Master in Engineering, Waseda University

博士(工学), カルフォルニア大学バークレー校　大学院　材料科学専攻

Doctor of Philosophy in Engineering, Department of Materials Science, University of California, Berkeley

HD-LED semiconductor optical and electrical characterization

半導体物性評価

発光ダイオード

有機金属気相成長法

化合物半導体

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

Nanotechnology/Materials, Thin-film surfaces and interfaces

Nanotechnology/Materials, Crystal engineering

May 1994
The University of California, Berkeley, Graduate School, Division of Materials Science, Electronic Material, United States

Mar. 1985
Waseda University, Graduate School, Division of Science and Engineering, 金属工学専攻

Mar. 1983
Waseda University, Faculty of Science and Engineering, 金属工学科

Waseda High School

Fabrication and characterization of an AlGaN light emitting diode with Al-doped ZnO as a current spreading tunnel junction layer
Shun Ukita; Takeyoshi Tajiri; Kazuo Uchida
AIP Advances, AIP Publishing, 13, 9, 01 Sep. 2023, We fabricated an AlGaN light emitting diode (LED) with a heavily Al-doped n-type ZnO layer on a p-type contact layer as a tunnel junction (TJ) to improve carrier injection into the LED. We characterized its electrical and optical properties and compared them to those of an AlGaN LED without ZnO. From the I–V characteristic of the LED with ZnO, we observed a threshold voltage of circa 2 V, which could be due to Zener breakdown of the type II heterostructure of n-ZnO/p-GaN as a TJ. From the electroluminescence measurement, we observed a similar emission peak in both AlGaN LEDs at ultraviolet (UV) wavelengths, but a broad emission band around 365 nm in the LED with ZnO. This emission could be originating from ZnO photoexcited by the UV LED emission. The dependence of these peak intensities on input currents shows that there is a monotonic increase in the light emission intensity for the UV LED emission, but a saturation behavior after the threshold voltage for the emission from the ZnO. This saturation behavior is attributed to an overflow of photoexcited electron–hole pairs into p-GaN, strongly suggesting that n-ZnO/p-GaN works as a TJ. Electroluminescence data also show that the presence of the ZnO film facilitates current spreading, which enables device operation at large input currents. Therefore, ZnO can work as a current spreading TJ layer and improve the performance of the AlGaN LED.
Scientific journal

Fabrication and optical characterization of GaN micro-disk cavities undercut by laser-assisted photo-electrochemical etching
T. Tajiri, S. Sosumi, K. Shimoyoshi, and K. Uchida
Japanese Journal of Applied Physics, The Japan Society of Applied Physics, 62/ SC1069, 4S, 1-5, 14 Feb. 2023, Peer-reviwed, False, Abstract

GaN micro-disk cavities undercut by laser-assisted photo-electrochemical (PEC) etching are fabricated and optically characterized. The laser source used in the PEC etching is tuned to be absorbed by the InGaN/GaN superlattice beneath the GaN disk to selectively etch the superlattice. Whispering gallery modes (WGMs) in fabricated GaN micro-disk cavities are evaluated by micro-photoluminescence spectroscopy of light emission from the embedded InGaN quantum wells. Quality factors estimated for the WGMs reach approximately 6700 at blue-violet wavelengths. Detailed analysis suggests that the high-Q WGMs are the fundamental WGMs. These results indicate the high applicability of laser-assisted PEC etching to the fabrication of air-clad GaN micro-cavities.
Scientific journal, English

Mode analysis of GaN two-dimensional photonic crystal nanocavities undercut by photo-electrochemical etching
Takeyoshi Tajiri, Masato Yoshida, Sho Sosumi, Kenshin Shimoyoshi and Kazuo Uchida
Japanese Journal of Applied Physics, The Japan Society of Applied Physics (in press), 0, 0, 1-17, 09 Feb. 2023, Peer-reviwed, False, Abstract

GaN two-dimensional (2D) photonic crystal nanocavities with a single embedded InGaN quantum well are undercut by photo-electrochemical (PEC) etching and optically characterized to investigate the fundamental mode. The PEC etching selectively removes an InGaN-based sacrificial layer to form air-suspended GaN photonic crystal cavity slabs. We investigated the resonant modes of the photonic crystal nanocavities by micro-photoluminescence spectroscopy measurement at room temperature. The wavelengths of the measured resonant peaks and their dependence on the photonic crystal period agreed well with numerical analysis, allowing us to determine the fundamental mode in the measured spectra. The highest quality factor for the fundamental mode reached 3400 at blue wavelengths. This work would contribute to the improvement of GaN 2D photonic crystal nanocavities using PEC etching as well as their applications towards integrated light sources in visible wavelengths.
Scientific journal, English

Deep level characterization improved by Laplace charge transient spectroscopy
Shumpei Koike; Kazuo Uchida; Shinji Nozaki
International Journal of Engineering and Applied Sciences, International Journal of Engineering and Applied Sciences, 5, 2, 66-69, Feb. 2018, Peer-reviwed
Scientific journal, English

Development of Laser Lift-off Process with a GaN/Al0.7Ga0.3N Strained-Layer Superlattice for Vertical UVC LED Fabrication
David Trung Doan; Shinji Nozaki; Kazuo Uchida
International Journal of Engineering and Applied Sciences, IJEAS, 4, 4, 51-56, 01 Apr. 2017, Peer-reviwed
Scientific journal, English

ZnO-nanorods: A Possible White LED Phosphor
Sachindra Nath Sarangi; T. Arun; Dinseh K. Ray; Pratap Kumar Sahoo; Shinji Nozaki; Noriyuki Sugiyama; Kazuo Uchida
61ST DAE-SOLID STATE PHYSICS SYMPOSIUM, AMER INST PHYSICS, 1832, 060022-1-060022-3, 2017, Peer-reviwed, The white light-emitting diodes (LEDs) have drawn much attention to replace conventional lighting sources because of low energy consumption, high light efficiency and long lifetime. Although the most common approach to produce white light is to combine a hlue LED chip and a yellow phosphor, such a white LED cannot be used for a general lighting application, which requires a hroad luminescence spectrum in the visible wavelength range. We have successfully chemically synthesized the ZnO nanorods showing intense broad luminescence in the visible wavelength range and made a white LED using the ZnO nanorods as phosphor excited with a blue LED. Their lengths and diameters were 2-10 and 200-800 nm, respectively. The wurtzite structure was confirmed by the x-ray diffraction measurement. The PL spectrum obtained by exciting the ZnO nanorods with the He-Cd laser has two peaks, one associated with the near band-edge recombination and the other with recombination via defects. The peak intensity of the near band-edge luminescence at 388 nm is much weaker than that of the defect-related luminescence. The latter luminescence peak ranges from 450 to 850 nm and broad enough to be used as a phosphor for a white LED. A white LED has been fabricated using a blue LED with 450 nm emission and ZnO nanorod powders. The LED performances show a white light emission and the electroluminescence measurement shows a stiff increase in white light intensity with increasing blue LED current. The Commission International del 'Eclairage (CIE) chromaticity colour coordinates of 450 nm LED pumped white emission shows a coordinate of (0.31, 0.32) for white LED at 350 mA. These results indicate that ZnO nanorods provides an altemate and effective approach to achieve high-performance white LEDs and also other optoelectronic devices.
International conference proceedings, English

Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor
Teuku Muhammad Roffi; Shinji Nozaki; Kazuo Uchida
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 451, 57-64, Oct. 2016, Peer-reviwed, Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O-2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O-2/Ni ratios. (C) 2016 Elsevier B.V. All rights reserved.
Scientific journal, English

InGaP/GaAs heterojunction photosensor powered by an on-chip GaAs solar cell for energy harvesting
Phuc Hong Than; Kazuo Uchida; Takahiro Makino; Takeshi Oshima; Shinji Nozaki
Japanese Journal of Applied Physics, The Japan Society of Applied Physics, 55, 4S, 04ES09-1-04ES09-6, 16 Mar. 2016, Peer-reviwed, In this study, an InGaP/GaAs heterojunction phototransistor (HPT) and a GaAs solar cell were monolithically integrated into an HPT epitaxial wafer, and the battery-free operation of the HPT was demonstrated for energy harvesting. Although the thickness and doping condition of the layers were optimized for the HPT performance, but not for the solar cell performance, the obtained short-circuit current was high enough to operate the InGaP/GaAs HPT in a two-terminal (2T) configuration. A collector photocurrent of 0.63 mA was obtained when the energy-harvesting InGaP/GaAs 2T-HPT was exposed to white light with a power density of 35 mW/cm², and it linearly increased with the power density. For a potential application of the energy-harvesting InGaP/GaAs HPT as a photosensor in space, the device was irradiated with electrons of 1 MeV energy and 10¹⁵cm⁻²fluence. No significant degradation of the fabricated energy-harvesting 2T-HPT after the high-energy electron irradiation guarantees its battery-free operation in space.
Scientific journal, English

Effects of Electrical Stress on the InGaP/GaAs Heterojunction Phototransistor
Phuc Hong Than; Kazuo Uchida; Shinji Nozaki
IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 15, 4, 604-609, Dec. 2015, Peer-reviwed, Although the effects of electrical stress on the performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) have been widely studied and reported, few or no reports on the InGaP/GaAs heterojunction phototransistors (HPTs) have been published. In this paper, we discuss the phototransistor characteristics before and after the electrical stress applied at room temperature and at high temperature, and assess the effectiveness of the emitter- ledge passivation, which was found to keep the InGaP/GaAs HBTs from degrading at higher temperature or due to electrical stress. A room- temperature electrical stress was applied to the HPTs by maintaining a current density of 37 A/cm(2) for 1 h at room temperature. The electrical stress was lower by two to three orders than the stress usually applied to the HBTs for the stress study and did not cause significant decreases in the room- temperature current gain and photoresponse, but it significantly degraded the characteristics of the InGaP/GaAs HPTs at 420 K. In order to accelerate the degradation, the high- temperature stress was applied to both HPTs with and without the emitter- ledge passivation at 420 K. Although the current density was the same and the stress time was reduced to 15 min, the high- temperature stress significantly decreased the current gain and collector photocurrent of the HPT without the emitter- ledge passivation over the entire measurement temperature range of 300- 420 K. The emitter- ledge passivation suppresses the recombination via defects at the emitter perimeter and is found to be more effective than that in the HBTs.
Scientific journal, English

Effects of electrical stress on the InGaP/GaAs heterojunction phototransistors
Phuc Hong Than; Kazuo Uchida; Shinji Nozaki
IEEE Transactions on Device and Materials Reliability, IEEE, 15, 4, 1-6, Dec. 2015, Peer-reviwed
Scientific journal, English

Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass
R. Usuda; K. Uchida; S. Nozaki
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 107, 18, 182903-1-182903-4, Nov. 2015, Peer-reviwed, Although a UV cure was found to effectively convert a perhydropolysilazane (PHPS) spin-on-glass film into a dense SiOx film at low temperature, the electrical characteristics were never reported in order to recommend the use of PHPS as a gate-oxide material that can be formed at low temperature. We have formed a high-quality gate oxide by UV irradiation on the PHPS film, and obtained an interface midgap trap density of 3.4 x 10(11) cm(-2) eV(-1) by the UV wet oxidation and UV post-metallization annealing (PMA), at a temperature as low as 160 degrees C. In contrast to the UV irradiation using short-wavelength UV light, which is well known to enhance oxidation by the production of the excited states of oxygen, the UV irradiation was carried out using longer-wavelength UV light from a metal halide lamp. The UV irradiation during the wet oxidation of the PHPS film generates electron-hole pairs. The electrons ionize the H2O molecules and facilitate dissociation of the molecules into H and OH-. The OH- ions are highly reactive with Si and improve the stoichiometry of the oxide. The UV irradiation during the PMA excites the electrons from the accumulation layer, and the built-in electric field makes the electron injection into the oxide much easier. The electrons injected into the oxide recombine with the trapped holes, which have caused a large negative flat band voltage shift after the UV wet oxidation, and also ionize the H2O molecules. The ionization results in the electron stimulated dissociation of H2O molecules and the decreased interface trap density. (C) 2015 AIP Publishing LLC.
Scientific journal, English

Visible-blind ultraviolet photodiode fabricated by UVoxidation of metallic zinc on p-Si
Dongyuan Zhang; Kazuo Uchida; Shinji Nozaki
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 118, 9, 094502-1-094502-8, Sep. 2015, Peer-reviwed, A UV photodiode fabricated by the UV oxidation of a metallic zinc thin film on p-Si has manifested unique photoresponse characteristics. The electron concentration found by the Hall measurement was 3 x 10(16) cm(-3), and such a low electron concentration resulted in a low visible photoluminescence. UV illumination enhances the oxidation at low temperatures and decreases the concentration of the oxygen vacancies. The I-V characteristic showed a good rectification with a four-order magnitude difference in the forward and reverse currents at 2V, and its linear and frequency independent C-2-V characteristic confirmed an abrupt pn junction. The photoresponse showed a visible blindness with a responsivity ratio of UV and visible light as high as 100. Such a visible-blind photoresponse was attributed to the optimum thickness of the SiO2 formed on the Si surface during the UV oxidation at 400 degrees C. A lower potential barrier to holes at the ZnO/SiO2 interface facilitates Fowler-Nordheim tunneling of the photo-generated holes during the UV illumination, while a higher potential barrier to electrons efficiently blocks transport of the photo-generated electrons to the ZnO during the visible light illumination. The presence of oxide resulted in a slow photoresponse to the turn-on and off of the UV light. A detailed analysis is presented to understand how the photo-generated carriers contribute step by step to the photocurrent. In addition to the slow photoresponse associated with the SiO2 interfacial layer, the decay of the photocurrent was found extremely slow after turn-off of the UV light. Such a slow decay of the photocurrent is referred to as a persistent photoconductivity, which is caused by metastable deep levels. It is hypothesized that Zn vacancies form such a deep level, and that the photo-generated electrons need to overcome a thermal-energy barrier for capture. The ZnO film by the UV oxidation at 400 degrees C was found to be rich in oxygen and deficient in zinc. (C) 2015 AIP Publishing LLC.
Scientific journal, English

Structural, electrical, and optical properties of CoxNi1-xO films grown by metalorganic chemical vapor deposition
Teuku Muhammad Roffi; Kazuo Uchida; Shinji Nozaki
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 414, 123-129, Mar. 2015, Peer-reviwed, Thin films of cobalt nickel oxide (CoxNi1-xO, x=0.01, 0.02, 0.08, 0.17, 022, 0.35, 0.56, 0.72) were grown on Al2O3 substrate by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD). The effect of the cobalt composition on the structural, morphological, optical, and electrical properties of the films was investigated. X-ray diffraction (XRD) analysis revealed that all of the films grew with a preferred orientation towards [1 1 1](Nio) and a twinned structure. Cobalt was well dispersed in the NiO structure up to x=0.08. Co alloys were formed from x=0.17 to x=0.22, while phase-separated NiO and CoxNi1-xO formed when x > 0.35. The bandgap of the CoxNi1-xO film was found to decrease with increasing cobalt composition. Four-point probe measurements showed that the resistivity of the film also decreased with increasing cobalt composition, reaching a minimum of 0.006 Omega cm. Hall measurements of the films revealed n-type conductivity. The correlation between the presence of cobalt in different ionization states and the observed decrease in resistivity as well as the type of conductivity in CoxNi1-xO is discussed. (C) 2015 Elsevier B.V. All rights reserved.
Scientific journal, English

New Task and Ambient Lighting System with Dual Light Distributions
Kazuo Uchida; Goro Terumichi
2015 IEEE INTERNATIONAL CONFERENCE ON BUILDING ENERGY EFFICIENCY AND SUSTAINABLE TECHNOLOGIES (ICBEST), IEEE, ICBEST2015, 1-4, 2015, Peer-reviwed, A new task and ambient solid-state lighting system with dual light distributions is embodied by a combination of optics techniques and appropriate illumination design. this system enables the emission of light that can be used comfortably in a working office environment with improved energy efficiency while simultaneously providing an urban landscape that enhances the overall value of the office building.
International conference proceedings, English

Effects of Electrical Stress and High-Energy Electron Irradiation on the InGaP/GaAs Heterojunction Phototransistor
P. H. Than; K. Uchida; T. Makino; T. Ohshima; S. Nozaki
Mat. Res. Soc. Symp. Proc., 1792, 2015, Peer-reviwed
International conference proceedings, English

NiO/Si heterostructures formed by UV oxidation of nickel deposited on Si substrates
Dongyuan Zhang; Shinji Nozaki; Kazuo Uchida
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, A V S AMER INST PHYSICS, 32, 3, 0131202-1-0131202-6, May 2014, Peer-reviwed, Nickel oxide (NiO) is one of few metal-oxide semiconductors showing a p-type conductivity and can be combined with an n-type semiconductor to fabricate a pn diode. In this study, isotype and anisotype heterojunction diodes were fabricated by ultraviolet (UV) oxidation at 350 degrees C of metallic Ni deposited on p- and n-Si substrates. The I-V characteristics of the NiO/p-Si diode do not show rectification, while those of the NiO/n-Si diode show rectification with a difference of two orders of magnitude between the currents at 2 and -2V. The linear C-2-V characteristics of the NiO/n-Si and secondary ion mass spectroscopy profile confirm that the UV oxidation temperature is low enough so as not to affect deep inside the Si. The NiO layers formed by the oxidation of Ni under UV illumination are found to be more conductive and more suitable for the diode fabrication than those by the thermal oxidation of Ni without UV illumination at the same temperature. Because the oxidation temperature is relatively low and can be further reduced, the UV oxidation can become an important process technology to form various metal-oxide semiconductors from printed metals for future printed flexible electronics. (C) 2014 American Vacuum Society.
Scientific journal, English

