of an etching process consisting of anodic oxidation and subsequent oxide dissolution are investigated both theoretically and experimentally. Anodic oxides formed on GaAs (001) and (111)B surfaces have the same composition and the same anodization parameters according to XPS, SEM and AFM measurements. The same applies to those formed on Al(0.3)Gi(0.7)As (001) and (111)B surfaces. The etching depth can be precisely controlled in nanometer scale by the anodization voltage. Selective etching was realized, using the lithography patterns. The surface morphology is much better than that in the standard wet chemical etching.
• Electrochemical formation of chaotic and regular nanostructures on (001) and (111)B InP substrates and their photoluminescence characterizations

  Toshiyuki Fujino, Takeshi Kimura, Taketomo Sato, Hideki Hasegawa, Tamotsu Hashizume

  e-Journal of Surface Science and Nanotechnology 4 184 - 191 1348-0391 2006/02/10 [Refereed][Not invited]
   

  Attempts were made to form various nanostructures on InP substrates using anodization process. Surprisingly wide varieties of nanostructures were obtained. They included zigzag pore arrays and chaotic porous structures on (111)B substrate, and quasi-periodic straight nanopore arrays on (001) substrate. Straight pore samples showed blue-shifted peaks due to quantum confinement whereas no clear energy shifts were observed in (111)B samples. Zigzag and straight pore samples also showed red-shifted PL emissions probably due to emission from surface state continuum. © 2006 The Surface Science Society of Japan.
• Growth simulation and actual MBE growth of triangular GaAs nanowires on patterned (111)B substrates

  Isao Tamai, Taketomo Sato, Hideki Hasegawa, Tamotsu Hashizume

  e-Journal of Surface Science and Nanotechnology 4 19 - 24 1348-0391 2006/01/12 [Refereed][Not invited]
   

  Attempts were made to further elaborate our experimental growth method and the theoretical growth simulation method for formation of AlGaAs/GaAs QWRs on the (111)B substrates, paying attention to Al composition dependence of growth. A series of repeated growth experiments were carried out on simple one-sided mesa patterns, and from their analysis of the results led to determination of parameter values needed for computer simulation based on the continuum model. The experimental evolution of the cross-sectional structures was well reproduced by simulation, not only on one-side mesa, but also on mesa stripes actually used for wire growth. Finally, an optimum growth design was derived for growth of an array of GaAs triangular QWRs with 40 nm base width on GaAs (111)B substrate by the simulation, and the actual growth experiment confirmed its realization. © 2006 The Surface Science Society of Japan.
• Dynamics and control of recombination process at semiconductor surfaces, interfaces and nano-structures

  Hideki Hasegawa, Taketomo Sato, Seiya Kasai, Boguslawa Adamowicz, Tamotsu Hashizume

  SOLAR ENERGY 80 (6) 629 - 644 0038-092X 2006 [Refereed][Invited]
   

  Characterization methods and fundamental aspects of surface/interface states and recombination process in Si and III-V materials are reviewed. Various measurement considerations are pointed out for the conventional metal-insulator-semiconductor (MIS) capacitance-voltage (C-P) method, a contactless C-V method, and the microscopic scanning tunneling spectroscopy (STS) method, and general features of surface states are discussed. Surface states are shown to have U-shaped distributions of donor acceptor continuum with a characteristic charge neutrality level, E-HO. Rigorous simulation of dynamics of surface recombination process has shown that the effective surface recombination velocity, S-eff, is not a constant of the surface, but its value changes by many orders of magnitude with the incident light intensity and the polarity and amount of fixed charge. From this, new methods of surface state characterization based on photoluminescence and cathodoluminescence are derived. Attempts to control surface states and Fermi level pinning at metal semiconductor interface and free surfaces of nano-structures are presented as efforts toward "nano-photovoltaics". (c) 2006 Elsevier Ltd. All rights reserved.
• Performance of electrodeposited Pt/InP Schottky diode as a hydrogen sensing head for InP-based wireless sensor chips

  Takeshi Kimura, Hideki Hasegawa, Taketomo Sato, Tamotsu Hashizume

  2006 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS CONFERENCE PROCEEDINGS 443 - + 2006 [Refereed][Not invited]
   

  Hydrogen-sensing performances of Pt/InP Schottky diodes and MESFETs are evaluated from a viewpoint of constructing a nanometer-scale hydrogen sensor head of a future wireless hydrogen sensor chip. To realize large Schottky barrier heights (SBHs), Pt films were deposited by a pulsed in-situ electrochemical process. Upon exposure to hydrogen in air, the Pt/InP Schottky diode exhibited remarkably large increase of forward and reverse currents. The sensing mechanism is explained in terms of SBH changes caused by interface dipole formed at Pt/InP interface due to the adsorbed atomic hydrogen. Quantitative relationships between response magnitude and speed have been established. The Pt/InP MESFET also showed hydrogen induced current changes, and their magnitudes were much larger than those of the Schottky diode. Based on these, a novel structure of a nanometer-scale hexagonal hydrogen sensing head is proposed.
• Toward ultra-low power III-V quantum large scale integrated circuits for ubiquitous network era

  Hasegawa Hideki, Kasai Seiya, Sato Taketomo

  Frontiers in Electronics 41 (2) 421 - 436 2006 [Refereed][Not invited]
  
• Liquid sensor using gateless AlGaN/GaN HEMT structure

  KOKAWA TAKUYA, KIMURA TAKESHI, SATO TAKETOMO, KASAI SEIYA, HASEGAWA HIDEKI, HASHIZUME TAMOTSU

  IEICE technical report. Electron devices 105 (326(ED2005 139-156)) 39 - 42 0913-5685 2005/10/07 [Not refereed][Not invited]
  
• Fabrication of AlGaN/GaN nano wire network using selective RF-MBE

  OIKAWA TAKESHI, SATO TAKETOMO, HASEGAWA HIDEKI, HASHIZUME TAMOTSU

  IEICE technical report. Electron devices 一般社団法人電子情報通信学会 105 (325(ED2005 118-138)) 89 - 92 0913-5685 2005/10/06 [Not refereed][Not invited]
   

  For fabrication of AlGaN/GaN quantum wire network structures, we studied feasibility of selective MBE growth of AlGaN/GaN wire structures on pre-patterned GaN(0001) substrates. A mesa stripe type pattern and a hexagonal network type pattern were prepared by ECR-RIBE dry etching. As for the mesa direction, <1-100>-direction and <11-20>-direction were compared, and <11-20>-oriented mesa was found to be suitable for the selective growth of wire structures due to larger growth selectivity of GaN/AlGaN layers. Fabricated wire network structure showed strong CL emission, originating form wire structure. For the realization of precise size control of quantum wire structure, time evolution of cross-sectional features and Al composition dependence of the growth selectivity were investigated in detail.
• Embedded Nanowire Network Growth and Node Device Fabrication for GaAs-Based High-Density Hexagonal BDD Quantum Circuits

  TAMAURA Takahiro, TAMAI Isao, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki, HASHIZUME Tamotsu

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2005 152 - 153 2005/09/13 [Not refereed][Not invited]
  
• Sensing Mechanism of InP Hydrogen Sensors Using Pt Schottky Diodes Formed by Electrochemical Process

  KIMURA Takeshi, HASEGAWA Hideki, SATO Taketomo, HASHIZUME Tamotsu

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2005 218 - 219 2005/09/13 [Not refereed][Not invited]
  
• Growth kinetics and theoretical modeling of selective molecular beam epitaxy for growth of GaAs nanowires on nonplanar (001) and (111)B substrates

  T Sato, Tamai, I, H Hasegawa

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 23 (4) 1706 - 1713 1071-1023 2005/07 [Refereed][Not invited]
   

  The growth kinetics involved in the selective molecular beam epitaxy growth of GaAs quantum wires (QWRs) on mesa-patterned substrates is investigated in detail experimentally, and an attempt is made to model the growth theoretically, using a phenomenological continuum model. Experimentally, <-110 >-oriented QWRs were grown on (001) and (113)A substrates, and <-1-12 >-oriented QWRs were grown on (I I I)B substrates. From a detailed investigation of the growth profiles, it was found that the lateral wire width is determined by facet boundaries (FBs) within AlGaAs layers separating growth regions on top facets from those on side facets of mesa structures. Evolution of FBs during growth was complicated. For computer simulation, measured growth rates of various facets were fitted into a theoretical formula to determine the dependence of a lifetime of adatoms on the slope angle of the growing surface. The continuum model using the slope angle dependent lifetime reproduced the details of the experimentally observed growth profiles very well for growth on (001), (113)A, and (111)B substrates, including the complex evolution of facet boundaries (c) 2005 American Vacuum Society.
• Effects of surface states and Si-interlayer based surface passivation on GaAs quantum wires grown by selective molecular beam epitaxy

  N Shiozaki, T Sato, H Hasegawa

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 23 (4) 1714 - 1721 1071-1023 2005/07 [Refereed][Not invited]
   

  Effects of surface states and surface passivation on photoluminescence (PL) properties of GaAs quantum wires (QWRs) are investigated. QWR samples were grown on (001) and (111)B substrates by the selective molecular beam epitaxy (MBE) method. For surface passivation, an ultrathin (about 1 nm) Si interface control layer (Si ICL) was grown by MBE as an interlayer. In both of the selectively grown QWRs on (001) and (111)B substrates, the PL intensity reduced exponentially with reduction of their wire-to-surface distance, being coexistent with a more gradual reduction due to carrier supply reduction. The exponential reduction was explained in terms of interaction between surface states and quantum confined states leading to tunneling assisted nonradiative recombination through surface states. Surface passivation by the Si-ICL method almost completely recovered PL intensities not only for QWRs on the (001) substrate, but also for QWRs on the (111)B substrate. (c) 2005 American Vacuum Society.
• Investigation of Side-gating Effects in GaAs-based Quantum Wire Transistor (QWRTr) utilizing Nanosized Schottky Gates

  JIA Rui, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  IEICE technical report. Electron devices 一般社団法人電子情報通信学会 105 (110) 31 - 36 0913-5685 2005/06/03 [Not refereed][Not invited]
   

  Side-gating effects inhibiting the high-density integration of devices GaAs-based quantum wire transistors (QWRTrs) with nanosized Schottky gates controlling etched nanowires were investigated experimentally. Side-gating behaviors depended on the distance between the side-gate and nanowire edge d_<sg>, and when d_<sg><500nm and nanowire mesa etching was shallow, the large side-gating effect occurred, which could not be explained by the electrostatic effect. At the same time, anomalously large side-gate leakage current due to electron tunneling was observed. Here, we propose a model for the ...
• Surface Passivation Using a Si Interface Control Layer for AlGaAs/GaAs Quantum Srctures Fabricated on GaAs(111)B Substrates

  AKAZAWA MASAMICHI, AKAZAWA MASAMICHI, SHIOZAKI NANAKO, SHIOZAKI NANAKO, SATO TAKETOMO, SATO TAKETOMO, HASEGAWA HIDEKI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 105 (110(ED2005 58-66)) 25 - 30 0913-5685 2005/06/03 [Not refereed][Not invited]
   

  We attempted to apply a Si-interface-control-layer (Si ICL)-based surface passivation method to the surfaces of quantum structures fabricated on GaAs(111)B substrates. The sample surfaces were investigated by an XPS study at each step of the fabrication process, and fabricated quantum structures were characterized by PL measurements. Shifts of surface Fermi level positions toward the conduction band edges at GaAs and AlGaAs(111)B surfaces were observed after the Si ICL formation. PL intensities reduced with reduction of distances between quantum structures and their surfaces. The surface passivation using the Si-ICL, however, recovered PL intensities for quantum structures.
• Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN (0001) substrates

  T Oikawa, F Ishikawa, T Sato, T Hashizume, H Hasegawa

  APPLIED SURFACE SCIENCE 244 (1-4) 84 - 87 0169-4332 2005/05 [Refereed][Not invited]
   

  This paper attempts to form AlGaN/GaN quantum wire (QWR) network structures on patterned GaN (0 0 0 1) substrates by selective molecular beam epitaxy (MBE) growth. Substrate patterns were prepared along < 1 1 2 0 > - and < 1 1 0 0 >-directions by electron cyclotron resonance assisted reactive-ion beam etching (ECR-RIBE) process. Selective growth was possible for both directions in the case of GaN growth, but only in the < 1 1 2 0 >-direction in the case of AlGaN growth. A hexagonal QWR network was successfully grown on a hexagonal mesa pattern by combining the < 1 1 2 0 >-direction and two other equivalent directions. AFM observation confirmed excellent surface morphology of the grown network. A clear cathodoluminescence (CL) peak coming from the embedded AlGaN/GaN QWR structure was clearly identified. (c) 2004 Published by Elsevier B.V.
• Electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures

  H Hasegawa, T Sato

  ELECTROCHIMICA ACTA 50 (15) 3015 - 3027 0013-4686 2005/05 [Refereed][Invited]
   

  This paper reviews recent efforts by authors' group to utilize electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures. Topics include precise photo-anodic and pulsed anodic etching of InP, formation of arrays of < 001 >-oriented straight nanopores in n-type (001)InP by anodization and their possible applications and macroscopic and nanometer-scale metal contact formation on GaAs, InP and GaN by a pulsed in situ electrochemical process, which remarkably reduces Fermi level pinning. All the results indicate that electrochemical processes can achieve unique and important results, which the conventional semiconductor technology cannot realize, anticipating their increased importance in future semiconductor nanotechnology and nanoelectronics. (c) 2005 Elsevier Ltd. All rights reserved.
• Surface-related reduction of photoluminescence in GaAs quantum wires and its recovery by new passivation

  N Shiozaki, S Anantathanasarn, T Sato, T Hashizume, H Hasegawa

  APPLIED SURFACE SCIENCE 244 (1-4) 71 - 74 0169-4332 2005/05 [Refereed][Not invited]
   

  Etched GaAs quantum wires (QWRs) and selectively grown (SG) QWRs were fabricated, and dependence of their photoluminescence (PL) properties on QWR width (W) and QWR distance to surface (d) were investigated. PL intensity greatly reduced with reduction of Wand d, due to non-radiative recombination through surface states. Surface passivation by growing a Si interface control layer (Si-ICL) on group III-terminated surfaces greatly improved PL properties. (c) 2004 Elsevier B.V. All rights reserved.
• Electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures

  H Hasegawa, T Sato

  ELECTROCHIMICA ACTA 50 (15) 3015 - 3027 0013-4686 2005/05 [Refereed][Not invited]
   

  This paper reviews recent efforts by authors' group to utilize electrochemical processes for formation, processing and gate control of III-V semiconductor nanostructures. Topics include precise photo-anodic and pulsed anodic etching of InP, formation of arrays of < 001 >-oriented straight nanopores in n-type (001)InP by anodization and their possible applications and macroscopic and nanometer-scale metal contact formation on GaAs, InP and GaN by a pulsed in situ electrochemical process, which remarkably reduces Fermi level pinning. All the results indicate that electrochemical processes can achieve unique and important results, which the conventional semiconductor technology cannot realize, anticipating their increased importance in future semiconductor nanotechnology and nanoelectronics. (c) 2005 Elsevier Ltd. All rights reserved.
• Growth of AlGaN/GaN quantum wire structures by radio-frequency-radical-assisted selective molecular beam epitaxy on prepatterned substrates

  T Sato, T Oikawa, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 (4B) 2487 - 2491 0021-4922 2005/04 [Refereed][Not invited]
   

  The feasibility of the selective molecular beam epitaxy (MBE) growth of AlGaN/GaN quantum wire (QWR) Structures on prepatterned substrates is investigated. The detailed studies on growth features have revealed that size-reducing selective Growth is possible on mesa patterns having the (11-20)-orientation, but not on those having the (1-100)-orientations. The behavior reflects complex growth kinetics on high-index crystalline facets. The lateral wire width of QWR structures formed selectively on a top mesa can be controlled by adjusting the growth thickness and the initial size of mesa patterns. From cathodoluminescence (CL) measurements, emission from the embedded AlGaN/GaN QWR structure has been clearly identified.
• Cross-sectional evolution and its mechanism during selective molecular beam epitaxy growth of GaAs quantum wires on (111)B substrates

  Tamai, I, T Sato, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 (4B) 2652 - 2656 0021-4922 2005/04 [Refereed][Not invited]
   

  The mechanism of the cross-sectional evolution during the selective growth of GaAs quantum wires (QWRs) on (111)B-patterned substrates was studied in detail both experimentally and theoretically. For this purpose, growth experiments were carried out on <-1-12 >-oriented wires by systematically changing growth conditions and pattern sizes. A detailed investigation on cross sections of wires has shown that the lateral wire width is determined by facet boundaries (FBs) within AlGaAs layers separating growth regions on top facets from those on side facets of mesa structures. FBs were found to be planar or curved, depending on initial pattern sizes and growth conditions. Computer simulation based on a phenomenological growth model was attempted, taking account of the facet-angle-dependent lifetime of adatoms. The simulation well reproduced the experimentally observed growth features including the evolution of FBs, indicating that the cross sections of wires grown on (111)B-patterned substrates are kinetically controlled by the pattern sizes and growth conditions.
• 量子細線ネットワークと論理回路応用

  長谷川英機, 葛西誠也, 佐藤威友

  応用物理 74 (3) 320 - 326 0369-8009 2005/03 [Refereed][Invited]
  
• Fabrication and Characterization of GaAs BDD Quantum Node Devices Utilized Selective MBE Growth Technique

  TAMURA TAKAHIRO, YUMOTO MIKI, TAMAI ISAO, KASAI SEIYA, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 104 (624(SDM2004 222-228)) 19 - 24 0913-5685 2005/01/20 [Not refereed][Not invited]
   

  For realization of future quantum-LSIs (Q-LSIs) based on the novel hexagonal binary decision diagram (BDD) circuit approach, quantum wire (QWR) switches and BDD node devices utilizing selectively MBE grown (SG) QWR networks were investigated. Fabricated SG QWR switches using <-110> and <510>-directed nanowires on GaAs (001) substrate operated as conventional FETs at low temperature up to room temperature and clear conductance quantization was observed at low temperature. Their gate control characteristics were studied by gate-dependent Shubnikov-de-Haas oscillation measurements and it was confirmed good gate controllability of SG QWR switches controlled by Shottky wrap gates (WPGs). Y-branch BDD node devices were successfully fabricated combining <-110> and <510>-directed QWRs and realized clear path-switching. Their speed and power performances were also estimated and values of switching speed τ=50ps and PDP=10^<-18>J were obtained.
• Fabrication of AlGaN/GaN nano wire network using selective RF-MBE

  OIKAWA TAKESHI, SATO TAKETOMO, HASEGAWA HIDEKI, HASHIZUME TAMOTSU

  電子情報通信学会技術研究報告，CPM CPM2005 (134) 89 - 92 2005 [Not refereed][Not invited]
  
• Electrodeposited Pt/InP Schottky barriers with large barrier heights and large hydrogen sensitivity for sensor chips using InP-Based uanturn wire networks

  T Kimura, T Sato, T Hashizume, H Hasegawa

  2005 International Conference on Indium Phosphide and Related Materials 533 - 536 1092-8669 2005 [Not refereed][Not invited]
   

  Pt Schottky diodes were fabricated on n-InP by pulsed electrodeposition, and their H-2 sensing properties were investigated. Deposition resulted in formation of Pt nanoparticles. As compared with diodes by vacuum deposition, electrodepositod diodes gave much higher Schottky barrier heights (SBHs) of 810 meV. They showed marked increase of the reverse current on exposure to H-2 gas in air. The magnitudes of current change and on-off transients depended on the partial pressure of H-2. The detection mechanism is explained in terms of SBH change caused by adsorption/desorption of atomic hydrogen at the Pt/semiconductor interface. Its behavior was strongly affected by the presence of oxygen in the atmosphere. Integration of the present sensor with a hexagonal quantum wire network is proposed for realization of a wireless hydrogen sensor chip.
• ゲートレス型AlGaN/GaN -HEMTを利用した溶液センサ

  KOKAWA TAKUYA, KIMURA TAKESHI, SATO TAKETOMO, KASAI SEIYA, HASEGAWA HIDEKI, HASHIZUME TAMOTSU

  電子情報通信学会技術研究報告，CPM 一般社団法人電子情報通信学会 CPM2005 (134) 39 - 42 0913-5685 2005 [Not refereed][Not invited]
   

  Liquid phase chemical sensors using gateless Al_<0.24>Ga_<0.76>N/GaN HEMT structure were fabricated, and their sensing performances including pH responses were investigated. The device was covered with a SiO_2 film except an open gate window which was exposed to various liquid solutions. Sensing characteristics were measured in a standard electrochmical cell with a potentiostat and a saturated caromel reference electrode, and the latter provided gate control of the device. The devices exhibited I-V characteristics similar to those of conventional HEMTs in various solutions, showing tight gate control and complete pinch off. The drain current in the linear region changed linearly with pH value of the solution, giving a surface potential variation rate of 50.4mV/pH value of the solution, giving a surface potential variation rate of 50.4mV/pH which is close to the Nernstian value. The diode also indicated feasibility of sensing of polarizable liquids through potential shift by dipoles.
• Hexagonal binary decision diagram quantum circuit approach for ultra-low power III-V quantum LSIs

  H Hasegawa, S Kasai, T Sato

  IEICE TRANSACTIONS ON ELECTRONICS E87C (11) 1757 - 1768 0916-8524 2004/11 [Refereed][Invited]
   

  A new approach for ultra-low-power LSIs based on quantum devices is presented and its present status and critical issues are discussed with a brief background review on the semiconductor nanotechnology. It is a hexagonal binary decision diagram (BDD) quantum logic circuit approach suitable for realization of ultra-low-power logic/mernory circuits to be used in new applications such as intelligent quantum (IQ) chips embedded in the ubiquitous network environment. The basic concept of the approach, circuit examples showing its feasibility, growth of high density nanostructure networks by molecular beam epitaxy (NIBE) for future LSI implementation, and the key processing issues including the device isolation issue are addressed.
• Growth of AlGaN/GaN Quantum Wire Structures by RF-Radical Assisted Selective MBE on Pre-Patterned Substrates

