bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Thin Cylindrical Shell Vibration on Resonant Frequency of Cylindrical Resonator-Type Sound Source
Authors: Shibata Hiroshi , Kikuchi Toshiaki , Tsuchiya Toshio , Akio Hasegawa Akio Hasegawa , Michio Ohki Michio Ohki
Published: October 2002

In recent years, the need for a low-frequency acoustic source for oceanic observation and long-distance propagation in the sea has been increasing. Generally, the attenuation loss of low frequency acoustic waves in water is very low compared to that of electromagnetic waves. Therefore, the low-frequency acoustic wave is an attractive option for remote sensing, communications, and sonar in the ocean. Accordingly, from among various types of sound sources, a cylindrical resonator-type sound source was focused on because this type of transducer has the merits of being simple in terms of structure and employable in deep-sea areas. Also, the development of a cylindrical resonator-type sound source with low Q, which is the acoustic quality factor, was attempted.
V/III Flux Ratio Dependence of InAs Epilayers Grown on GaAs Subsutrates by Molecular Beam Epitaxy
Authors: Kotaro Okamoto Kotaro Okamoto , Ryoji Hananoki Ryoji Hananoki
Published: October 2002

InAs epilayers 2 µm thick were grown on (100) GaAs substrates. Under the As stabilized condition, the epilayer growth progresses in the mode of 2-dimensional (2D)-3D-2D growth. The lattice constant changes sharply from that of GaAs to the bulk value of InAs in the early stage of growth. A high density of small islands are formed in the initial stage and strain due to lattice mismatching is relaxed by the occurrence of island merging. As a result, the 2-µm-thick epilayers show smooth surface morphology and high electrical quality. On the other hand, when the epilayer growth is carried out under the In-stabilized condition, the lattice constant shows two-step saturation. The lattice constant saturates once in the initial stage, and after some time begins to increase toward the bulk value of InAs. In this case, the island density is low and each island grows laterally. Then, rather large strain is incorporated in the epilayers even after island merging and, as a result, dislocations are widely distributed in the latter half of epilayer growth. As a result, the 2-µm-thick epilayers show rather rough surface morphology, and the electrical properties also deteriorate.
Alloyed and Non-Alloyed Ohmic Contacts for AlInAs/ InGaAs High Electron Mobility Transistors
Authors: Yoshida Naohito , Yamamoto Yoshitsugu , Takano Hirozou , Sonoda Takuji , Saburou Takamiya Saburou Takamiya , Shigeru Mitsui Shigeru Mitsui
Published: October 2002

AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R
c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R
c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R
c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R
c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g
m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.
Properties of Sputter-Deposited CdS/CdTe Heterojunction Photodiode
Authors: Tomita Yasuhiro , Hatanaka Toshiaki Kawai
Published: October 2002

The CdS/CdTe heterojunction photodiode has been fabricated by the RF sputtering method and its electrical and photonic characteristics investigated. This heterojunction diode shows a low leakage current of 10 nA·cm-2 at the reverse bias of 20 V and high photoresponsivity of 0.5 µA·cm-2·lx-1, which can be considered good characteristics for applications in devices. The X-ray-induced current of this photodiode consisting of a 10-µm-thick CdTe layer is 200 nA·cm-2 for 2.58 mC·kg-1·min-1, which is 4.5 times larger than that of a conventional PbO X-ray sensor. A study of time response characteristics for pulsive light using light-emitting diodes (LEDs) of green, red and infrared regions shows that there are two types of decays, short and long decays. The short decay is influenced by the trapping states of the CdTe layer at the heterojunction interface, and long decay is caused by the trapping states of the CdS layer.
Observations of Structure, Phase and Composition on Unidirectional Solidified Y–Ba–Cu–O Samples
Authors: Kase Jun-ichiro , Shimoyama Jun-ichi , Eiji Yanagisawa Eiji Yanagisawa , Takeshi Morimoto Takeshi Morimoto
Published: October 2002