High-quality gate oxide formed at 150 °c for flexible electronics
Yasuhiro Iijima; Ryo Usuda; Kazuo Uchida; Shinji Nozaki
Japanese Journal of Applied Physics, Japan Society of Applied Physics, 53, 8, 08LC05-1-08LC05-5, 2014, Peer-reviwed, This study describes the low temperature process to form the gate oxide of MOSFETs using a SiO nano-powder and post UV oxidation. The highquality SiO 2 gate oxide was successfully formed on a silicon substrate by vacuum evaporation of the SiO nano-powder followed by the post UV oxidation in steam at 200 °C. However, further lowering of the oxidation temperature to 150 °C degraded the insulating property and increased the interface trap density. In order to improve the SiO2/Si interface quality, the Si surface was irradiated by vacuum UV (VUV) using a Xe excimer lamp before evaporation of the SiO nano-powder. This substrate treatment has substantially improved the SiO2/Si interface quality. The physical mechanisms of the VUV and UV oxidation are discussed in order to understand the low-temperature formation of the SiO2. © 2014 The Japan Society of Applied Physics.
International conference proceedings, English

Hydrothermal growth of zinc oxide nanorods and glucose-sensor application
Shinji Nozaki; Sachindra N. Sarangi; Kazuo Uchida; Surendra Sahu
Soft Nanoscience Letters, 3, -, 23-26, Dec. 2013, Peer-reviwed
Scientific journal, English

Highly p-typed superlattices consist of undoped InAs and carbon-doped GaAs layers
Kazuo Uchida; Heisuke Kanaya; Hiroshi Imanishi; Atushi Koizumi; Shinji Nozaki
Journal of Crystal Growth, Elsevier B.V., 370, 197-199, 01 May 2013, Peer-reviwed, The strained-layer-superlattice (SLS) consisting of undoped InAs and carbon-doped GaAs (GaAs:C) layers were successfully grown on InP substrates by LP-MOVPE. The grown superlattice shows the p-type conductivity with a hole concentration of 1×1019 cm-3 and Hall mobility of 70 cm2 V-1 s-1 at room temperature. The resistivity is low enough to be used as an electrically equivalent highly p-type InGaAs base layer of an InP/InGaAs heterojunction bipolar transistor (HBT). The High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) images reveal that the InAs/GaAs:C superlattice has an interface more abrupt than the undoped InAs/GaAs superlattice. It is attributed to the suppressed In diffusion from InAs to GaAs due to carbon doping in GaAs. © 2012 Elsevier B.V. All rights reserved.
Scientific journal, English

Characterization of partially ordered GaInP/GaAs heterointerfaces by the quantum Hall effect
Kazuo Uchida; Kiwamu Satoh; Keita Asano; Atsushi Koizumi; Shinji Nozaki
Journal of Crystal Growth, Elsevier B.V., 370, 136-140, 01 May 2013, Peer-reviwed, The new approach to the characterization of semiconductor interfacial properties by the quantum Hall effect (QHE) and the scanning near field optical microscopy (SNOM) is demonstrated to the heterointerfaces of partially ordered GaInP/GaAs grown by low-pressure Metal Organic Vapor Phase Epitaxy. The Shubnikov de-Haas (SdH) oscillations and the Hall plateaus are observed in the heterointerfaces of both the less-ordered and more-ordered GaInP/GaAs samples with a large clover-shape, but these samples exhibit both 2D and 3D electron behaviors. In contrast to large clover-shaped samples, the distinct SdH oscillations and the Hall plateaus in the less-ordered sample, while the single SdH oscillation and the corresponding large plateau in the more-ordered small Hall-bar sample are observed. These results suggest that there may be many domains, each having a different carrier density and sizes in the less-ordered sample, while one or few large domains with uniform carrier concentration and sizes in the more-ordered sample. In SNOM measurements, PL intensity varies in the mapping of the more-ordered sample and it is concluded that the variation of the PL intensity may result from an inhomogeneous distribution of non-radiative recombination centers in the more-ordered sample. © 2012 Elsevier B.V. All rights reserved.
Scientific journal, English

Selective growth of ZnO nanorods by the hydrothermal technique
Shinji Nozaki; Sachin N Sarangi; Surendra N Sahu; Kazuo Uchida
Advances in Natural Sciences: Nanoscience and Nanotechnology, IOP PUBLISHING LTD, 4, 1, 015008, Mar. 2013, Peer-reviwed, Zinc oxide nanorods were selectively grown on engineered substrates, Ag-patterned and photoresist-patterned substrates, by the hydrothermal technique using zinc nitrate (Zn(NO3)2) and hexamethylenetetramine ((CH2)6N4). The nanorod growth was affected by the substrate to be used. The nanorods were vertically grown on a GaN substrate but not on a Si substrate because of lattice mismatch. However, since the nanorods were grown on a thick Ag film no matter what substrate was used, a thick Ag film was deposited on a Si substrate to prepare the Ag-patterned substrate. Accordingly, the nanorods were grown only on the Ag pads. When the sizes of Ag pads were small such as 100 nm×100 nm, one single nanorod was grown on an Ag pad. As another engineered substrate, the photoresist was patterned to prepare an array of holes on a GaN-on-sapphire substrate by e-beam lithography. When the hole size was 10 nm×10 nm and higher, concentrations of Zn(NO3)2 and ((CH2)6N4) were employed, all holes were successfully filled with a single nanorod.© 2013 Vietnam Academy of Science &
Technology.
Scientific journal, English

E-1/E-2 traps in 6H-SiC studied with Laplace deep level transient spectroscopy
A. Koizumi; V. P. Markevich; N. Iwamoto; S. Sasaki; T. Ohshima; K. Kojima; T. Kimoto; K. Uchida; S. Nozaki; B. Hamilton; A. R. Peaker
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 102, 3, 032104-1 – 032104-4, Jan. 2013, Peer-reviwed, Electrically active defects in n-type 6H-SiC diode structures have been studied by deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. It is shown that the commonly observed broadened DLTS peak previously ascribed to two traps referenced as E-1/E-2 has three components with activation energies for electron emission of 0.39, 0.43, and 0.44 eV. Further, defects associated with these emission signals have similar electronic structure, each possessing two energy levels with negative-U ordering in the upper half of the 6H-SiC gap. It is argued that the defects are related to a carbon vacancy at three non-equivalent lattice sites in 6H-SiC. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4788814]
Scientific journal, English

InGaP/GaAsヘテロ接合フォトトランジスタの温度特性
Phuc Hong THAN; 高木保志; 内田和男; 野崎眞次
電子情報通信学会論文誌 C, The Institute of Electronics, Information and Communication Engineers, J96-C, 9, 238-244, 2013, Peer-reviwed, InGaP/GaAsヘテロ接合バイポーラトランジスタ(HBT)の温度特性はこれまで多く調べられ,報告されているが,InGaP/GaAsヘテロ接合フォトトランジスタ(HPT)の温度特性についてはほとんど報告例がない.本研究では,白色光に対する光応答の高感度検出への応用を目的に,InGaP/GaAs HPTを作製し,300〜400Kの温度範囲でInGaP/GaAs HPTの電流利得β及び受光感度Sを測定した.その結果,電流利得βは温度とともに減少し,受光感度Sは320Kまで増加するがその後は減少した.これらの実験結果は,HPTの三端子等価回路により説明された.また,HBTにおいて露出した高濃度GaAsベース表面でのキャリヤの再結合を抑制し,電流利得を高めるエミッタレッジパッシベーションのHPTにおける効果も検証した.エミッタレッジパッシベーションは,HPTにおいても全ての測定温度で高い電流利得β及び受光感度Sを維持するのに有効であった.特にエミッタレッジパッシベーションは,HBT以上にHPTの高性能化に貢献することが明らかとなった.
Scientific journal, Japanese

Effect of O2/Ni ratio on structure and surface morphology of atmospheric pressure MOCVD grown NiO thin films
Teuku M. Roffi; Motohiko Nakamura; Kazuo Uchida; Shinji Nozaki
Materials Research Society Symposium Proceedings, Materials Research Society, 1577, 42-47, 2013, Peer-reviwed, Effect of oxygen to nickel molar ratio (O2/Ni) on the crystallinity of atmospheric pressure metal organic chemical vapor deposition (APMOCVD) grown NiO at 500°C is reported. X-ray diffraction (XRD) analysis including grazing incident angle θ of 0.6°, θ-2θ, Φ and rocking curve scan are employed for crystallographic characterization. Furthermore, surface roughness is studied by atomic force microscopy (AFM). No evidence of diffraction peaks in X-ray grazing incident angle measurement confirms that all the grown NiO films are well oriented along a certain direction. θ-2θ scan results further indicate that the samples are highly oriented only along [111] direction on (0001) sapphire substrates. The analysis of full width at half maximum (FWHM) of rocking curve scan of (111) plane shows that higher O2/Ni ratio results in better crystallinity. The best crystallinity is achieved with FWHM as low as 0.106° at (111) rocking curve scan corresponding to 82.57nm grain size. AFM measurement shows that NiO films grown with higher O2/Ni ratio have smoother surface morphology. © 2013 Materials Research Society.
International conference proceedings, English

Fabrication of a p-NiO/n-Si heterojunction diode by UV oxidation of Ni deposited on n-Si
Dongyuan Zhang; Kazuo Uchida; Shinji Nozaki
Materials Research Society Symposium Proceedings, 1494, 305-309, 2013, Peer-reviwed, The metallic nickel (Ni) deposited on an n-Si substrate with resistivity of 4-6 Ω·cm was oxidized by the ultra-violet (UV) oxidation technique to form a p-NiO/n-Si heterojunction diode. The rectifying current-voltage (I-V) characteristic confirmed formation of a pn junction. The capacitance-voltage (C-V) characteristic further identified an abrupt p+n junction between NiO and n-Si. The photocurrent increased with the increased wavelength of laser under illumination of the diode. The voltage-dependent photocurrent suggests that the carriers generated in the depletion region of Si was effectively collected but not outside the depletion region. A low diffusion length of holes was attributed to Ni diffusion in Si caused by the substrate heating during the UV oxidation. © 2013 Materials Research Society.
International conference proceedings, English

Intense ultraviolet photoluminescence observed at room temperature from NiO nano porous thin films grown by the hydrothermal technique
Sachindra Nath Sarangi; Dongyuan Zhang; Pratap Kumar Sahoo; Kazuo Uchida; Surendra Nath Sahu; Shinji Nozaki
Materials Research Society Symposium Proceedings, 1494, 203-208, 2013, Peer-reviwed, We have successfully formed high-quality nanoporous NiO films by the hydrothermal technique and observed intense ultraviolet (UV) luminescence at room temperature. The SEM image reveals nanoporous NiO films with pore diameters from 70 to 500 nm. The results of XRD, Micro Raman and FTIR characterizations confirm the cubic structure of NiO. The optical band gaps estimated from the absorption spectrum are found to be 3.86 and 4.51 eV. The former is similar to that of bulk NiO, while the latter is much higher than that of bulk NiO. The increased band gap was attributed to the quantum confinement in the NiO nanocrystals, which may be present in the nanoporous NiO film. The room-temperature photoluminescence (PL) spectrum shows a peak of intense luminescence at 3.70 eV and several other peaks in the UV and near-UVwavelength regions. The intense UV luminescence at 3.70 eV was associated with the near band-edge emission and the others with defect-related emission. The high-quality wall of nanoporous NiO with a large surface-to-volume ratio provided the intense UV emission. © 2012 Materials Research Society.
International conference proceedings, English

Defects in an Electron-Irradiated 6H-SiC Diode Studied by Alpha Particle Induced Charge Transient Spectroscopy: Their Impact on the Degraded Charge Collection Efficiency
N. Iwamoto; A. Koizumi; S. Onoda; T. Makino; T. Ohshima; K. Kojima; S. Koike; K. Uchida; S. Nozaki
SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2, TRANS TECH PUBLICATIONS LTD, 717-720, 267-+, 2012, Peer-reviwed, Defects in electron-in-adiated 6H-SiC diodes have been studied by single alpha particle induced charge transient spectroscopy and deep level transient spectroscopy (DLTS) in order to identify critical defects responsible for the charge collection efficiency (CCE) decreased by high-energy electron irradiation. The defect X-2 detected by the charge transient spectroscopy and the electron trap E-i, detected by the DLTS had a similar activation energy of around 0.50 eV. In addition, the annealing at 473K completely removed defects X-2 and E-i, and restored the CCE. The defect X-2 is attributed to the electron trap E-i, and responsible for the decreased CCE.
International conference proceedings, English

High-quality single crystalline NiO with twin phases grown on sapphire substrate by metalorganic vapor phase epitaxy
Kazuo Uchida; Ken-Ichi Yoshida; Dongyuan Zhang; Atsushi Koizumi; Shinji Nozaki
AIP Advances, AMER INST PHYSICS, 2, 4, 042154-1-042154-5, 2012, Peer-reviwed, High-quality single crystalline twin phase NiO grown on sapphire substrates by metalorganic vapor phase epitaxy is reported. X-ray rocking curve analysis of NiO films grown at different temperatures indicates a minimum full width at half maximum of the cubic (111) diffraction peak of 0.107° for NiO film grown at as low as 550 °C. Detailed microstructural analysis by Φ scan X-ray diffraction and transmission electron microscopy reveal that the NiO film consists of large single crystalline domains with two different crystallographic orientations which are rotated relative to each other along the [111] axis by 60°. These single crystal domains are divided by the twin phase boundaries. © 2012 Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.
Scientific journal, English

Defects in an Electron-Irradiated 6H-SiC Diode Studied by Alpha Particle Induced Charge Transient Spectroscopy: Their Impact on the Degraded Charge Collection Efficiency
N. Iwamoto; A. Koizumi; S. Onoda; T. Makino; T. Ohshima; K. Kojima; S. Koike; K. Uchida; S. Nozaki
SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2, TRANS TECH PUBLICATIONS LTD, 717-720, 267-+, 2012, Peer-reviwed, Defects in electron-in-adiated 6H-SiC diodes have been studied by single alpha particle induced charge transient spectroscopy and deep level transient spectroscopy (DLTS) in order to identify critical defects responsible for the charge collection efficiency (CCE) decreased by high-energy electron irradiation. The defect X-2 detected by the charge transient spectroscopy and the electron trap E-i, detected by the DLTS had a similar activation energy of around 0.50 eV. In addition, the annealing at 473K completely removed defects X-2 and E-i, and restored the CCE. The defect X-2 is attributed to the electron trap E-i, and responsible for the decreased CCE.
International conference proceedings, English

Single-Alpha-Particle-Induced Charge Transient Spectroscopy of the 6H-SiC p(+)n Diode Irradiated With High-Energy Electrons
Naoya Iwamoto; Atsushi Koizumi; Shinobu Onoda; Takahiro Makino; Takeshi Ohshima; Kazutoshi Kojima; Shunpei Koike; Kazuo Uchida; Shinji Nozaki
IEEE TRANSACTIONS ON NUCLEAR SCIENCE, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 58, 6, 3328-3332, Dec. 2011, Peer-reviwed, The defects formed in a 6H-SiC p(+)n diode by irradiation with 1 MeV electrons have been studied by both single-alpha-particle-induced charge transient spectroscopy and conventional deep level transient spectroscopy (DLTS). The charge collection efficiency was significantly degraded by the electron irradiation. A radiation-induced defect (X) was observed by charge transient spectroscopy. We assign this defect to the electron trap Ei already known in literature and observed by us with DLTS, as its activation energy, 0.50 eV, and annealing behavior, are similar. Moreover, as peaks related to X/Ei disappear after annealing at 250 degrees C and charge collection efficiency also significantly recover after annealing at 250 degrees C, we conclude that this defect is mainly responsible for the decreased charge collection efficiency.
Scientific journal, English

Transient Analysis of an Extended Drift Region in a 6H-SiC Diode Formed by a Single Alpha Particle Strike and Its Contribution to the Increased Charge Collection
N. Iwamoto; S. Onoda; T. Makino; T. Ohshima; K. Kojima; A. Koizumi; K. Uchida; S. Nozaki
IEEE TRANSACTIONS ON NUCLEAR SCIENCE, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 58, 1, 305-313, Feb. 2011, Peer-reviwed, Charge collection of a 6H-SiC p(+)n diode has been studied. The collected charges of the diode are measured using a single alpha particle strike at various reverse bias voltages, then analyzed using both the low-injection charge collection model and the DESSIS device simulator. It is found that the total collected charges at lower bias voltages cannot be well understood based on the low-injection model. In distinct contrast, the device simulator successfully predicts the total collected charges at all voltages including the lower ones. The transient analysis of carrier and electric field distributions after the strike shows insignificant collapse of the original depletion region and time-dependent extension of the electric field beyond the original depletion region. A new physics is proposed to explain slower rearrangement of carriers, compared to Si devices, and formation of an extended drift region in the 6H-SiC diode based on the results of the transient analysis.
Scientific journal, English

In situ CBrCl3 etching to control size and density of InAs/GaAs quantum dots
Atsushi Koizumi; Hiroshi Imanishi; Kazuo Uchida; Shinji Nozaki
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 315, 1, 106-109, Jan. 2011, Peer-reviwed, The effects of in situ CBrCl3 etching of InAs quantum dots (QDs) grown on GaAs by metal-organic vapor phase epitaxy have been studied in detail for control of the size and density of InAs dots. The width and height distributions of InAs dots after etching for various etching times and CBrCl3 flow rates suggest that the CBrCl3 etching is ineffective in decreasing the width but effective in decreasing the height. The density of the InAs dots are controlled over more than 2 orders of magnitude by changing the flow rate from 0 to 22 mu mol/min. Although the atomic force microscopic (AFM) image for 22 mu mol/min does not show any dots because of a detection limit, the PL peak associated with the QDs evidences presence of dots whose density is less than 2 x 10(6) cm(-2). Such a low density is suitable for single QD device applications. The PL spectra for various CBrCl3 flow rates suggest less effective etching of the Ga-rich InGaAs wetting layer and the decreased size of QDs with the increased flow rates. (C) 2010 Elsevier B.V. All rights reserved.
Scientific journal, English