  SATO Taketomo, OIKAWA Takeshi, HASHIZUME Tamotsu, HASEGAWA Hideki

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2004 814 - 815 2004/09/15 [Not refereed][Not invited]
  
• Cross-Sectional Evolution and Its Mechanism during Selective MBE Growth of GaAs Quantum Wires on (111)B Substrates

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  Extended abstracts of the ... Conference on Solid State Devices and Materials 2004 880 - 881 2004/09/15 [Not refereed][Not invited]
  
• Evolution mechanism of heterointerface cross-section during growth of GaAs ridge quantum wires by selective molecular beam epitaxy

  T Sato, Tamai, I, S Yoshida, H Hasegawa

  APPLIED SURFACE SCIENCE 234 (1-4) 11 - 15 0169-4332 2004/07 [Refereed][Not invited]
   

  The mechanism determining heterointerface cross-sections is studied for GaAs ridge quantum wires (QWRs) grown by selective molecular beam epitaxy (MBE). Arrays of (-110)- and (-1-12)-orientated QWRs were grown on (001) and (111)B GaAs patterned substrates, respectively. A detailed investigation of cross-sections of wires has shown that the boundary planes appear on both sides of QWRs, keeping a constant angle, theta, with respect to the flat top of the substrate pattern, and they determine the lateral wire width. Their evolution mechanism has turned out to be a kinetic process, reflecting differences in migration and atom incorporation rates on different facets. Simple formulas for theta have been derived, and they have shown excellent agreements with experiment. This has led to precise kinetic control of the wire width by growth conditions. (C) 2004 Elsevier B.V. All rights reserved.
• Growth kinetics and modeling of selective molecular beam epitaxial growth of GaAs ridge quantum wires on pre-patterned nonplanar substrates

  T Sato, Tamai, I, H Hasegawa

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 22 (4) 2266 - 2274 1071-1023 2004/07 [Refereed][Not invited]
   

  The growth kinetics involved in the selective molecular beam epitaxial growth of GaAs ridge QWRs is investigated in detail experimentally and an attempt is made to model the growth theoretically. For this purpose, detailed experiments were carried out on the growth of <110>-oriented AlGaAsGaAs ridge quantum wires on mesa-patterned (00 1) GaAs substrates. A phenomenological modeling was done based on the continuum approximation including parameters such as group III adatom lifetime, diffusion constant and migration length. Computer simulation using the resultant model well reproduces the experimentally observed growth features such as the cross-sectional structure of the ridge wire and its temporal evolution, its temperature dependence and evolution of facet boundary planes. The simple phenomenological model developed here seems to be very useful for design and precise control of the growth process. (C) 2004 American Vacuum Society.
• Selective molecular beam epitaxy growth of GaAs hexagonal nanowire networks on (111)B patterned substrates

  S Yoshida, Tamai, I, T Sato, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (4B) 2064 - 2068 0021-4922 2004/04 [Refereed][Not invited]
   

  In view of applications to hexagonal binary decision diagram (BDD) quantum circuits, the growth of hexagonal GaAs nanowire networks was attempted by selective molecular beam epitaxy (MBE) on (111)B prepatterned substrates. The basic feasibility of <112>-oriented straight nanowires was first investigated. GaAs nanowires were selectively formed on the top (111)B plane of AlGaAs mesa structures with high uniformity. The lateral width of the wires was determined by two facet boundary planes separating the growth regions on the top and the side facets of the mesa structures. The angle of the boundary planes remained constant during growth, resulting in the wire width being precisely controlled by the thickness of the AlGaAs barrier layer. Then, GaAs/AlGaAs hexagonal nanowire networks were grown on the patterned substrates consisting of three equivalent <112>-oriented wires for a (111)B plane. The results of detailed structural and optical studies showed that highly uniform and smoothly connected hexagonal nanowire networks having threefold symmetry were successfully fabricated by the present selective MBE growth technique.
• 内部交差量子細線構造の深さ分解/面内分布カソードルミネッセンス評価

  石川史太郎, 及川武, 玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集 51st (3) 1540  2004/03/28 [Not refereed][Not invited]
  
• Formation of high-density GaAs hexagonal nano-wire networks by selective MBE growth on pre-patterned (001) substrates

  Tamai, I, T Sato, H Hasegawa

  PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 (2-4) 521 - 526 1386-9477 2004/03 [Refereed][Not invited]
   

  Attempts were made to grow high-density GaAs hexagonal nano-wire networks on (001) patterned substrates by selective molecular beam epitaxy. To form a hexagon, (110)- and (510)-directions were combined. By the growth of straight wire arrays in each direction, the growth mode, conditions and mechanism were investigated. The wire width was shown to be determined for both directions by the facet boundary planes resulting from the growth rate difference on different facets. By optimizing growth conditions, highly uniform and smoothly connected hexagonal nano-wire networks with a density of 3 x 10(8) cm(-2) were successfully formed. (C) 2003 Elsevier B.V. All rights reserved.
• Formation of high-density GaAs hexagonal nano-wire networks by selective MBE growth on pre-patterned (001) substrates

  Tamai, I, T Sato, H Hasegawa

  PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 (2-4) 521 - 526 1386-9477 2004/03 [Refereed][Not invited]
   

  Attempts were made to grow high-density GaAs hexagonal nano-wire networks on (001) patterned substrates by selective molecular beam epitaxy. To form a hexagon, (110)- and (510)-directions were combined. By the growth of straight wire arrays in each direction, the growth mode, conditions and mechanism were investigated. The wire width was shown to be determined for both directions by the facet boundary planes resulting from the growth rate difference on different facets. By optimizing growth conditions, highly uniform and smoothly connected hexagonal nano-wire networks with a density of 3 x 10(8) cm(-2) were successfully formed. (C) 2003 Elsevier B.V. All rights reserved.
• Fabrication and Characterization of Quantum Wire Switch for Hexagonal BDD Quantum Integrated Circuits

  YUMOTO MIKI, TAMURA TAKAHIRO, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 103 (631(SDM2003 213-221)) 15 - 19 0913-5685 2004/01/30 [Not refereed][Not invited]
   

  In view of applications to hexagonal binary decision diagram (BDD) LSIs, a first attempt is made to form quantum BDD node switches on selectively grown (SG) embedded quantum wires (QWRs) by molecular beam epitaxy (MBE). SG QWR branch switches controlled by Schottky wrap gate (WPG) were successfully fabricated by MBE growth and subsequent device processing. Gate control characteristics were studied by gate-dependent Shubnikov-de-Haas measurements, and the behavior was found to be similar to that of devices fabricated on wires by etching. The switch exhibited clear conductance quantization at low temperature, and temperature dependence of the voltage slope of conductance jump was clarified. A Y-branch BDD node device using two SG branch switches was successfully fabricated, and they realized clear path switching characteristics.
• Formation of GaAs Quantum Wire Networks on (111)B patterned substrates using MBE Selective Growth

  YOSHIDA SOICHI, TAMAI ISAO, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 103 (630(SDM2003 207-212)) 23 - 28 0913-5685 2004/01/29 [Not refereed][Not invited]
   

  In view of applications to hexagonal BDD diagram quantum circuits, the growth of hexagonal GaAs nanowire networks was attempted by MBE selective growth. The basic feasibility of <112>-oriented straight nanowires was first investigated. GaAs nanowires were selectively formed on the top of (111)B plane of AlGaAs mesa structures with high uniformity. The wire width was controlled by the growth conditions. Then, GaAs hexagonal networks were grown on patterned substrates. The results of detailing structural and optical studies showed that highly uniform and smoothly connected hexagonal networks were successfully fabricated by selective MBE growth technique.
• Fabrication of BDD quantum node switches on embedded GaAs quantum wires grown by selective MBE

  M Yumoto, T Tamura, T Sato, H Hasegawa

  SUPERLATTICES AND MICROSTRUCTURES 34 (3-6) 485 - 491 0749-6036 2003/09 [Refereed][Not invited]
   

  In view of applications to hexagonal binary decision diagram (BDD) LSIs, a first attempt is made to form quantum BDD node switches on selectively grown (SG) embedded quantum wires (QWRs) by molecular beam epitaxy (MBE). SG branch switches controlled by a Schottky wrap gate (WPG) were successfully fabricated by MBE growth and subsequent device processing. Gate control characteristics were studied by gate-dependent Shubnikov-de-Haas measurements, and the behavior was found to be similar to that of devices fabricated on wires by etching. The switch exhibited clear conductance quantization at low temperature, and temperature dependence of the voltage slope of conductance jump was clarified. A Y-branch BDD node device using two SG branch switches was successfully fabricated, and realized clear path switching characteristics. (C) 2004 Elsevier Ltd. All rights reserved.
• Selective MBE Growth of Hexagonal Nano-wire Networks on GaAs Patterned Substrates

  SATO TAKETOMO, TAMAI ISAO, YOSHIDA SOICHI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 103 (117(ED2003 50-57)) 29 - 34 0913-5685 2003/06/13 [Not refereed][Not invited]
   

  Attempts were made to grow GaAs ridge nano-wires and hexagonal GaAs nanowire networks by selective MBE growth on (001) and (111)B pre-patterned substrates. Growth on mesa stripes produced embedded GaAs ridge quantum wires (QWRs) on the top of AlGaAs ridge structures. From the detail investigation on growth process, the size of GaAs ridge wires was geometrically determined by the difference of growth rate on two kinds of crystal facets of ridge structures, where the wire size can be kinetically controlled by growth conditions and initial pattern size. Uniform hexagonal nano-wire networks were successfully fabricated on hexagonal patterned substrates by combining <-110>- and two <510>-wire directions for (001) substrates and on hexagonal patterned substrates by combining three <-1-12> wire directions for (111)B substrates.
• Selective MBE Growth of GaAs Ridge Quantum Wires for Formation of Hexagonal Nanowire Networks.

  SATO TAKETOMO, TAMAI ISAO, YOSHIDA SOICHI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 102 (640(SDM2002 244-251)) 27 - 32 0913-5685 2003/02/10 [Not refereed][Not invited]
   

  Attempts were made to grow GaAs ridge nano-wires and hexagonal GaAs nanowire networks by selective MBE growth on (001) pre-pattemed substrates.<-110>-and<510>-oriented mesa stripes produced embedded GaAs ridge quantum wires (QWRs) on the top of AlGaAs ridge structures. From the detail investigation on growth process, the size of GaAs ridge wires was geometrically determined by the difference of growth rate on two kinds of crystal facets of ridge structures, where the wire size can be kinetically controlled by growth conditions and initial pattern size. Based on underlying growth mechanism, uniform hexagonal nano-wire networks were successfully fabricated on hexagonal patterned substrates by combining<-110>-and<510>-wire directions.
• Effects of surface states on control characteristics of nano-meter scale Schottky gates formed on GaAs

  A Kameda, S Kasai, T Sato, H Hasegawa

  SOLID-STATE ELECTRONICS 47 (2) 323 - 331 0038-1101 2003/02 [Refereed][Not invited]
   

  Effects of surface states on gate control characteristics of nano-meter scale Schottky gates formed on GaAs are investigated both theoretically and experimentally. Special sample structures are used. They are metal-insulator-semiconductor structures having nano-meter scale Schottky dot arrays for capacitance-voltage (C-V) measurements and metal-semi-conductor field effect transistor structures having nano-meter scale grating Schottky gates for current-voltage (I-V) measurements. Measured C-V and I-V results are compared with results of theoretical calculation on a computer. The effects of surface states are found to be two-fold. Namely, it is shown that control characteristics of nano-meter scale Schottky gates are strongly degraded by the presence of Fermi level pinning caused by surface states on the free surface surrounding the gate. It is also shown that a significant amount of gate-induced lateral charging of surface states takes place around the gate periphery, effectively increasing the gate dimension. These results indicate the critical importance of control of surface states in nano-devices using nano-meter scale Schottky gates. (C) 2002 Elsevier Science Ltd. All rights reserved.
• Selective MBE growth of GaAs ridge quantum wire arrays on patterned (001) substrates and its growth mechanism

  T Sato, Tamai, I, H Hasegawa

  COMPOUND SEMICONDUCTORS 2002 174 (3) 145 - 148 0951-3248 2003 [Refereed][Not invited]
   

  Selective MBE growth of an array of <-110>-oriented GaAs ridge QWRs was attempted on pre-patterned (001) substrates. Arrow-head shaped GaAs QWRs were selectively formed on the top (I 13)A facets of GaAs ridge structures. The underlying growth mechanism was clarified, and based on this, the wire width could be kinetically controlled by the growth process.
• Prospects of III-V quantum LSIs based on hexagonal BDD approach

  Seiya Kasai, Taketomo Sato, Hideki Hasegawa

  2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings 482 - 483 2003 [Refereed][Not invited]
   

  Explosive growth of intemets and wireless telephones starting in the late 20th century has opened up prospects towards an advanced ubiquitous network society. This also opens up new directions in the device research in addition to the continued efforts of scale down of Si CMOS device along the roadmap.
• Electrochemical formation of self-assembled InP nanopore arrays and their use as templates for molecular beam epitaxy growth of InGaAs quantum wires and dots

  T Hirano, A Ito, T Sato, F Ishikawa, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 (2B) 977 - 981 0021-4922 2002/02 [Refereed][Not invited]
   

  Attempts were made to optimize the parameters of the electrochemical process to form uniform nanopore arrays and utilize them as templates for molecular beam epitaxy (MBE) growth of InP-based quantum wires and quantum dots. Template parameters such as pore depth, diameter and period were strongly dependent on anodization conditions. In particular, in the pulsed anodization mode, the pore depth could be well controlled in the nanometer range by adjusting the number of the applied pulses. InGaAs MBE growth was attempted using the nanopore templates. Growth of InGaAs in pores occurred at a substantial depth of about 20-60 nm. The measured photoluminescence (PL) spectra had a new peak at about 1.2 eV in addition to the PL emission from the InP substrate and that from the InGaAs top layer. The new peak was tentatively assigned to the peak arising from InGaAs quantum wire arrays embedded in InP pores with a possible alloy composition change.
• Fabrication of GaAs/AlGaAs Quantum Wires and Quantum Network Structures using MBE selective growth.

  TAMAI ISAO, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 101 (617(ED2001 224-231)) 15 - 20 0913-5685 2002/01/28 [Not refereed][Not invited]
  
• Fabrication of porous InP structure by Electrochemical Process and itsApplication.

  HIRANO TETSURO, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 101 (617(ED2001 224-231)) 49 - 54 0913-5685 2002/01/28 [Not refereed][Not invited]
  
• MBE選択成長法によるGaAs/AlGaAs量子細線の形成とその結合ネットワークへの応用

  TAMAI ISAO, SATO TAKETOMO, HASEGAWA HIDEKI

  電子情報通信学会研究会技術研究報告 ED2001 (101/617) 15 - 20 2002 [Not refereed][Not invited]
  
• Selective MBE growth of GaAs/AlGaAs nanowires on patterned GaAs (001) substrates and its application to hexagonal nanowire network formation

  T Sato, Tamai, I, C Jiang, H Hasegawa

  COMPOUND SEMICONDUCTORS 2001 170 (170) 325 - 330 0951-3248 2002 [Refereed][Not invited]
   

  Feasibility of formation of GaAs/AlGaAs hexagonal nanowire networks by selective MBE growth on patterned (001) substrates is investigated. First, the process for forming <(1) over bar 10>-oriented straight QWR arrays is studied and optimized with respect to wire shape, size and uniformity. SEM and PL studies showed that arrow-head shaped GaAs nanowires can be formed on the top of (113) AlGaAs ridge with excellent size controllability and high uniformity. Feasibility study of hexagonal nanowire network formation by combining different pattern orientations has shown combination of <(1) over bar 10>- and <510>- directions is most promising.
• Selective MBE Growth of <-110>- and <510>- Oriented GaAs Ridge Quantum Wires on Patterned (001) Substrates for Formation of Hexagonal Nanowire Networks

  Sato Taketomo, Tamai Isao, Jiang Chao, Hasegawa Hideki

  The Second International Workshop on Quantum Nonplanar Nanostructures & Nanoelectronics 283 - 286 2002 [Not refereed][Not invited]
  
• 電気化学的手法によるInPポーラス構造の形成と応用

  HIRANO Tetsuro, SATO Taketomo, HASEGAWA Hideki

  電子情報通信学会研究会技術研究報告 ED2001 (101-617/) 49 - 54 2002 [Not refereed][Not invited]
  
• 電気化学プロセスによるInPポーラス構造の形成とその応用(2)

  平野哲郎, 佐藤威友, 伊藤章, 石川史太郎, 長谷川英機

  応用物理学会学術講演会講演予稿集 62nd (3) 1059  2001/09/11 [Not refereed][Not invited]
  
• Current transport and capacitance-voltage characteristics of GaAs and InP nanometer-sized Schottky contacts formed by in situ electrochemical process

  T Sato, S Kasai, H Hasegawa

  APPLIED SURFACE SCIENCE 175 181 - 186 0169-4332 2001/05 [Refereed][Not invited]
   

  The electrical properties of nanometer-sized Schottky contacts which were successfully formed on n-GaAs and n-InP substrates by a combination of an electrochemical process and an electron-beam (EB) lithography. were characterized both experimentally and theoretically. The detailed I-ri measurements using a conductive AFM system showed nonlinear log I-ii characteristics with large n value in range of 1.2-2.0 which cannot be explained by a standard 1D thermionic emission model. A computer simulation showed that this nonlinear characteristics can be explained by a new 3D thermionic emission model where Fermi-level pinning on the surrounding free surface modifies the potential distribution underneath the nano-contact. Calculation of C-V characteristics showed an extremely small change of the depletion layer width with bias due to the environmental Fermi-level pinning. On the other hand, it was also found that Fermi-level pinning at the metal-semiconductor interface itself is greatly reduced, resulting in a strong dependence of barrier height on the metal workfunction. (C) 2001 Elsevier Science B.V. All rights reserved.
• 電気化学プロセスによるInPポーラス構造の形成とその応用

  平野哲郎, 佐藤威友, 伊藤章, 石川史太郎, 長谷川英機

  応用物理学関係連合講演会講演予稿集 48th (3) 1378  2001/03/28 [Not refereed][Not invited]
  
• Electrical properties of nanometer-sized Schottky contacts for gate control of III-V single electron devices and quantum devices

  T Sato, S Kasai, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 40 (3B) 2021 - 2025 0021-4922 2001/03 [Refereed][Not invited]
   

  The electrical properties of nanometer-sized Schottky contacts formed on n-GaAs and n-InP substrates by an in situ electrochemical process were studied both experimentally and theoretically to understand and improve their gate control behavior in single electron devices and quantum devices. From the current-voltage (I-V) measurements using a conductive atomic force microscope (AFM) system, the nano-Schottky contacts showed nonlinear log I-V characteristics with large and voltage-dependent n values which cannot be explained by the 1D thermionic emission model. The behavior was explained by a novel 3D thermionic emission model including 3D potential distribution modified by an environmental Fermi-level pinning. The depletion characteristics were calculated on the basis of the new model including the environmental effects. The results showed small changes of the depletion layer width with a bias underneath the nano-Schottky contacts due to the environmental Fermi-level pinning. Control of Fermi-level pinning is thus crucial to obtain nano devices in the quantum regime that exhibit good behavior.
• Electrical properties of nanometer-sized Schottky contacts for gate control of III-V single electron devices and quantum devices

  T Sato, S Kasai, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 40 (3B) 2021 - 2025 0021-4922 2001/03 [Refereed][Not invited]
   

  The electrical properties of nanometer-sized Schottky contacts formed on n-GaAs and n-InP substrates by an in situ electrochemical process were studied both experimentally and theoretically to understand and improve their gate control behavior in single electron devices and quantum devices. From the current-voltage (I-V) measurements using a conductive atomic force microscope (AFM) system, the nano-Schottky contacts showed nonlinear log I-V characteristics with large and voltage-dependent n values which cannot be explained by the 1D thermionic emission model. The behavior was explained by a novel 3D thermionic emission model including 3D potential distribution modified by an environmental Fermi-level pinning. The depletion characteristics were calculated on the basis of the new model including the environmental effects. The results showed small changes of the depletion layer width with a bias underneath the nano-Schottky contacts due to the environmental Fermi-level pinning. Control of Fermi-level pinning is thus crucial to obtain nano devices in the quantum regime that exhibit good behavior.
• Effects of surface fermi level pinning and surface state charging on control characteristics of nanometer scale Schottky gates formed on GaAs

  A Kameda, S Kasai, T Sato, H Hasegawa

  2001 INTERNATIONAL SEMICONDUCTOR DEVICE RESEARCH SYMPOSIUM, PROCEEDINGS 626 - 629 2001 [Not refereed][Not invited]
  
• Electrochemical formation of self-assembled nanopore arrays as templates for MBE growth of InP-based quantum wires and dots

  T Hirano, A Ito, T Sato, F Ishikawa, H Hasegawa

  2001 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 378 - 381 1092-8669 2001 [Not refereed][Not invited]
   

  In this study, attempts were made to optimize the parameters of the electrochemical process to form uniform nanopore arrays in order to utilize them as templates for MBE growth of InP-based quantum wires and quantum dots. Template parameters such as the pore depth, diameter and period were strongly dependent on anodization conditions. Especially, in the pulsed anodization mode, the pore depth could be well controlled in the nanometer range by changing the number of the applied pulses. InGaAs MBE growth was attempted using the nanopore templates. Growth of InGaAs in pores took place into a substantial depth of about 100-200 nm. The measured PL spectrum had a new peak at about 1.2 eV in addition to the PL emission from the InP substrate and that of InGaAs top layer. The new peak was tentatively assigned to be from InGaAs quantum wire arrays embedded in InP pores with a possible alloy composition change.
• Unpinning of Fermi level in nanometer-sized Schottky contacts on GaAs and InP