We have performed the unidirectional solidification in the Y–Ba–Cu–O system and successfully produced textured YBa2Cu3O7-δ samples with Y2BaCuO5 precipitates. The addition of Y2BaCuO5 to YBa2Cu3O7-δ at the start of the process plays an important role in achieving continuous textured growth because it prevents a liquid change in composition. We found a segregation of matrix at the bottom region of the sample after solidification. In this paper, we report the observations of structure, phase and composition on unidirectionally solidified Y–Ba–Cu–O samples.
Harmonics of Thomson Backscattered X-Rays
Authors: Chen Jizhong , Fujita Masayuki , Imasaki Kazuo , Yamanaka Chiyoe , Asakawa Makoto , Yamamoto Tatsuya , Nakai Sadao , Asakuma Takashi
Published: October 2002

A new concept of harmonic generation of Thomson backscattered X-rays by the angular alignment between the axes of the electron beam and incident laser beam has been proposed. Various properties of the backscattered X-ray harmonic radiation are examined, including the linewidth, radiation pattern on the observation plane, and the behavior of the radiation spectra at ultrahigh laser intensities. It is shown by the simulation results that when the electron beam is deliberately aligned at a suitable small angle in the polarization plane of the linearly polarized laser, both even and odd harmonics along the electron beam axis are generated, which is different from the perfectly aligned case where only odd harmonic radiations peak on the electron-laser axis. Moreover the high harmonics on the angularly aligned electron-laser configuration may have several times higher intensities compared with the axial intensity of the fundamental harmonic in a perfectly aligned case.
Analysis of Charge-Controlled Gray Scale in Ferroelectric Liquid Crystal Optically Addressed Spatial Light Modulator
Authors: Tanaka Yukio , Akio Takimoto Akio Takimoto , Hisahito Ogawa Hisahito Ogawa
Published: October 2002

In an optically addressed spatial light modulator (OASLM) with ferroelectric liquid crystal (FLC) and p-i-n photodiode hydrogenated amorphous Si (a-Si:H), the gray scale characteristics can be explained by the charge-control principle; the amount of charge supplied from the a-Si:H photodiode determines the FLC polarization state between the bistable states. We construct an equivalent circuit model based on this principle, formulate the operation of the OASLM, and show that this theory agrees with various experimental results. We also show that the OASLM gray scale is realized not by FLC multidomain switching, but by uniform director rotation between bistable states.
Crystallization and Growth Process of Lead Titanate Fine Particles from Alkoxide-Prepared Powders
Authors: Ishikawa Kenji , Okada Nagaya , Takada Kazumasa , Takashi Nomura Takashi Nomura , Minoru Hagino Minoru Hagino
Published: October 2002

Lead titanate particles of controlled size around the nanometer range were prepared by hydrolyzing a mixture of the constituent metal alkoxides. The hydrolysate powder was crystallized by calcination into a tetragonally distorted perovskite structure. The hydrolysate started to crystallize by calcination at 470° C for one hour and the increase of the particle size due to the coalescence began at about 530° C. The increase continued beyond 900° C. The particle calcined at temperatures higher than 700° C seemed to become poly-crystalline. X-ray analysis shows that the strain in the particle was less than 0.2%. The smallest size of a well crystallized particle was about 15 nm.
Gas Source Molecular Beam Epitaxial Growth of ZnSe Using Metal Zn and H2Se
Authors: Imaizumi Masayuki , Endoh Yasuyuki , Ken-ichi Ohtsuka Ken-ichi Ohtsuka , Toshiro Isu Toshiro Isu
Published: October 2002

ZnSe films were grown on GaAs substrates by gas source molecular beam epitaxy using metal Zn and H2Se as sources. H2Se was thermally cracked in a high pressure gas cell. The effects of growth temperature, VI/II ratio and H2Se cracking temperature on ZnSe growth were investigated. Under the condition where the cracked- H2Se flux controlled the growth rate, ZnSe films with smooth surface morphology were obtained at growth temperatures between 250 and 410° C. With increasing cracked- H2Se flux and/or H2Se cracking temperature, facets emerged on the growing surface and surface morphology was degraded.
Crystallographic Investigation of Columnar Grain Structure in Obliquely Deposited Fe–Co Films
Authors: Hashimoto Takashi , Okamoto Kunito , Fujiwara Hiroshi , Itoh Kikuo , Kamiya Masao , Hara Kazuhiro
Published: October 2002

In order to establish the crystallographic contribution to the formation of the columnar grain structure we investigated two characteristics of the columnar grain structure (inclination and bundling of columnar grains) and the appearance of the crystal habit in Fe1-
x