Compensation-dependent carrier transport of Al-doped p-type 4H-SiC
Atsushi Koizum; Naoya Iwamoto; Shinobu Onoda; Takeshi Ohshima; Tsunenobu Kimoto; Kazuo Uchida; Shinji Nozaki
Materials Science Forum, 679-680, 201-204, 2011, Peer-reviwed, The effects of compensation on the hole concentration and mobility in Al-doped 4H-SiC have been investigated by theoretical calculations using the parameters taken from our experimental results on the less-compensated epilayers. The hole concentrations, hole Hall mobilities and resistivities obtained by experiment and calculations are compared and discussed. © (2011) Trans Tech Publications.
International conference proceedings, English

Improvement of high-power-white-LED lamp performance by liquid injection
T. M. Roffi; I. Idris; K. Uchida; S. Nozaki; N. Sugiyama; H. Morisaki; F. X.N. Soelami
Proceedings of the 2011 International Conference on Electrical Engineering and Informatics, ICEEI 2011, IEEE, 1-6, 2011, Peer-reviwed, Performance of a high-power-white-LED lamp is mostly hindered by its poor thermal characteristic. This characteristic is accessed by its thermal resistance. Besides thermal characteristic, light quality of a high-power-white-LED lamp is also an important issue. This parameter is accessed by its luminous efficiency. Both thermal characteristic and light quality need to be optimized in order to develop a high-power-white-LED lamp. In this study we made an attempt to improve the characteristic features (both the thermal resistance and luminous efficiency) of a high-power-white-LED lamp by liquid injection in the lamp package. Experiments were carried out on a highpower- white-LED lamp consisting of 5 blue LED chips, 5 phosphor-epoxy layers and 3M Fluorinert FC-43 as an injected liquid. Furthermore, the light extraction with the total internal reflection was simulated to confirm the improvement by liquid injection. It is found from the experimental results that liquid injection has significantly improved the thermal dissipation of the lamp with the decreased thermal resistance by 14 %. It has also improved the lamps light quality with the increase in the luminous efficiency by 18 %. © 2011 IEEE.
International conference proceedings, English

Comparative Study on Reliability of InP/InGaAs Heterojunction Bipolar Transistors with Highly Zn- and C-Doped Base Layers
Atsushi Koizumi; Kazuki Oshitanai; Jaesung Lee; Kazuo Uchida; Shinji Nozaki
RELIABILITY AND MATERIALS ISSUES OF SEMICONDUCTOR OPTICAL AND ELECTRICAL DEVICES AND MATERIALS, MATERIALS RESEARCH SOC, 1195, 2010, Peer-reviwed, The reliability of InP/InGaAs heterojunction bipolar transistors (HBTs) with highly carbon-doped and zinc-doped InGaAs base layers grown by metal-organic vapor phase epitaxy has been investigated. The Raman spectroscopy reveals that the post-growth annealing for the carbon-doped InGaAs base improves the crystallinity to become as good as that of the zinc-doped InGaAs base. However, the photoluminescence intensity remains lower than that of the zinc-doped InGaAs even after the post-growth annealing. The current gains of the carbon-and zinc-doped base InP/InGaAs HBTs are 63 and 75, respectively, and they are affected by the base crystallinity. After the 15-min current stress test, the current gains decreased by 40 and 3% from the initial current gains for zinc-and carbon-doped base HBTs, respectively, are observed. These results indicate that the carbon-doped base HBT is much more reliable than that of zinc-doped base HBT, though it has a lower current gain.
International conference proceedings, English

Charge Collection Efficiency of 6H-SiC P+N Diodes Degraded by Low-Energy Electron Irradiation
N. Iwamoto; S. Onoda; T. Ohshima; K. Kojima; A. Koizumi; K. Uchida; S. Nozaki
SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2, TRANS TECH PUBLICATIONS LTD, 645-648, 921-+, 2010, Peer-reviwed, The effect of electron irradiation on the charge collection efficiency of a 6H-SiC p(+)n diode has been studied. The diodes were irradiated with electrons of energies from 100 keV to 1 MeV. The charge collection efficiencies of the samples were measured for alpha particles before and after the electron irradiation. The electron irradiation at 100 keV does not affect the charge collection efficiency, while the electron irradiation at 200 keV or higher decreases the charge collection efficiency. The degree of the degradation of the diodes correlates with the energy of the electron irradiation.
International conference proceedings, English

Comparative Study on Reliability of InP/InGaAs Heterojunction Bipolar Transistors with Highly Zn- and C-Doped Base Layers
Atsushi Koizumi; Kazuki Oshitanai; Jaesung Lee; Kazuo Uchida; Shinji Nozaki
RELIABILITY AND MATERIALS ISSUES OF SEMICONDUCTOR OPTICAL AND ELECTRICAL DEVICES AND MATERIALS, MATERIALS RESEARCH SOC, 1195, 35-42, 2010, Peer-reviwed, The reliability of InP/InGaAs heterojunction bipolar transistors (HBTs) with highly carbon-doped and zinc-doped InGaAs base layers grown by metal-organic vapor phase epitaxy has been investigated. The Raman spectroscopy reveals that the post-growth annealing for the carbon-doped InGaAs base improves the crystallinity to become as good as that of the zinc-doped InGaAs base. However, the photoluminescence intensity remains lower than that of the zinc-doped InGaAs even after the post-growth annealing. The current gains of the carbon-and zinc-doped base InP/InGaAs HBTs are 63 and 75, respectively, and they are affected by the base crystallinity. After the 15-min current stress test, the current gains decreased by 40 and 3% from the initial current gains for zinc-and carbon-doped base HBTs, respectively, are observed. These results indicate that the carbon-doped base HBT is much more reliable than that of zinc-doped base HBT, though it has a lower current gain.
International conference proceedings, English

Compensation-dependent carrier transport of Al-doped p-type 4H-SiC
A. Koizumi; N. Iwamoto; S. Onoda; T. Ohshima; T. Kimoto; K. Uchida; S. Nozaki
Abstract of ECSCRM8th, TP-230, 2010, Peer-reviwed
International conference proceedings, English

Characterization of MOVPE-grown p-InGaAs/n-InP interfaces
Kazuo Uchida; HIdenori Yamato; Yoshikuni Tommioka; Atsushi Koizumi; Shinji Nozaki
Journal of Crystal Growth, ELSEVIER, 311, 16, 4011-4015, Jul. 2009, Peer-reviwed, The low-pressure MOVPE-grown p-InGaAs-on-n-InP and n-InP-on-p-InGaAs diodes were characterized by I-V and C-V measurements to study the effects of the growth conditions on the heterointerface. The obtained band discontinuity in the conduction band Delta E-c ranged from 0.19 to 0.32 eV. It was found that Delta E-c was very sensitive to the growth interruption at the InP/InGaAs heterointerface. The n-InP-on-p-InGaAs diodes tend to show higher Delta E-c than the p-InGaAs-on-n-InP diodes. The decreased Delta E-c at InGaAs-on-InP heterointerface might be attributed to the graded layer of InGaAsP formed by intermixing at the interface. It is concluded from the estimated Delta E-c that the InP-on-InGaAs heterointerface is more abrupt than the InGaAs-on-InP heterointerface. An improvement of the InGaAs-on-InP heterointerface is mandatory for fabrication of high-performance double heterojunction bipolar transistors with InP collector layers. (C) 2009 Elsevier B.V. All rights reserved.
Scientific journal, English

High-quality oxide formed by evaporation of SiO nanopowder: Application to MOSFET’s on plastic substrates and GaN epilayers
S. Nozaki; S. Kimura; A. Koizumi; H. Ono; K. Uchida
Materials Science in Semiconductor Processing, 11, 384-389, 2009, Peer-reviwed
Scientific journal, English

High-quality oxide formed by evaporation of SiO nanopowder: Application to MOSFET’s on plastic substrates and GaN epilayers
S. Nozaki; S. Kimura; A. Koizumi; H. Ono; K. Uchida
Materials Science in Semiconductor Processing, 11, 384-389, Jan. 2009, Peer-reviwed
Scientific journal, English

InGaP/GaAs HETEROINTERFACES STUDIED BY CROSS-SECTIONAL SCANNING TUNNELING MICROSCOPY AND THEIR IMPACT ON THE DEVICE CHARACTERISTICS
S. Nozaki; A. Koizumi; K. Uchida; H. Ono
PHYSICS, CHEMISTRY AND APPLICATION OF NANOSTRUCTURES, WORLD SCIENTIFIC PUBL CO PTE LTD, 18-+, 2009, Peer-reviwed, An InGaP/GaAs double heterojunction bipolar transistor (DHBT) was fabricated. Early effect observed in the normal operation of the DHBT suggests the interdiffusion or mixing of III and V elements at the GaAs-on-InGaP heterointerface. The analysis of both heterointerfaces in the atomic STM images confirms that the GaAs-on-InGaP heterointerface is rougher than the InGaP-on-GaAs heterointerface.
International conference proceedings, English

Photoluminescence of Si nanocrystals formed by the photosynthesis
S. Nozaki; C. Y. Chen; S. Kimura; H. Ono; K. Uchida
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 517, 1, 50-54, Nov. 2008, Peer-reviwed, Photosynthesis, which could control the size and position of Si nanocrystals being formed, as a novel nanofabrication technique making the best use of the strong interaction between photons and nanoparticles, is discussed in great detail. A nanocrystal growth is self-limited to the laser power and the laser-exposure time. The model is proposed to explain the self-limited growth and luminescence from the Si-rich oxide which was exposed to the laser. When the balance between the formation and loss of small amorphous Si clusters on the nanocrystal surface is maintained at a certain size, the nanocrystal growth will stop, and the final average size of the Si nanocrystals is achieved for each laser wavelength. The photoluminescence (PL) is observed when the Si nanocrystals are formed. The origin of the PL is associated with the small amorphous Si clusters, and its intensity increases with the increasing density of the Si clusters or photosynthesized Si nanocrystals. These small amorphous Si clusters remain particularly in the SiO nanopowder, which was made by thermal CVD using SiH(4) and O(2), even when the final average size is reached. The PL peak wavelength is well determined by the laser wavelength, which affects the structure of the small amorphous Si clusters and their light-emission energy. The photosynthesis is found to not only selectively form Si nanocrystals at low temperature, but also controls their size and even light-emission energy. (c) 2008 Elsevier B.V. All rights reserved.
Scientific journal, English

Growth and optical properties of SnO2 ultra-small nanorods by the novel micelle technique
S. Rath; S. Nozaki; H. Ono; K. Uchida; S. Kojima
Materials Research Society Mat. Res. Soc. Symp. Proc., 1087, 29, 2008, Peer-reviwed
International conference proceedings, English

Photo-modification and synthesis of semiconductor nanocrystals
S. Nozaki; C. Y. Chen; H. Ono; K. Uchida
SURFACE SCIENCE, ELSEVIER SCIENCE BV, 601, 13, 2549-2554, Jul. 2007, Peer-reviwed, Both photo-oxidation and photosynthesis manifest a strong interaction between nanoparticles and photons due to the large surface area-to-volume ratio. The final sizes of the semiconductor nanocrystals are determined by the photon energy during these phenomena. The photosynthesis is demonstrated in a Si-rich oxide and is similar to thermal synthesis, which involves the decomposition of SiOx into Si and SiO2, that is well known and often employed to form Si or Ge nanocrystals embedded in SiO2 by annealing SiOx at high temperature. However, photosynthesis is much faster, and allows the low-temperature growth of Si nanocrystals and is found to be pronounced in the SiO nanopowder, which is made by thermal CVD using SiH4 and O-2. The minimum laser power required for the photosynthesis in the SiO nanopowder is much lower than in the Si-rich oxide formed by the co-sputtering of Si and SiO2. This is attributed to the weak bond strength of Si-Si and Si-O in the SiO nanopowder. Photosynthesis, which can control the size and position of Si nanocrystals, is a novel nanofabrication technique making the best use of the strong interaction between photons and nanoparticles. (C) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English

Yellowish-white photoluminescence from ZnO nanoparticles doped with Al and Li
J. Nayak; S. Kimura; S. Nozaki; H. Ono; K. Uchida
SUPERLATTICES AND MICROSTRUCTURES, ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD, 42, 1-6, 438-443, Jul. 2007, Peer-reviwed, ZnO nanoparticles codoped with Al and Li were chemically synthesized with a low temperature drying process. They are crystalline and can be made as small as 5 nm. Intense yellowish white photoluminescence, was observed from smaller ZnO nanoparticles with a higher concentration of Al and Li. The photoluminescence peak consists of yellow and green emission bands. Both peak intensities increase with increasing the Al and Li concentrations and with decreasing the size of ZnO nanoparticles. The green and yellow emission bands were attributed to donor-acceptor-pair recombination involving Zn vacancies and lithium as the acceptor state, respectively, and the donor responsible for both emissions to oxygen vacancies. Both enhanced emissions by codoping may be explained by an increase in the number of electrons occupying the deep donor level on account of doping with Al. Although the yellowish white emission decays with time, passivation of the crystallite surface with poly (p-phenylene vinylene) suppresses the degradation. The observed high-intensity and stable yellowish white emission makes PPV-passivated ZnO nanoparticles, codoped with Al and Li, more attractive as a candidate for "white" phosphor. (c) 2007 Elsevier Ltd. All rights reserved.
Scientific journal, English

Mechanically strong ultralow-k nanoporous silica made of SiOx nanoparticles
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida
Advanced Metallization Conference 2006 (AMC 2006), MATERIALS RESEARCH SOCIETY, 413-417, 2007, Peer-reviwed, We have successfully improved the mechanical strength of nanoporous silica thin films by the gas-evaporation technique since we first reported ultralow-k nanoporous silica made of SiOx nanoparticles. The key to the success is the increased substrate temperature during deposition of SiOx nanoparticles, which causes firm bonding of adjacent nanoparticles. The obtained nanoporous silica thin film with a dielectric constant of 1.8, whose modulus and hardness are 15 and 2.1 GPa, respectively, is suitable for the interdielectric to be used in the next-generation ULSI.
International conference proceedings, English

Correlation between the base-emitter interface crystalline quality and the current gain in InGaP/GaAs HBTs grown by MOVPE
K. Uchida; A. Kurokawa; F. Yang; Z. Jin; S. Nozaki; H. Morisaki
Jornal of Crystal Growth, ELSEVIER SCIENCE BV, 298, 861-866, Nov. 2006, Peer-reviwed, We demonstrated that the InGaP emitter ledge passivation in InGaP/GaAs heterojunction bipolar transistor (HBT) could suppress the recombination components in I-B induced by the extrinsic base surface and the defects activated by the current stress. Similar suppression of I-B by the current stress was found in unpassivated HBT with the 2 min growth interruption at the base-emitter interface under PH3 partial pressure and we attributed this to the existence of an intermediate layer at the base-emitter interface that would improve the interface crystalline quality and reduce the recombination component of I-B induced by defects at the base-emitter edge. Unpassivated HBT with the shorter post-growth annealing in time in hydrogen atmosphere, however, showed the increase in the current gain beta with the current stress because of the burn-in effect rather than the decrease in beta due to the increase of I-B induced by defects. (c) 2006 Elsevier B.V. All rights reserved.
Scientific journal, English

Selective formation of size-controlled silicon nanocrystals by photosynthesis in SiO nanoparticle thin film
Changyong Chen; Seiji Kimura; Shinji Nozaki; Hiroshi Ono; Kazuo Uchida
IEEE TRANSACTIONS ON NANOTECHNOLOGY, IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 5, 6, 671-676, Nov. 2006, Peer-reviwed, The SiOx thin film with a thickness of about 1 mu m was formed on a GaAs substrate by bar-coating with the organic solution of the SiOx nanoparticles (similar to 40 nm). The as-formed SiOx thin film consists of the SiOx nanoparticles; thus the thin film is macroscopically discontinuous and is referred to as a nanoparticle thin film. Although there were no silicon (Si) nanocrystals in the as-formed SiOx nanoparticle thin film, Si nanocrystals were observed by Raman scattering measurement after the thin film was exposed to the laser beam. The growth of Si nanocrystals by laser irradiation is referred to as photosynthesis. The photosynthesis of Si nanocrystals is found to be a self-limiting process. After the average size reaches a certain value, further increase of irradiation time or laser power does not increase the average size. The photosynthesis is similar to the thermal synthesis of Si nanocrystals from SiOx but much faster and low-temperature growth of Si nanocrystals from SiOx. Furthermore, the laser irradiation makes nanoparticles larger by merging. This suggests a possibility of low-temperature formation of a Si-nanocrystal array embedded in a SiO2 thin film. Such a structure has many potential device applications.
Scientific journal, English

Passivation of InP-based HBTs
Z. JIn; K. Uchida; S. Nozaki; W. Prost; F.-J. Tegude
Applied surface science, 252, 7664-7670, May 2006, Peer-reviwed
Scientific journal, English

Position and size-controlled photosynthesis of silicon nanocrystals in SiO2 films
C. Y. Chen; S. Kimura; S. Sen; S. Nozaki; H. Ono; K. Uchida; H. Morisaki
2006 IEEE CONFERENCE ON EMERGING TECHNOLOGIES - NANOELECTRONICS, IEEE, 289-+, 2006, Peer-reviwed, The SiOx thin film made of the SiOx nanoparticles (similar to 40 mu m) shows a strong reaction to laser irradiation. The photosynthesis of silicon (Si) nanocrystals (NC's) is found to be self-limited to the laser power and exposure time. Furthermore, the laser irradiation of the SiOz film not only produces Si NC's, also transforms (.) the SiOx. film from the powder-like to the continuous. The photosynthesis of Si NC's has several advantages such as low-temperature process and good control in the size and positioning over the conventional synthesis methods and has many potential applications.
International conference proceedings, English