  H Hasegawa, T Sato, S Kasai

  APPLIED SURFACE SCIENCE 166 (1-4) 92 - 96 0169-4332 2000/10 [Refereed][Not invited]
   

  Transport properties of two types of electrochemically produced nanometer-sized GaAs and InP Schottky contacts were investigated. One is macroscopic contacts containing many nano-dots and the other is isolated single-dot contacts. Macroscopic contacts showed near ideal thermionic emission characteristics with ideality factors close to unity. I-V characteristics of single nano-dor, contacts directly measured by a conductive AFM probe showed nonlinear log I-V behavior with large and voltage-dependent ideality factors. The latter was explained by potential profile modification due to Fermi level pinning on surrounding free surfaces. Both types of contacts indicated that Fermi level pinning disappears as the dot size is reduced, indicating that strong Fermi level pinning is not intrinsic to Schottky contacts. (C) 2000 Elsevier Science B.V. All rights reserved.
• Electrical properties of nanometer-sized Schottky contacts on n-GaAs and n-InP formed by in situ electrochemical process

  T Sato, S Kasai, H Okada, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 39 (7B) 4609 - 4615 0021-4922 2000/07 [Refereed][Not invited]
   

  The current transport characteristics of nanometer-sized Schottky contacts were investigated from theoretical and experimental viewpoints. A theoretical calculation of the three dimensional (3D) potential distributions showed that the potential shape underneath the nano-Schottky contacts was considerably modified by the surface Fermi level pinning on the air exposed free surfaces, producing a saddle point in the potential. The curl ent-voltage (I-V) curves were strongly influenced by this saddle point potential and resulted in nonlinear log I-V characteristics. Experimentally, the Pt nano-particles were selectively formed using the in situ electrochemical process on n-type GaAs and n-type InP substrates patterned using electron-beam (EB) lithography. Their I-V measurements were carried out using an atomic force microscopy (AFM) system equipped with a conductive probe. The log I-V curves of the nano-Schottky contacts showed nonlinear characteristics with large n values of 1.96 for n-GaAs and 1.27 for n-InP and could be very well explained by the theoretical I-V curves considering the "environmental" Fermi level pinning.
• Electrochemical formation of uniform and straight nano-pore arrays on (001) InP surfaces and their photoluminescence characterizations

  H Fujikura, AM Liu, A Hamamatsu, T Sato, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 39 (7B) 4616 - 4620 0021-4922 2000/07 [Refereed][Not invited]
   

  Recently, (001)-oriented nanometer-sized pores (nano-pores) without side branches, unlike porous Si, have been realized by our group on (001) n-InP surfaces by means of electrochemical anodization in 1M HCl solution. However, they exhibit large structural nonuniformity including the presence of an irregular top layer, random pore positioning and wavy pore walls. In this study, attempts have been made to improve pore uniformity and to clarify their optical properties. Anodization in 1M HCl + HNO3 solution realized highly uniform nano-pore arrays consisting of square-shaped straight pores defined by four crystalline (011) facets. This improvement is explained in terms of preferential etching along the vertical (001)-direction at the pore tip due to the slow etching rate along the lateral (011)-direction as well as the uniform supply of reactant species to pore tips realized by the removal of the irregular top layer during the anodization process. The nano-pore arrays show strong blue- and red-shifted photoluminescence emissions at high and low temperatures, respectively. These are assigned as emissions due to the transition between electron and hole quantum states inside the pore walls and that involving a broad surface state continuum at pore wall surfaces, respectively.
• Electrical Characterization on Nano-Schottky Contacts Fabricated Using the Electrochemical Process.

  SATO TAKETOMO, KASAI SEIYA, OKADA HIROSHI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 99 (616(ED99 306-318)) 79 - 84 0913-5685 2000/02/10 [Not refereed][Not invited]
   

  The current transport characteristics of nanometer-sized Schottky contacts were investigated from theoretical and experimental viewpoints. A theoretical calculation of the 3D potential distributions has shown that the potential shape underneath the nano-Schottky contacts is greatly modified by the surface Fermi level pinning on the air exposed free surfaces. This leads to non-linear log I-V characteristics which are different from a standard thermionic emission characteristics obtained on the macro-Schottky contacts. On the other hand, the Pt nano-particles were selectively formed using the in situ electrochemical process, their I-V measurements were made using an conductive AFM system. The log I-V curves of the nano-Schottky contacts showed non-linear characteristics and could be very well explained by the theoretical I-V curves considering the "environmental" Fermi level pinning.
• Self-assembled formation of InP nanopore arrays by electrochemical anodization

  H Fujikura, AM Liu, T Sato, T Hirano, H Hasegawa

  2000 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS 510 - 513 1092-8669 2000 [Refereed][Not invited]
   

  High density, uniform arrays of (001)-oriented straight nanopores were successfully formed on (001) n-InP surfaces in a self-assembled fashion by electrochemical anodization in 1M HCl + HNO3 solution. Unlike porous Si, the pores do not have side branches and possessed nearly equal-sized square-shapes defined by four crystalline flat (110) facets. Preferential etching along vertical (001)-direction due to slow etching rates on (110) side facets may be responsible for formation of such a uniform structure. At low temperature, the nanopore arrays showed strong red-shifted photoluminescence (PL) emission probably due to a transition involving a broad surface state continuum at the pore wall surfaces. On the other hand, a strong blue-shifted PL emission was observed at room temperature, confirming presence of quantum size effect in the pore walls as expected from the structural observations.
• Properties of nanometer-sized metal-semiconductor interfaces of GaAs and InP formed by an in situ electrochemical process

  H Hasegawa, T Sato, C Kaneshiro

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 17 (4) 1856 - 1866 1071-1023 1999/07 [Refereed][Not invited]
   

  The properties of GaAs and InP Schottky diodes having nanometer-sized metal dots were investigated in order to clarify whether or not strong Fermi level pinning is an intrinsic property of the metal-semiconductor interface. Macroscopic Schottky diode samples having many nanometer-sized metal dots as well as single-dot Schottky diode samples were prepared by an in situ electrochemical process which consisted of pulsed anodic etching of the semiconductors followed by subsequent de or pulsed cathodic deposition of the metal. Strong Fermi level pinning was not seen in the GaAs and InP macroscopic samples. The Schottky barrier height SBH values were strongly dependent on the metal work function and on the electrochemical processing conditions. Of particular interest, the difference in the dot size changed the SBH almost 340 meV in Pt/InP macroscopic Schottky diodes, indicating that Fermi level pinning disappears as the dot size is sufficiently reduced. X-ray photoelectron spectroscopy and Raman measurements indicated that these interfaces are oxide and stress free. Use of an atomic force microscope with a conductive probe allowed direct I-V measurements on single-dot samples. The metal work function and dot size dependencies of the SBHs in these samples were similar to those in macroscopic samples. Large ideality factors observed in the single-dot sample were explained in terms of environmental Fermi level pinning which produces a saddle point potential. The metal work function dependence of the SBHs measured as well as the relationship between the SBH and the ideality factor were both far from what was found in recent predictions based on the metal-induced gap state model. All the experimental results were consistently explained by the disorder-induced gap state model which asserts that strong Fermi level pinning is an extrinsic property of the metal-semiconductor interface. (C) 1999 American Vacuum Society. [S0734-211X(99)04704-6].
• Fabrication of Nano-Schottky Contacts on Compound Semiconductor by Pulsed Mode Electrochemical Process and Its Characterization.

  SATO TAKETOMO, OKADA HIROSHI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 99 (21(ED99 1-10)) 39 - 44 0913-5685 1999/04/22 [Not refereed][Not invited]
   

  Nanometer-sized Schottky contacts were successfully formed on InP and related materials by combining an in situ electrochemical process and a standard electron beam (EB) lithography. At the initial stage of the optimized electrochemical process, uniform Pt particles with diameter of 26 nm were formed in a self-assembled fashion on unmasked n-InP subdtrates, and this led to a highest Schottky barrier heights (SBHs) of 0.86 eV Under this optimized condition, a mushroom type Pt gate could be formed on EB patterned n-InAlAs substrates. Furthermore, regular arrays of Pt dot with a diameter of 30nm were selectively fabricated Within open circular windows. l-V characteridtics measured using a conductive atomic force microscopy (AFM) tip indicated that a single Pt dot formed a wel1-behaved nanometer Schottky contact.
• Formation of size- and position-controlled nanometer size Pt dots on GaAs and InP substrates by pulsed electrochemical deposition

  T Sato, C Kaneshiro, H Okada, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (4B) 2448 - 2452 0021-4922 1999/04 [Refereed][Not invited]
   

  Attempts were made to form regular arrays of size- and position-controlled Pt-dots on GaAs and InP by combining an ir? situ electrochemical process with the electron beam (EB) lithography. This utilizes the precipitation of Pt nano-particles at the initial stage of electrodeposition. First, electrochemical conditions were optimized in the mode of self-assembled dot array formation on unpatterned substrates. Minimum in-plane dot diameters of 22 nm and 26 nm on GaAs and InP. respectively, were obtained under the optimal pulsed mode. Then, Pt dots were selectively formed on patterned substrates with open circular windows formed by EB lithography, thereby realizing dot-position control. The Pt dot was round to have been deposited at the center of each open window, and the in-plane diameter of the dot could be controlled by the number, width and period of the pulse-waveform applied to substrates. A minimum diameter of 20 nm was realized in windows with a diameter of 100 nm, using a single pulse. Current-voltage (I-V) measurements using an atomic force microscopy (AFM) system with a conductive probe indicated that each Pt dot/n-GaAs contact possessed a high Schottky barrier height of about 1 eV.
• The strong correlation between interface microstructure and barrier height in Pt/n-InP Schottky contacts formed by an in situ electrochemical process

  T Sato, C Kaneshiro, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (2B) 1103 - 1106 0021-4922 1999/02 [Refereed][Not invited]
   

  In order to investigate the correlation between the microstructure of a metal/semiconductor (M/S) interface and the Schottky barrier height (SBH), Pt Schottky contacts were formed on n-type InP by an in situ electrochemical process under various electrochemical conditions; they were then investigated using scanning electron microscopy (SEM), current-voltage (I-V) and capacitance-voltage (C-V) measurements. Electrodeposition resulted in the formation of arrays of nanometer-sized Pt particles whose distribution strongly depended on electrochemical conditions. The SBH values exhibited a strong correlation with the particle distribution, leading to a high SBH value of 0.86 eV under the condition of the most uniform distribution of the smallest particles. The result is discussed from the viewpoint of the disorder-induced gap state (DIGS) model.
• Electrochemical etching of indium phosphide surfaces studied by voltammetry and scanned probe microscopes

  C Kaneshiro, T Sato, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (2B) 1147 - 1152 0021-4922 1999/02 [Refereed][Not invited]
   

  Using voltammetry, X-ray photoemission spectroscopy (XPS), in situ electrochemical scanning tunneling microscopy (STM), ex situ atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements, electrochemical etching modes for n-InP surfaces were investigated and optimized for uniform and controlled etching in an HCl electrolyte. The voltammograms indicated the presence of active and passive regions. The surfaces obtained in the active region were clean and featureless with an rms roughness of 1.8 nm. On the other hand, the oxide cove:red surfaces obtained in the passive region were nonuniform and porous. Etching characteristics of the d.c. photo-anodic mode and the pulsed avalanche mode were then investigated and compared. Both modes were found to be highly controllable and produced uniform and clean surfaces, consuming eight holes per molecule of InP. In particular, the pulsed avalanche etching mode realized an extremely high etch depth controllability of 3 x 10(-5) nm/pulse.
• Realization of strongly metal-dependent Schottky barrier heights on n-GaAs by in situ electrochemical process

  C Kaneshiro, T Sato, H Hasegawa

  COMPOUND SEMICONDUCTORS 1998 (162) 585 - 590 0951-3248 1999 [Refereed][Not invited]
   

  K Ni, Co and Sn Schottky barriers were formed on n-GaAs by an in situ electrochemical process which consists of anodic etching and subsequent metal deposition in the same electrolyte. All the fabricated diodes showed nearly ideal thermionic emission transport. The Schottky barrier heights were found to be strongly dependent on the metal work function, giving a large value of slope factor of S=0.18-0.55. The result was far away from the recent prediction based on MIGS model. Based on SEM/AFK XPS and Raman measurements, the result was explained by the DIGS model.
• GaAs-based single electron logic and memory devices using electrodeposited nanometer Schottky gates

  Hiroshi Okada, Taketomo Sato, Kei-ichiroh Jinushi, Hideki Hasegawa

  Microelectronic Engineering 47 (1-4) 285 - 287 1999 [Not refereed][Not invited]
  
• Formation of Size- and Position-Controlled Nanometer Size Pt Dots on GaAs and InP Substrates by Pulsed Electrochemical Deposition

  SATO Taketomo, KANESHIRO Chinami, OKADA Hiroshi, HASEGAWA Hideki

  Extended abstracts of the ... Conference on Solid State Devices and Materials 1998 74 - 75 1998/09/07
• Formation and control of Schottky contacts on compound semiconductors by in situ electrochemical process.

  KANESHIRO CHINAMI, SATO TAKETOMO, KOYAMA YUJI, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 98 (185(ED98 84-97)) 55 - 60 0913-5685 1998/07/22 [Not refereed][Not invited]
   

  Well-controlled Schottky contacts were successfully formed on compound semiconductors, such as GaAs, Inp and GaN, by an in situ electrochemical process. The fabricated diodes showed nearly ideal thermionic emission transport characteristics. In the initial stage of metal deposition, metal particles with a size of 20-30nm were formed on semiconductor surfaces. This process can realize oxide-, defect-, and stress-free metal-semiconductor interfaces, and Schottky barrier heights were found to be strongly dependent on metal workfunction.
• Fabrication of the Metal dot array by Electrochemical Process.

  SATO TAKETOMO, KANESHIRO CHINAMI, OKADA HIROSHI, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 98 (184(ED98 76-83)) 21 - 26 0913-5685 1998/07/21 [Not refereed][Not invited]
   

  Pt dot arrays were formed on n-GaAs by combining the electrochemical process with the electron-beam(EB) lithoghography. In order to define dot positions, dot-array windows were patterned on GaAs by EB lithography. It is possible to form the metal particles on only the opened areas of EB patterned substrates, thereby realizing precise dot-positions control. In this study, Pt particles with a diameter of 20nm could be formed in the center of each naked GaAs surface patterned with a period of 200nm. In the measurements by the AFM system with conductive probes, I-V characteristics of each Pt dots/n-GaAs contact showed rectifying behavior due to Schottky barrier formation.
• Strong correlation between interface microstructure and barrier height in N-InP Schottky contacts formed by in situ electrochemical process

  T Sato, C Kaneshiro, H Hasegawa

  1998 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS - CONFERENCE PROCEEDINGS 623 - 626 1092-8669 1998 [Refereed][Not invited]
   

  InP and related materials are attractive materials for high speed electronic and optoelectronic devices. Technologically, well-controllable metal/semiconductor (M/S) interface with high Schottky barrier heights (SBHs) in nano-scale are required for the realizability and the high reliability of nano-scaled electronic devices. However, metal/n-InP contacts generally produces low SBH values of typically about 450meV. SBH values can not be increased by using contact metals with large workfunctions due to so-called Fermi-level pinning. In contrast to this, we have recently shown that the SBH value of the Pt/n-InP contacts can be increased up to 860meV[1] by using an in situ pulsed electrochemical process. This process has also been shown to be useful for the Schottky gate formation for MESFETs and HEMTs[2,3]. The purpose of this paper is to optimize the electrochemical process for high SBHs by investigating the correlation between the microstructures of metal/n-InP interfaces having nano-scale metal particles and the SBHs.
• Highly controllable electrochemical etching of InP studied by voltammetry and scanned probe microscope

  C Kaneshiro, T Sato, H Hasegawa

  1998 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS - CONFERENCE PROCEEDINGS 191 - 194 1092-8669 1998 [Refereed][Not invited]
   

  Electrochemical etching of n-InP surfaces is studied by using voltammetry, XPS, in situ electrochemical STM, ex situ AFM and SEM measurements in order to characterize and optimize the etching process. The voltammograms indicated occurrence of the active-passive transition. The surfaces etched by the optimal anodic condition were clean and featureless with an rms roughness of 2.5 nm, whereas the surfaces obtained in the passive region were porous. The optimum avalanche pulse etching mode realized an extremely high etch depth controllability of 6 x 10(-5) nm/pulse.
• Electrochemical formation and characterization of Schottky in-plane and wrap gate structures for realization of GaAs- and InP-based quantum wires and dots

  H Hasegawa, T Sato, H Okada, K Jinushi, S Kasai, Y Satoh

  APPLIED SURFACE SCIENCE 123 335 - 338 0169-4332 1998/01 [Refereed][Not invited]
   

  In order to realize high temperature operating quantum devices, this paper attempts to form nm-size Schottky in-plane gate (IPG) and wrap gate (WPG) structures on GaAs- and InP-based nanostructures by an in-situ electrochemical process. Pulsed electrodeposition of Pt was found to be optimal, realizing nearly pinning-free high Schottky barrier heights as well as fine and highly uniform nm-size grains with minimal stress. Using the optimized process, quantum wire transistors and single electron transistors were successfully realized on GaAs etched 2DEG bars and on MBE grown InGaAs ridge quantum wires. (C) 1998 Elsevier Science B.V.
• Control of Schottky Barrier Heights on Indium Phosphite-Based Materials by In-Situ Electrochemical Process and Its Mechanism.

  SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 97 (158(ED97 65-74)) 13 - 18 0913-5685 1997/07/14 [Not refereed][Not invited]
   

  Well-controlled Schottky barriers were successfully formed on InP-based materials by a novel in-situ electrochemical process. The Pt contacts by this process realized oxide-, defect- and stress-free Schottky interfaces, resulting in substantially increased Schottky barrier heights (SBHs) of 0.86eV, 0.50eV and 0.89eV for n-InP, n-InAlAs and n-InGaAs, respectively. The mechanism of the SBH enhancement was explained by the disorder induced gap state (DIGS) model.
• Evolution mechanism of nearly pinning-free platinum/n-type indium phosphide interface with a high Schottky barrier height by in situ electrochemical process

  H Hasegawa, T Sato, T Hashizume

  JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 15 (4) 1227 - 1235 1997/07 [Refereed][Not invited]
   

  Recently, unusually high Schottky barrier heights (SBHs) have been realized by our group on n-type InP and related materials by an in situ electrochemical deposition of Pt. In an attempt to understand the underlying mechanism of the SBH enhancement, this article investigates in detail the evolution process of the metal (Pt, Ni, Co, and Ag)-InP interface during the in situ electrochemical process, using current-voltage, capacitance voltage, deep level transient spectroscopy, x-ray photoelectron spectroscopy, Raman, atomic force microscope, and scanning electron microscope measurements. Pt deposition by the electrochemical process realized an oxide-free, defect-free, stress-free, and nearly pinning-free interface, whereas Pt deposition by conventional electron beam evaporation and sputtering processes as well as Ag, Ni, and Co deposition by the electrochemical process gave rise to stressed and pinned interfaces. The observed large process dependence of SBH can be explained by none of the metal induced gap state model, the unified defect model, and the effective workfunction model. It is explained here by the disorder induced gap state model. (C) 1997 American Vacuum Society.
• Large Schottky barrier heights on indium phosphide-based materials realized by in-situ electrochemical process

  T Sato, S Uno, T Hashizume, H Hasegawa

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 36 (3B) 1811 - 1817 0021-4922 1997/03 [Refereed][Not invited]
   

  Pt Schottky barriers were formed on InP-based materials by a novel in-situ, electrochemical process. electrical characteristics, surfaces and interfaces of the Schottky diodes were investigated by current-voltage (IV), capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and atomic force microscopy (AFM) measurements. The mechanism for increasing the Schottky barrier heights (SBH) was explained in terms of possible ordered interface formation from the viewpoint of the disorder induced gap state (DIGS) model.
• Formation of pinning-free Schottky barriers on InP and related materials by novel in-situ electrochemical process and its mechanism

  T Sato, H Hasegawa

  1997 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS - CONFERENCE PROCEEDINGS 517 - 520 1092-8669 1997 [Refereed][Not invited]
   

  Recently the so-called InP-based materials such as InP, In0.52Al0.48As and In0.53Ga0.47As have become important materials for high speed electronic and optoelectronic devices. A common drawback of these materials is, however, that Schottky barrier heights (SBHs) on n-type materials are generally low. Typical SBH values are 0.45eV, 0.60eV and 0.20eV for n-InP, In0.52Al0.48As and In0.53Ga0.47As, respectively. Technologically low SBH values are problematic and impose severe limitations on the realizability of MESFETs and MSM photoditectors, and performance and reliability of HEMTs. In an attempt to overcome this difficulty, we have recently found that the SBH value of the Pt/n-InP Schottky diode can be increased up to 0.86 eV by using a novel in-situ electrochemical process,[1] and have succeeded in realization of well-behaved InP MESFETs[2] for the first time. The purpose of the present paper is further to understand and optimize the electrochemical process in view of its possible application to formation of fine Schottky gate electrodes for InP-based HEMTs utilizing InAlAs/InGaA s/InAlAs/InP heterostructures. First, electrodeposition conditions and metal selection were optimized for InP for higher SBHs. Then, applicability of the electrochemical process for formation of Schottky gate was confirmed directly on HEMT wafers. Finally, the possible mechanism for the observed SBH increase is briefly discussed.
• High Schottky Barrier Formation on Indium Phosphide-Based Materials by In-Situ Electrochemical Process.

  SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電子情報通信学会技術研究報告 一般社団法人電子情報通信学会 96 (352(ED96 112-119)) 9 - 15 0913-5685 1996/11/08 [Not refereed][Not invited]
   

  Pt Schottky barriers were formed on InP-based materials by a novel in-situ electrochemical process. The electrical characteristics, surfaces and interfaces of the Schottky diodes were investigated by I-V, C-V, DLTS and AFM measurements. The Schottky Barrier heights (SBHs) formed by this electrochemical process were much higher than those formed by the electron-beam (EB) deposition process. The mechanism for increase of SBH was explained by the disorder induced gap state (DIGS) model.
• Enhancement of Schottky Barrier Heights on Indium Phosphide-Based Materials by In-Situ Electrochemical Process and Its Mechanism

  SATO Taketomo, UNO Shouichi, HASHIZUME Tamotsu, HASEGAWA Hideki

  Extended abstracts of the ... Conference on Solid State Devices and Materials 1996 106 - 108 1996/08/26 [Not refereed][Not invited]
  
• Fabrication of high-performance InP MESFETs with in-situ pulse-plated metal gates

  S Uno, T Hashizume, T Sato, H Hasegawa

  1996 EIGHTH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS 338 - 341 1996 [Refereed][Not invited]
  

MISC

• 窒化物半導体の光電気化学エッチングと電子デバイス応用—Photo-electrochemical Etching of Nitride Semiconductors and Electron Device Applications—電子デバイス/半導体電力変換合同研究会・パワーデバイス・パワーエレクトロニクスとその実装技術

  佐藤 威友  電気学会研究会資料. SPC = The papers of technical meeting on semiconductor power converter, IEE Japan / 半導体電力変換研究会 [編]  2022-  (172-177・179-190)  61  -64  2022/12/01
• 窒化物半導体の光電気化学エッチングと電子デバイス応用—Photo-electrochemical Etching of Nitride Semiconductors and Electron Device Applications—電子デバイス/半導体電力変換合同研究会 パワーデバイス・パワーエレクトロニクスとその実装技術

  佐藤 威友  電気学会研究会資料. EDD = The papers of technical meeting on electron devices, IEE Japan / 電子デバイス研究会 [編]  2022-  (32-37・39-50)  61  -64  2022/12/01
• Fabrication of recessed-gate AlGaN/GaN HEMTs utilizing contactless photoelectrochemical (CL-PEC) etching (2)

  渡久地政周, 三輪和希, 堀切文正, 福原昇, 成田好伸, 市川磨, 磯野僚多, 田中丈士, 佐藤威友  応用物理学会春季学術講演会講演予稿集(CD-ROM)  68th-  2021
• Fabrication of recessed-gate AlGaN/GaN HEMTs utilizing contactless photoelectrochemical (CL-PEC) etching

  渡久地政周, 三輪和希, 堀切文正, 福原昇, 成田好伸, 市川磨, 磯野僚多, 田中丈士, 佐藤威友  応用物理学会春季学術講演会講演予稿集(CD-ROM)  67th-  2020
• 電気化学的手法によるⅢ-Ⅴ族半導体多孔質構造の形成と高感度化学センサへの応用

  佐藤 威友, 渡部 晃生, 熊崎 祐介  Proceedings of the Chemical Sensor Symposium  56-  64  -66  2014/03
• Electrochemical formation and sensor application of InP porous nanostructures

  SATO Taketomo, FUJINO Toshiyuki, HASHIZUME Tamotsu  IEICE technical report  107-  (110)  269  -272  2007/06/18  

  A two-step electrochemical process was developed to form high-density array of InP porous nanostructures. By the subsequent cathodic decomposition after the porous formation, the thickness of InP pore walls was precisely controlled in the nanometer-scale range from 30 to 15 nm, resulted in formation of the unique nanostructures with a high aspect ratio. The current response of the porous samples to a hydrogen peroxide (H_2O_2) was increased due to the large surface area, as compared with the planar InP substrate. The results indicate that the present nanostructures is promising for the application to bio-chemical sensors.
• Control of defect and impurity states at AlGaN surfaces for sensor application

  HASHIZUME T., KANEKO M., KOTANI J., KOKAWA T., KIMURA T., SATO T.  IEICE technical report  106-  (137)  93  -98  2006/06/26  

  We proposed a surface control process for suppressing tunneling leakage currents of Schottky contacts on AlGaN/GaN heterostrcutures. The process consisted of the nitrogen radical treatment, the deposition of an ultrathin Al layer, the UHV annealing and finally the removal of the Al layer. The Ni/Au Schottky gates fabricated on the processed AlGaN surfaces showed pronounced reduction of leakage current and clear temperature dependence of I-V curves. The H_2 gas-sensing characteristics of Pd Schottky diodes formed on AlGaN/GaN heterostructure were investigated. The Pd/AlGaN/GaN diode showed the systematic shift in the C-V curve for different partial pressure of H_2, keeping the shape of the curve approximately the same. The maximum shift in the threshold voltage obtained was about 1200mV which is much larger than 500mV reported for the Pd-based Si MOS sensors. Liquid-phase sensing characteristics of open-gate AlGaN/GaN HEMT structures were investigated in aqueous solutions. We observed a fine parallel shift in the transfer curves according to change in pH value in a solution, indicating the corresponding potential change at the AlGaN surface. The sensitivity for the potential change was 57.5mV/pH.

Books etc

• 半導体製造におけるウェット／ドライエッチング

  株)ISTL 礒部, 服部コンサルティングインターナショナル 服部, 毅, グロスバーグ合同会社, 大山, 聡, 式田 光宏, アドヒージョン(株, 河合 晃, サムコ(株, 中野 博彦, サムコ(株, 扇谷 浩通, 浜口, 智志, 豊田 紀章, 唐橋 一浩, 江利口 浩二, 寒川, 誠二, 株, 日立製作所, 篠田 和典, 佐藤 威友, 有馬, 健太 (Contributor第４章第３節GaNの光電気化学（PEC）エッチング)
  (株)R&D支援センター 2022/10 (ISBN: 9784905507611)
• Lateral Alignment of Epitaxial Quantum Dots

  HASEGAWA Hideki, SATO Taketomo, KASAI Seiya (Contributor24 Large-Scale Integration of Quantum Dot Devices on MBE-Based Quantum Wire Networks)
  Springer 2007

Presentations

• Self-terminating photo-electrochemical (PEC) etching for recessed-gate fabrication on AlGaN/GaN HEMTs  [Not invited]

  Takuya Togashi, Kosaku Ito, Taketomo Sato

  2022 International Conference on Solid State Devices and Materials (SSDM 2022)
• Mgドープp-GaNを用いたMOS構造のC-V特性に対する光電気化学エッチングの効果  [Not invited]

  忽滑谷 崇秀, 玉村 祐也, 久保 広大, 佐藤 威友, 赤澤 正道

  第83回応用物理学会秋季学術講演会
• 光電気化学(PEC)エッチングの自己停止とAlGaN/GaN HEMTのゲートリセス加工  [Not invited]

  富樫 拓也, 伊藤 滉朔, 越智 亮太, 佐藤 威友

  第83回応用物理学会秋季学術講演会
• n型及びp型GaN表面の電気化学的評価  [Not invited]

  高津 海, 久保 広太, 佐藤 威友

  第83回応用物理学会秋季学術講演会
• n-GaN加工表面に対するコンタクトレス光電気化学(CL-PEC)エッチング (2)  [Not invited]

  大澤 由斗, 大神 洸貴, 越智 亮太, 堀切 文正, 福原 昇, 佐藤 威友

  第83回応用物理学会秋季学術講演会
• Effect of parallel conduction on the current linearity of AlGaN/GaN MIS-HEMTs  [Not invited]

  Ryota Ochi, Tamotsu Hashizume, Taketomo Sato

  14th Topical Workshop on Heterostructure Microelectronics (TWHM2022)
• Contactless-Photoelectrochemical (CL-PEC) etching on process-damaged n-GaN surface

  Yoshito Osawa, Hiroki Ogami, Masachika Toguchi, Fumimasa Horikiri, Noboru Fukuhara, Taketomo Sato

  14th Topical Workshop on Heterostructure Microelectronics (TWHM2022)
• 電気化学反応を利用した窒化ガリウムのウェットエッチングと機能性材料  [Not invited]

  佐藤威友, 渡久地 政周

  電子情報通信学会電子デバイス研究会
• n-GaN加工損傷面に対するコンタクトレス光電気化学（CL-PEC）エッチング  [Not invited]

  大神洸貴, 大澤由斗, 渡久地政周, 堀切文正, 福原昇, 佐藤威友

  第69回応用物理学会春季学術講演会
• AlGaN/GaN MIS-HEMTsにおけるパラレル伝導評価  [Not invited]

  越智亮太, 橋詰保, 佐藤 威友

  第69回応用物理学会春季学術講演会
• Fabrication of Recessed-gate AlGaN/GaN HEMTs by Low-Damage Contactless Photo-Electrochemical Etching  [Invited]

  M. Toguchi, K. Miwa, F. Horikiri, N. Fukuhara, Y. Narita, O. Ichikawa, R. Isono, T. Tanaka, T. Sato

  4th International Symposium on Advanced Plasma Science and its Applications for Nitrides and Nanomaterials
• 低損傷コンタクトレス光電気化学エッチングを利用したリセスゲーAlGaN/GaN HEMTsの作製  [Not invited]

  渡久地 政周, 三輪 和希, 堀切 文正, 福原 昇, 成田 好伸, 市川 磨, 磯野 僚多, 田中 丈士, 佐藤 威友

  電子情報通信学会電子デバイス研究会
• 光電気化学エッチング法を用いたAlGaInN/AlGaN HFETの作製  [Not invited]

  伊藤 滉朔, 小松裕斗, 渡久地 政周, 井上暁喜, 田中さくら, 三好実人, 佐藤 威友

  電子情報通信学会電子デバイス研究会
• HfSiOx-gate AlGaN/GaN MOS HEMTs with improved operation stability  [Not invited]

  R. Ochi, T. Nabatame, T. Hashizume, T. Sato

  2021 International Conference on Solid State Devices and Materials
• 光電気化学エッチング法を用いたAlGaInN/AlGaNリセスゲートHFETの作製  [Not invited]

  伊藤滉朔, 小松裕斗, 渡久地政周, 井上暁喜, 三好実人, 佐藤威友

  第68回応用物理学会春季学術講演会
• コンタクトレス光電気化学エッチングによるリセスゲートAlGaN/GaN HEMT の作製  [Not invited]

  渡久地政周, 三輪和希, 堀切文正, 福原昇, 成田好伸, 吉田丈洋, 佐藤威友

  第68回応用物理学会春季学術講演会
• Precise control in threshold voltage of AlGaN/GaN HEMTs utilizing a photoelectrochemical (PEC) etching  [Not invited]

  T. Sato, M. Toguchi, K. Itoh, T. Hashizume

  The 8th Asian Conference on Crystal Growth and Crystal Technology (CGCT-8)
• Recessed-gate AlGaN/GaN HEMTs fabricated by photo-electrochemical (PEC) etching  [Not invited]

  T. Sato, T. Hashizume

  Virtual Workshop on Materials Science and Advanced Electronics Created by Singularity
• Cathode-electrode on photoelectrochemical (PEC) etching for n-GaN on n+GaN substrate

  福原昇, 堀切文正, 渡久地政周, 三輪和希, 大神洸貴, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2021
• 半導体ナノ構造を利用した高感度化学センサの開発（依頼講演）  [Invited]

  佐藤威友

  第6回北海道大学部局横断シンポジウム  2020/10
• Fabrication of Recessed-Gate AlGaN/GaN HEMTs Utilizing Contactless Photo-Electrochemical (CLPEC) Etching  [Not invited]

  M. Toguchi, K. Miwa, F. Horikiri, N. Fukuhara, Y. Narita, O. Ichikawa, R. Isono, T. Tanaka, T. Sato

  2020 Pacific Rim Meeting on Electrochemical and Solid State Science (PRiME 2020)
• Photo-Electrochemical Etching and Porosification of III-Nitride Semiconductors (Invited)  [Invited]

  T. Sato, M. Toguchi

  2020 Pacific Rim Meeting on Electrochemical and Solid State Science (PRiME 2020)
• GaN Wet Etching Process for HEMT Devices (invited)  [Invited]

  F. Horikiri, N. Fukuhara, M. Toguchi, T. Sato

  International symposium on Advanced Plasma Science and its Applications for Nitrides and Nanomaterials
• Characterization of ICP-RIE-processed n-GaN surface using an electrochemical method

  武田健太郎, 山田真嗣, 山田真嗣, 渡久地政周, 加地徹, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2020
• Thermal assisted contactless photoelectrochemical (PEC) etching for GaN

  堀切文正, 福原昇, 太田博, 浅井直美, 成田好伸, 吉田丈洋, 三島友義, 渡久地政周, 三輪和希, 大神洸貴, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2020
• Thermal-assisted generation of sulfate radicals for contactless photo electrochemical (PEC) etching of n-GaN

  三輪和希, 大神洸貴, 渡久地政周, 堀切文正, 福原昇, 成田好伸, 吉田丈洋, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2020
• 電気めっき法によるGaNへのPt電極の形成と電気特性評価

  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  2020
• Simple Photoelectrochemical Etching for Recess Gate GaN HEMT

  堀切文正, 福原昇, 渡久地政周, 三輪和希, 成田好伸, 市川磨, 磯野僚多, 田中丈士, 佐藤威友

  電子情報通信学会技術研究報告  2020
• Simple Photoelectrochemical Etching of GaN for RF Application  [Not invited]

  F. Horikiri, N. Fukuhara, Y. Narita, T. Yoshida, M. Toguchi, K. Miwa, T. Sato

  Materials Research Meeting 2019
• Contactless Photoelectrochemical Etching of n-GaN in K2S2O8 solution  [Not invited]

  M. Toguchi, K. Miwa, F. Horikiri, N. Fukuhara, Y. Narita, T. Yoshida, T. Sato

  Materials Research Meeting 2019
• Precise Control in Threshold Voltage of AlGaN/GaN HEMTs by Photoelectrochemical Etching  [Not invited]

  Y. Komatsu, M. Toguchi, T. Sato

  Materials Research Meeting 2019
• Fabrication of GaN nanowires by wet processes using electrodeless photo-assisted electro- chemical etching and alkaline solution treatment  [Not invited]

  M. Shimauchi, K. Miwa, M. Toguchi, T. Sato, J. Motohisa

  The 9th Asia-Pacific Workshop on Widegap Semiconductors
• Evaluation of Radical Production Rate from S2O82- ions for GaN Etching  [Not invited]

  M. Toguchi, K. Miwa, F. Horikiri, N. Fukuhara, Y. Narita, T. Yoshida, T. Sato

  The 9th Asia-Pacific Workshop on Widegap Semiconductors
• Simple Photoelectrochemical Etching for GaN HEMT Application  [Not invited]

  F. Horikiri, N. Fukuhara, Y. Narita, T. Yoshida, M. Toguchi, K. Miwa, T. Sato

  The 9th Asia-Pacific Workshop on Widegap SemiconductorsThe 9th Asia-Pacific Workshop on Widegap Semiconductors
• Precise control in recessed-gate etching for AlGaN/GaN HEMTs by utilizing photo- electrochemical reactions  [Not invited]

  Y. Komatsu, M. Toguchi, T. Sato

  The 9th Asia-Pacific Workshop on Widegap Semiconductors
• Wet Etching of III-V Compound Semiconductors – Focusing a Recent Topics on Nitride Semiconductors –  [Invited]

  Taketomo Sato, Masachika Toguchi

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• Fabrication GaN nanowires by electrodeless photo-assisted electrochemical etching and wet etching  [Not invited]

  Michihito Shimauchi, Kazuki Miwa, Masachika Toguchi, Taketomo Sato, Junichi Motohisa

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• Study on photo-electrochemical etching on high-doped n-type GaN substrates  [Not invited]

  Kazuki Miwa, Masachika Toguchi, Taketomo Sato

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• Photo-electrochemical (PEC) etching on AlGaInN/AlGaN heterostructures (2)  [Not invited]

  Y. Komatsu, M. Toguchi, S. Saito, M. Miyoshi, T. Sato

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• Contactless Photoelectrochemical Etching of n-GaN in K2S2O8/H3PO4 Mixed Solution  [Not invited]

  M. Toguchi, K. Miwa, F. Horikiri, N. Fukuhara, Y. Narita, T. Yoshida, T. Sato

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• Characterization of processed n-GaN surface using an electrochemical impedance spectroscopy (2)  [Not invited]

  Kentaro Takeda, Masachika Toguchi, Taketomo Sato

  2019 第80回 応用物理学会 秋季学術講演会  2019/09
• GaN Wet Etching Process for Power and RF Devices  [Invited]

  F. Horikiri, N. Fukuhara, H. Ohta, N. Asai, Y. Narita, T. Yoshida, T. Mishima, M. Toguchi, K. Miwa, T. Sato

  2019 International Conference on Solid State Devices and Materials  2019/09
• Characterization of processing-damage induced on n-GaN surface utilizing electrochemical methods  [Not invited]

  Kentaro Takeda, Masachika Toguchi, Taketomo Sato

  13th Topical Workshop on Heterostructure Microelectronics  2019/08
• Photo-electrochemical etching optimized for high-doped n-type GaN  [Not invited]

  Kazuki Miwa, Masachika Toguchi, Taketomo Sato

  13th Topical Workshop on Heterostructure Microelectronics  2019/08
• GaN Wet Etching Process  [Invited]

  Fumimasa Horikiri, Noboru Fukuhara, Hiroshi Ohta, Naomi Asai, Yoshinobu Narita, Takehiro Yoshida, Tomoyoshi Mishima, Masachika Toguchi, Kazuki Miwa, Taketomo Sato

  13th Topical Workshop on Heterostructure Microelectronics  2019/08
• 窒化物半導体の電気化学エッチングとデバイス応用（招待講演）  [Invited]

  日本表面真空学会 関西支部 合同セミナー２０１９  2019/07
• GaN Wet Etching Process for Power and RF Devices  [Invited]

  Fumimasa Horikiri, Noboru Fukuhara, Hiroshi Ohta, Naomi Asai, Yoshinobu Narita, Takehiro Yoshida, Tomoyoshi Mishima, Masachika Toguchi, Kazuki Miwa, Taketomo Sato

  2019 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices  2019/07
• Damage-less Wet Etching for Normally-off AlGaN/GaN HEMTs using Photo-electrochemical Reactions  [Invited]

  Taketomo Sato, Keisuke Uemura, Masachika Toguchi

  2019 International Conference on Compound Semiconductor Manufacturing Technology  2019/05  Minneapolis, USA
• Electrochemical characterization of etching damage induced to n-GaN surface  [Not invited]

  K. Takeda, M. Toguchi, T. Sato

  11th International Symposium on Advanced Plasma Science and its Applications for Nitride and Nanomaterials  2019/03
• Low-damage wet etching for AlGaN/GaN recessed-gate HEMTs using photo-electrochemical reactions  [Not invited]

  K. Uemura, Y. Komatsu, T. Sato

  11th International Symposium on Advanced Plasma Science and its Applications for Nitride and Nanomaterials  2019/03
• 光電気化学エッチングによる窒化ガリウムの微細加工の検討  [Not invited]

  島内道人, 三輪和希, 渡久地政周, 佐藤威友, 本久順一

  第66回応用物理学会春季学術講演会  2019/03
• AlGaInN/AlGaNヘテロ構造の光電気化学エッチング  [Not invited]

  小松祐斗, 植村圭佑, 佐藤威友

  第66回応用物理学会春季学術講演会  2019/03
• ペルオキソ二硫酸イオン(S2O82-)含有電解液におけるGaNの電気化学特性  [Not invited]

  渡久地政周, 三輪和希, 堀切文正, 福原昇, 成田好伸, 吉田丈洋, 佐藤威友

  第66回応用物理学会春季学術講演会  2019/03
• GaNの光電気化学（PEC）エッチングが有する可能性②コンタクトレスでのエッチング  [Not invited]

  堀切文正, 福原昇, 太田博, 浅井直美, 成田好伸, 吉田丈洋, 三島友義, 渡久地政周, 三輪和希, 佐藤威友

  第66回応用物理学会春季学術講演会  2019/03  東京工業大学大岡山キャンパス，東京都目黒区
• Effect of Photo-electrochemical Etching and Post-metallization Annealing on Gate-controllability of AlGaN/GaN High Electron Mobility Transistors  [Not invited]

  K. Uemura, M. Deki, Y. Honda, H. Amano, T. Sato

  International Workshop on Nitride Semiconductors 2018 (IWN2018)  2018/11
• Low-damage Etching for GaN-based Electronic Devices utilizing Photo-electrochemical Reactions  [Invited]

  SATO Taketomo

  4th Intensive Discussion on Growht of Nitride Semiconductors  2018/11
• Fabrication of GaN Porous Nanostructures utilizing Electrochemical Reactions  [Not invited]

  T. Sato

  HU-SNU Joint Symposium  2018/11
• Precise thickness control in recess-etching for normally-off AlGaN/GaN HEMTs using a photo-electrochemical reaction  [Not invited]

  K. Uemura, Y. Komatsu, T. Sato

  HU-SNU Joint Symposium  2018/11
• Electrochemical Formation and Application of Porous Gallium Nitride  [Invited]

  T. Sato, M. Toguchi

  Americas International Meeting on Electrochemistry and Solid State Science (AiMES 2018)  2018/10
• AlGaN/GaNヘテロ構造トランジスタを基盤とする高感度化学センサの検討  [Not invited]

  小松祐斗, 植村圭佑, 渡久地政周, 佐藤威友

  電気化学秋季大会講演要旨集(CD‐ROM)  2018/09
• 窒化ガリウム加工基板に対する選択的光電気化学エッチングの検討  [Not invited]

  渡久地政周, 武田健太郎, 佐藤威友

  電気化学秋季大会講演要旨集(CD‐ROM)  2018/09
• 電気化学インピーダンス法を用いたn‐GaN加工表面の評価  [Not invited]

  武田健太郎, 渡久地政周, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2018/09
• Recessed-gate AlGaN/GaN High Electron Mobility Transistors (HEMTs) Prepared by Photo-electrochemical Etching and Post-metallization Annealing  [Not invited]

  K. Uemura, M. Deki, Y. Honda, H. Amano, T. Sato

  第79 回応用物理学会秋季大会、19p-CE-4（日韓ジョイントシンポジウム  2018/09
• Control of Pore Depth in GaN Porous Structures Utilizing a Photoabsorption Process Under below-Bandgap Illumination  [Not invited]