–Co

x

(x = 0–1) films. The films were vapor-deposited at an incidence angle of 65° on glass substrates heated at 673 K. Replica electron microscopy and the X-ray Schulz method showed that (i) the inclination angle of columnar grains depends on x, but the bundle is not formed in all the films, and (ii) in the bcc phase (x<0.85) the columnar grains exhibit the {100} and {110} habits not only on their tops but also on their sides. By analyzing directions of the column axis and the habit planes we concluded that the formation of the columnar grain structure is affected by the crystal habit.
Removal Conditions of Films Deposited on Probe Surface
Authors: Kato Isamu , Tsuyoshi Shimoda Tsuyoshi Shimoda , Toshihiro Yamagishi Toshihiro Yamagishi
Published: October 2002

Silicon nitride films deposited on a cylindrical probe surface are removed by ion bombardment in pure N2 plasma in the chamber of the double-tubed coaxial-line-type microwave plasma chemical vapor deposition system, and removal rates of the films are measured. The experiments are carried out with variation of the probe position in the chamber and the bombardment voltage applied to the probe. It has been clarified that the removal rate is proportional to the ion flux density. From this result, general removal conditions of silicon nitride films by ion bombardment have been clarified.
Measurement of Anisotropic Soft X-Ray Emission during Radio-Frequency Current Drive in the JFT-2M Tokamak
Authors: Kawashima Hisato , Hasegawa Mitsuru , Fuchs Gerhard , Matoba Tohru , Uesugi Yoshihiko , Hoshino Katsumichi , Tomohide Kawakami Tomohide Kawakami , Takumi Yamamoto Takumi Yamamoto
Published: October 2002

A new vertical soft X-ray pulse height analyzer (PHA) system and a tangential PHA system were used to measure the anisotropy of soft X-ray emission during lower-hybrid current drive (LHCD) and also during current drive by the combination of LHCD and electron cyclotron resonance heating (ECRH) in the JFT-2M tokamak. The strong soft X-ray emission was measured in the parallel forward direction during LHCD. When ECRH was applied during LHCD, the perpendicular emission was enhanced. The high-energy electron velocity distribution was evaluated by comparing the measured and calculated X-ray spectra. The distribution form was consistent with the theoretical prediction based on the electron Landau damping of lower-hybrid waves and the electron cyclotron damping of electron cyclotron waves for reasonable energy ranges.
Fabrication of 0.1 µm Line-and-Space Patterns using Soft X-Ray Reduction Lithography
Authors: Nagata Hiroshi , Ohtani Masayuki , Murakami Katsuhiko , Oshino Tetsuya , Oizumi Hiroaki , Maejima Yukihiko , Watanabe Takeo , Taguchi Takao , Yamashita Yoshio , Atoda Nobufumi
Published: October 2002

Soft X-ray projection lithography with a reduction rate of 32 was examined using Mo/Si-multilayer-coated Schwarzschild optics. The optics were designed to function at 13 nm, and were aligned with the synchrotron radiation light source. The patterns on a transmission mask were imaged in a 0.18-µm-thick polymethyl methacrylate resist. Line-and-space patterns down to 0.1 µ m were fabricated.
Scanning Tunneling Microscope Observation of Si(111) δ7×7 Formed by Si Deposition
Authors: Tanaka Hideyuki , Takashi Yokoyama Takashi Yokoyama , Isao Sumita Isao Sumita
Published: October 2002

Using scanning tunneling microscopy (STM), we study the initial stage of silicon deposition on Si(111)7×7 at room temperature. At less than 0.1 monolayer, three kinds of adsorbed structures are observed. The most common (70%) is a structure which has four maxima around a center dimer in its STM image. The position of the protrusions observed by STM changes drastically in the empty and the filled state. The bias voltage dependence is explained by the molecular orbitals between s
p
3 bonds which are formed upon the breaking of backbonds of adatoms. Based on the measured diffusion length on the surface, the molecular beam is also analyzed. Si2 is suggested to sublimate from the resistivity-heated Si source.
Scanning Tunneling Microscope Observation of Aggregation Structures in Polar Organic Molecules
Authors: Matsushige Seiji Taki
Published: October 2002