Synthesis, properties and applications of germanium nanocrystals
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida; Hiroshi Morisaki
NANO-SCALE MATERIALS: FROM SCIENCE TO TECHNOLOGY, NOVA SCIENCE PUBLISHERS, INC, 35-42, 2006, Peer-reviwed, We present an overview of the synthesis, properties and applications of germanium (Ge) nanocrsytals, referring to our recent review article published in Encyclopedia of Nanoscience and Nanotechnology [1]. We developed two fabrication techniques; the cluster-beam evaporation and the gas evaporation with a supersonic jet nozzle, to obtain smaller Ge nanocrystals with a good size distribution and observed unique optical and electrical phenomena such as photooxidation, blue-light emission, coulomb blockade. and phase-transformation. Although light-emitting devices may be the first choice among the device applications of Ge nanocrystals similar to Si nanocrystals, the short-term development of such devices is hindered by a low luminescence efficiency and the broad peak of the luminescence spectra. A new application that makes the best use of the properties of Ge nanocrystals and that cannot be realized with any other material must be explored for Ge nanocrystals to become more industrially important.
International conference proceedings, English

Low-temperature formation of high-quality SiOx thin films by evaporation of SiO nanopowder
S. Nozaki; S. Kimura; H. Ono; K. Uchida
The 13th International Workshop on Active-Matrix Flatpanel Displays and Devices (Digest of Technical Papers), 19-22, 2006, Peer-reviwed
International conference proceedings, English

Material Issues in high-frequency GaInP/GaAs heterojunction bipolar transistors
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida; Hiroshi Morisaki
Proceedings of the XIII International Workshop on Physics of Semiconductor Devices, vol. II, 741-747, Dec. 2005, Peer-reviwed
International conference proceedings, English

Self-limited photo-assisted synthesis of silicon nanocrystals
CY Chen; S Kimura; S Seo; S Nozaki; H Ono; K Uchida; H Morisaki
Group-IV Semiconductor Nanostructures, MATERIALS RESEARCH SOCIETY, 832, 249-254, 2005, Anomalous growth of silicon (Si) nanocrystals (NCs) was observed during Raman scattering measurements of nanosilica SiOx (x=0.9) powder with an average diameter of 40 nm. It was found that Si NCs were formed by exposure to the laser beam. This photo-assisted synthesis is similar to the thermal synthesis of Si NCs, which forms Si NCs by thermally decomposing SiOx into Si and SiO2. However, the photo-assisted synthesis is more effective in forming Si NCs than the thermal synthesis. Even one second after irradiation of the nanosilica SiOx powder with laser, Si NCs with an average size of 5 nm were formed. The Si NC size increases with increasing the laser power and exposure time. It is interesting to observe a self-limited size for higher laser power and prolonged exposure. The photo-assisted synthesis of Si NCs is proved to be a promising technique with a wide range of applications in nanotechnology.
International conference proceedings, English

Self-limited photo-assisted synthesis of silicon nanocrystals
CY Chen; S Kimura; S Seo; S Nozaki; H Ono; K Uchida; H Morisaki
Group-IV Semiconductor Nanostructures, MATERIALS RESEARCH SOCIETY, 832, 249-254, 2005, Peer-reviwed, Anomalous growth of silicon (Si) nanocrystals (NCs) was observed during Raman scattering measurements of nanosilica SiOx (x=0.9) powder with an average diameter of 40 nm. It was found that Si NCs were formed by exposure to the laser beam. This photo-assisted synthesis is similar to the thermal synthesis of Si NCs, which forms Si NCs by thermally decomposing SiOx into Si and SiO2. However, the photo-assisted synthesis is more effective in forming Si NCs than the thermal synthesis. Even one second after irradiation of the nanosilica SiOx powder with laser, Si NCs with an average size of 5 nm were formed. The Si NC size increases with increasing the laser power and exposure time. It is interesting to observe a self-limited size for higher laser power and prolonged exposure. The photo-assisted synthesis of Si NCs is proved to be a promising technique with a wide range of applications in nanotechnology.
International conference proceedings, English

Low temperature photoluminescence of GaAs/GaInP heterostructures measured under hydrostatic pressure
T Kobayashi; A Nagata; AD Prins; Y Homma; K Uchida; J Nakahara
Physics of Semiconductors, Pts A and B, AMER INST PHYSICS, 772, 1, 931-932, 2005, Peer-reviwed, A study of 11 K photoluminescence measurements of metalorganic vapor phase epitaxy grown GaAs/GaInP quantum wells is reported for the first time at pressures up to similar to 5 GPa. The use of low temperature allows us to study the true nature of a peak at similar to 1.46 eV, which dominates instead of the GaAs QW emission, even at very low excitation intensities to pressures well above the Gamma-X crossover in GaInP. Our results suggest that the similar to 1.46 eV emission is a spatially indirect transition of electrons and holes separated at the interface in a type II band alignment.
International conference proceedings, English

Excitation and pressure effects on low temperature photoluminescence from GaAs/GaInP heterostructures
A Nagata; T Kobayashi; AD Prins; Y Homma; K Uchida; J Nakahara
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, WILEY-V C H VERLAG GMBH, 241, 14, 3279-3284, Nov. 2004, Peer-reviwed, We report for the first time the results of a study of 11 K photoluminescence (PL) measurements of metal-organic vapor phase epitaxy grown GaAs/GaInP quantum wells at pressures up to similar to5 GPa and examine the effects of laser excitation energy and intensity. The use of low temperature allows us to study the true nature of a peak at similar to 1.46 eV, which dominates instead of the GaAs QW emission, even at very low excitation intensities to pressures well above the F-X crossover in GaInP. Our results suggest that the similar to1.46 eV emission is a spatially indirect transition of electrons and holes separated at the interface in a type-II band alignment.
Scientific journal, English

Fabrication of nanostructured palladium-doped SiO2 films with variable temperature coefficient of resistivity
T Ichinohe; S Masaki; K Uchida; S Nozaki; H Morisaki
THIN SOLID FILMS, ELSEVIER SCIENCE SA, 466, 1-2, 27-33, Nov. 2004, Peer-reviwed, Electrical characteristics of palladium (Pd)-doped glass films of various Pd concentrations, which contain nanometer-sized Pd ultrafine particles, were studied. Temperature dependence showed that the temperature coefficient of resistivity (alpha) increased with decreasing resistivity; also, the sign of alpha changed from negative to positive. The critical resistivity at which alpha = 0 was within the range of 10(0)-10(-2) Omega cut, where temperature-independent resistance films can be designed. In films within this resistivity range, the sign of a changed to positive after annealing at 500 degreesC, demonstrating a metal-insulator transition characteristic before and after heat treatment. In a metallic regime having lower resistivity, the value of alpha and resistivity remained sufficiently small and higher than ordinary bulk metal, which phenomenon was discussed with a conduction model. (C) 2004 Elsevier B.V. All rights reserved.
Scientific journal, English

Growth and characterization of p-type InGaAs on InP substrates by LP-MOVPE using a new carbon-dopant source, CBrCl3
Kazuo Uchida; Kazuma Takahashi; Shogo Kabe; Shinji Nozaki; Hiroshi Morisaki
Journal of Crystal Growth, 272, 658-663, Oct. 2004, Peer-reviwed
Scientific journal, English

Real-time measurement of rocking curves during MOVPE growth of GaxIn1-xP/GaAs
S Bhunia; T Kawamura; Y Watanabe; S Fujikawa; J Matsui; Y Kagoshima; Y Tsusaka; K Uchida; N Sugiyama; M Furiya; S Nozaki; H Morisaki
APPLIED SURFACE SCIENCE, ELSEVIER SCIENCE BV, 216, 1-4, 382-387, Jun. 2003, Peer-reviwed, Measurement of real-time rocking curves of semiconductor heterostructures at various stages of metal organic vapor epitaxy (MOVPE) process may provide useful informations about the composition, thickness and in-built strain in the growing epilayer. In this study, we have used a previously grown lattice-matched GaInP/GaAs heterostructure as the reference substrate on which Ga(x)ln(1-x)P epilayers of different composition and thickness were successively grown by MOVPE while recording rocking curves of each layer in real-time during the growth by using synchrotron X-ray source. Strain redistribution at the interface of the GaInP/GaAs substrate due to the different linear thermal expansion coefficients of GaInP and GaAs was determined from rocking curve of the heterostructure measured at 570 degreesC. We could detect the change in rocking curve due to the growth of as thin as 16 nm of In-rich Ga0.42In0.58P epilayer at the initial stage of growth. Data from the simulation of each intermediate rocking curve during growth was systematically used to grow a lattice-matched GaInP epilayer. We believe, this is the first report of measurement of rocking curves at high temperature and during MOVPE growth of GaxIn1-xP. (C) 2003 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Heavily carbon doping of GaAs by MOVPE using a newdopant source CBrCl3 and characterization of the epilayers
K. Uchida; S. Bhunia; N. Sugiyama; M. Furiya; M. Katoh; S. Katoh; S. Nozaki; H. Morisaki
J. Crystal Growth, 248, 124-129, Mar. 2003, Peer-reviwed
Scientific journal, English

Metal organic vapor phase epitaxial growth of heavily carbon-doped GaAs using a dopant source of CCl3Br and quantitative analysis of the compensation mechanism in the epilayers
S Bhunia; K Uchida; S Nozaki; N Sugiyama; M Furiya; H Morisaki
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 93, 3, 1613-1619, Feb. 2003, Peer-reviwed, Heavy carbon doping of GaAs by metal organic vapor phase epitaxy has been carried out using a dopant source of carbon trichloro bromide (CCl3Br), an intersubstituted compound of the two highly efficient dopant sources of CCl4 and CBr4. Results are being reported in the doping range of 1.76 x 10(19)-1.12 x 10(20) cm(-3), achieved at growth temperatures between 570 and 600degreesC and VIII ratios between 10 and 50. The compensation mechanism of the carriers in the samples and its effect on the electrical and optical properties were systematically studied using double crystal x-ray diffraction, mobility, and photoluminescence measurements. A data analysis technique has been presented to quantitatively calculate the level of compensation in the layers from conventional lattice mismatch measurements. The antisite incorporation of carbon was found to be the dominant compensation mechanism for hole concentrations above 7.36 x 10(19) cm(-3). Room temperature mobility data of the samples showed a sharp deviation from the usual Hilsum's fitting after the carrier concentration of 7.36 x 10(19) cm(-3), due to increased self-compensation of the epilayers. The optical properties of the samples were correlated to the. self-compensation effect by the photoluminescence measurements carried out in the temperature range of 10-140 K. (C) 2003 American Institute of Physics. [DOI: 10.1063/1.1534377].
Scientific journal, English

Photoluminescence Studies of GaAs/partially ordered GaInP quantum wells grown by metalorganic vapor phase epitaxy
T. Kobayashi; H. Tomoda; A. D. Prins; Y. Homma; K. Uchida; J. Nakahara
Phisica status solidi (b), 235, 2, 277-281, Jan. 2003, Peer-reviwed
Scientific journal, English

A photo-oxidation generated low-k dielectric film deposited by reactive evaporation of SiO
JJ Si; Y Show; S Banerjee; H Ono; K Uchida; S Nozaki; H Morisaki
MICROELECTRONIC ENGINEERING, ELSEVIER SCIENCE BV, 60, 3-4, 313-321, Apr. 2002, Peer-reviwed, A non-stoichiometric silicon oxide film has been deposited by evaporating SiO as a source material in Ar and 0, mixed gas. The film is composed of SiO and SiO2 and has a porous structure. The SiO, results from some part of SiO reacting with O-2 and its amount depends on the pressure in the chamber. The residual SiO in the film can be photo-oxidized into SiO, by ultraviolet radiation with a Hg lamp. The dielectric constant of the film after photo-oxidation is similar to1.89 +/- 0.04 (at frequency of 1 MHz), which shows that this porous structure film is promising for potential application as a low-k dielectric. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Real-time observation of surface morphology of indium phosphide MOVPE growth with using X-ray reflectivity technique
T Kawamura; Y Watanabe; S Fujikawa; S Bhunia; K Uchida; J Matsui; Y Kagoshima; Y Tsusaka
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 237, 398-402, Apr. 2002, Peer-reviwed, The results of real-time X-ray reflectivity measurements of MOVPE grown indium phosphide surface are presented. At the low growth temperature of 450degreesC, large decreases of reflectivity were observed. Suggesting the formation of indium islands. At higher growth temperature of 550degreesC, only small changes were observed at high growth rate, indicating the step-flow growth mode. Oscillations longer than mono-layer growth were also observed at 500degreesC and 550degreesC, and roughness changes obtained from these oscillations were less than 0.01-nm suggesting small islands formation on the terrace or step-edge fluctuation during the growth. (C) 2002 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Real-time observation of step-flow limited metal organic vapor phase epitaxial growth of InP and their characteristics
S Bhunia; T Kawamura; Y Watanabe; S Fujikawa; K Uchida; S Nozaki; H Morisaki; J Matsui; Y Kagoshima; Y Tsusaka
COMPOUND SEMICONDUCTORS 2001, IOP PUBLISHING LTD, 170, 647-652, 2002, Peer-reviwed, Using our recently developed technique of near-grazing angle x-ray surface reflection, we have studied the real-time atomic surface kinetics during metal organic vapor phase epitaxy of InP by monitoring the monolayer scale roughness during the growth. The evolution of the surface roughness for various group III and group V precursor flows has been reported. The step-flow mode of growth was observed at the growth temperatures of 550 degreesC and 525 degreesC and their characteristics have been discussed in details.
Scientific journal, English

Ultralow k nanoporous silica by oxidation of silicon nanoparticles
S Nozaki; H Ono; K Uchida; H Morisaki; N Ito; M Yoshimaru
PROCEEDINGS OF THE IEEE 2002 INTERNATIONAL INTERCONNECT TECHNOLOGY CONFERENCE, IEEE, 69-71, 2002, Peer-reviwed, We have successfully fabricated ultralow-k (as low as 1.3) nanoporous silica with closed nanometer-size voids by oxidation of the silicon (Si) nanoparticles which were deposited by evaporation of Si in argon gas. The pores in the nanoporous silica films obtained by low-temperature dry oxidation of the Si nanoparticles are found to be closed voids by the small-angle x-ray scattering. Because of closed voids, the nanoporous silica films with low dielectric constants are tolerant of water absorption. The obtained nanoporous silica thin film is a good candidate for a low-k dielectric in the future Si VLSI.
International conference proceedings, English

Real-time observation of surface morphology at nanometer scale using x-ray specular reflection
T. Kawamura; Y. Watanabe; S. Fujikawa; S. Bhunia; K. Uchida; J. Matsui; Y. Kagoshima; Y. Tsusaka
Surf. Interface Anal., 35, 72-75, 2002, Peer-reviwed
Scientific journal, English

Capacitance-Voltage (C-V) hysteresis in the Metal-Oxide-Semiconductor capacitor with Si nanocrystals deposited by the gas evaporation technique
P Mishra; S Nozaki; R Sakura; H Morisaki; H Ono; K Uchida
MATERIALS ISSUES IN NOVEL SI-BASED TECHNOLOGY, MATERIALS RESEARCH SOC, 686, 153-158, 2002, Capitance-Voltage (C-V) hysteresis was observed in the Metal-Oxide-Semiconductor (MOS) capacitor with silicon nanocrystals. The MOS capacitor was fabricated by thermal oxidation of Si nanocrystals, which were deposited on an ultra-thin thermal oxide grown previously on a p-type Si substrate. The Si nanocrystals were deposited by the gas evaporation technique with a supersonic jet nozzle. The size uniformity and the crystallinity of the Si nanocrystals are found to be better than those fabricated by the conventional gas evaporation technique. The C-V hysteresis in the MOS capacitor is attributed to electron charging and discharging of the nanocrystals by direct tunneling though the ultra-thin oxide between the nanocrystals and the substrate. The flat-band voltage shift observed during the C-V measurement depends on the size and density of the nanocrystals and also on the magnitude of the positive gate bias for charging. The retention characteristic is also discussed.
International conference proceedings, English

Correlation between the dielectric constant and porosity of nanoporous silica thin films deposited by the gas evaporation technique
JJ Si; H Ono; K Uchida; S Nozaki; H Morisaki; N Itoh
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 79, 19, 3140-3142, Nov. 2001, Peer-reviwed, Nanoporous silica thin films with low dielectric constants were deposited by gas evaporation of SiO2 nanoparticles in an argon atmosphere. With increasing gas pressure during the evaporation, the dielectric constant decreases, while the porosity increases. The correlation between the dielectric constant and porosity is well modeled by a serial connection of two capacitors, one with air and the other with SiO2 as the dielectric medium. This suggests that the dielectric constant of the nanoporous silica thin film using the gas evaporation technique is more effectively lowered by forming "uniformly" distributed voids of closed gaps than those of the nanoporous silica films with pores extending from the back to front surface. Therefore, the former nanoporous silica thin film requires less porosity to obtain a low dielectric constant and is regarded as an ideal low-k material. (C) 2001 American Institute of Physics.
Scientific journal, English

Spectroscopic study of partially ordered semiconductor heterojunction under high pressure and high magnetic field
PY Yu; G Martinez; J Zeman; K Uchida
JOURNAL OF RAMAN SPECTROSCOPY, JOHN WILEY & SONS LTD, 32, 10, 835-839, Oct. 2001, Peer-reviwed, Photoluminescence upconversion (PLU) is a phenomenon in which a sample emits photons with energy higher than that of the excitation photon. This effect has been observed in many materials, including rare earth ions doped in insulating hosts and semiconductor heterostructures without using high-power lasers as the excitation source. Recently this effect has been observed also in partially CuPt-ordered GaInP2 epilayers grown on GaAs substrates. As a spectroscopic technique, PLU is particularly well suited for studying band alignment at heterojunction interfaces. The value of band offset has been determined with meV precision using magneto-photoluminescence. Using the fact that the pressure coefficient of electrons in GaAs is higher than that in GaInP2 we have been able to 'manipulate' the band offset at the GaInP/GaAs interface. By converting the band offset from type I to type II we were able to demonstrate that the efficiency of the upconversion process is greatly enhanced by a type II band offset. Copyright (C) 2001 John Wiley & Sons, Ltd.
Scientific journal, English