  M. Toguchi, S. Matsumoto, T. Sato

  233rd ECS Meeting  2018/05
• Precisely-controlled etching of gallium nitride utilizing electrochemical reactions  [Invited]

  T. Sato, M. Toguchi

  Nanotech Malaysia 2018  2018/05
• 表面加工を施した窒化ガリウムの特異的光吸収特性と光電気化学エッチングの制御  [Not invited]

  渡久地政周, 佐藤威友

  電気化学会大会講演要旨集(CD-ROM)  2018/02
• 光電気化学反応を利用した窒化物半導体の低損傷エッチングと電子デバイスへの応用  [Not invited]

  植村圭佑, 松本悟, 渡久地政周, 伊藤圭亮, 佐藤 威友

  電子情報通信学会 電子デバイス研究会  2017/12
• Improved wet-etching processes for GaN-based electron devices  [Invited]

  T. Sato, K. Uemura, T. Hashizume

  2017 MRS Fall Meeting and Exhibit  2017/11
• Photo-electrochemical Formation of Porous Nanostructures on n-type GaN utilizing Franz-Keldysh Effect  [Not invited]

  M. Toguchi, S. Matsumoto, T. Sato

  The 8th International Symposium on Surface Science (ISSS8)  2017/10
• Removal of reactive-ion-etching damage from n-GaN surface using a photoelectrochemical process  [Not invited]

  S. Matsumoto, M. Toguchi, T. Sato

  2017 International Conference on Solid State Devices and Materials (SSDM 2017)  2017/09
• Franz‐Keldysh効果を用いた窒化ガリウムの光電気化学反応制御  [Not invited]

  渡久地政周, 佐藤威友

  電気化学秋季大会講演要旨集(CD‐ROM)  2017/08
• 光電気化学反応を利用したn‐GaN表面層の低損傷エッチング  [Not invited]

  松本悟, 佐藤威友, 成田哲生, 成田哲生, 加地徹, 橋詰保, 橋詰保

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2017/08
• 光電気化学(PEC)反応を利用したリセスゲートAlGaN/GaN HEMTの作製  [Not invited]

  植村圭佑, 佐藤威友, 橋詰保

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2017/08
• Highly-controllable etching for AlGaN/GaN recessed-gate structures utilizing low-damage electrochemical reactions  [Not invited]

  K. Uemura, Y. Kumazaki, T. Sato, T. Hashizume

  12th Topical Workshop on Heterostructure Microelectronics (TWHM 2017)  2017/08
• Precise thickness control in recess-etching for normally-off AlGaN/GaN HEMTs using a low damage photo-electrochemical reaction  [Not invited]

  T. Sato, K. Uemura, Y. Kumazaki, T. Hashizume

  12th International Conference on Nitride Semiconductors (ICNS 12)  2017/07
• 2段階異方性エッチングによる窒化ガリウム多孔質構造の形成と形状制御  [Not invited]

  佐藤威友, 熊崎祐介, 松本悟

  電気化学会大会講演要旨集(CD-ROM)  2017/03
• GaN多孔質構造の形状およびキャリア濃度の違いとインピーダンス特性について  [Not invited]

  伊藤圭亮, ZHANG Xiaoyi, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2017/03
• 光電気化学反応を利用したn‐GaN表面ダメージ層の除去  [Not invited]

  枝元将彰, 松本悟, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2017/03
• 電気化学堆積法によるCu₂O/InPヘテロ界面の形成(3)  [Not invited]

  近江沙也夏, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2017/03
• 電気化学的手法を用いたGaN多孔質構造の選択領域形成  [Not invited]

  松本悟, 熊崎祐介, 佐藤威友

  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  2017/01
• AlGaN/GaNヘテロ構造の電気化学的リセス加工における反応キャリア供給過程の影響  [Not invited]

  植村圭佑, 熊崎祐介, 佐藤威友

  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  2017/01
• GaN多孔質構造の形状によるインピーダンス特性の分析  [Not invited]

  伊藤圭亮, ZHANG Xiaoyi, 熊崎祐介, 佐藤威友

  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  2017/01
• Electrochemical formation of N-type GaN and N-type InP porous structures for chemical sensor applications  [Not invited]

  T. Sato, X. Zhang, K. Ito, S. Matsumoto, Y. Kumazaki

  IEEE SENSORS 2016  2016/11
• Precise Structural Tuning of Porous GaN Using Two-Step Anisotropic Etching for Optical and Photo-Electric Applications  [Not invited]

  Y. Kumazaki, S. Matsumoto, T. Sato

  2016 Pacific Rim Meeting on Electrochemistry and Solid State Science (PRiME 2016)  2016/10
• Electrochemical Formation and Characterization of Cu2O Films on n-type InP Porous Structures  [Not invited]

  S. Omi, Y. Kumazaki, T. Sato

  2016 Pacific Rim Meeting on Electrochemistry and Solid State Science (PRiME 2016)  2016/10
• GaN多孔質構造の選択領域形成に関する検討  [Not invited]

  松本悟, 熊崎祐介, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2016/09
• 電気化学堆積法によるCu₂O/InP多孔質構造ヘテロ界面の形成  [Not invited]

  近江沙也夏, 熊崎祐介, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2016/09
• 金属有機化合物分解法によるGaN表面へのNiO粒子の形成(2)  [Not invited]

  喜田弘文, 伊藤圭亮, 熊崎祐介, 渡久地政周, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2016/09
• 電気化学インピーダンス分光法によるGaN多孔質構造の評価  [Not invited]

  伊藤圭亮, ZHANG Xiaoyi, 喜田弘文, 熊崎祐介, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2016/09
• AlGaN/GaNヘテロ構造の光電気化学特性と低損傷加工技術への応用  [Not invited]

  熊崎祐介, 植村圭佑, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2016/09
• 電気化学堆積法によるCu₂O/InPヘテロ界面の形成  [Not invited]

  近江沙也夏, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2016/03
• 異方性ウェットエッチングによるGaN多孔質構造の作製と光学特性評価  [Not invited]

  熊崎祐介, 松本悟, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2016/03
• 金属有機化合物分解法によるGaN表面へのNiO粒子の形成  [Not invited]

  喜田弘文, 伊藤圭亮, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2016/03
• 光電気化学反応を利用したGaN表面の陽極酸化  [Not invited]

  枝元将彰, 熊崎祐介, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2016/03
• Interface control technologies for high-power GaN transistors: Self-stopping etching of p-GaN layers utilizing electrochemical reactions  [Invited]

  T. Sato, Y. Kumazaki, M. Edamoto, M. Akazawa, T. Hashizume

  SPIE Photonics West 2016  2016/02
• Photoelectric energy conversion in GaN porous nanostructures formed by electrochemical process  [Invited]

  T. Sato, Y. Kumazaki, T. Hashizume

  Energy, Materials and Nanotechnology  2015/12
• Size-controlled formation of high-aspect ratio porous nanostructures on GaN substrates utilizing photo-assisted electrochemical etching for photovoltaic applications  [Not invited]

  Y. Kumazaki, Z. Yatabe, T. Sato

  2015 MRS Fall Meeting & Exhibit  2015/11
• Effect of High Electric Field on Photoabsorption Properties of GaN Porous Structures  [Not invited]

  T. Sato, Y. Kumazaki, Z. Yatabe

  228th ECS meeting, Hyatt Regency Phoenix and Phoenix Convention Center  2015/10
• Formation of Self-aligned Pore Arrays on n-GaN Substrates by Photo-assisted Electrochemical Etching Process  [Not invited]

  Y. Kumazaki, T. Sato, Z. Yatabe

  2015 International Conference on Solid State Devices and Materials (SSDM 2015)  2015/09
• 裏面光照射電気化学法によるGaN陽極酸化表面の分析  [Not invited]

  枝元将彰, 熊崎祐介, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2015/08
• 電気化学堆積法によるCu₂O/InPヘテロ構造の形成と特性評価  [Not invited]

  近江沙也夏, 熊崎祐介, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2015/08
• Cu₂O/GaNヘテロ構造の電気化学形成と光学的特性評価  [Not invited]

  熊崎祐介, 近江沙也夏, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2015/08
• 光触媒水分解システムを用いたn‐GaN多孔質構造の光電気化学的評価  [Not invited]

  喜田弘文, 熊崎祐介, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2015/08
• High-selective etching of p-GaN layers on AlGaN/GaN heterostructures by electrochemical process  [Not invited]

  M. Edamoto, Y. Kumazaki, Z. Yatabe, T. Sato, T. Hashizume

  11th Topical Workshop on Heterostructure Microelectronics (TWHM 2015)  2015/08
• Electrochemical Formation of Cu2O Films on n-type InP and n-type GaN Substrates  [Not invited]

  S. Omi, Y. Kumazaki, Z. Yatabe, T. Sato

  11th Topical Workshop on Heterostructure Microelectronics (TWHM 2015)  2015/08
• Photoelectrochemical characterization of n-type GaN porous structures for use in photocatalytic water-splitting system  [Not invited]

  H. Kida, Y. Kumazaki, Z. Yatabe, T. Sato

  11th Topical Workshop on Heterostructure Microelectronics (TWHM 2015)  2015/08
• Influence of dry etching on Al2O3/AlGaN/GaN MOS interface properties  [Not invited]

  Z. Yatabe, J. Ohira, T. Sato, T. Hashizume

  11th Topical Workshop on Heterostructure Microelectronics (TWHM 2015)  2015/08
• Electrochemical formation of GaN porous structures for photocatalytic applications  [Invited]

  T. Sato, Y. Kumazaki, Z. Yatabe

  11th Topical Workshop on Heterostructure Microelectronics (TWHM 2015)  2015/08
• Electrochemical formation and UV photoresponse properties of GaN porous structures  [Not invited]

  喜田弘文, 熊崎祐介, 谷田部然治, 佐藤威友

  電子情報通信学会技術研究報告  2015/07
• Spectro-electrochemical characterization of GaN/electrolyte interface and its application to the nanostructure formation  [Not invited]

  熊崎祐介, 渡部晃生, 谷田部然治, 佐藤威友

  電子情報通信学会技術研究報告  2015/05
• ドライエッチングがAl₂O₃/AlGaN/GaN構造のMOS界面特性に与える影響  [Not invited]

  谷田部然治, 大平城二, 佐藤威友, 橋詰保

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2015/02
• 電気化学堆積法によるCu₂O/GaNヘテロ構造の形成と特性評価  [Not invited]

  熊崎祐介, 近江沙也夏, 谷田部然治, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2015/02
• 電気化学エッチングによるGaN多孔質構造の形成  [Not invited]

  渡部晃生, 熊崎祐介, 谷田部然冶, 佐藤威友

  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  2015/01
• デバイス応用に向けた6H‐SiC上グラフェンの高品質・多機能化  [Not invited]

  宮本貴雄, 小西敬太, 佐藤威友

  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  2015/01
• Correlation between growth time and carrier density in epitaxial graphene on 6H-SiC  [Not invited]

  T. Miyamoto, K. Konishi, T. Sato

  The 7th International Symposium on Surface Science (ISSS2014)  2014/11
• Structural Properties and Control of GaN Porous Nanostructures Formed by Photo-assisted Electrochemical Process  [Not invited]

  A. Watanabe, Y. Kumazaki, Z. Yatabe, T. Sato

  The 7th International Symposium on Surface Science (ISSS2014)  2014/11
• Enhanced spin-orbit interaction in the hydrogenated epitaxial graphene on silicon carbide  [Not invited]

  K. Konishi, T. Miyamoto, K. Yoh, T. Sato

  27th International Microprocesses and Nanotechnology Conference (MNC2014)  2014/11
• Electrochemical Formation of GaN Porous Structures Under UV-Light Irradiation for Photoelectrochemical Application  [Not invited]

  T. Sato, A. Watanabe, Y. Kumazaki, Z. Yatabe

  2014 ECS and SMEQ Joint International Meeting  2014/10
• 電気化学エッチングを用いた窒化物半導体多孔質構造の形成  [Not invited]

  渡部晃生, 熊崎祐介, 谷田部然治, 佐藤威友

  電気化学秋季大会講演要旨集  2014/09
• III‐V族化合物半導体の電気化学エッチングと微細加工への応用  [Not invited]

  佐藤威友, 熊崎祐介, 渡部晃生, 谷田部然治

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2014/09
• 6H‐SiC上グラフェンにおける成長時間とキャリア密度の関係  [Not invited]

  宮本貴雄, 小西敬太, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2014/09
• 電気化学エッチングによるGaN多孔質構造の形成と形状制御の向上  [Not invited]

  熊崎祐介, 渡部晃生, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2014/09
• Correlation between Structural and Optical Properties of GaN Porous Structures Formed by Photo-assisted Electrochemical Etching  [Not invited]

  Y. Kumazaki, A. Watanabe, Z. Yatabe, T. Sato

  The International Workshop on Nitride Semiconductors 2014 (IWN2014)  2014/08
• Interface Trap States in Al2O3/AlGaN/GaN Structure Induced by ICP Etching of AlGaN Surfaces  [Invited]

  Z. Yatabe, T. Sato, T. Hashizume

  The International Workshop on Nitride Semiconductors 2014 (IWN2014)  2014/08
• Structural control of GaN porous structures for high-sensitive chemical sensors  [Not invited]

  A. Watanabe, Y. Kumazaki, Z. Yatabe, T. Sato

  The 6th IEEE International Nanoelectronics Conference 2014 (INEC-2014)  2014/07
• Electrochemical Formation of III-V Semiconductor Porous Nanostructures  [Invited]

  T. Sato, Y. Kumazaki, A. Watanabe, Z. Yatabe

  The 6th IEEE International Nanoelectronics Conference 2014 (INEC-2014)  2014/07
• 電気化学的手法によるIII-V族半導体多孔質構造の形成と高感度化学センサへの応用  [Not invited]

  SATO Taketomo, WATANABE Akio, KUMAZAKI Yusuke

  公益社団法人電気化学会第81回大会  2014/03
• ELECTROCHEMICAL FORMATION OF III-V SEMICONDUCTOR POROUS STRUCTURES FOR HIGHT-SENSITIVE SENSOR APPRICATIONS  [Not invited]

  佐藤威友, 渡部晃生, 熊崎祐介

  Chem Sens  2014/03
• GaNパワー素子のための絶縁膜界面制御  [Invited]

  HASHIZUME Tamotsu, YATABE Zenji, SATO Taketomo

  電気学会電子デバイス研究会  2014/03
• 窒化物半導体異種接合の評価と制御  [Invited]

  佐藤威友, 赤澤正道, 橋詰保

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2014/03
• AlGaN/GaNヘテロ構造上に形成したp‐GaN層の選択的電気化学エッチング  [Not invited]

  熊崎祐介, 佐藤威友, 橋詰保, 橋詰保

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2014/03
• GaN多孔質構造の形状制御と化学センサへの応用  [Not invited]

  渡部晃生, 熊崎祐介, 谷田部然冶, 佐藤威友

  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  2013/12
• Photoabsorption and Photoelectric Conversion Properties of InP Porous Structures Formed by Electrochemical Process  [Not invited]

  SATO Taketomo, KUMAZAKI Yusuke, JINBO Ryohei, YATABE Zenji

  224th Meeting of the Electrochemical Society（CD-ROM）  2013/10
• Structural and Optical Characterization of GaN Porous Structures Formed by Photo-assisted Electrochemical Process  [Not invited]

  KUMAZAKI Yusuke, WATANABE Akio, YATABE Zenji, SATO Taketomo

  224th Meeting of the Electrochemical Society（CD-ROM）  2013/10
• 電気化学的手法と裏面光照射によるGaN多孔質ナノ構造の形成  [Not invited]

  渡部晃生, 熊崎祐介, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2013/08
• GaN多孔質ナノ構造の表面形状と光電気化学特性  [Not invited]

  熊崎祐介, 渡部晃生, 谷田部然治, 佐藤威友

  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  2013/08
• Selective etching of p-GaN layers for normally-off AlGaN/GaN HEMTs by electrochemical process  [Not invited]

  KUMAZAKI Yusuke, AZUMAISHI Naoki, UEDA Hiroyuki, KANECHIKA Masakazu, TOMITA Hidemoto, SATO Taketomo, HASHIZUME Tamotsu

  10th International Conference on Nitride Semiconductors (ICNS-10)  2013/08
• Electrochemical Formation and Optical Characterization of GaN Porous Structures  [Not invited]

  KUMAZAKI Yusuke, WATANABE Akio, JINBO Ryohei, YATABE Zenji, SATO Taketomo

  32nd Electronic Materials Symposium (EMS32)  2013/07
• 電気化学的手法による半導体多孔質構造の形成と機能素子への応用  [Invited]

  SATO Taketomo

  第 29 回ライックセミナー・第 19 回若手研究者交流会  2013/06
• 電気化学的手法によるGaN多孔質構造の形成と光学特性の評価  [Not invited]

  KUMAZAKI Yusuke, WATANABE Akio, YATABE Zenji, SATO Taketomo

  第 29 回ライックセミナー・第 19 回若手研究者交流会  2013/06
• Photoabsorption and Photoelectric Conversion Properties of InP Porous Structures Formed by the Electrochemical process  [Not invited]

  KUMAZAKI YUSUKE, JIMBO RYOHEI, YATABE ZENJI, SATO TAKETOMO

  電子情報通信学会技術研究報告  2013/05
• Electrochemical Formation and Optical Characterization of GaN Porous Structures  [Not invited]

  KUMAZAKI Yusuke, WATANABE Akio, JINBO Ryohei, YATABE Zenji, SATO Taketomo

  The 40th International Symposium on Compound Semiconductors (ISCS2013)  2013/05
• 電気化学的手法によるGaN多孔質構造の形成と光学特性の評価  [Not invited]

  熊崎祐介, 渡部晃生, 神保亮平, 谷田部然治, 佐藤威友

  応用物理学会春季学術講演会講演予稿集(CD-ROM)  2013/03
• InP多孔質構造孔壁表面の機能化による光電変換素子への応用  [Not invited]

  神保亮平, 渡部晃生, 佐藤威友

  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  2013/01
• High-sensitive ISFETs Based on Semiconductor Porous Nanostructures  [Invited]

  SATO Taketomo

  BIT’s 3rd Annual World Congress of NanoMedicine-2012  2012/11
• Photoelectric-conversion Devices Based on InP Porous Structure  [Not invited]

  SATO Taketomo, JINBO Ryohei, YATABE Zenji

  2012 Pacific Rim Meeting on Electrochemical and Solid-State Science  2012/10
• Optical Absorption Properties of InP Porous Structures Formed by Electrochemical Process  [Not invited]

  KUMAZAKI Yusuke, KUDO, Tomohito, YATABE Zenji, SATO Taketomo

  2012 International Conference on Solid State Devices and Materials  2012/09
• pn接合基板上に形成したInP多孔質構造の光学応答特性の評価  [Not invited]

  熊崎祐介, 工藤智人, 谷田部然冶, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2012/08
• ポリスチレン微小球の自己組織化配列とリソグラフィ技術を利用した半導体加工基板の作製  [Not invited]

  神保亮平, 今井雄大, 谷田部然治, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2012/08
• 電気化学的手法によるInP多孔質構造の形成と孔の位置制御  [Not invited]

  神保亮平, 谷田部然冶, 佐藤威友

  応用物理学関係連合講演会講演予稿集(CD-ROM)  2012/02
• Photo-electrical response of InP porous structures formed on pn substrates  [Not invited]

  KUDO Tomohito, SATO Taketomo

  Extended Abstracts of the 2011 International Symposium on Surface Science  2011/12
• Photoelectric Conversion Devices based on InP Porous Structures  [Not invited]

  JINBO Ryohei, KUDO Tomohito, SATO Taketomo

  Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials  2011/09
• 電気化学的手法を用いたInP多孔質構造の形成と光電変換素子への応用  [Not invited]

  神保亮平, 岡崎拓行, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2011/08
• pn接合基板に形成したInP多孔質構造の光応答特性  [Not invited]

  工藤智人, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2011/08
• ポリスチレン微小球の自己組織化配列とリソグラフィ技術を利用した多孔質構造の形成  [Not invited]

  今井雄大, 神保亮平, 谷田部然治, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2011/08
• ドライエッチしたGaNおよびAlGaN表面の評価と制御  [Not invited]

  谷田部然冶, 東石直樹, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集(CD-ROM)  2011/08
• ポリスチレン微小球の自己組織化配列とリソグラフィ技術を利用した半導体パターニング技術  [Not invited]

  今井雄大, 岡崎拓行, 佐藤威友

  応用物理学関係連合講演会講演予稿集(CD-ROM)  2011/03
• InP多孔質構造を利用した光電変換素子の検討  [Not invited]

  工藤智人, 岡崎拓行, 佐藤威友

  応用物理学関係連合講演会講演予稿集(CD-ROM)  2011/03
• 電気化学的手法によるInPポーラス孔壁表面の機能化と電気的特性の評価  [Not invited]

  岡崎拓行, 神保亮平, 佐藤威友

  化学系学協会北海道支部冬季研究発表会講演要旨集  2011/02
• ポリスチレン微小球の自己組織化配列を利用した半導体マイクロパターニング技術  [Not invited]

  今井雄大, 岡崎拓行, 佐藤威友

  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  2011/01
• pn接合基板上に形成したInP多孔質構造の光応答特性  [Not invited]

  工藤智人, 岡崎拓行, 佐藤威友

  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  2011/01
• High-Sensitive ISFETs based on InP Porous Structures  [Not invited]

  SATO Taketomo, YOSHIZAWA Naoki

  The 61st Annual Meeting of the International Society of Electrochemistry（CD-ROM）  2010/09
• 電気化学的手法によるInP多孔質構造の形成と孔壁表面の機能化  [Not invited]

  岡崎拓行, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2010/08
• ポリスチレン微小球の自己組織化配列を利用したマイクロパターニングと半導体微細加工への応用  [Not invited]