The molecular aggregation structures of two kinds of new polar liquid crystals, 5-( p-dodecyloxyphenyl)pyrazine-2-carbonitrile (DOPPC) and 6-(dodecyloxy-phenyl)-3-chloropyridazine (DOPCP) adsorbed on a graphite substrate were examined using a scanning tunneling microscope (STM). The STM images revealed several different features of aggregation structures of these molecules with polar head groups and alkyl chains. The essential factors in the formation of these molecular aggregation structures were analyzed by considering the mutual electric interactions between the polar head groups in neighboring molecules, as well as van der Waals interaction between the alkyl chains and the graphite crystal lattice.
Atomic-Order Planarization of Ultrathin SiO2/Si(001) Interfaces
Authors: Niwa Masaaki , Kouzaki Takashi , Okada Kenji , Sinclair Masaharu Udagawa
Published: October 2002

Conventional wet cleaning and ultrahigh vacuum (UHV) heated cleaning prior to thermal oxidation were compared with respect to their effects on extremely thin SiO2/Si(001) interface roughness. Atomically flat SiO2/Si(001) interfaces were realized by preparing the Si(001) reconstructed surface in UHV followed by thermal oxidation. In contrast to conventional wet cleaning, this planarization is significant in the range of oxide thickness (T
ox)<9 nm which is an important thickness for future gate oxides. As for the conventional wet-cleaned surfaces, maximum roughness of the interface was observed at T
ox≃4 nm which corresponds to the “initial oxide thickness” which appeared in the oxide growth kinetics.
Effect of High-Energy Carbon Ion Irradiation in Aligned and Random Directions on Microstructure of (111) Au Films
Authors: Nakao Setsuo , Saitoh Kazuo , Ikeyama Masami , Niwa Hiroaki , Tanemura Seita , Yoshiko Miyagawa Yoshiko Miyagawa , Soji Miyagawa Soji Miyagawa
Published: October 2002

(111)-Oriented Au films were irradiated with 1.8 MeV C ion beams in <111>-aligned and random directions at 450 and 650° C. The structural changes induced by the irradiations were examined. The results showed that the grain growth and the reduction of dislocations and stacking faults occurred upon irradiation. Furthermore, the aligned irradiation more strongly effected the structural changes of the Au films than the random irradiation at 450° C.
Ohmic Contact in Electron Cyclotron Resonance Chemical Vapor Deposition-TiN/Si Structure
Authors: Harada Yusuke , Akahori Takashi , Hiroshi Onoda Hiroshi Onoda
Published: October 2002

This is the first report that indicates chemical vapor deposition (CVD)-titanium nitride(TiN)/Si ohmic characteristics. The contact resistance of TiN/Si structure that was formed by the electron cyclotron resonance (ECR)CVD method using TiCl4, N2, H2 and Ar gases has been investigated. Ohmic characteristics were obtained in both n+- and p+-Si contacts with only a TiN film without a Ti layer under the TiN film. The contact resistance depends on ECR plasma pretreatment using Ar and H2 gases just prior to TiN deposition and TiCl4/N2 gas introduction sequence control. TiN/Si interface analysis indicates that ECRCVD-TiN/Si ohmic contacts were obtained by the removal of native oxide on Si with ECR plasma pretreatment, and by suppression of Si nitridation with gas sequence control on the Si surface.
In Situ Study of the Interfaces Between Plasma-Deposited Amorphous Silicon and Silicon Dioxide by UV-IR Spectroellipsometry
Authors: Shirai Hajime , Razvigor Ossikovski Razvigor Ossikovski , Bernard Drévillon Bernard Drévillon
Published: October 2002

An in situ ellipsometry study of the interfaces between plasma-deposited amorphous silicon (a-Si:H) and silicon dioxide ( a-SiO2) is presented. In order to achieve a more detailed description of the interface formation, measurements obtained by UV-visible and infrared (IR) spectroellipsometry are combined. Intermixing layers, about 30–40 Å thick, are clearly revealed at the interface independent of the deposition sequence used. In particular, the presence of SiO and (O)SiH

n

bonds in the first few monolayers of the growth of the “top” a-Si:H is identified. Likewise, hydrogen accumulation, revealed by SiH vibrations, is observed during the early stage of the growth of a-SiO2 on top of a-Si:H. The behaviours of the a-Si:H-a-SiO2 and a-Si:H-a-SiN

x

interfaces are compared.
Electron Cyclotron Resonance Discharge of Sublimation Gas of Decaborane and Its Application to Preparation of Boron Thin Films
Authors: Yoshifumi Ito Yoshifumi Ito , Naoki Kanazawa Naoki Kanazawa , Takashi Arakawa Takashi Arakawa , Masahiro Saidoh Masahiro Saidoh , Masahiro Nishikawa Masahiro Nishikawa
Published: October 2002