In-situ study of growth mode by reflection of synchrotron x-ray during the metal organic vapor phase epitaxial growth of InP（共著）
S. Bhunia; K. Uchida; S. Nozaki; H. Morisaki; T. Kawamura; Y. Watanabe; S. Fujikawa; J. Matsui; Y. Kagoshima; Y. Tsusaka
International Conference on Crystal Growth - 13 in Conjunction with Vapor Growth and Epitaxy - 11, Kyoto, Japan, July 30 - Aug. 4., ?, Jul. 2001
International conference proceedings, English

Raman scattering studies of the ZnSe/GaAs interface
P. Y. Yu; G. Martinez; J. Zeman; K. Uchida
Journal of Raman Spectroscopy, 32, 10, 852-856, 2001, Peer-reviwed, Raman spectroscopy was used to study the band bending at the interface of ZnSe/GaAs hetero-structures. A series of samples, which contained a ZnSe buffer layer, 0-35 nm thick, grown at a lower temperature than the much thicker ZnSe epilayer, by metal-organic chemical vapor phase deposition, were investigated. Compared with that of the GaAs substrate, an enhancement of the intensity of the LOGaAs phonon was found in samples grown without and with a thick (≥28 nm) buffer layer, but not in a sample grown with a 4 nm thick buffer layer. The enhancement is attributed to the electric field induced Raman scattering, resulted from a strong band bending on the GaAs side of the hetero-structure. The results suggest that the direction of the interfacial electric field on the GaAs side will reverse with increasing buffer layer thickness. Between this reversal, a near flat band condition can be achieved, as was found in a sample grown with a 4 nm buffer layer. This suggestion is consistent with the concomitant improvement of the structure of the epilayer and of the interfacial quality of the hetero-junction, which unpins the Fermi level and affects the band bending. Copyright © 2001 John Wiley &
Sons, Ltd.
Scientific journal, English

Wurtzite silicon nanocrystals deposited by the cluster-beam evaporation technique
JY Zhang; H Ono; K Uchida; S Nozaki; H Morisaki
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, WILEY-V C H VERLAG GMBH, 223, 1, 41-45, Jan. 2001, Peer-reviwed, Wurtzite silicon nanocrystals have been fabricated by using the cluster-beam evaporation technique, The X-ray diffraction patterns of the as-deposited films indicate the presence of Si crystallites with sizes in the nanometer range. The Bragg angles of the reflection peaks are not of the ordinary diamond structure but of the wurtzite structure. The Raman spectra further support the presence of the wurtzite structure. X-ray photoelectron spectroscopy shows that these Si nanocrystals are enclosed in the oxide matrix. It is hypothesized that the wurtzite Si phase is formed by the non-equilibrium cluster formation process through adiabatic gaseous expansion.
Scientific journal, English

High pressure photoluminescence study of the GaAs/partially ordered GaInP interface
T Kobayashi; K Inoue; AD Prins; K Uchida; J Nakahara
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, WILEY-V C H VERLAG GMBH, 223, 1, 123-128, Jan. 2001, Peer-reviwed, Using time-resolved (TRPL) and continuous-wave photoluminescence (CWPL) we have studied GaAs/partially ordered Ga0.5In0.5P single quantum well samples at pressures up to approximate to5 GPa. In such samples emission from the quantum well is only seen if intermediate cap layers an grown between the GaAs and GalnP and is otherwise masked by anomalous bands at around 1.46 eV. Examination of the TRPL spectra shows large differences in the pressure dependence of this emission because of the inequivalence of the GaAs/GaInP interfaces. For the sample with no thin GaP layer between the upper interface this emission has a very long PL-decay time and a stronger blueshift with excitation intensity at higher pressures. The pressure-dependent PL behavior at lower excitation intensity is close to that of the GaInP barrier. The 1.46 eV emission can be attributed to the spatially indirect transitions at the interface with no GaP layer.
Scientific journal, English

Study on pressure working time and releasing rate for phase transformation of Ge
M Oh-Ishi; S Akiyama; K Uchida; S Nozaki; H Morisaki
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, WILEY-BLACKWELL, 223, 2, 391-395, Jan. 2001, Peer-reviwed, The direct transformation from Ge-I to Ge-III has been investigated by Raman spectroscopy measurements. The Gc sample, which consisted of the Ge-I phase at atmospheric pressure. did not transform to another phase under a pressure of 6 GPa for 10 days. After the slow release of pressure at a rate of 1 GPa/h to atmospheric pressure, a peak around 302 cm(-1) and two indistinct peaks around 274 and 285 cm(-1) have been noted. The sample was thought to consist of a mixture of GU-I, wurtzite, and Gc-III phases. After 4 h, the peak corresponding to Ge-III almost disappeared. The presence of both Ge-I and Gc-III phases has also been noted in photo-oxidized Ge nanocrystalline films using ultraviolet light exposure.
Scientific journal, English

A study of the GaAs/partially ordered GaInP interface
T Kobayashi; K Inoue; AD Prins; K Uchida; J Nakahara
PROCEEDINGS OF THE 25TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, PTS I AND II, SPRINGER-VERLAG BERLIN, 87, 1, 473-474, 2001, Peer-reviwed, Ga-As/partially ordered Ga0.5In0.5P single quantum well structures grown by metalorganic vapor phase epitaxy were studied using time-resolved and continuous-wave photoluminescence at pressures up to similar to5 GPa. Quantum well emission from GaAs/GaInP structures can be masked by anomalous bands at 1.35 similar to1.46 eV. The introduction of two thin (similar to2 nm) GaP layers between the GaAs and GaInP restores this emission. The true nature of the 1.46 eV peak can only be determined at low excitation intensities and provides evidence of the spatially indirect transitions in a type II band alignment.
International conference proceedings, English

Formation of Ge nanocrystals passivated with Si by gas evaporation of Si and Ge
J. J. Si; H. Ono; K. Uchida; S. Nozaki; H. Morisaki
638, F14.4.1, Nov. 2000, Peer-reviwed
International conference proceedings, English

Influence of short-range ordering on roughness of (AlGa)As interfaces studied with cross-sectional scanning tunneling microscopy
TCG Reusch; M Wenderoth; AJ Heinrich; KJ Engel; N Quaas; K Sauthoff; RG Ulbrich; ER Weber; K Uchida; W Wegscheider
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 76, 26, 3882-3884, Jun. 2000, Peer-reviwed, Cross-sectional scanning tunneling microscopy was used to identify individual Al atoms on cleaved surfaces of two sets of (AlGa)As heterostructure samples grown with metalorganic vapor-phase epitaxy and molecular-beam epitaxy. We determined the average Al concentration profile perpendicular to the GaAs-(AlGa)As interfaces. Based on former investigations of short-range ordering in (AlGa)As bulk material grown with metalorganic vapor-phase epitaxy, we conclude that short-range ordering during growth of the interfacial layers contributes significantly to the observed interface roughness. (C) 2000 American Institute of Physics. [S0003-6951(00)01126-8].
Scientific journal, English

High-pressure study of deep emission band at GaAs/partially ordered GaInP interface
T Kobayashi; T Ohmae; T Ito; K Uchida; J Nakahara
JOURNAL OF LUMINESCENCE, ELSEVIER SCIENCE BV, 87-9, 408-410, May 2000, Peer-reviwed, We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at pressures up to similar to 5 GPa, and investigated the characteristics of the 1.46 eV deep emission band. It has a very long decay time of 200-400 ns. Tn addition, unlike the emission from the GaAs well, a strong blueshift of the spectral position with excitation intensity is observed. With increasing pressure, the deep emission shows a sublinear shift towards higher energy, while the GaAs well exhibits a linear shift. The pressure-dependent PL behavior at lower excitation intensity is rather similar to those observed for partially ordered GaInP alloys. These results suggest that the presence of ordered GaInP layers plays an important role in the radiative recombination at 1.46 eV, and the 1.46 eV deep emission is related to the interface transitions of electrons and holes localized at the heterointerface. (C) 2000 Elsevier Science B.V. All rights reserved.
Scientific journal, English

An analysis of temperature dependent piezoelectric Franz-Keldysh effect in AlGaN
YT Hou; KL Teo; MF Li; K Uchida; H Tokunaga; N Akutsu; K Matsumoto
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 76, 8, 1033-1035, Feb. 2000, Peer-reviwed, Strong Franz-Keldysh oscillations near the band gap of AlGaN are observed in the contactless electroreflectance (CER) studies of a GaN/InGaN/AlGaN multilayer structure. The line shape analysis of the CER spectra at different temperatures provides an accurate determination of the AlGaN band gap energies and the built-in electric fields. Using the existing data of the thermal expansion coefficients of GaN and sapphire, and the piezoelectric constants of AlGaN, the temperature dependence of the electric field is estimated and is in good agreement with the experimental results between 15 and 300 K. We attribute such electric field to the piezoelectric strain effect. (C) 2000 American Institute of Physics. [S0003-6951(00)02308-1].
Scientific journal, English

Ultralow KSiO2 thin films with nano-voids by gas-evaporation technique
S Nozaki; S Banerjee; K Uchida; H Ono; H Morisaki
PROCEEDINGS OF THE IEEE 2000 INTERNATIONAL INTERCONNECT TECHNOLOGY CONFERENCE, IEEE, 140-142, 2000, We have developed the gas evaporation technique to deposit ultralow-k (as low as 1.7) SiO2 thin films with nanometer-size voids. In the technique silicon (Si) in a boat was evaporated in argon gas containing a small amount of oxygen. Although the film contains many nanometer-size voids, it is tolerant of moisture and does not show a change in the dielectric constant or the resistance with time. The SiO2, film deposited by the gas evaporation technique is a coed candidate for a low-k dielectric in the future Si VLSI.
International conference proceedings, English

Selective excitation and thermal quenching of the yellow luminescence of GaN
JS Colton; PY Yu; KL Teo; ER Weber; P Perlin; Grzegory, I; K Uchida
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 75, 21, 3273-3275, Nov. 1999, Peer-reviwed, We report the observation of narrower structures in the yellow luminescence of bulk and thin-film n-type GaN, using the technique of selective excitation. These fine structures exhibit thermal quenching associated with an activated behavior. We attribute these fine structures to phonons and electronic excitations of a shallow donor-deep acceptor complex, and determine its activation energy for delocalization. Our results suggest that in addition to distant donor-acceptor pairs, the yellow luminescence can also involve emission complexes of shallow donors and deep acceptors. (C) 1999 American Institute of Physics. [S0003-6951(99)04347-8].
Scientific journal, English

自然超格子を有するGaInP/GaAsヘテロ構造におけるホトルミネッセンス・アップコンバージョンの高圧及び高磁場を用いた研究
内田和男; P. Yu; J. Zeman; G. Martinez; 松本功
The Transactions of the Institute of Electronics, Information and Communication Engineers C-II, The Institute of Electronics, Information and Communication Engineers, J82-C II, 7, 392-397, Jul. 1999, Peer-reviwed, Metal-Organic Vapor Phase Epitaxy法で成長した自然超格子を有するGaInPとGaAsで構成されるシングルへテロ構造において観察されたホトルミネッセンスアップコンバージョン(PLU)を高磁場, 静水圧下で評価した. 高磁場による実験より, PLUを示すサンプルはタイプIIのGaInP/GaAsバンド不連続とGaInP中に局在する発光中心を有することが明らかとなった. また一連のサンプルの中でPLUを示さないタイプIのGaInP/GaAsバンド不連続を有するサンプルに1.2GPaの静水圧を加えることでバンド不連続をタイプIIに調整することにより, PLUが観察され, これら結果よりタイプIIバンド不連続がPLU具現化のための条件の一つであることが確認された.
Scientific journal, English

Nanometer size determination of type-II domains in CuPt-ordered GaInP2 with high-pressure magneto-luminescence
J Zeman; S Jullian; G Martinez; PY Yu; K Uchida
EUROPHYSICS LETTERS, E D P SCIENCES, 47, 2, 260-266, Jul. 1999, Peer-reviwed, Photoluminescence originating from the GaAs/(ordered)GaInP2 interface has been studied under the simultaneous application of high magnetic field and high pressure. A sharp threshold dependence on magnetic field was observed in the intensity of the spatially indirect. transition between electrons in GaInP2 and holes in GaAs. A model involving trapping of electrons from GaAs into "quantum boxes" formed by type-II ordered GaInP2 domains is proposed. This model reproduces the pressure-induced variations of the quantum box sizes and demonstrates the ability of this technique to study the properties of nanometer size systems.
Scientific journal, English

Short-range ordering in AlxGa1-xAs grown with metal-organic vapor-phase epitaxy
AJ Heinrich; M Wenderoth; KJ Engel; TCG Reusch; K Sauthoff; RG Ulbrich; ER Weber; K Uchida
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 59, 15, 10296-10301, Apr. 1999, Peer-reviwed, Atomically resolved, cross-sectional scanning tunneling microscopy was used to identify Al atoms in the surface layer of Ab(0.15)Ga(0.85)As grown with metal-organic vapor-phase epitaxy. Characteristic fingerprints of individual and clusters of Al atoms were analyzed to identify surface-layer Al atoms resulting in atom maps of the Al positions. By quantitatively comparing the measured Al configuration with simulated images of a random Al incorporation, statistically significant deviations of the measured from a random Al distribution were found. These deviations are explained with a clear tendency of the Al atoms to form short-range ordered structures in the GaAs matrix. This ordering results in strings of Al atoms of a length of up to Rye Al atoms along low-indexed crystallographic directions. [S0163-1829(99)05415-6].
Scientific journal, English

Pressure dependence of photoluminescence in GaAs/partially ordered GaInP interface
T Kobayashi; T Ohmae; K Uchida; J Nakahara
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 38, 2B, 1004-1007, Feb. 1999, Peer-reviwed, We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at pressures up to similar to 5 GPa, and investigated the characteristics of the 1.46 eV deep emission band. It has a very long decay time of 200-400 ns. In addition, at normal pressure, unlike the emission from the GaAs well, a strong blueshift of the spectral position with excitation intensity is observed. With increasing pressure, the deep emission shows a sublinear shift towards higher energy while the GaAs well exhibits a linear shift. The pressure-dependent PL behavior at lower excitation intensity is rather similar to those observed for partially ordered GaInP alloys. These results suggest that the presence of ordered GaInP layers plays an important role in the radiative recombination at 1.46 eV, and the 1.46 eV deep emission is related to the interface transitions of electrons and holes localized at the heterointerface.
Scientific journal, English

Pressure dependence of photoluminescence in GaAs/partially ordered GaInP interface
T Kobayashi; T Ohmae; K Uchida; J Nakahara
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, JAPAN J APPLIED PHYSICS, 38, 2B, 1004-1007, Feb. 1999, Peer-reviwed, We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at pressures up to similar to 5 GPa, and investigated the characteristics of the 1.46 eV deep emission band. It has a very long decay time of 200-400 ns. In addition, at normal pressure, unlike the emission from the GaAs well, a strong blueshift of the spectral position with excitation intensity is observed. With increasing pressure, the deep emission shows a sublinear shift towards higher energy while the GaAs well exhibits a linear shift. The pressure-dependent PL behavior at lower excitation intensity is rather similar to those observed for partially ordered GaInP alloys. These results suggest that the presence of ordered GaInP layers plays an important role in the radiative recombination at 1.46 eV, and the 1.46 eV deep emission is related to the interface transitions of electrons and holes localized at the heterointerface.
Scientific journal, English

Time-resolved photoluminescence study of GaAs ordered GaInP interface under high pressure
T Kobayashi; A Matsui; T Ohmae; K Uchida; J Nakahara
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, WILEY-V C H VERLAG GMBH, 211, 1, 247-253, Jan. 1999, Peer-reviwed, We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at pressure up to approximate to 5 GPa, and investigated the characteristics of the 1.46 eV deep emission band. It has a very long decay time of several hundred nanoseconds. In addition, unlike the emission from the GaAs well, a strong blue-shift of its peak energy with excitation intensity is observed. With increasing pressure, the emission peak shows a sublinear shift towards higher energy, while the GaAs quantum well exhibits a linear peak shift. The pressure dependence of the spectral peak position at higher excitation intensity tends to reflect that of the adjacent 1.49 eV emission band which has a faster decay profile. The pressure-dependent PL behavior at lower excitation intensity is rather similar to those observed for partially ordered GaInP alloys. These results suggest that the presence of ordered GaInP layers plays an important role in the radiative recombination at 1.46 eV and the deep emission is related to the transitions of electrons and holes localized at the GaAs/ordered GaInP heterointerface.
Scientific journal, English

GaAs/(ordered)GaInP2 heterostructures under pressure and high magnetic fields
J Zeman; G Martinez; PY Yu; SH Kwok; K Uchida
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, WILEY-V C H VERLAG GMBH, 211, 1, 239-246, Jan. 1999, Peer-reviwed, The results of extended studies of photoluminescence (PL) and up-converted PL (UPL) of partially ordered GaInP2 alloy layers under hydrostatic pressure and high magnetic field are presented. It appears that the efficient UPL is observed when the GaAs/GaInP2 interface has a type II alignment. This condition can be reached also by hydrostatic pressure. Dramatic changes of the character of PL spectra measured on less ordered samples are explained by pressure and/or magnetic field induced localization of electrons in small domains in GaInP2 nearby the interface.
Scientific journal, English

Temperature dependent of piezoelectric effect in GaN
Y. T. Hou; K. L. Teo; M. F. Li; K. Uchida; H. Tokunaga; N. Akutsu; K.Matsumoto
Appl. Phys. Lett., 76, 1033-1035, 1999, Peer-reviwed
English