  今井雄大, 岡崎拓行, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2010/08
• InP多孔質構造の光吸収特性と光電変換  [Not invited]

  佐藤威友, 岡崎拓行

  応用物理学会学術講演会講演予稿集(CD-ROM)  2010/08
• 多孔質構造を有するイオン感応性電界効果トランジスタ  [Not invited]

  佐藤威友, 岡崎拓行

  応用物理学会学術講演会講演予稿集(CD-ROM)  2010/08
• pn接合基板上に形成したInP多孔質構造の電気的評価  [Not invited]

  工藤智人, 岡崎拓行, 佐藤威友

  応用物理学会学術講演会講演予稿集(CD-ROM)  2010/08
• Optical and Electrical Properties of InP Porous Structures Formed on P-N Substrates  [Not invited]

  OKAZAKI Hiroyuki, SATO Taketomo, YOSHIZAWA Naoki, HASHIZUME Tamotsu

  2010 International Conference on Indium Phosiphide and Related Materials  2010/05
• 電気化学的手法を用いて形成したInPポーラス構造の電気的特性  [Not invited]

  岡崎拓行, 吉澤直樹, 佐藤威友, 橋詰保

  応用物理学関係連合講演会講演予稿集(CD-ROM)  2010/03
• Optical and electrical properties of InP porous structures formed on p-n substrates  [Not invited]

  OKAZAKI Hiroyuki, YOSHIZAWA Naoki, SATO Taketomo, HASHIZUME Tamotsu

  2010 International RCIQE/CREST Joint Workshop  2010/03
• InP‐pn接合基板へのポーラス構造作製と形状および位置の制御  [Not invited]

  岡崎拓行, 吉澤直樹, 佐藤威友

  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  2010/01
• InP‐pn接合基板へのポーラス構造形成および電気的特性評価  [Not invited]

  吉澤直樹, 岡崎拓行, 佐藤威友, 橋詰保

  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  2010/01
• Low Reflectance Surface Observed on InP Porous Structures after Photoelectrochemical Etching  [Not invited]

  SATO Taketomo, YOSHIZAWA Naoki, OKAZAKI Hiroyuki, HASHIZUME Tamotsu

  216th Meeting of the Electrochemical Society（CD-ROM）  2009/10
• InP‐pn接合基板へのポーラス構造作製と形状制御  [Not invited]

  岡崎拓行, 吉澤直樹, 佐藤威友

  応用物理学会学術講演会講演予稿集  2009/09
• ポーラス構造を形成したInP‐pn接合基板の電気的特性  [Not invited]

  吉澤直樹, 岡崎拓行, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2009/09
• Formation and application of InP porous structures on p-n substrates  [Not invited]

  SATO Taketomo, YOSHIZAWA Naoki, OKAZAKI Hiroyuki, HASHIZUME Tamotsu

  2009 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices（CD-ROM）  2009/06
• pH Response Characteristics of Liquid-phase Chemical Sensors using InP Open-gate FETs  [Not invited]

  YOSHIZAWA Naoki, SATO Taketomo, MIZOHATA Akinori, HASHIZUME Tamotsu

  2009 RCIQE International Seminar on "Advanced Semiconductor Materials and Devices"  2009/03
• Electrochemical formation and sensor application of InP porous nanostructures  [Not invited]

  SATO Taketomo, MIZOHATA Akinori, YOSHIZAWA Naoki, HASHIZUME Tamotsu

  2009 RCIQE International Seminar on "Advanced Semiconductor Materials and Devices"  2009/03
• pH Sensitivity of Liquid-phase Chemical Sensors using InP Open-gate FETs  [Not invited]

  YOSHIZAWA Naoki, SATO Taketomo, MIZOHATA Akinori, HASHIZUME Tamotsu

  2008 International Symposium on Surface Science and Nanotechnology  2008/11
• Liquid-phase Chemical Sensors using InP-based Open-gate FETs  [Not invited]

  YOSHIZAWA Naoki, SATO Taketomo, MIZOHATA Akinori

  The Seventh IEEE Conference on Sensors  2008/10
• Complete Removal of Irregular Top Layer for Sensor Applications of InP Porous Nanostructures  [Not invited]

  SATO Taketomo, MIZOHATA Akinori, YOSHIZAWA Naoki, HASHIZUME Tamotsu

  2008 Pacific Rim Meeting on Electrochemicao and Solid-State Science (CD-ROM)  2008/10
• InPイオン感応性電界効果トランジスタのpH応答特性  [Not invited]

  吉澤直樹, 溝畑彰規, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2008/09
• グリコール水溶液を用いた陽極酸化によるGaN表面の電気的・光学的安定化  [Not invited]

  塩崎奈々子, 塩崎奈々子, 佐藤威友, 佐藤威友, 橋詰保, 橋詰保

  応用物理学会学術講演会講演予稿集  2008/09
• InPポーラス構造を基盤とする電流検出型化学センサの作製  [Not invited]

  溝畑彰規, 吉澤直樹, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2008/09
• 電気化学プロセスによるInPポーラス構造の形成と縦および横方向へのエッチング制御  [Not invited]

  佐藤威友, 溝畑彰規, 吉澤直樹, 橋詰保

  応用物理学会学術講演会講演予稿集  2008/09
• Electrochemical formation and functionalization of InP porous nanostructures and their application to chemical sensors  [Not invited]

  MIZOHATA Akinori, YOSHIZAWA Naoki, SATO Taketomo, HASHIZUME Tamotsu

  2008 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices  2008/07
• 電気化学的手法によるGaN表面酸化膜形成と表面安定化への応用  [Not invited]

  塩崎奈々子, 佐藤威友, 橋詰保

  応用物理学関係連合講演会講演予稿集  2008/03
• 電気化学的手法によるInP表面の機能性修飾と電流検出型化学センサへの応用  [Not invited]

  溝畑彰規, 佐藤威友, 橋詰保

  応用物理学関係連合講演会講演予稿集  2008/03
• Electrochemical formation and sensor application of highly-ordered InP nanostructures  [Not invited]

  SATO Taketomo, MIZOHATA Akinori, YOSHIZAWA Naoki, HASHIZUME Tamotsu

  2008 RCIQE International Seminar on "Advanced Semiconductor Materials and Devices"  2008/03
• 電気化学的手法によるInP表面の機能性修飾と化学センサへの応用  [Not invited]

  溝畑彰規, 佐藤威友, 橋詰保

  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  2008/01
• 陽極酸化によりn‐GaN上に形成された酸化膜の評価と応用  [Not invited]

  塩崎奈々子, 石川史太郎, TRAMPERT A, GRAHN H. T, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2007/09
• 電気化学的手法によるInPポーラスナノ構造の形成と化学センサへの応用  [Not invited]

  佐藤威友, 溝畑彰規, 橋詰保

  応用物理学会学術講演会講演予稿集  2007/09
• グリコール水溶液を用いた電気化学プロセスによるGaN表面酸化薄膜の形成  [Not invited]

  塩崎奈々子, 佐藤威友, 橋詰保

  応用物理学関係連合講演会講演予稿集  2007/03
• 二段階電気化学プロセスによるInPナノ構造の形成とサイズ制御  [Not invited]

  佐藤威友, 佐藤威友, 藤野敏幸, 藤野敏幸, 橋詰保, 橋詰保

  応用物理学関係連合講演会講演予稿集  2007/03
• SiNx/CN/GaN構造を用いた炭素固相拡散の検討  [Not invited]

  木村健, 佐藤威友, 橋詰保

  応用物理学関係連合講演会講演予稿集  2007/03
• Electrochemical formation and optical characterization of size-controlled InP porous nanostructures  [Not invited]

  SATO Taketomo, FUJINO Toshiyuki, HASHIZUME Tamotsu

  The 4th International Symposium on Ubiquitous Knowledge Network Environment, Meme-Media Technology Approach to the R&D of Next-Generation Information Technologies  2007/03
• Chemical sensors using open-gate AlGaN/GaN transistor structures  [Not invited]

  KOKAWA Takuya, SATO Taketomo, HASHIZUME Tamotsu

  The 4th International Symposium on Ubiquitous Knowledge Network Environment, Meme-Media Technology Approach to the R&D of Next-Generation Information Technologies  2007/03
• Electrochemical formation of high-density array of InP nanostructures  [Not invited]

  SATO TAKATOMO

  2007 RCIQE International Seminar on "Advanced Semiconductor Materials and Devices"  2007/02
• Electrochemical Formation and Sensor Application of InP Porous Nanostructures  [Not invited]

  2007 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices  2007
• Electrochemical Formation of InP Porous Nanostructures and Its Application to Amperometric Chemical Sensors  [Not invited]

  2007 European Materials Research Society Fall Meeting  2007
• 電気化学的連続プロセスによるInPポーラス構造のサイズ制御  [Not invited]

  藤野敏幸, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2006/08
• 電気化学プロセスを施したGaNおよびAlGaN表面構造の評価  [Not invited]

  塩崎奈々子, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2006/08
• ヘキサゴナルBDD回路高密度実装に適した化合物半導体ナノ細線デバイスの検討  [Not invited]

  田村隆博, 葛西誠也, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2006/08
• AlGaN/GaNオープンゲートHFETの溶液中でのふるまい  [Not invited]

  古川拓也, 佐藤威友, 橋詰保

  応用物理学会学術講演会講演予稿集  2006/08
• Ptショットキーゲートを用いた高感度InP水素センサーの検討  [Not invited]

  木村健, 佐藤威友, 橋詰保, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2006/03
• AlGaN/GaNオープンゲートFETを用いた化学センサ  [Not invited]

  古川拓也, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学関係連合講演会講演予稿集  2006/03
• 陽極酸化エッチングプロセスを用いた化合物半導体微細構造の作製  [Not invited]

  塩崎奈々子, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学関係連合講演会講演予稿集  2006/03
• 加工基板へのGaN/AlGaNヘテロ構造の選択的MBE成長と埋め込み細線の形成  [Not invited]

  佐藤威友, 佐藤威友, 及川武, 及川武, 長谷川英機, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2006/03
• MBE選択成長GaAsヘキサゴナルネットワークの形成とBDD節点デバイスの集積化  [Not invited]

  田村隆博, 玉井功, 葛西誠也, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学関係連合講演会講演予稿集  2006/03
• 電気化学プロセスにより作製したInPナノ構造の光学的特性  [Not invited]

  藤野敏幸, 木村健, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学関係連合講演会講演予稿集  2006/03
• Optical Properties of Size-controlled Porous Nanostructures Formed on n-InP (001) Substrates by Electrochemical Process  [Not invited]

  FUJINO Toshiyuki, SATO Taketomo, HASHIZUME Tamotsu

  2006 International Conference on Solid State Devices and Materials  2006
• Self-assembled Formation of Uniform Arrays of InP Nanopores and Nanowires by Electrochemical Process  [Not invited]

  SATO Taketomo, FUJINO Toshiyuki, HASHIZUME Tamotsu

  210th Meeting of the Electrochemical Society  2006
• Self-Assembled Formation of Uniform Arrays of InP Nanopores and Nanowires by Electrochemical Process  [Not invited]

  210th Joint International Meeting of Electrochemical Society  2006
• Selective MBE Growth of Shape- Size- and Position- Controlled GaAs Nanowire Networks on (111)B Patterned Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  International Semiconductor Device Research Symposium  2005/12
• Self-Organized Formation of Chaotic and Regular Nanostructures on (001) and (111) InP Substrates by Electrochemical Anodization Process  [Not invited]

  FUJINO Toshiyuki, KIMURA Takeshi, SATO Taketomo, HASEGAWA Hideki, HASHIZUME Tamotsu

  International Symposium on Surface Science and Nanotechnology  2005/11
• Growth Simulation and Actual MBE Growth of Triangular GaAs Nanowires on Patterned (111)B Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki, HASHIZUME Tamotsu

  International Symposium on Surface Science and Nanotechnology  2005/11
• Embedded Nanowire Network Growth and Node Device Fabrication for GaAs-Based High-Density Hexagonal BDD Quantum Circuits  [Not invited]

  TAMURA Takahiro, TAMAI Isao, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki, HASHIZUME Tamotsu

  2005 Solid State Devices and Materials  2005/09
• Sensing Mechanism of InP Hydrogen Sensors Using Pt Schottky Diodes Formed by Electrochemical Process  [Not invited]

  KIMURA Takeshi, HASEGAWA Hideki, SATO Taketomo, HASHIZUME Tamotsu

  2005 Solid State Devices and Materials  2005/09
• MBE選択成長GaAs量子細線ネットワークの形成とヘキサゴナルBDD回路応用への検討  [Not invited]

  田村隆博, 玉井功, 葛西誠也, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• RF‐MBE法によるGaN(0001)加工基板へのAlGaN/GaN成長と,その選択性  [Not invited]

  及川武, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• 電気化学プロセスによるInPポーラス構造の形成と制御  [Not invited]

  藤野敏幸, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• (001)面メサ型加工基板への選択的MBE成長によるGaAs/AlGaAs細線の形成機構  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学会学術講演会講演予稿集  2005/09
• Pt/InPショットキーダイオードによる水素センシングのメカニズム考察  [Not invited]

  木村健, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• 陽極酸化とエッチングプロセスによるGaAs,AlGaAs微細加工の検討  [Not invited]

  塩崎奈々子, 佐藤威友, 赤沢正道, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• MBE選択成長法を用いたGaAs(111)B加工基板へのGaAs/AxGa1-xAs量子細線の形成  [Not invited]

  玉井功, 佐藤威友, 長谷川英機, 橋詰保

  応用物理学会学術講演会講演予稿集  2005/09
• Precisely Controlled Anodic Etching for Processing of GaAs-based Quantum Nanostructures and Devices  [Not invited]

  SHIOZAKI Nanako, SATO Taketomo, AKAZAWA Masamichi, HASEGAWA Hideki

  10th International Conference on the Formation of Semiconductor Interfaces (ICFSI-10)  2005/07
• Selective MBE growth ofAlGaN/GaN quantum wire structures on pre-patterned GaN (0001) substrates and its growth mechanism  [Not invited]

  OIKAWA Takeshi, SATO Taketomo, HASEGAWA Hideki

  8th International Conference on Atomically Controlled Surfaces Interfaces and Nanostructures  2005/06
• MBE Growth and Si-interlayer Based Surface Passivation of GaAs Quantum Wires  [Not invited]

  SHIOZAKI Nanako, SATO Taketomo, AKAZAWA Masamichi, HASEGAWA Hideki

  29th Workshop on Compound Semiconductor Devices and Integrated Circuit  2005/05
• Electrodeposited Pt/InP Schottky Barriers with Large Barrier Heights and Large Hydrogen Sensitivity for Sensor Chips Using InP-based Quantum Wire Networks  [Not invited]

  KIMURA Takeshi, MATSUO Kazushi, SATO Taketomo, HASHIZUME, Tamotsu, HASEGAWA Hideki

  17th Indium Phosphide and Related Materials Conference  2005/05
• MBE選択成長法によるGaN(0001)加工基板上へのAlGaN/GaNナノ構造形成メカニズム  [Not invited]

  及川武, 佐藤威友, 橋詰保, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• MBE選択成長GaAs量子細線ネットワークを適用したBDD量子節点デバイスの試作と評価  [Not invited]

  田村隆博, 湯元美樹, 玉井功, 葛西誠也, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• GaAs(111)B加工基板へのMBE選択成長法による量子細線の形成とその形成メカニズム(2)  [Not invited]

  玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• GaAs(001)および(111)B基板に作製したGaAs/AlGaAs量子細線の表面パッシベーション  [Not invited]

  塩崎奈々子, 玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• 〈-110〉方向に沿ったメサ型加工基板へのMBE成長とGaAsリッジ細線の形成過程  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• InP系材料を用いたPtショットキーダイオードによる水素ガスセンシング  [Not invited]

  木村健, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2005/03
• Growth Kinetics and Theoretical Modeling of Selective Molecular Beam Epitaxy for Growth of GaAs Nanowires on Non-planar Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  2005 RCIQE International Seminar for 21st Century COE Program: Quantum Nanoelectronics for Meme-Media-Based Information Technologies (III)  2005/02
• Investigation of Side-Gating Effects in GaAs-based Quantum Wire Transistor  [Not invited]

  JIA Rui, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  2005 RCIQE International Seminar for 21st Century COE Program: Quantum Nanoelectronics for Meme-Media-Based Information Technologies (III)  2005/02
• High-Density Hexagonal Nanowire Networks on Pre-Patterned GaAs (001) and (111)B Substrates by Selective MBE Growth  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  2005 RCIQE International Seminar for 21st Century COE Program: Quantum Nanoelectronics for Meme-Media-Based Information Technologies (III)  2005/02
• Effects of Surface States and Si-interlayer Based Surface Passivation on GaAs Quantum Wires Grown by Selective Molecular Beam Epitaxy  [Not invited]

  SHIOZAKI Nanako, SATO Taketomo, HASEGAWA Hideki

  32nd Conference on the Physics and Chemistry of Semiconductor Interfaces  2005/01
• Growth Kinetics and Theoretical Modeling of Selective Molecular Beam Epitaxy for Growth of GaAs Nanowires on Non-planar (111)B Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  32nd Conference on the Physics and Chemistry of Semiconductor Interfaces  2005/01
• Self-assembled formation of InP nanopore arrays by photoelectrochemical anodization in HCl based electrolyte  [Not invited]

  SATO Taketomo, FUJINO Toshiyuki, HASEGAWA Hideki

  8th International Conference on Atomically Controlled Surfaces Interfaces and Nanostructures  2005/01
• Growth of GaN Based Quantum Wire Arrays and Networks by RF Radical Assisted Selective Molecular Beam Epitaxy  [Not invited]

  SATO Taketomo, OIKAWA Takeshi, HASEGAWA Hideki

  The 5th International Conference on Low Dimensional Structures and Devices (LDSD2004)  2004/12
• Hexagonal BDD Quantum Circuit Architecture for Intelligent Quantum (IQ) Chips  [Not invited]

  HASEGAWA Hideki, KASAI Seiya, YUMOTO Miki, SATO Taketomo

  11th Advanced Heterostructure Workshop  2004/12
• Selective MBE Growth of High-Density Hexagonal Nanowire Networks on Pre-Patterned GaAs (001) and (111)B Substrates International Symposium on Nanoscale Devices and Materials  [Not invited]

  TAMAI Isao, SATO Taketomo, HASHIZUME Tamotsu, HASEGAWA Hideki

  206th Meeting of ECS  2004/10
• Design and Implementation of Ultra-Small and Ultra-Low-Power Digital Systems Utilizing A Hexagonal BDD Quantum Circuits on GaAs-based Hexagonal Nanowire Network Structures  [Not invited]

  KASAI Seiya, YUMOTO Miki TAMURA Takahiro, TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  International Symposium on Nanoscale Devices and Materials:206th Meeting of ECS  2004/10
• Molecular Beam Epitaxial Growth of GaAs- and GaN-Based Quantum Wire Arrays and Networks on Pre-Patterned Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, OIKAWA Takeshi, HASEGAWA Hideki

  7th China-Japan Symposium on Thin Films (CJSTF-7)  2004/09
• Growth of AlGaN/GaN Quantum Wire Structures by RF-Radical Assisted MBE on Pre-Patterned Substrates  [Not invited]

  SATO Taketomo, OIKAWA Takeshi, HASHIZUME Tamotsu, HASEGAWA Hideki

  International Conference on Solid State Devices and Materials 2004  2004/09
• Cross-sectional Evolution and Its Mechanism during Selective MBE Growth of GaAs Quantum Wires on (111)B Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  International Conference on Solid State Devices and Materials 2004  2004/09
• Investigation of Current and Potential Control Characteristics by Nanosized Schottky Gate on AlGaAs/GaAs Surfaces  [Not invited]

  JIA Rui, SATO Taketomo, KASAI Seiya, HASEGAWA Hideki

  31st International Symposium on Compound Semiconductors  2004/09
• Investigation of Current and Potential Control Characteristics by Nanosized Schottky Gate on AlGaAs/GaAs Surfaces  [Not invited]

  SATO TaketomoJia Rui, Sato Taketomo, Kasai Seiya, Hasegawa Hideki

  応用物理学会学術講演会講演予稿集  2004/09
• GaAs(111)B加工基板へのMBE選択成長法による量子細線の形成とその形成メカニズム  [Not invited]

  玉井功, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• MBE選択成長法によるInP(111)B基板上へのInGaAs量子細線ネットワークの形成  [Not invited]

  木村健, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• Si界面制御層を用いたGaAs/AlGaAs量子細線の表面パッシベーション  [Not invited]

  塩崎奈々子, 佐藤威友, 橋詰保, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• ECRドライエッチングとMBE選択成長法による加工基板上へのAlGaN/GaNナノ構造の作製と評価  [Not invited]

  及川武, 佐藤威友, 橋詰保, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• MBE選択成長を用いたGaAs BDD量子節点デバイスの試作と性能評価  [Not invited]

  田村隆博, 湯元美樹, 玉井功, 佐藤威友, 葛西誠也, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• RFラジカル支援MBE法によるGaN(0001)加工基板へのGaN/AlGaNヘテロ構造の成長  [Not invited]

  佐藤威友, 及川武, 橋詰保, 長谷川英機

  応用物理学会学術講演会講演予稿集  2004/09
• Selective MBE Growth of GaAs Hexagonal Nano-wire Network on Pre-patterned Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  Hokkaido Univ. and Seoul National Univ. Joint Symposium  2004/07
• Growth Mechanism of GaAs Ridge Quantum Wires on Patterned Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  Hokkaido Univ. and Seoul National Univ. Joint Symposium  2004/07
• Sidegating Effect Study in AlGaAs/GaAs Quantum Wire Transistors  [Not invited]

  JIA Rui, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  Hokkaido Univ. and Seoul National Univ. Joint Symposium  2004/07
• GaAs BDD Quantum Node Switches Fabricated on Selectively MBE Grown Quantum Wire Networks  [Not invited]