Piezoelectric Franz-Keldysh effect in a GaN/InGaN/AlGaN multilayer structure
YT Hou; KL Teo; MF Li; K Uchida; H Tokunaga; N Akutsu; K Matsumoto
PHOTONICS TECHNOLOGY INTO THE 21ST CENTURY: SEMICONDUCTORS, MICROSTRUCTURES, AND NANOSTRUCTURES, SPIE-INT SOC OPTICAL ENGINEERING, 3899, 46-53, 1999, Peer-reviwed, Contactless electroreflectance (CER) of a GaN/InGaN/AlGaN multilayer structure grown on sapphire has been measured in the temperature range of 15 K and 450 K. Except for the GaN exciton structures, well-defined Franz-Keldysh Oscillations (FKO's) are observed above the AlGaN band gap. An electromodulational model based on complex Airy functions is used to analyse the FKO's line shape. The temperature dependence of transition energies is obtained both for GaN and AlGaN. The magnitude of the built in electric field in AlGaN layer is also determined. The temperature dependence of the electric field is found to be consistent with the variation of thermal strain in the epilayer. It is demonstrated that the built-in electric field can be identified to be due to the piezoelectric effect.
International conference proceedings, English

Folding of X-point phonons and conduction-band valleys in partially CuPt-ordered Ga0.52In0.48P grown on GaAs
SH Kwok; PY Yu; K Uchida
PHYSICAL REVIEW B, AMER PHYSICAL SOC, 58, 20, 13395-13398, Nov. 1998, Peer-reviwed, We report the observation of a folded zone-edge phonon mode, in addition to the folded L point mode reported already in Raman scattering from GaxIn1-xP epitaxial layers grown on GaAs and containing two variants of CuPt ordering. This Raman mode becomes observable as a result of resonant enhancement at an electronic transition at 2.25 eV reported previously in electroreflectance measurements. Our results suggest that a folding of the Brillouin zone along the [001] direction occurs in partially ordered GaxIn1-xP samples due to the existence of antiphase boundaries. [S0163-1829(98)53344-9].
Scientific journal, English

Optical studies of GaInP(ordered)/GaAs and GaInP(ordered)/GaP/GaAs heterostructures
SH Kwok; PY Yu; J Zeman; S Jullian; G Martinez; K Uchida
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 84, 5, 2846-2854, Sep. 1998, Peer-reviwed, We report on a detailed optical study of emission from a series of GaInP (ordered)/GaAs heterostructures. Some of these structures contain one or two thin (similar to 2 nm) layers of GaP between the GaInP and GaAs layers. A so-called "deep emission" band at 1.46 eV is observed in all our samples. However, at high excitation power, an emission above the band gap of GaAs (previously identified as quantum well emission) emerges only in structures where GaP layers are inserted on both sides in between the GaAs well and its GaInP barriers. From the pressure dependence we have identified the deep emission peak as due to donor-acceptor pair transitions at the GaAs/GaInP interface. The insertion of GaP layers between the GaInP (ordered) and GaAs layers helps to suppress the defects which contribute to this deep emission. By applying pressure to the sample which exhibits quantum well emission we have determined its band alignments. We show that the GaP layers form two effective barriers for confining electrons within the GaAs well. However, the magnetic field dependence of the quantum well emission reveals that the electrons form only a quasi-two-dimensional gas inside the GaAs well. (C) 1998 American Institute of Physics. [S0021-8979(98)05117-2].
Scientific journal, English

An analysis of temperature dependent photoluminescence line shapes in InGaN
KL Teo; JS Colton; PY Yu; ER Weber; MF Li; W Liu; K Uchida; H Tokunaga; N Akutsu; K Matsumoto
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 73, 12, 1697-1699, Sep. 1998, Peer-reviwed, Photoluminescence (PL) line shapes in InGaN multiple quantum well structures have been studied experimentally and theoretically between 10 and 300 K. The higher temperature PL spectra can be fitted quantitatively with a thermalized carrier distribution and a broadened joint-density-of-states. The low temperature PL line shapes suggest that carriers are not thermalized, as a result of localization by band-gap fluctuations. We deduce a localization energy of similar to 7 meV as compared with an activation energy of similar to 63 meV from thermal quenching of the PL intensity. We thus conclude that this activation energy and the band-gap fluctuation most likely have different origins. (C) 1998 American Institute of Physics.
Scientific journal, English

The study of piezoelectric effect in wurtzite GaN/InGaN/AlGaN multilayer structures
W Liu; KL Teo; MF Li; SJ Chua; K Uchida; H Tokunaga; N Akutsu; K Matsumoto
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 189, 648-651, Jun. 1998, Peer-reviwed, By using phatovoltaic spectroscopy and contactless electroreflectance spectroscopy, large electric field was found to exist in wurztite GaN/InGaN/AlGaN multilayer structures. The electric field strengths in the GaN layer and the AlCaN layer were obtained from the analysis of the Franz-Keldysh oscillations in contactless electroreflectance spectra, These electric fields were attributed to be induced by the piezoelectric effect in wurztite nitride systems. (C) 1998 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Phonon-assisted photoliminescence in wurtzite GaN epilayer
W. Liu; M. F. Li; S. J. Xu; Kazuo Uchida; Koh Matsumoto
Semiconductor Science and Technology, 13, 769-772, Jun. 1998, Peer-reviwed
Scientific journal, English

Electron confinement in (ordered)GaInP2/GaAs/(ordered)GaInP2 single quantum well
J Zeman; G Martinez; SH Kwok; PY Yu; K Uchida
PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 249, 735-739, Jun. 1998, Peer-reviwed, Quantum confinement of electrons in a series of undoped (ordered)GaInP2/GaAs/(ordered)GaInP2 single quantum well (QW) samples was studied by magnetophotoluminescence measurements. The electron confinement is observed only in the sample with two thin GaP barriers inserted on both sides of the GaAs QW. The excitonic photoluminescence peak related to the transition between confined electron and hole states does not exactly obey the B cos(Theta) law in the tilted magnetic field which is explained by the quasi-two-dimensional nature of electrons confined in the well by partially transmitting GaP barriers. (C) 1998 Elsevier Science B.V. All rights reserved.
Scientific journal, English

Ordering in ternary compound semiconductors studied with cross-sectional scanning tunneling microscopy
AJ Heinrich; M Wenderoth; MA Rosentreter; K Engel; MA Schneider; RG Ulbrich; ER Weber; K Uchida
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, SPRINGER VERLAG, 66, S959-S962, Mar. 1998, Peer-reviwed, We present atomically resolved, cross-sectional scanning tunneling microscopy images of Al0.2Ga0.8As and Ga0.5In0.5P layers grown by metal organic vapor phase epitaxy. On the AlGaAs layers, we have found large homogeneous areas with typical diameters of 2-5 nm that have a low Al concentration. These areas are surrounded by dipole-like pairs of enhanced and depressed As atoms. We have also found extended Al-related defects along the [1 (1) over bar 2] and [ (1) over bar 12] directions and propose a model structure containing small platelets of AlAs on {111} planes. On the GaInP2 layers, with ordering parameter of gamma = 0.42, we have been able to image the natural superlattice on the atomic scale in filled-state images as alternating enhanced and depressed P rows. In addition, we have found a long-period modulation induced by electronic contrasts, with a typical wavelength of about 4 nm.
Scientific journal, English

Investigation of phonon-assisted photoluminescence in wurtzite GaN epilayer
W Liu; MF Li; SJ Xu; K Uchida; K Matsumoto
OPTOELECTRONIC MATERIALS AND DEVICES, SPIE-INT SOC OPTICAL ENGINEERING, 3419, 27-34, 1998, Peer-reviwed, Photoluminescence of wurztite GaN epilayer was measured in the range of 4K to 300K. At low temperature, the neutral-donor bound exciton emission dominates the spectra, while with increasing temperature, free exciton emissions grow rapidly and finally become the dominant lines. The exciton linewidth due to exciton-phonon interaction was studied. LO phonon-assisted photoluminescence associated with both the bound exciton and the free exciton were also observed. The temperature dependence of LO phonon-assisted emissions can be well explained by the phonon-assisted free exciton emission theory established for II-VI compound semiconductors. in particular, the study of 2LO phonon replica can provide information of the temperature dependence of the concentration and recombination lifetime of free excitons in GaN.
International conference proceedings, English

GaN room temperature exciton spectra by photovoltaic measurement
W Liu; MF Li; SJ Chua; YH Zhang; K Uchida
NITRIDE SEMICONDUCTORS, MATERIALS RESEARCH SOCIETY, 482, 593-598, 1998, Peer-reviwed, Exciton absorption peak has been clearly observed at room temperature by photovoltaic spectra, on a GaN layer grown on (0001)-plane Sapphire by metalorganic chemical vapor deposition. From the spectra, we obtained A and B exciton transition energies to be 3.401 eV, 3.408 eV, and the energy gap to be 3.426 eV in wurztite GaN, respectively. We have also performed photovoltaic measurements with various incidence angles of light, and observed the polarization behavior of exciton absorption in GaN. Finally, we used UV-polarizer to further confirm the polarization properties of GaN. In conjuction with previous room temperature photoreflectance measurements, this work provide direct and reliable assessment of the excitonic properties and crystal quality of GaN semiconductor layers.
International conference proceedings, English

High pressure studies of quantum well emission and deep emission in GaInP(ordered)-GaAs heterostructures
SH Kwok; PY Yu; K Uchida; T Arai
HIGH-PRESSURE MATERIALS RESEARCH, MATERIALS RESEARCH SOCIETY, 499, 195-200, 1998, We report on a high pressure study of emission from a series of GaInP(ordered)/GaAs heterostructures. A so-called "deep emission" band at 1.46 eV is observed in all our samples. At high excitation power, quantum well emission emerges in only one structure where thin Cap layers are inserted on both sides of the GaAs well. From the pressure dependent emission in this sample we have determined its band alignments. The role of the GaP layers in suppressing the deep emission is elucidated.
International conference proceedings, English

A study of band alignment in GaAs/GaInP(partially ordered) heterostructures with high pressure
K Uchida; PY Yu; J Zeman; SH Kwok; KL Teo; ZP Su; G Martinez; T Arai; K Matsumoto
HIGH-PRESSURE MATERIALS RESEARCH, MATERIALS RESEARCH SOCIETY, 499, 381-392, 1998, Peer-reviwed, In this paper we review the use of high pressure techniques to investigate the optical properties of partially ordered GaInP epitaxial layers grown on GaAs substrates. In particular, we demonstrate the ability of high pressure to modify the band alignment at the GaInP/GaAs interface and hence to alter the optical properties of heterostructures fabricated from partially ordered GaInP on GaAs.
International conference proceedings, English

High-Pressure Study of Deep Emission Band at GaInP/GaAs Interface
Toshihiko Kobayashi; Kazuya Takashima; Kazuo Uchida
Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu, 7, 715-717, 1998, Peer-reviwed, We have measured the photoluminescence (PL) spectra of GaAs/GaInP single quantum wells at 77 K and at pressures up to~5 GPa to investigate the characteristics of the 1.46 eV deep emission band. It shows a very long decay time, and might be attributed to spatially indirect recombinations of electrons and holes at the ordered GaInP/GaAs interface. With increasing pressure, the PL peak shifts towards higher energies at a rate slightly smaller than that of the 1.52 eV band from the GaAs well. The PL behavior observed at high pressures can be partly explained by the presence of repulsion between the T-folded energy states in ordered GalnP. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.
Scientific journal, English

Pressure Dependence of Time-Resolved Photoluminescence in Ordered Ga0.5In0.5P
Naohisa Tsuji; Kazuya Takashima; Toshihiko Kobayashi; Kazuo Uchida; Jun'ichiro Nakahara
Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu, 7, 763-765, 1998, Peer-reviwed, We have measured the time-resolved photoluminescence (TRPL) spectra of ordered Ga0.5In0.5P alloys at 12K and for pressures up to ∼4 GPa. At lower pressures below ∼2 GPa, the PL spectra are found to consist of three emission bands whose decay profiles are quite different from each other. Above 3 GPa the PL spectra shows fast decays, which do not depend on the detection energy. We propose a model of type-II band alignment to explain the PL behavior observe at high pressures. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.
Scientific journal, English

Phonon-assisted photoluminescence in wurtzite GaN epilayer
Liu, Wei; Ming Fu Li; ShiJie Xu; Kazuo Uchida; Koh Matsumoto
Proc. SPIE, 3419, 311905, 1998, Peer-reviwed
International conference proceedings, English

GaN exciton photovoltaic spectra at room temperature
W Liu; MF Li; SJ Chua; YH Zhang; K Uchida
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 71, 17, 2511-2513, Oct. 1997, Peer-reviwed, Clear exciton absorption peak has been observed at room temperature by photovoltaic spectra, on a GaN layer grown on (0001)-plane sapphire by metalorganic chemical vapor deposition. From the spectra, we obtained the wurtzite GaN room temperature A and B exciton transition energies, and the energy gap to be 3.401, 3.408, and 3.426 eV, respectively. We have also performed photovoltaic measurements with varied light incidence angles, and observed the polarization behavior of exciton absorption in GaN. In conjunction with previous room temperature photoreflectance measurements, this work provided direct and reliable assessment of GaN semiconductor crystal layers. (C) 1997 American Institute of Physics. [S0003-6951(97)00543-3].
Scientific journal, English

Band alignments in GaInP/GaP/GaAs/GaP/GaInP quantum wells
SH Kwok; PY Yu; K Uchida; T Arai
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 71, 8, 1110-1112, Aug. 1997, Peer-reviwed, Pressure-dependent photoluminescence (PL) in several GaInP(ordered)-GaAs quantum well structures grown by metal organic vapor phase epitaxy is reported. Quantum well emission from GaAs is observed only in structures when thin (similar to 2 nm) GaP layers an inserted between the GaAs well and the GaInP barrier. By extrapolating the energies of the various inter and intralayer PL transitions observed under pressures (up to 5.5 GPa) to zero pressure, the different band offsets of the heterostructure have been determined. (C) 1997 American Institute of Physics.
Scientific journal, English

Band alignment and photoluminescence up-conversion at the GaAs/(ordered)GaInP2 heterojunction
J Zeman; G Martinez; PY Yu; K Uchida
PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 55, 20, 13428-13431, May 1997, Peer-reviwed, The up-conversion of photoluminescence in a series of GaAs/(ordered)GaInP2 heterojunctions has been investigated using high magneticfield and high pressure. Samples which exhibit this effect have been demonstrated to have a type-II band alignment and also localization centers in GaInP2, Some samples revealing a type-I band alignment do not show this effect at atmospheric pressure. However, such a sample exhibits up-conversion under a hydrostatic pressure of 1.2 GPa. Our results establish a type-II band alignment as one of the key elements for explaining the observed up-conversion.
Scientific journal, English

PL spectra of InGaN film grown by MOCVD system with three laminar flow injection reactor
N Akutsu; H Tokunaga; K Uchida; K Matsumoto
REPORT OF RESEARCH CENTER OF ION BEAM TECHNOLOGY, HOSEI UNIVERSITY, SUPPLEMENT NO 15, MARCH 1997, HOSPITAL JOINT DISEASES, 77-82, 1997, Peer-reviwed, InxGa1-xN (0<x<0.15) films were grown on sapphire substrates at temperatures ranging from 650-750 degrees C using a novel metalorganic chemical vapor deposition (MOCVD) system with a three layered laminar now injection reactor developed by Nippon Sanso. This reactor was designed for high speed gas now in order to suppress thermal convection and undesirable reactant gas reaction. Sharp and strong band edge PL spectra were observed at mom temperature from low InN molar fraction InxGa1. N-x(x=0.07)/GaN double heterostructure films, while InxGa1-xN/GaN double heterostructure films with higher InN molar fraction (x=0.15) exhibited a band edge emission and a broad unknown emission which looked like blue-green by human eye.
International conference proceedings, English

Deep emission band at GaInP/GaAs interface
K Uchida; T Arai; K Matsumoto
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 81, 2, 771-776, Jan. 1997, Peer-reviwed, We have investigated the 1.46 eV deep emission band observed in the photoluminescence (PL) spectra of 100-Angstrom-thick GaAs/Ga0.52In0.48 single quantum wells grown by metal-organic vapor-phase epitaxy. We have found that the application of GaP layers at both lower and upper GaAs/Ga0.52In0.48P interface is necessary to achieve 1.52 eV emission from the well; otherwise only the deep emission band at 1.46 eV is observed in the 77 K PL spectrum. Time-resolved PL and temperature-dependent PL measurements show that the 1.46 eV deep emission is due to recombination of electrons in the conduction band of Ga0.52In0.48P and holes bound to accepters in GaAs at the GaAs/Ga0.52In0.48P interface, which forms type-II band alignment. We propose that the application of GaP layers modifies the band alignment from type II to type I, and makes the emission from the well observable. (C) 1997 American Institute of Physics.
Scientific journal, English

III-V nitrides growth by atmospheric-pressure MOVPE with a three layered flow channel
K Uchida; H Tokunaga; Y Inaishi; N Akutsu; K Matsumoto; T Itoh; T Egawa; T Jimbo; M Umeno
III-V NITRIDES, MATERIALS RESEARCH SOCIETY, 449, 129-134, 1997, We introduce m-V nitrides growth including GaN as well as InGaN by a newly developed atmospheric-pressure metal-organic vapor phase epitaxy system with a three layered flow channel which is a promising system for a large scale production. First, we have shown through computer simulation that a laminar flow of gases is maintained at 1000 degrees C in the three layered flow channel. Second, as a part of epitaxial results, we have found that the surface roughness of a low temperature grown buffer layer on sapphire substrates, which can be measured by atomic force microscope, should be minimum in order to grow high quality GaN. We also report the growth of a double heterostructure of In0.15Ga0.85N/GaN which shows a strong near band-edge emission in room temperature photoluminescence.
International conference proceedings, English

Time-resolved photoluminescence study of ordered Ga0.5In0.5P under high pressure
T Kobayashi; M Minaki; K Takashima; K Uchida; J Nakahara
PHYSICA STATUS SOLIDI B-BASIC RESEARCH, AKADEMIE VERLAG GMBH, 198, 1, 49-55, Nov. 1996, Peer-reviwed, We have measured time-resolved photoluminescence (TR-PL) spectra in ordered and disordered Ga0.5In0.5P alloys at 12 K and at pressures up to 3 GPa to investigate the characteristics of the main broad PL spectrum at approximate to 1.91 eV in nominally ordered alloys. At normal pressure, unlike the disordered alloy, the PL-decay profiles far the ordered alloys change remarkably for small changes in detection energy. This indicates the presence of adjacent overlapping emissions of different nature. Together with the prolonged nonexponential decay curves, a gradual red-shift of the low-energy peak with delay time is observed for the first time, indicating spatially indirect recombinations. With increasing pressure, the constituent emissions shift toward higher energies at rates slightly smaller than that for the disordered alloy. At 3 GPa, the PL decay appears to be insensitive to the detection energy, and a faster decay is observed.
Scientific journal, English

Mechanisms of photoluminescence upconversion at the GaAs/(ordered) GaInP2 interface
ZP Su; KL Teo; PY Yu; K Uchida
SOLID STATE COMMUNICATIONS, PERGAMON-ELSEVIER SCIENCE LTD, 99, 12, 933-936, Sep. 1996, Peer-reviwed, F.A.J.M. Driessen [Appl. Phys. Lett. 67, 1995, 2813] recently reported emission from GaAs/(partially ordered) GaInP2 quantum wells grown on GaAs when the excitation photon energy was above the band gap of GaAs. We found that such upconverted emission could be excited from partially ordered GaInP2 grown on GaAs even when the photon energy was below the band gap of GaAs. Auger processes are found to be inadequate in explaining our results. Instead we propose a two-step two-photon excitation mechanism together with a model in which the GaAs and GaInP2 conduction bands are almost degenerate. Copyright (C) 1996 Elsevier Science Ltd
Scientific journal, English

Magnetic field dependence of up-converted photoluminescence in partially ordered GaInP2/GaAs up to 23 T
J. zeman; G. Martinez; P. Y. Yu; K. Uchdia
493-496, 1996
International conference proceedings, English

Upconversion of near GaAs bandgap photons to GaInP2 emission at the GaAs/(ordered) GaInP2 heterointerface
K. L. Teo; Z. P. Su; P. Y.YU; K. Uchida
489-492, 1996
International conference proceedings, English

The formation of radiative defects at GaAs/GaInP interface
K Uchida; T Arai; K Matsumoto
OPTOELECTRONIC MATERIALS: ORDERING, COMPOSITION MODULATION, AND SELF-ASSEMBLED STRUCTURES, MATERIALS RESEARCH SOC, 417, 319-324, 1996, Peer-reviwed
International conference proceedings, English

Raman and photoluminescence studies on atmospheric pressure MOVPE grown GaN on sapphire substrates
T. Suski; J. Krueger; C. Kisielowski; E. Weber; K. Uchida; H. Tokunaga; N. Akutsu; K. Matsumoto
20, 1996
International conference proceedings, English

COMPARATIVE-STUDY OF PHOTOLUMINESCENCE IN ORDERED AND DISORDERED GAINP ALLOYS UNDER HIGH-PRESSURE
H KOJIMA; H KAYAMA; T KOBAYASHI; K UCHIDA; J NAKAHARA
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, PERGAMON-ELSEVIER SCIENCE LTD, 56, 3-4, 345-348, Mar. 1995, Peer-reviwed, We have measured the photoluminescence (PL) spectra of ordered and disordered Ga0.5In0.5P alloys grown by metalorganic vapor phase epitaxy under pressures from 0 to 6 Cpa at three different temperatures (T = 12, 77 and 300 K). At atmospheric pressure, the band-gap energy E(0), derived from the PL spectrum, of the ordered GaInP is about 70 meV lower than that of the disordered alloy. With increasing pressure the PL spectrum exhibits a rapid shift toward higher energies. The band-gap energy E(0) of the ordered GaInP shows a sublinear pressure dependence up to about 4 GPa, while that of the disordered alloy increases almost linearly up to the highest pressures (3.0-3.5 GPa) beyond which the PL emission disappears. At lower temperatures (T = 12 and 77 K) the PL peak energy for the ordered GaInP is also found to decrease in energy for pressures above 4 GPa. These results can be partly related to the existence of the repulsion between the Gamma-folded energy states in the CuPt-type ordered structure, which affects E(0) and also the Gamma-X crossover under high pressure in these materials.
Scientific journal, English

Control of defects in GaAs/GaInP interface grown by MOVPE
T Arai; K Uchida; H Tokunaga; K Matsumoto
ICDS-18 - PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE ON DEFECTS IN SEMICONDUCTORS, PTS 1-4, TRANSTEC PUBLICATIONS LTD, 196-, 196-201, 539-542, 1995, Peer-reviwed, We have studied photoluminescence deep emission observed at GaAs/InGaP quantum well at around 8450 Angstrom. An insertion of a thin GaP layers in both GaInP/GaAs and GaAs/GaInP interfaces is effective to suppress the deep emission. The effects of the thin GaP interlayer are detailed. Further, the time-resolved photoluminescence measurement has revealed that this deep emission has a long decay time and the onset of the emission occurs about 20 ns after the incident of the pulse laser at 77K while the delay is absent at 300K. Since these results suggest that this deep emission is predominantly nonexcitonic and cannot be explained by the previous model such as the band to band emission from the GaInAsP intermediate layer at the GaAs/GaInP interface, we propose that the deep emission is more Likely caused by an atomic configrational defect in the GaAs/GaInP interface.
Scientific journal, English

Raman spectroscopy study on order disordered Ga0.52In0.48P on GaAs grown by MOVPE
K UCHIDA; PY YU; ER WEBER; N NOTO
SEVENTH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS, I E E E, 261-264, 1995, Peer-reviwed
International conference proceedings, English

COMPARISON BETWEEN PHOTOLUMINESCENCE AND RAMAN-SCATTERING IN DISORDERED AND ORDERED ALLOYS IN GAINP
K UCHIDA; PY YU; N NOTO; Z LILIENTALWEBER; ER WEBER
PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES, TAYLOR & FRANCIS LTD, 70, 3, 453-466, Sep. 1994, Peer-reviwed, We have studied the photoluminescence spectra in both ordered and disordered phases of Ga0.5In0.5P alloy as a function of pressure. We found evidence of a pressure-induced conversion of Ga0.5In0.5P from a direct band gap semiconductor to an indirect band gap semiconductor owing to lowering of the X conduction band valleys relative to the minimum at the zone centre. Raman spectra in Ga0.5In0.5P samples doped with Se donors are reported. In ordered Ga0.5In0.5P electronic Raman scattering from single-particle excitations indicates the existence of a high-density electron gas which is absent in a similarly doped disordered sample.
Scientific journal, English

ENERGY OF X CONDUCTION BAND MINIMA IN DISORDERED AND ORDERED GaInP2 ALLOYS
K. Uchida; P.Y. YU; N. Noto; E. R. Webe
Proc. of the 22nd ICPS, 177-180, Aug. 1994, Peer-reviwed
International conference proceedings, English

PRESSURE-INDUCED GAMMA-X CROSSOVER IN THE CONDUCTION-BAND OF ORDERED AND DISORDERED GAINP ALLOYS
K UCHIDA; PY YU; N NOTO; ER WEBER
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 64, 21, 2858-2860, May 1994, Peer-reviwed, Pressure-dependent photoluminescence in both ordered and disordered Ga0.5In0.5P is reported. In ordered Ga0.5In0.5P, emissions are observed from both the direct band gap at the Brillouin zone center (GAMMA) and from the indirect band gap involving the conduction band at the X point of the Brillouin zone. The conduction-band minima at X and GAMMA in the ordered phase are found to be lowered in energy by the same amount with respect to those in the disordered phase. Our results support the existence of ordering along the [001] direction in GaInP as proposed recently by Kurtz.
Scientific journal, English

HYDROSTATIC-PRESSURE DEPENDENCE OF EG-100 MEV PHOTOLUMINESCENCE EMISSIONS IN N-TYPE ALGAAS
K UCHIDA; P SEGUY; H WONG; PL SOUZA; PY YU; ER WEBER; K MATSUMOTO
JAPANESE JOURNAL OF APPLIED PHYSICS, VOL 32, SUPPLEMENT 32-1, JAPANESE JOUR APPLIED PHYSICS, 32, 1, 246-248, 1993, Peer-reviwed
International conference proceedings, English

PHOTOLUMINESCENCE OF DEEP LEVELS INDUCED BY SUP-PPM H2O IN ALGAAS GROWN BY MOVPE
K MATSUMOTO; K UCHIDA
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 115, 1-4, 484-489, Dec. 1991, Peer-reviwed, A photoluminescence (PL) peak has sometimes been observed at about 100 meV below the band edge emission in MOVPE grown n-AlxGa1-xAs: (Se and Si) (0 less-than-or-equal-to x less-than-or-equal-to 0.3). It was studied in samples grown in the presence of H2O of 30-500 ppb. The deep level emission intensity (I(D)) at 77 K was proportional to the H2O concentration (P(H2O)) in the growth ambient. I(D) decreased as the growth temperature was increased. The oxygen concentrations in the epilayers were measured by a SIMS technique, and tended to follow the variation of I(D), however, the correlation was not direct. The energy position of the peak nearly followed the variation of the GAMMA band as a function of the Al contents. But the peak was not observed for epi-GaAs. The intensity of deep-level emission tended to saturate and its position was shifted towards higher energies as the excitation power density was raised. Our results suggest that this deep-level emission comes from a distant pair transition between a shallow donor and a deep acceptor induced by the presence of sub-ppm H2O in the MOVPE growth ambient.
Scientific journal, English

ANISOTROPY IN THE DOPING CHARACTERISTICS OF DIMETHYLCADMIUM IN GAAS GROWN BY MOVPE ON (100) GAAS
K MATSUMOTO; J HIDAKA; K UCHIDA
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 99, 1-4, 329-332, Jan. 1990, Peer-reviwed
Scientific journal, English

THE EFFECTS OF GROWTH TEMPERATURE ON THE DIMETHYL-CD DOPING OF GAAS BY METALORGANIC VAPOR-PHASE EPITAXY - EVIDENCE OF IMPURITY-INDUCED NUCLEATION OF TWO-DIMENSIONAL CLUSTERS
K MATSUMOTO; J HIDAKA; K UCHIDA
JOURNAL OF APPLIED PHYSICS, AMER INST PHYSICS, 65, 10, 3849-3851, May 1989, Peer-reviwed
Scientific journal, English

The effects of growth temperature on the dimethyl-Cd doping of GaAs by MOCVD
K. Matsumoto; J. Hidaka; K. Uchida
J. Appl. Phys., 65, 3849-3851, 1989, Peer-reviwed
Scientific journal, English

MOCVD GROWTH AND CHARACTERIZATION OF GAAS AND GAP GROWN ON SI SUBSTRATES
T SOGA; Y KOHAMA; K UCHIDA; M TAJIMA; T JIMBO; M UMENO
JOURNAL OF CRYSTAL GROWTH, ELSEVIER SCIENCE BV, 93, 1-4, 499-503, Nov. 1988, Peer-reviwed
Scientific journal, English

QUALITY IMPROVEMENT OF METALORGANIC CHEMICAL VAPOR-DEPOSITION GROWN GAP ON SI BY ASH3 PREFLOW
Y KOHAMA; K UCHIDA; T SOGA; T JIMBO; M UMENO
APPLIED PHYSICS LETTERS, AMER INST PHYSICS, 53, 10, 862-864, Sep. 1988, Peer-reviwed
Scientific journal, English

High quality Gap growth on Si sudstrates by MOCVD
K. Uchida; Y. Kohama; M. Tajima; T. Soga; T. Jimbo; M. Umeno
116, 319-322, 1988, Peer-reviwed
International conference proceedings, English

Nano-Scale Materials: From Science to Technology
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida; Hiroshi Morisaki
Scholarly book, English, Joint work, Nova Science Publishers, Inc., 2006, 1594549109

Spectroscopic Study of the Interface and Band alignment at the GaInP(Partially-ordered)/GaAs Heterojunction using High Pressure and High Magnetic Field. Spontaneous Ordering in Semiconductor Alloys, edited by A. Mascarenhas,
P. Y. Yu; G. Martinez; J. Zeman; K. Uchida
English, Joint work, Kluwer Academic/Plenum Publishers, New York,, 2002

Fabrication and optical characterization of GaN microdisk cavities undercut by laser-assisted photo-electrochemical etching
S. Sho; K. Shimoyoshi; K. Uchida; T. Tajiri
Oral presentation, English, 2022 International Conference on solid-state devices and materials (SSDM), International conference
28 Sep. 2022

TEGaと酸素ガスを用いた大気圧MOVPEによるβ-Ga2O3薄膜の結晶成長
浮田 駿; 中村 海太; 田尻 武義; 内田 和男
Oral presentation, Japanese, 第83回応用物理学会 秋季学術講演会, Domestic conference
23 Sep. 2022

マイクロマニピュレーション法によるGaNスラブ型光ナノ構造の積層
惣角 翔; 吉田 理人; 下吉 賢信; 内田 和男; 田尻 武義
Oral presentation, Japanese, 第83回応用物理学会 秋季学術講演会, Domestic conference
22 Sep. 2022

二段階光電気化学エッチングによるGaN二次元フォトニック結晶共振器の作製と光学評価
吉田 理人; 惣角 翔; 下吉 賢信; 内田 和男; 田尻 武義
Oral presentation, Japanese, 第83回応用物理学会 秋季学術講演会, Domestic conference
21 Sep. 2022

トンネル接合形成を目的としたZnO付加によるAlGaN LEDの発光特性への影響
浮田 駿; SUN ZHENG; 田尻 武義; 内田 和男
Oral presentation, Japanese, 第69回応用物理学会春季学術講演会, Domestic conference
24 Mar. 2022

レーザアシスト光電気化学エッチングによる GaNマイクロディスク共振器の作製と光学評価
下吉 賢信; 浮田 駿; 内田 和男; 田尻 武義
Oral presentation, Japanese, 第82回 応用物理学会 秋季学術講演会, Domestic conference
13 Sep. 2021

Fabrication and characterization of AlGaN p-n diode with n-ZnO as a tunnel junction layer
S.Ukita; J. Morimoto; M. Daikoku; S. Zheng; T. Tajiri; K. Uchida
Oral presentation, English, 2021 International Conference on solid-state devices and materials (SSDM), International conference
08 Sep. 2021

Fabrication of deeply undercut GaN micro-disks by selective photo-electrochemical etching of thick InGaN/GaN superlattice
K. Shimoyoshi; S.Ukita; K. Uchida; T. Tajiri
Oral presentation, English, 2021 International Conference on solid-state devices and materials (SSDM), International conference
08 Sep. 2021

厚膜InGaN系犠牲層の光電気化学エッチングによる中空GaNマイクロディスク構造の作製
下吉 賢信; 浮田 駿; 内田 和男; 田尻 武義
Oral presentation, Japanese, 第68回応用物理学会春季学術講演会, Domestic conference
17 Mar. 2021

p型コンタクト層にn-ZnO層を接合したAlGaN系pnダイオードのEL特性評価
孫 錚; 王 新磊; 森元 諄; 田尻 武義; 内田 和男
Poster presentation, Japanese, 第68回応用物理学会春季学術講演会, Domestic conference
16 Mar. 2021

正孔注入促進に向けたp-AlGaN/n-ZnOトンネル接合のバンド構造解析
浮田 駿; 田尻 武義; 内田 和男
Poster presentation, Japanese, 第68回応用物理学会春季学術講演会, Domestic conference
16 Mar. 2021

紫波長帯にフォトニックバンドギャップを有する窒化ガリウム二次元フォトニック結晶スラブの設計
下吉 賢信; 浮田 駿; 内田 和男; 田尻 武義
Oral presentation, Japanese, 第81回応用物理学会秋季学術講演会, Domestic conference
11 Sep. 2020

p型コンタクト層にn-ZnOトンネル層を有するAlGaN系pnダイオードの作製及び電気的評価
孫 錚; 森元 諄; 大黒 将也; 田尻 武義; 内田 和男
Oral presentation, Japanese, 第81回応用物理学会秋季学術講演会, Domestic conference
10 Sep. 2020

InGaP/GaAs heterointerfaces studied by cross-sectional scanning tunneling microscopy and their impact on the device characteristics
S. Nozaki; A. Koizumi; K. Uchida; H. Ono
Oral presentation, English, Physics, Chemistry and Application of Nanostructures
2009

水熱法によるZnOナノロッドの作製
粕谷仁一; 野崎眞次; 内田和男; 小野 洋
Oral presentation, Japanese
Mar. 2007

酸化銅ナノロッドの太陽電池への応用
崎野晃滋; 野崎眞次; 内田和男; 小野 洋
Oral presentation, Japanese
Mar. 2007

InP/InGaAs HBTデバイスに向けたp型InGaAs層の作製及び、TCADによる評価
芋川 直; 内田和男; 野崎眞次; 小野 洋
Oral presentation, Japanese
Mar. 2007

SiO nanopowder with metastable Si-Si networks
C. Y. Chen; S. Kimura; S. Nozaki; K. Uchida; H. Ono
Oral presentation, English, 電気通信大学・東京農工大学21世紀COEプログラム
Dec. 2006

Mechanically strong ultralow-k nanoporous silica made of SiOx nanoparticles
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida
Oral presentation, Japanese, 電気通信大学・東京農工大学21世紀COEプログラム
Dec. 2006

Bi添加SiOによるワイドギャップ半導体の作製
宮田浩正; 木村誠二; 野崎眞次; 内田和男; 小野 洋
Oral presentation, Japanese, 応用物理学会
Nov. 2006