  TAMURA Takahiro, YUMOTO Miki, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  46th Electronic Materials Conference (EMC2004)  2004/06
• Controlled growth of GaAs ridge quantum wire network by selective MBE and its application to hexagonal BDD quantum logic circuits  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, TAMURA Takahiro, TAMAI Isao, YUMOTO Miki

  12th Int. Symposium on Nanostructures Physics and Technology  2004/06
• Surface-related reduction of photoluminescence from GaAs quantum wires and effects of surface passivation using Si interface control layer  [Not invited]

  SHIOZAKI Nanako, ANANTATHANASARN Sanguan, SATO Taketomo, HASHIZUME Tamotsu, HASEGAWA Hideki

  The 12th International Conference on Solid Films and Surfaces  2004/06
• Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN(0001) substrates  [Not invited]

  OIKAWA Takeshi, ISHIKAWA Fumitaro, SATO Taketomo, HASHIZUME Tamotsu, HASEGAWA Hideki

  The 12th International Conference on Solid Films and Surfaces  2004/06
• MBE選択成長を用いたGaAs量子細線スイッチの作製と評価  [Not invited]

  田村隆博, 湯元美樹, 玉井功, 佐藤威友, 葛西誠也, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2004/03
• 加工基板を用いたMBE選択成長法によるGaAsリッジ細線の形成メカニズム  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2004/03
• MBE選択成長法による高密度GaAsヘキサゴナル細線ネットワークの形成(2)  [Not invited]

  玉井功, 吉田崇一, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2004/03
• MBE選択成長による(111)B加工基板上への高密度GaAs量子細線ネットワークの作製と評価  [Not invited]

  吉田崇一, 玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2004/03
• 内部交差量子細線構造の深さ分解/面内分布カソードルミネッセンス評価  [Not invited]

  石川史太郎, 及川武, 玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2004/03
• Growth Kinetics and Modeling of Selective Molecular Beam Epitaxial Growth of GaAs Ridge Quantum Wires on Pre-Patterned Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  2004 International Seminar for 21st Century COE Program: Quantum Nanoelectronics for Meme-Media-Based Infromation Technology (II)  2004/02
• Mechanism of Selective Growth of GaAs Ridge Quantum Wires on Non-planar Substrates during Molecular Beam Epitaxy  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  31st Conference on the Physics and Chemistry of Semiconductor Interfaces  2004/01
• Prospects of III-V quantum LSIs based on hexagonal BDD approach  [Invited]

  KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  2003/12
• Selective MBE Growth of GaAs Hexagonal Nano-wire Networks on (111)B Patterned Substrates  [Not invited]

  YOSHIDA Souichi, TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  International Conference on Solid State Devices and Materials  2003/09
• Control of Heterointerface Cross-Sections of GaAs Ridge Quantum Wires by Selective Molecular Beam Epitaxy  [Not invited]

  SATO Taketomo, TAMAI Isao, YOSHIDA Souichi, HASEGAWA Hideki

  The 9th International Conference on the Formation of Semiconductor Interfaces (ICFSI-9)  2003/09
• MBE選択成長法を用いた高密度GaAsヘキサゴナル細線ネットワークの形成  [Not invited]

  玉井功, 吉田崇一, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2003/08
• (111)B加工基板上へのMBE選択成長によるGaAs量子細線ネットワークの形成  [Not invited]

  吉田崇一, 玉井功, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2003/08
• GaAs加工基板上へのMBE選択成長法によるGaAs/AlGaAsリッジ細線の形成メカニズム  [Not invited]

  佐藤威友, 玉井功, 吉田崇一, 長谷川英機

  応用物理学会学術講演会講演予稿集  2003/08
• Formation of High Density GaAs Hexagonal Nanowire Networks by Selective MBE Growth on Pre-patterned (001) Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  11th International Conference on Modulated Semiconductor Structures (MSS11)  2003/07
• Kinetic Evolution of Facet Boundary Planes during Growth of III-V Ridge Quantum Wire Arrays by Selective Molecular Beam Epitaxy  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, JIANG Chao, MURANAKA Tsutomu

  Symposium on Surface Science 2003 (3S03)  2003/03
• MBE選択成長法を用いたGaAs/AlGaAsヘキサゴナル細線ネットワークの形成とその評価 (2)  [Not invited]

  玉井功, 吉田崇一, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2003/03
• MBE選択成長法によるGaAs(111)B加工基板上へのGaAs系量子構造の作製と評価  [Not invited]

  吉田崇一, 玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2003/03
• 加工基板を用いたMBE選択成長によるGaAs/AlGaAsリッジ細線の形成とデバイス応用  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2003/03
• Selective MBE Growth of GaAs Ridge Quantum Wires for Formation of Hexagonal Nanowire Networks  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  2003 RCIQE International Seminar on Quantum Nanoelectronics for Meme-Media-Based Information Technologies  2003/02
• Selective MBE Growth of GaAs Ridge Quantum Wire Arrays on Patterned (001) Substrates and Its Growth Mechanism  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  29th International Symposium on Compound Semiconductors (ISCS2002)  2002/10
• GaAs上に形成したナノショットキーゲート電極のポテンシャル制御特性 (2)  [Not invited]

  亀田篤志, 葛西誠也, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2002/09
• 加工基板を用いたMBE選択成長法によるGaAs/AlGaAs量子細線の形成と評価 (2)  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学会学術講演会講演予稿集  2002/09
• MBE選択成長法を用いたGaAs/AlGaAsヘキサゴナル細線ネットワークの形成とその評価  [Not invited]

  玉井功, 吉田崇一, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2002/09
• Selective MBE Growth of <-110> and <510>-Oriented GaAs Ridge Quantum Wires on Patterned (001) Substrates for Formation of Hexagonal Nanowire Networks  [Not invited]

  SATO Taketomo, TAMAI Isao, HASEGAWA Hideki

  The Second International Workshop on Quantum Nonplanar Nanostructures & Nanoelectronics (QNN02)  2002/09
• Mechanism and Suppression of Anomalously Large Reverse Leakage Currents in n-type GaN Schottky Contacts  [Not invited]

  SATO Taketomo, OYAMA Susumu, HASEGAWA Hideki

  26th International Conference on the Physics of Semiconductors  2002/07
• Selective MBE Growth of High Density GaAs/AlGaAs Hexagonal Nanowire Network Structures on Pre-Patterned GaAs Substrates  [Not invited]

  TAMAI Isao, SATO Taketomo, HASEGAWA Hideki

  2002 Electronic Materials Conference  2002/06
• Understanding and Control of Current Transport in GaN Schottky Contacts with Large Reverse Leakage Currents  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, OYAMA Susumu

  26th Workshop on Compound Semiconductor Devices and Integrated Circuits held in Europe (WOCSDICE)  2002/05
• MBE選択成長法により形成したGaAs/AlGaAs結合量子細線構造の評価  [Not invited]

  玉井功, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2002/03
• GaAs上に形成したナノショットキーゲート電極のポテンシャル制御特性  [Not invited]

  亀田篤志, 葛西誠也, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2002/03
• 電気化学プロセスによるInPポーラス構造の形成とその応用 (3)  [Not invited]

  平野哲郎, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2002/03
• 加工基板を用いたMBE選択成長法によるGaAs/AlGaAs量子細線の形成と評価  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2002/03
• 電気化学プロセスによるInPポーラス構造の形成とその応用(2)  [Not invited]

  平野哲郎, 佐藤威友, 伊藤章, 石川史太郎, 長谷川英機

  応用物理学会学術講演会講演予稿集  2001/09
• 加工基板を用いたMBE選択成長法によるGaAsリッジ構造の形成と評価  [Not invited]

  佐藤威友, 玉井功, 長谷川英機

  応用物理学会学術講演会講演予稿集  2001/09
• 電気化学プロセスによるInPポーラス構造の形成とその応用  [Not invited]

  平野哲郎, 佐藤威友, 伊藤章, 石川史太郎, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2001/03
• 化合物半導体ナノショットキー接触界面の電気的特性とその制御(2)  [Not invited]

  佐藤威友, 亀田篤志, 葛西誠也, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2001/03
• Effects of Surface Fermi Level Pinning and Surface State Charging on Control Characteristics of Nanometer Scale Schottky Gates Formed on GaAs  [Not invited]

  KAMEDA Atsuchi, KASAI Seiya, SATO Taketomo, HASEGAWA Hideki

  2001 International Semiconductor Device Research Symposium (ISDRS2001)  2001
• Selective MBE Growth of GaAs/AlGaAs Hexagonal Nanowire Network Structures on (001) Patterned GaAs Substrates  [Not invited]

  SATO Taketomo, TAMAI Isao, JIANG Chao, HASEGAWA Hideki

  28th International Symposium on Compound Semiconductors (ISCS2001)  2001
• Electrochemical Formation of Self-Assembled Nanopore Arrays As Templates for MBE Growth of InP-based Quantum Wires and Dots  [Not invited]

  HIRANO Tetsuro, ITO Akira, SATO Taketomo, ISHIKAWA Fumitaro, HASEGAWA Hideki

  2001 International Conference on Indium Phosphide and Related Materials (IPRM2001)  2001
• 微小金属ドットを有する化合物半導体単電子デバイス構造(5)  [Not invited]

  岡田浩, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  2000/09
• 化合物半導体ナノショットキー接触界面の電気的特性とその制御  [Not invited]

  佐藤威友, 葛西誠也, 長谷川英機

  応用物理学会学術講演会講演予稿集  2000/09
• 微小金属ドットを有する化合物半導体単電子デバイス構造(4)  [Not invited]

  岡田浩, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2000/03
• 電気化学プロセスを用いて作製した化合物半導体ナノショットキー接触の電気的特性  [Not invited]

  佐藤威友, 葛西誠也, 岡田浩, 長谷川英機

  応用物理学関係連合講演会講演予稿集  2000/03
• Electrical Properties of Nanometer-Sized Schottky Contacts for Gate Control of III-V Single Electron Devices  [Not invited]

  SATO Taketomo, KASAI Seiya, HASEGAWA Hideki

  International Symposium on Formation Physics and Device Application of Quantum Dot Structures  2000
• Current Transport and Capacitance-Voltage Characteristics of GaAs and InP Nanometer-Sized Schottky Contacts Formed by in situ Electrochemical Process  [Not invited]

  SATO Taketomo, KASAI Seiya, HASEGAWA Hideki

  10 th International Conference on Solid Films and Surfaces  2000
• Formation and Characterization of Nanometer-Sized Schottky Contacts on III-V Materials by In-SItu Electrochemical Process  [Not invited]

  SATO Taketomo, KASAI Seiya, HASEGAWA Hideki

  42nd Electronic Materials Conference  2000
• Self-Assembled Formation of InP Nanopore Arrays by Electrochemical Anodization  [Not invited]

  FUJIKURA Hajime, LIU Aimin, SATO Taketomo, HIRANO Tetsuro, HASEGAWA Hideki

  2000 International Conference on Indium Phosphide and Related Materials (IPRM2000)  2000
• ナノショットキー接触の電気的特性  [Not invited]

  佐藤威友, 葛西誠也, 岡田浩, 長谷川英機

  電気関係学会北海道支部連合大会講演論文集  1999/10
• 微小金属ドットを有する化合物半導体単電子デバイス構造 (3)  [Not invited]

  岡田浩, 佐藤威友, 長谷川英機

  応用物理学会学術講演会講演予稿集  1999/09
• 電気化学プロセスを用いて作製したナノショットキー接触の電気的特性  [Not invited]

  佐藤威友, 葛西誠也, 岡田浩, 長谷川英機

  応用物理学会学術講演会講演予稿集  1999/09
• 微小金属ドットを有する化合物半導体単電子デバイス構造 (2)  [Not invited]

  岡田浩, 佐藤威友, 長谷川英機

  応用物理学関係連合講演会講演予稿集  1999/03
• 電気化学プロセスを用いたInP系材料に対するナノショットキー接触の形成  [Not invited]

  佐藤威友, 岡田浩, 長谷川英樹

  応用物理学関係連合講演会講演予稿集  1999/03
• 電気科学プロセスによるIII‐V族化合物半導体表面・ショットキー界面の制御  [Not invited]

  橋詰保, 兼城千波, 佐藤威友, 長谷川英機

  電気化学会大会講演要旨集  1999/03
• Properties of nanometer-sized metal contacts on GaAs, InP and their related materials  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, KASAI Seiya

  Surfaces and Interfaces of Mesoscopic Devices  1999
• Electrochemical Formation of Nanometer-Sized Straight Pore Arrays on (001) InP Surfaces  [Not invited]

  LIU Aimin, HAMAMATSU Akihito, SATO Taketomo, FUJIKURA Hajime, HASEGAWA Hideki

  International Symposium on Surface Science for Micro- and Nano-Device Fabrication  1999
• Electrical Properties of Nanometer-Sized Schottky Contacts on n-GaAs and n-InP Formed by in situ Electrochemical Process  [Not invited]

  SATO Taketomo, KASAI Seiya, OKADA Hiroshi, HASEGAWA Hideki

  International Symposium on Surface Science for Micro- and Nano-Device Fabrication  1999
• Unpinning of Fermi Level in Nanometer-Sized Schottky Contacts on GaAs and InP  [Not invited]

  HASEGAWA Hideki, SATO Taketomo

  7th International Conference on Formation of Semiconductor Interfaces  1999
• Subnano-Scale Selective Etching and Nano-Scale Pore Array Formation on InP (001) Surfaces by a Wet Electrochemical Process  [Not invited]

  HAMAMATSU Akihito, KANESHIRO Chinami, SATO Taketomo, FUJIKURA Hajime, HASEGAWA Hideki

  International Conference on 1999 Indium Phosphide and Related Materials (IPRM99)  1999
• Formation on Nanometer-Sized Schottky Contacts on InP and Related Materials by in situ Electrochemical Process  [Not invited]

  SATO Taketomo, OKADA Hiroshi, HASEGAWA Hideki

  11th International Conference on Indium Phosphide and Related Materials (IPRM99)  1999
• Formation of Fermi Level Pinning Free Nano-scale Schottky Contacts on Compound Semiconductor and Their Application to Single Electron Devices  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, OKADA Hiroshi

  Symposium on Surface Physics  1999
• Compound semiconductor single electron device structures having nano-metal dots.  [Not invited]

  OKADA HIROSHI, SATO TAKETOMO, KANESHIRO CHINAMI, JINUSHI KEIICHIRO, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1998/09
• Formation of porous InP by anodization.  [Not invited]

  HAMAMATSU AKIHITO, SATO TAKETOMO, KANESHIRO CHINAMI, FUJIKURA HAJIME, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1998/09
• Electrochemical etching of n-InP surface in an acid solution.  [Not invited]

  KANESHIRO CHINAMI, SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1998/09
• Formation of metal particles and its application to metal/semiconductor nano-structure by erectrochemical process.  [Not invited]

  SATO TAKETOMO, OKADA HIROSHI, KANESHIRO CHINAMI, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1998/09
• Formation and characterization of metal nano-grain array by electrochemical process.  [Not invited]

  SATO TAKETOMO, OKADA HIROSHI, KANESHIRO CHINAMI, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1998/03
• Schottky barrier hights for a range of metals deposited on n-GaAs sureface by using electrochemical process.  [Not invited]

  KANESHIRO CHINAMI, SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1998/03
• Photo-voltaic characterization of Pt-dots/InP surfaces in electrolytic solutions.  [Not invited]

  HAMAMATSU AKIHITO, KANESHIRO CHINAMI, SATO TAKETOMO, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1998/03
• Formation and control of Schottky contacts formed by in situ electrochemical process.  [Not invited]

  SATO TAKETOMO, KANESHIRO CHINAMI, SOKOLOV D V, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1998/03
• Properties of Nanometer-Sized Metal-Semiconductor Interfaces of GaAs, InP and GaN Formed by An In-Situ Electrochemical Process  [Not invited]

  HASEGAWA Hideki, SATO Taketomo, KANESHIRO Chinami, KOYAMA Yuuji

  1999 International Conference on Physics and Chemistry of Semiconductor Interfaces  1998
• Realization of Strongly Metal-Dependent Schottky Barrier Heights on n-GaAs by In Situ Electrochemical Process  [Not invited]

  KANESHIRO Chinami, SATO Taketomo, HASHIZUME Tamotsu, HASEGAWA Hideki

  25th International Symposium on Compound Semiconductors  1998
• Surface Modification of InP By Photoelectrohcemical Process  [Not invited]

  HAMAMATSU Akihito, KANESHIRO Chinami, SATO Taketomo, FUJIKURA Hajime, HASEGAWA Hideki

  International Symposium on Electrochemistry of Ordered Interfaces  1998
• Formation of Size- and Position-Controlled Nanometer Size Pt Dots on GaAs and InP Substrates by Pulsed Electrochemical Deposition  [Not invited]

  SATO Taketomo, KANESHIRO Chinami, OKADA Hiroshi, HASEGAWA Hideki

  International Conference on Solid State Devices and Materials  1998
• Fabrication of Regular Arays of Nanometer-Sized Pt Dots on III-V Substrates by Electron Beam Lithography and Electrochemical Deposition  [Not invited]

  SATO Taketomo, KANESHIRO Chinami, OKADA Hiroshi, HASEGAWA Hideki

  40th Electronic Matterials Conference (EMC'98)  1998
• Highly Controllable Electrochemical Etching of InP studied by Voltammetry and Scanned Probe Microscope  [Not invited]

  KANESHIRO Chinami, SATO Taketomo, HASEGAWA Hideki

  10th International Conference on Indium Phosphide and Related Materials (IPRM98)  1998
• Strong Correlation Between Interface Microstructure and Barrier Height in n-InP Schottky Contacts Formed by In Situ Electrochemical Process  [Not invited]

  SATO Taketomo, KANESHIRO Chinami, HASEGAWA Hideki

  10th International Conference on Indium Phosphide and Related Materials (IPRM98)  1998
• Formation of Pt Dot Array by erectrochemical process.  [Not invited]

  SATO TAKETOMO, OKADA HIROSHI, KANESHIRO CHINAMI, HASEGAWA HIDEKI

  電気関係学会北海道支部連合大会講演論文集  1998
• In Situ STM obsersvation of InP surface in an solution.  [Not invited]

  KANESHIRO CHINAMI, SATO TAKATOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1997/10
• Photo-voltac characterization of Schottky contacts on InP-based materials.  [Not invited]

  HAMAMATSU AKIHITO, SATO TAKETOMO, KANESHIRO CHINAMI, SAITO TOSHIYA, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1997/10
• Fomation and control of Schottky contacts formed by in situ electrochemical process.  [Not invited]

  SATO TAKATOMO, KANESHIRO CHINAMI, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1997/10
• Schottky Barrier Formation to Compound Semiconductors by in-situ Electrochemical Process and Its Controllability.  [Not invited]

  SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電気化学秋季大会講演要旨集  1997/08
• Preparation of sputter-deposited Pt/InP interfaces.  [Not invited]

  NOYA ATSUSHI, TAKEYAMA MAYUMI, SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1997/03
• Formation of Schottky contacts to InP-based materials by in-situ electrochemical process.  [Not invited]

  SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1997/03
• Formation of Pinning-Free Schottky Barriers on InP and Related Materials by Novel In-Situ Electrochemical Process and Its Mechanism  [Not invited]

  SATO Taketomo, HASEGAWA Hideki

  9th International Conference on Indium Phosphide and Related Materials (IPRM97)  1997
• Evolution of Nearly Pinning-Free Metal-Semiconductor Interfaces on InP and Related Materials by Novel In-Situ Electrochemical Process  [Not invited]

  SATO Taketomo, HASHIZUME Tamotsu, HASEGAWA Hideki

  1997 International Conference on Physics and Chemistry of Semiconductor Interfaces  1997
• In situ observation of InP surface in acid solutions by EC STM.  [Not invited]

  KANESHIRO CHINAMI, SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電気関係学会北海道支部連合大会講演論文集  1997
• Formation of Schottky contacts by in situ electrochemical process.  [Not invited]

  SATO TAKETOMO, KANESHIRO CHINAMI, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電気関係学会北海道支部連合大会講演論文集  1997
• Formation of Schottky contacts with high Schottky barrier heights to InP-based materials and its mechanism.  [Not invited]

  SATO TAKETOMO, UNO SHOICHI, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学会学術講演会講演予稿集  1996/09
• Formation of Schottky barriers to InP based materials by In Situ electrochemical process.  [Not invited]

  UNO SHOICHI, SATO TAKETOMO, KASAI SEIYA, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  応用物理学関係連合講演会講演予稿集  1996/03
• Enhancement of Schottky Barrier Heights on Indium Phosphide-Based Materials by In-Situ Electrochemical Process and Its Mechanism  [Not invited]

  SATO Taketomo, UNO Shouichi, HASHIZUME Tamotsu, HASEGAWA Hideki

  International Conference on Solid State Devices and Materials  1996
• Fabrication of high-performance InP MESFETs with in-situ pulse-plated metal gates  [Not invited]

  UNO Shouichi, Tamotsu Hashizme, SATO Taketomo, FUJIKURA Hajime, HASEGAWA Hideki

  International Conference on Indium Phosphide and Related Materials (IPRM96)  1996
• Formation of high Schottky barrier heights to InP-based materials by in-situ electrochemical process and its mechanism.  [Not invited]

  SATO TAKETOMO, HASHIZUME TAMOTSU, HASEGAWA HIDEKI

  電気関係学会北海道支部連合大会講演論文集  1996

Association Memberships

• The Electrochemical Society   電子情報通信学会   Japanese Society of Applied Physics   The Electrochemical Society of Japan   

Works

• 電子情報工学実験 テキストの作成・更新

  佐藤 威友
• 量子集積エレクトロニクス研究センター ホームページの更新

  佐藤 威友

Research Projects

• 窒化物半導体異種界面パラレル伝導制御とマルチチャネル高周波トランジスタの開発

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2023/04 -2026/03 

  Author : 佐藤 威友, 三好 実人, 赤澤 正道
• 超ワイドギャップAlN系半導体を用いたパワートランジスタの開発

  日本学術振興会：科学研究費助成事業 基盤研究(B)

  Date (from‐to) : 2021/04 -2024/03 

  Author : 三好 実人, 佐藤 威友

   

  窒化アルミニウム(AlN)は、GaNの3.4eV、SiCの3.2eVを大きく上回る6.2eVという極めて大きなバンドギャップエネルギーを持つ究極的なパワーデバイス用半導体材料である。AlNの絶縁破壊電界は非常に高く、パワーデバイスとして利用した場合のOFF耐圧はGaNやSiCの約10倍にもなると予想されている。一方、AlNは、化学的安定性が高く機械的強度・硬度に優れることも大きな特徴となっているが、これらの諸物性は機能デバイスへの応用を考えた際の技術的困難さも生じさせている。本研究では、将来社会の省エネ化ニーズに応えるアイテムとして、GaN, SiC以上の超ワイドバンドギャップ半導体である窒化アルミニウム(AlN)系ヘテロ構造をベースとしたパワートランジスタを着想、その実現に向けた課題と方策を以下のように設定し、研究計画を策定した。 (1) AlN系ヘテロ構造のエピタキシャル成長技術確立： 目標のトランジスタ構造を実現するために表面平坦で且つ所望の電気特性を示すAlN系ヘテロ構造のエピタキシャル成長技術を確立する。 (2) AlN系トランジスタのデバイス化技術構築： デバイス化にあたってのキーとなるオーミック電極形成、およびノーマリOFF動作のための精密微細加工に係るプロセス技術を構築する。 (3) AlN系トランジスタの試作と到達性能の確認： 上記2項目に対応したうえでデバイス試作と評価を進め、理想デバイスの設計と到達性能の理論推定を行う。以上のような学理的なアプローチを以て、AlN系トランジスタが既存品を超えて真に将来有望なデバイスとなり得るかを検証する。
• Development of wet etching technology for nitride semiconductors using strong oxidizing agents and application to transistors

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2020/04 -2023/03 

  Author : 佐藤 威友, 三好 実人, 橋詰 保

   

  (1)硫酸ラジカル（SO4*-）を使った窒化物半導体混晶（AlGaN）のエッチング 前年度に得られた知見を基に、窒化アルミニウムガリウム（AlGaN）のウェットエッチングに成功した。UVC照射強度とともに硫酸ラジカル（SO4*-）の生成レートは上昇し、エッチングレートが増大した。また、反応初期では、エッチング深さはUVC照射時間に比例して増大したが、時間の経過とともにエッチング量が飽和し自己停止した。自己停止深さは、試料表面に形成する陰極パッドの材質により大きく変化することを明らかにした。陰極パッドの役割は、UVC照射によって生成した電子-正孔対のうち、エッチング反応に利用されない電子を効率的に反応面から遠ざけることにあり、試料表面との接触抵抗が低い材料を陰極パッドに用いた場合に、エッチングレートが増大することを示した。さらに、開発したウェットエッチング法を、AlGaN/GaNヘテロ構造を利用したヘテロ構造電界効果トランジスタ（HFET）のゲートリセス加工に適用した。AlGaN層内でエッチングを自己停止することにより、同一チップ上に作製したトランジスタの閾値電圧のばらつきを抑えることに成功した。 (2)溶液とp-GaN界面の電気化学的評価 電気化学容量-電圧（ECV）法、電気化学インピーダンス分光（EIS）法により、水溶液／p-GaN界面の電気的特性評価を行った。本測定により得られたp-GaNのアクセプタ密度は、大気中で測定したショットキーダイオードの結果と矛盾なく、設計通りの値を示した。また、溶液中で正の電圧（陽極電圧）を印加すると、p-GaN表面に酸化膜が形成され内蔵電位や周波数応答特性の違いとして検出されることを明らかにした。p-GaNの電気化学エッチング量は、時間や通過電荷量で制御可能であることを示した。
• Interface control of heterojunctions including singularity structures for advanced electron devices

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2016/06 -2021/03 

  Author : Hashizume Tamotsu

   

  We have investigated interface properties of Schottky and MOS structures with a non-polar m-plane GaN surface and processed GaN surfaces by a plasma-assisted etching, an ion implantation and a high-temperature annealing. The detailed electrical characterization detected various kinds of electronic states created at the GaN surfaces. Then, a chemically stable HfSiOx gate with a high permittivity has been applied to AlGaN/GaN high-electron-mobility transistors (HEMTs), resulting in excellent I-V characteristics with a slight fluctuation of threshold voltage. In addition, a recess-gate GaN MOS HEMT was fabricated using an electrodeless photo-assisted electrochemical etching. The DC characterization showed a precise control of threshold voltage in the I-V characteristics of the recess-gate MOS HEMT.
• 省エネルギー社会の実現に資する次世代半導体研究開発（パワーデバイス・システム領域）

  文部科学省：委託事業-再委託機関

  Date (from‐to) : 2016 -2021
• 社会実装を目指したＧａＮ縦型パワーデバイス作製技術の確立

  文部科学省：革新的パワーエレクトロニクス創出基盤技術開発事業（パワーデバイス領域）

  Date (from‐to) : 2021
• GaNの光電気化学エッチングに関する研究

  株式会社サイオクス：共同研究

  Date (from‐to) : 2021
• GaNの光電気化学プロセス

  三菱電機株式会社：共同研究

  Date (from‐to) : 2021
• Low-damage Processing of Nitride Semiconductors Based on Self-stoping Oxdization and Transistor Applications

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

  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.
• Low-damage Processing of Nitride Semiconductors Based on Self-stoping Oxdization and Transistor Applications

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2017/04 -2020/03 

  Author : SATO Taketomo
• GaNの光電気化学エッチングに関する研究

  株式会社サイオクス：共同研究

  Date (from‐to) : 2020
• GaNの光電気化学プロセス

  三菱電機株式会社：共同研究

  Date (from‐to) : 2020
• GaNの光電気化学エッチングに関する研究

  株式会社サイオクス：共同研究

  Date (from‐to) : 2019
• Visible light responsive photocatalysts utilizing nitride semiconductor-based nanostructures for artificial photosynthesis

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory 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).
• 窒化物半導体周期的ナノ構造を基盤とした可視光応答型光触媒の開発と人工光合成応用

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Challenging Exploratory Research

  Date (from‐to) : 2015/04 -2018/03 

  Author : SATO Taketomo
• III-V族化合物半導体の酸化腐食に関する研究

  オルガノ株式会社：共同研究

  Date (from‐to) : 2015 -2018
• Nanoscale control of nitride semiconductor surface using low-damaged process for high-sensitive chemical sensors

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Scientific Research (B)

  Date (from‐to) : 2013/04 -2016/03 

  Author : SATO Taketomo
• 絶縁膜物性・界面状態のGaNトランジスタの性能と関係性の研究

  住友電気工業株式会社：共同研究

  Date (from‐to) : 2016 -2016
• Nanoscale control of nitride semiconductor surface using low-damaged process for high-sensitive chemical sensors

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2013 -2015 

  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.
• GaN HEMTのためのプロセス技術と接合界面評価

  トヨタ自動車株式会社：共同研究

  Date (from‐to) : 2012 -2015
• Exploration of novel materials for photochemical water splitting based on semiconductor nanowires and nanostructures

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory 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.
• Exploration of novel materials for photochemical water splitting based on semiconductor nanowires and nanostructures

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Challenging Exploratory Research

  Date (from‐to) : 2012 -2014 

  Author : Junichi MOTOHISA
• High-density formation of functionalized nano-interfaces based on semiconductor porous structures for high-sensitive chemical-sensing technology

  文部科学省：Grant-in-Aid for Young Scientists (A)

  Date (from‐to) : 2009 -2012 

  Author : SATO Taketomo

   

  We proposed a novel ion-sensitive field-effect transistor (ISFET) having a porous-gate structure and established necessary basic technologies. The straight pores were successfully formed vertically on the substrate by the optimized electrochemical conditions. The functionalization of the pore surface was achieved by the deposition of the metal particles and organic molecules after the complete removal of the irregular top layer form the porous structures. Our proposed ISFETs with porous structures demonstrated good performance with a large current signal in the electrolyte, showing promise for high-sensitive chemical sensors.
• Reliability improvement of GaN transistors based on the control of electronic states and a nobel gate structure

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Scientific Research (A)

  Date (from‐to) : 2009 -2012 

  Author : Tamotsu HASHIZUME, 古賀 裕明, 久保 俊晴, 佐藤 威友, 赤澤 正道

   

  To improve the operation stability of GaN-heterostructure transistors, we have carried out characterization and control of electronic states at insulator-semiconductor interfaces, fabrication and characterization of the multi-mesa-channel (MMC) transistors, and the related experiments. By applying the novel simulation and photo-assisted capacitance-voltage methods to Al_2O_3/ AlGaN/GaN structures, we determined the density distribution of electronic states at the Al_2O_3/AlGaN for the first time. It was also found that the MMC structure is very effective in improving the current stability of the GaN-based transistors.
• 化合物半導体配列ナノ構造を基盤とする超接合光吸収体の創成と太陽電池応用

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Challenging Exploratory Research

  Date (from‐to) : 2009 -2010 

  Author : SATO Taketomo, 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...
• 窒化物半導体混晶のバルク準位評価とナノ構造表面制御

  Ministry of Education, Culture, Sports, Science and Technology：Grant-in-Aid for Scientific Research on Priority Areas

  Date (from‐to) : 2009 -2010 

  Author : Tamotsu HASHIZUME, 古賀 裕明, 佐藤 威友

   

  AlGaNおよびAlInGaNのバルク欠陥準位と表面・端面における表面電子準位を系統的に評価し、その理解を基盤として、短波長光学素子の高効率化・動作安定化のための電子準位制御法を構築することを目的として研究を展開した。本年度の主な成果を以下にまとめる。1)減圧有機金属気相法により成長したn-AlGaN(膜厚:1μm、Al組成:25、37、60%)の深い準位を評価し、伝導帯下端より1eV以上のエネルギーを持つ電子準位を検出した。支配的準位エネルギーのAl組成依存性は、フェルミ準位安定化エネルギーの計算値に良く追従することを明らかにし、逆位置欠陥と空孔欠陥ペアの複合型欠陥が深い準位の成因である可能性を指摘した。2)原子層堆積により形成したAl_2O_3/AlGaN/GaN構造に、詳細な計算解析とバンドギャップ以下のエネルギーを持つ光支援測定法を適用し、その容量-電圧特性を評価した。その結果、Al_2O_3/AlGaN界面には1x10^<12>cm^<-2>eV^<-1>以上の密度を持つ電子準位が存在することを初めて明らかにした。3)AlGaN表面に電気化学酸化法を適用し、平坦で均一性の高い母体酸化膜を形成することができた。形成した酸化膜の組成は母体AlGaNの組成とほぼ同等であることが分かり、この手法によりAlGaNの表面準位密度を低減できることを明らかにした。また、プロセスによ...
• 次世代センサーネットワークの実現に向けた化合物半導体化学センサの開発と高性能化に関する研究

  小澤・吉川記念エレクトロニクス研究助成基金：小澤・吉川記念エレクトロニクス研究助成基金

  Date (from‐to) : 2008 -2009 

  Author : 佐藤 威友
• Formation of three-dimensional quantum nanostructure networks based on compound semiconductor porous structuresq

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(若手研究(B))

  Date (from‐to) : 2007 -2008 

  Author : Taketomo SATO

   

  電解液と半導体界面の電気化学反応により形成される多孔質(ポーラス)構造を利用し、少ない電子を局所的に閉じ込めて制御する「3次元量子ナノネットワーク」の基礎技術を確立した。本構造は、直径数100nm 深さ数μm の直線的な孔が配列した高密度ナノ構造が基盤となっており、非常に大きな表面積と優れた伝導特性および光学的特性を有し、高感度化学センサや高効率太陽光発電素子の基本構造として有望性を示す一連の研究成果を得た。
• III族窒化物半導体混晶の欠陥準位・表面準位の評価と制御

  文部科学省：科学研究費補助金(特定領域研究)

  Date (from‐to) : 2007 -2008 

  Author : 橋詰 保, 金子 昌充, 佐藤 威友

   

  発光素子の効率・安定動作・信頼性には、バルクの結晶欠陥とともに、ヘテロ界面での禁制帯内連続電子準位(界面準位)や端面での表面準位の特性が影響する場合が多いが、これらの特性は明らかになっていない。本研究では、GaNおよびAlGaNのバルク欠陥準位と表面・端面・ヘテロ界面における表面電子準位を詳細に評価し、その特性の理解と制御を目的として研究を展開した。1) Al組成26%のAlGaN混晶にショットキー接合を形成し、暗中および光照射下での過渡容量応答評価を行なった。伝導帯下端より1.0eVおよび禁制帯中央付近の深い準位からの応答を検出し、詳しい解析の結果、5-8×10^<16>cm^<-3>程度の比較的高い密度を有することを明らかにした。2) 保護膜高温熱処理によるp-GaN表面の特性変化を詳細に評価した。XPS解析より1000℃以上の熱処理によりGa原子の外方拡散とMg原子の表面偏析が明らかになった。また、電流-電圧測定とPL評価より深い準位の生成による表面抵抗の増大が観測され、Ga空孔や格子間Mgに関連する複合欠陥の存在が示唆された。3) 電気化学酸化によるGaNおよびAlGaNの表面制御を検討した。酸化膜を溶液除去した表面に金属接合を形成した場合、接合特性の均一性が向上することが確認された。また、ドライエッチングで形成したナノ細線側面を選択的に酸化した場合、細線の伝導特性が...
• High-efficiency energy-conversion devices based on semiconductor nanostructures

  Date (from‐to) : 2008
• 選択的結晶成長による窒化ガリウム系ナノワイヤ・ネットワークの作製

  池谷科学技術振興財団：池谷科学技術振興財団研究助成金

  Date (from‐to) : 2006 -2007 

  Author : 佐藤 威友
• 化合物半導体ナノ構造の自己組織化形成と高感度化学センサへの応用

  村田学術振興財団：村田学術振興財団研究助成

  Date (from‐to) : 2006 -2007 

  Author : 佐藤 威友
• Reliability improvement of GaN-based devices by controlling defects and interfaces

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(B))

  Date (from‐to) : 2005 -2006 

  Author : Tamotsu HASHIZUME, 葛西 誠也, 佐藤 威人友, 金子 昌充

   

  The purpose of the research is to improve the stability of the GaN-based devices by controlling defects and interfaces. We have characterized electronic states of defects and impurities in GaN and A1GaN, as well as their correlation with degradation phenomena in various kinds of devices, such as the current collapse, the gate leakage current, electric breakdown, etc.1)We performed deep level transient spectroscopy (DLTS) measurements on the Schottky contacts fabricated on the Al_0.26Ga_0.74N surfaces, and detected a deep electron trap with an activation energy of 0.9 eV and a density higher...
• 半導体2次元電子ガスのプラズマ波によるミリ波・テラヘルツ進行波デバイスの研究

  文部科学省：科学研究費補助金(萌芽研究)

  Date (from‐to) : 2005 -2005 

  Author : 長谷川 英機, 葛西 誠也, 佐藤 威友, 賈 鋭

   

  テラヘルツ(THz)帯の周波数領域では、効率よく電磁波を発生・増幅・検波する技術が確立されておらず「テラヘルツギャップ」とよばれている。本研究の目的は、ミリ波・テラヘルツ帯におい.て増幅・検波機能を果たす新しい進行波型半導体デバイスの可能性を、理論的および実験的に検討することにある。その原理は、半導体の2次元電子ガス中に発生するドリフトプラズマ波と、遅波構造による電磁波の空間高調波との相互作用を利用することにある。(1)電子の慣性項を取り入れたより厳密なプラズマ方程式をもとに、TMモード解析とグリーン関数を含むFredholm積分方程式による空間高調波解析を行い、その結果ミリ波・THz帯で、大きな負性コンダクタンスが得られことを確認した。そして、その機構が高周波では1サイクルあたりの衝突頻度が飛躍的に減ることにあることを示した。(2)さらに、解析を半導体の表面準位の効果を含むものに拡張し、表面状態による電界分布の変化やスクリーニングが、デバイスに悪影響を及ぼすことを見出した。(3)AlGaAs/GaAsヘテロ接合上に、インターディジタル型遅波構造を形成したデバイスについて、マイクロ・ミリ波帯で予備実験を行い、おおきなコンダクタンス変調を観測するとともに、理論解析と実験がよく一致することを実証した。これらは、Jpn.J.Appl.Physの正規論文やISDRS(Dec.2005...
• ギガ・ノード超高密度量子ナノ集積構造の作製と表面制御技術の開発

  文部科学省：科学研究費補助金(若手研究(B))

  Date (from‐to) : 2004 -2005 

  Author : 佐藤 威友

   

  本研究の目的は、化合物半導体低損傷プロセスによる高密度量子ナノ集積構造の形成手法と、その表面および界面のナノスケール制御手法を開発し、量子集積回路実現のための基礎技術を確立することである。平成17年度の研究成果は以下のようにまとめられる。1.分子線エピタキシャル成長法(MBE)により、ガリウム砒素(GaAs)(111)B加工基板上へGaAs/AlGaAs量子細線構造の選択的成長を行い、その形成メカニズム/サイズ制御性について調べた。成長温度、材料組成を系統的に変えて行なった一連の実験結果と、吸着原子の拡散方程式に基づく成長シミュレーションの結果から、加工基板が持つ結晶面方位の違いや材料原子の種類により、表面吸着原子の拡散/取り込まれ寿命が異なり、その表面拡散論的な成長機構により、GaAs細線の断面形状が説明されることがわかった。これらの結果を基礎とし、GaAs細線の位置とサイズを数nmオーダーの精度で制御することを可能にした。また、シミュレーションにより得られた成長条件を使って、断面が1辺40nmの三角形となるGaAs細線を実験的に作製することにも成功した。2.上で開発した成長シミュレーションプログラムを、窒化ガリウム(GaN)(0001)加工基板上への選択成長に適用した。Ga原子とAl原子に対して適切な拡散係数と表面取込み寿命を設定することにより、材料組成、結晶面方位など成...
• Fabrication of Photonic Crystals by Selective-Area Metalorganic Vapor Phase Epitaxy and Their Application to Devices

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(A))

  Date (from‐to) : 2003 -2005 

  Author : Junichi MOTOHISA, プリミーラ モハン, 佐野 栄一, 福井 孝志, 佐藤 威友, 楊 林

   

  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 ...
• 選択的半導体結晶成長法による量子集積回路作製プロセスの研究開発

  ノーステック財団：ノーステック財団基盤的研究開発育成事業（若手研究補助金）

  Date (from‐to) : 2003 -2004 

  Author : 佐藤 威友
• 量子集積回路の実現に向けた高性能ナノショットキーゲート電極の開発

  文部科学省：科学研究費補助金(若手研究(B))

  Date (from‐to) : 2002 -2003 

  Author : 佐藤 威友

   

  本研究課題では、微細ゲート電極形成技術および量子集積構造作製技術といった、量子集積回路の実現に向けた量子集積プロセスの開発を目的としている。平成15年度の研究成果は、以下のようにまとめられる。1.MBE選択成長法を用いて、量子集積回路の基本構造として有望なヘキサゴナル量子ナノ細線ネットワーク構造の作製に成功した。GaAs(001)加工基板上にMBE選択成長法により、<-110>方向-<510>方向の細線からなるヘキサゴナルGaAs/AlGaAsリッジ細線ネットワークの作製に成功した。細線の位置およびサイズは、成長条件と初期加工基板の設計により精密に制御可能である。また、構造および光学的特性の評価から、1mm四方以上(ヘキサゴナルノードで約1x10^7個分の領域)の広範囲にわたり、エネルギー半値幅20meVの均一な量子閉じこめ構造が形成されていることを確認した。同様に、GaAs(111)B加工基板を用いて、三回対称性を利用したヘキサゴナル細線ネットワークを形成することにも成功した。達成したヘキサゴナルノードの密度は、約10^9cm^<-2>であり、量子デバイスの高密度化に非常に有望な結果を得た。2.MBE選択成長法により作製した量子ナノ構造をベースに、量子細線トランジスタ・二分岐スイッチングデバイスの作製に成功した(論文投稿中)。(001)GaAs加工基板上にMBE選択成長法に...
• Formation of Photonic Crystals by Selective Area Growth and Their Applications

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(B))

  Date (from‐to) : 2000 -2002 

  Author : Junichi MOTOHISA, 韓 哲九, 安 海岩, 藤倉 序章, 佐藤 威友, 橋詰 保

   

  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...
• 電気化学プロセスによる金属-化合物半導体界面の制御とその電子デバイスへの応用

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  Date (from‐to) : 1998 -2000 

  Author : 佐藤 威友
• Self-assembled formation of semiconductor nanostructures using electrochemcial process and its application to sensors

  Date (from‐to) : 1997

Industrial Property Rights

• 特許第6952983号:エッチング方法及びエッチング装置  

  佐藤威友, 熊崎祐介, 橋詰保
• 特許第6694102号:構造体の製造方法と製造装置および中間構造体  

  堀切 文正, 福原 昇, 佐藤 威友, 渡久地 政周  株式会社サイオクス, 住友化学株式会社  202003007817566446
• 特許第5339377号:センサ及びセンサの製造方法  

  佐藤 威友  国立大学法人北海道大学  201403049007057533
• 特許第5302553号:半導体装置とその製造方法  

  杉本 雅裕, 副島 成雅, 上杉 勉, 加地 徹, 橋詰 保, 佐藤 威友  トヨタ自動車株式会社, 株式会社豊田中央研究所, 国立大学法人 北海道大学  201303050739924338

Social Contribution

• 公開講義（札幌南高等学校）

  Date (from-to) : 2018/10/18

  Role : Lecturer

  Sponser, Organizer, Publisher  : 北海道大学・札幌南高等学校
• 公開講義（札幌開成中等教育学校）

  Date (from-to) : 2018/08/08

  Role : Lecturer

  Sponser, Organizer, Publisher  : 北海道大学・札幌開成中等教育学校