Ni酸化物の物性評価とp-GaNオーミックコンタクトへの応用
斉藤貴夫; 内田和男; 野崎眞次; 小野 洋
Oral presentation, Japanese, 応用物理学会
Nov. 2006

Mechanically strong ultralow-k nanoporous silica made of SiOx nanoparticles
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida
Oral presentation, English, IEEE
Oct. 2006

走査型トンネル顕微鏡によるGaInP/GaAsへテロ界面の粗さ解析
大塚史之; 渡邊明広; 野崎真次; 内田和男; 小野 洋
Oral presentation, Japanese, 応用物理学会
Sep. 2006

Mechanically strong ultralow-k nanoporous silica made of SiOx nanoparticles
Shinji Nozaki; Hiroshi Ono; Kazuo Uchida
Oral presentation, Japanese, 応用物理学会
Sep. 2006

Yellowish-white photoluminescence from ZnO nanoparticles
J. Nayak; S. Nozaki; H. Ono; K. Uchida
Oral presentation, English, E-MRS
May 2006

自然超格子を有するInGaP/GaAs HBTへテロ接合界面におけるバンド不連続の研究
触澤宣晶; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 応用物理学会
Mar. 2006

表面プラズモン効果を用いたラマン分光法による低密度のGe超微粒子の分析
寺田 力; セン・ソマディティヤ; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 応用物理学会
Mar. 2006

InGaP/GaAsヘテロ接合バイポーラトランジスタ特性への表面再結合の影響
黒川愛里; 金 智; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 電子情報通信学会
Jan. 2006

バラスト抵抗用Ni微粒子混合誘電体薄膜の作製と評価
横山 彩; 野崎眞次; 内田和男; 小野 洋; 森崎 弘
Oral presentation, Japanese
Nov. 2005

BiドープSiOx導電膜の特性評価
牛田賢志; 木村誠二; 森崎 弘; 野崎眞次; 内田和男; 小野 洋
Oral presentation, Japanese
Nov. 2005

NiO薄膜を用いたp-GaNオーミックコンタクトに関する研究
内藤寛人; 斉藤貴夫; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese
Nov. 2005

バラスト抵抗用Ni微粒子混合Si3N4薄膜の作製と評価
横山 彩; 野崎眞次; 内田和男; 小野 洋; 森崎 弘
Oral presentation, Japanese, 電気学会
Oct. 2005

走査型トンネル顕微鏡によるGaInP氏前兆格子構造の観察
平川長規; 大塚史之; 野崎真次; 小野 洋; 内田和男; 森崎 弘
Oral presentation, Japanese, 応用物理学会
Sep. 2005

ナノポーラスシリカLow-k膜の低温熱処理と膜機械強度
倪 威; 小野 洋; 内田和男; 野崎真次; 森崎 弘
Oral presentation, Japanese, 応用物理学会
Sep. 2005

階段状ドーピングプロファイルによるバラクターダイオードの高性能化
中島誠幸; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 電子情報通信学会2005年総合大会エレクトロニクスソサイエティ
Mar. 2005

Pdナノクリスタル含有SiO2の大気中及び低真空中SPM観察
平川長規; 野崎眞次; 小野 洋; 内田和男; 森崎 弘
Oral presentation, Japanese, 第52回応用物理学関係連合講演会
Mar. 2005

Self-limiting photo-assisted synthesis of silicon nanocrystals
C. Y. Chen; S. Kimura; S. Sen; S. Nozaki; H. Ono; K. Uchida; H. Morisaki
Oral presentation, English, 東京農工大学・電気通信大学21世紀COEプログラム合同シンポジウム予稿集「ナノ未来材料とコヒーレント光科学」
Dec. 2004

Self-limiting photo-assited synthesis of silicon nanocrystals
C. Y. Chen; S. Kimura; S .Sen; S. Nozaki; H. Ono; K. Uchida; H. Morisaki
Oral presentation, English, Materias Research Society Fall Meeting
Dec. 2004

金属酸化物透明電極を用いた白色LEDの高機能化に関する研究
伊藤 純; 内田 和男; 野崎 眞次; 森崎 弘; 長岡 亜季則; 内藤 寛人
Oral presentation, Japanese, 日本光学会年次学術講演会
Nov. 2004

ITO薄膜における深さ方向の構造についての光学的研究
長岡 亜季則; 野崎 眞次; 内田 和男; 森崎 弘; 伊藤 純; 内藤 寛人
Oral presentation, Japanese, 薄膜材料デバイス研究会、アブストラクト集
Nov. 2004

超高真空走査型トンネル顕微鏡によるInGaP/GaAs超格子断面の観察
郡司 貢; 平川 長規; 千葉 綾子; 小野 洋; 内田 和男; 野崎 眞次; 森崎 弘
Oral presentation, Japanese, 日本結晶学会年会、講演要旨集
Nov. 2004

ナノ構造分散系としての金属ドープガラス薄膜の電気伝導とデバイス応用（共著）
椛木 弘美; 一戸 隆久; 野崎 眞次; 森崎 弘; 正木 進
Oral presentation, Japanese, 薄膜材料デバイス研究会アブストラクト集
Nov. 2004

CBrCL3をドーパント源としたp-InGaAsのMOVPE成長
加部正吾; 触澤宣晶; 小野洋; 内田和男; 野崎真次; 森崎弘
Oral presentation, Japanese, 第６５回応用物理学会学術講演会講演予稿集
Sep. 2004

紫外線照射による高品位SiOx膜の作成
越川智朗; 木村誠二; 小野洋; 内田和男; 野崎真次; 森崎弘
Oral presentation, Japanese, 第６５回応用物理学会学術講演会講演予稿集
Sep. 2004

Ge超微粒子フローティングゲートMOSキャパシタの作製と電気的特性
杉本武; 寺田力; Somaditya Sen; 小野洋; 内田和男; 野崎真次; 森崎弘
Oral presentation, Japanese, 第６５回応用物理学会学術講演会講演予講集
Sep. 2004

超音速ジェットノズルによるシリコン超微粒子浮遊ゲートMOSキャパシターの作製
野村政人; 野崎真次; 小野 洋; 内田和男; 森崎 弘
Oral presentation, Japanese, 応用物理学会分科会シリコンテクノロジーNo.46「量子サイズシリコン系素子－新機能と応用―」特集号
Nov. 2002

ダブルヘテロGaAs/GaInP HBTのDC特性変化
降矢美保; 高橋一真; 浜 俊彦; 小野 洋; 内田和男; 野崎真次; 森崎 弘; 本城和彦
Oral presentation, Japanese, 第63回応用物理学会学術講演会予稿集、新潟大学五十嵐キャンパス
Sep. 2002

超高真空断面走査型トンネル顕微鏡によるGaInP/GaAsヘテロ界面原子像の観察
茶圓 聡; 郡司 貢; 小野 洋; 内田和男; 野崎真次; 森崎 弘
Oral presentation, Japanese, 第63回応用物理学会学術講演会予稿集、新潟大学五十嵐キャンパス
Sep. 2002

Si超微粒子熱酸化によるナノポーラスシリカ膜の作製(共著)
安富大祐; 木原尚志; 小野 洋; 内田和男; 野崎真次; 森崎 弘; 吉丸正樹
Others, Japanese, 電気通信大学共同研究センター第7回共同研究成果発表会
May 2002

アンジュレーター放射光によるMOVPEのin situ評価(IV)-GaInP/GaAs成長のリアルタイム制御-
S.Bhunia; 川村朋晃; 藤川誠司; 渡辺義夫; 内田和男; 杉山智之; 降矢美保; 野崎眞次; 森崎弘; 松井純爾; 篭島靖; 津坂佳幸
Oral presentation, Japanese, 第49回応用物理学関係連合講演会、29p-ZQ-7,2002年3月29日、東海大学湘南キャンパス。
Mar. 2002

"固相Siナノクラスターによる半導体メモリー"（共著）
野崎真次; 佐倉 竜太; Puspashree Mishra; 内田和男; 森崎 弘
Invited oral presentation, Japanese, ナノ・インテリジェント材料シンポジウム、未踏科学技術協会・インテリジェント材料フォーラム主催、平成１３年１１月１３日、東京青学会館 （招待講演）
Nov. 2001

SiO_2_超微粒子薄膜のLow-k応用
木原尚志; 安富大祐; 内田和男; 小野 洋; 野崎真次; 森崎 弘
Oral presentation, Japanese, 第60回半導体・集積回路技術シンポジウム，電気化学会電子材料委員会主催，平成13年6月6-7日，大阪国際交流センター
Jun. 2001

超高真空断面走査形トンネル顕微鏡による半導体へテロ界面GaInP/GaAsの観察
三保基陽; 茶圓 聡; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 第48回応用物理学関係連合講演会，30a-ZX-8，2001年3月30日，明治大学
Mar. 2001

銅フタロシアニン／シリコンヘテロ接合ダイオードの特性
小野 洋; 岩本卓三; 内田和男; 野崎眞次; 伊藤進夫; 森崎 弘
Oral presentation, Japanese, 第48回応用物理学関係連合講演会，29a-ZG-11，2001年3月29日，明治大学
Mar. 2001

MOVPE成長GaInP材料物性とGaInP/GaAs HBT DC特性に関する報告
池上隆幸; 杉山智之; 降矢美保; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 第48回応用物理学関係連合講演会，28p-YC-9，2001年3月28日，明治大学
Mar. 2001

水素終端したSi（111）2x1劈開面のSTSによる評価
西方 誠; 三保基陽; NS. McAlpine; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 第47回応用物理学関係連合講演会，青山学院大学，30p-YH-10，2000年3月30日
Mar. 2000

全反射X線を用いたSiO2多孔質膜の誘電率測定
木原尚志; 舟崎秀夫; 伊藤進夫; S. Banerjee; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 第47回応用物理学関係連合講演会，青山学院大学，29p-YA-7，2000年3月29日
Mar. 2000

新低誘電材料としての酸化Si超微粒子膜の作製と評価
舟崎秀夫; 小野 洋; 内田和男; 野崎眞次; 森崎 弘
Oral presentation, Japanese, 第47回応用物理学関係連合講演会，青山学院大学，29p-YA-7，2000年3月29日
Mar. 2000

低誘電絶縁材料としてのSi酸化物超微粒子の作製と評価（1）
道又重臣; 小澤宏之; 舟崎秀夫; 佐藤井一; 小野 洋; 内田和男; 野崎真次; 森崎 弘
Oral presentation, Japanese, 第46回応用物理学関係連合講演会講演予稿集，30pZQ9/II，1999.3.30
Mar. 1999

トリメチルアミンを用いた高周波プラズマCVD法によるGaNの作製
島袋淳一; 池上隆幸; 内田和男; 野崎真次; 森崎 弘
Oral presentation, Japanese, 第46回応用物理学関係連合講演会講演予稿集，28pX1/III，1999.3.28
Mar. 1999

固体クラスターの粒子サイズ効果による電子・光機能
野崎真次; 内田和男; 小野 洋; 森崎 弘
Oral presentation, Japanese, ナノスペースラボ・シンポジウム '99
Jan. 1999

A study of band alignment in GaAs/GaInP（Partially ordered）heterostructureswith high pressure
K. Uchida; P. Yu; J. Zeman; S. Kwon; K. Teo; Z. Su; G. Martinez; T. Arai; K. Matsumoto
Invited oral presentation, English, Mat. Res. Soc. Symp, High-Pressure Materials Reseach., Proc. of Mat. Res. Soc. Symp, High-Pressure Materials Reseach. ed. by R.Wentzcovitch, R. Hemley, W. Nellis and P. Yu, Boston, Dec. 1997，499, Boston, US, International conference
Dec. 1997

Innovative Comprehensive Communications Design 1
The University of Electro-Communications

イノベイティブ総合コミュニケーションデザイン1
電気通信大学

Mechanics
The University of Electro-Communications

力学
電気通信大学

Fundamental Electronics
The University of Electro-Communications

基礎電子工学
電気通信大学

基礎科学実験A
The University of Electro-Communications

基礎科学実験A
電気通信大学

固体照明工学特論
The University of Electro-Communications

大学院技術英語
The University of Electro-Communications

応用数学
The University of Electro-Communications

半導体工学（その他コース）
The University of Electro-Communications

半導体工学（電子コース）
The University of Electro-Communications

半導体工学（その他コース）
The University of Electro-Communications

半導体工学（その他コース）
電気通信大学

半導体工学（電子コース）
The University of Electro-Communications

半導体工学（電子コース）
電気通信大学

固体照明工学特論
The University of Electro-Communications

固体照明工学特論
電気通信大学

大学院技術英語
The University of Electro-Communications

大学院技術英語
電気通信大学

応用数学
The University of Electro-Communications

応用数学
電気通信大学

応用物理学会

米国物理学会

米国材料研究学会

Fabrication of Nanocrystal Memories by Position Controlled Deposition of Ge Nanocrystals
NOZAKI Shinji; UCHIDA Kazuo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Ccmmunications, Grant-in-Aid for Scientific Research (B), In this research project, we made an attempt to make a nanocrystal memory using a silicon substrate on which Ge nanocrystalls are deposited with a good control of the positioning and size. Dr. Berbezier at CRMC2, Marseille, France provided the Si substrates with Ge nanocrystals deposited by MBE, and we made MOS capacitors by embedding Ge nanocrsytals in SiO_2. The most important but difficult part of the project is to deposit Ge nanocrstals with a good control of positioning and size. Dr. Berbezier and her group members developed a technique to grow the Ge nanocrstals on the FIB-patterned Si substrates. In this technique, the Ga is implanted in the Si substrates by focused ion beam (FIB) and farms the defective area locally. It was found the Ge selectively grew on the damaged area in the MBE growth of Ge. Using this selective epitaxy of Ge, Ge nanocrystals can be arranged. With the optimized growth condition, Dr. Berbezier successfully achieved an array of Ge nanocrystals on Si. However, the array was not one monolayer, and some Ge nanocrystals were stacked. Such a sample did not show a significant flatband voltage shift by injecting electrons in Ge nanocrystals. Nozaki and his group proposed a technique to form a high-density of Ge nanocrystals in a monolayer. In this technique, the Ge nanocrystals were deposited on the tunnel oxide by the gas evaporation with a supersonic jet nozzle. Using this deposition method, the Ge nanocrystals with a good uniformity in the size were obtained. They are, however, stacked. The Ge nanocrystals were annealed to remove the extra naocrystals on the monolayer. Because of strength of bonding between Ge nanocrystals and SiO_2, one monolayer of Ge nanocrystals remained without losing any nanocrystals on SiO_2 after complete removal of the extra nanocrystals. Then, the Ge nanocrystals were exposed to UV light for photo-oxidation, which electrically isolates the Ge nanocrystals by oxidizing the Ge nanocrystals. After depositing the control oxide on the Ge nanocrystals, the MOS capacitors with the Ge nanocrystals as a floating gate were fabricated. The C-V showed the hysteresis to confirm the electron injection in the nanocrystals. Although the gate electrode with the Ge nanocrystals proved to be useful in the nanocrystal memories, the further improvement of charge retention is required for practical application., 14350183
2002 - 2004

Collaboration of Education/Research on Nano-Structgured Semiconductor Devices
MORISAKI Hiroshi; ONO Hiroshi; NOZAKI Shinji; UCHIDA Kazuo
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Scientific Research (B), The aim of the research program is to develop international collaboration of education and research on nano-structured semiconductor materials and devices between Griffith University Group (GUG headed by Professor Barry Harrison) and our group (UECG). We have invited twice Mr. J.Combes, a post-graduate student of GUG as an : exchange student, who has made excellent contribution to the progress of the research on the semiconductor position sensitive detector. As a research interchange between GUG and UECG, several academic staffs from both. Universities have visited each other to develop nana-structured semiconductor devices using various semiconductor process facilities in both Universities. We have developed the position sensitive devices using a current-dividing resistor composed of granular metal as well as many GalnP/GaAs photo-detectors. We: have also investigated the phase transformation induced by nano-structuring of semiconductors.' In addition to the discovery of the new phase of nano-structured Ge, we have also found that nano-structured Si can transform to the Wurzite structure, a high-pressure form of crystalline Si. The stability of the high-pressure forms of crystalline Ge have been studied by applying hydrostatic pressure as high as 10GPa. The cluster-size in nano-structured Ge films deposited by the cluster-beam evaporation technique becomes very uniform by the photo-oxidation. We have found that the photo-oxidized Ge films can show the coulomb blockade effect even at the room temperature. The possible single electron devices using this phenomenon has been discussed in both UECG and GUG., 11695042
1999 - 2001

NANO-POROUS SiOx THIN FILMS FOR APPLICATION OF LOW DIELECTRIC MATERIALS
UCHIDA Kazuo; ONO Hiroshi
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, The University of Electro-Communications, Grant-in-Aid for Scientific Research (C), We have fabricated and characterized the nano-porous thin films of SiOx grown by Gasevaporation technique in oxygen atmosphere for the application of inter-dielectric in future VLSI technology. It was found that most of the samples had the dielectric constant below 2 as measured by the capacitance method and their porosity were over 90% as measured by the X-ray total reflection method. However, due to high porosity, water absorption into films, measured by FT-IR, was found to be inevitable and resulted in the increase of dielectric constant. In order to avoid this water absorption, we have proposed the HMDS (Hexamethyl disilan) method. We found that the dielectric constant of the film grown at 0.5 torr oxygen atmosphere with HMDS treatment was as low as 1.4. In comparison, we measured the dielectric constant of as-deposited sample in vacuum that was annealed at 623 K and found that it was as low as 1.3. On the other hand, we have fabricated nano-porous thin films of SiOx by post oxidation Si nano-porous grown by Gas-evaporation technique. These samples contained less absorbed water than SiOx samples grown by Gas-evaporation technique in oxygen atmosphere. Typical dielectric constant of these samples were as low as 1.4 without HMDS or high temperature annealing. These results prove that our SiOx films grown by simple Gas-evaporation technique are versatile and can be applied to future VLSI technology without modifying existing systems., 11650317
1999 - 2000