Plasmas are produced by electron cyclotron resonance (ECR) discharge of a mixture of hydrogen and sublimation gas of decaborane B10H14 in its solid state. Emissions from boron atoms B and boron hydride BH in the plasmas are measured spectroscopically. Hydrogenated boron films are prepared using the ECR plasmas. The hydrogen concentration in the boron films is about 2% at the substrate temperature T
s of 300°C. Apparent activation energy of the growth reactions of the boron films is estimated to be about -0.06 eV.
Wettability of Silicon Oxide with Poly-Crystalline Silicon
Authors: Miyasaka Mitsutoshi , Itoh Wataru , Komatsu Tadakazu , Ichio Yudasaka Ichio Yudasaka , Hiroyuki Ohshima Hiroyuki Ohshima
Published: October 2002

Stoichiometric change of underlying silicon oxide has been found to have a great influence upon the properties of thin poly-crystalline silicon (poly-Si) films deposited on an underlying silicon oxide, resulting in important characteristics changes of the poly-Si thin film transistors (TFTs) made on it. The silicon oxide containing excessive silicon atoms has fairly good wettability with silicon so that the thin poly-Si deposited on it is in a continuous film state even if it is as thin as 25 nm and is deposited under infra-low pressure. The thin poly-Si on the stoichiometricaly perfect silicon dioxide, on the other hand, is in a separate island-like state but consists of large crystallites. The best TFTs will be fabricated by optimizing the amount of silicon content in the underlying silicon oxide, the poly-Si deposition condition, and the thickness of poly-Si film.
Transport and Deposition Processes of Sputtered Particles in RF-Microwave Hybrid Sputtering Discharges
Authors: Tuda Mutumi , Kouichi Ono Kouichi Ono , Akimasa Yuuki Akimasa Yuuki
Published: October 2002

Transport and deposition processes of sputtered particles from a (Ba, Sr) TiO3 target have been investigated in rf-microwave hybrid discharges with Ar/O2. Deposition experiments were made over the gas pressure range of 0.5–10 mTorr using trenched substrates. Moreover, numerical simulations were carried out to reveal the effects of gas-phase scattering and surface re-emission of particles on their trajectories and the resulting deposition profiles in trenches. In the experiments, the step coverages of narrower trenches with aspect ratios above unity were found to be improved with decreasing pressure; such deposition behavior was predicted by the simulations, and was ascribed to the higher directionality of depositing fluxes onto the substrate at lower pressures.
Crystallization Process of Polycrystalline Silicon by KrF Excimer Laser Annealing
Authors: Watanabe Hiroyuki , Miki Hirofumi , Sugai Shigeru , Kawasaki Koji , Kioka Toshihide
Published: October 2002

We have investigated the crystallization of a-Si films by means of pulsed KrF excimer laser annealing as a function of irradiation energy density (E
L), using transmission electron microscopy (TEM), Raman scattering spectroscopy and secondary ion mass spectrometry (SIMS). The grain size increased gradually at 0.2–0.4 J/cm2, while a drastic enlargement of grains occurred with lateral growth at 0.6–0.8 J/cm2. The stress in the films decreased with a decrease in the thickness of the fine grain (FG) layer until the FG layer finally disappeared. We proposed a model in which a drastic enlargement of grains at high E
L is controlled by the nucleation rate, the solidification velocity, and the nucleus density of initial growth. It was found that poly-Si films with large grains ( 0.5–0.9 µm), high purity of C ( ∼3×1016 cm-3) and low stress were obtained in the high E
L regime ( 0.6–0.8 J/cm2).
Dopant Redistribution Effect on Post-Junction Silicide Scheme Shallow Junction and a Proposal of Novel Self-Aligned Silicide Scheme
Authors: Ohtomo Atsushi , Ida Jiro , Yonekawa Kiyotaka , Kai Kazuhiko , Aikawa Izumi , Akio Kita Akio Kita , Kenji Nishi Kenji Nishi
Published: October 2002

It is concluded that in a shallow junction of post-junction silicide (PJS) scheme self-aligned silicide (SALICIDE) process, the decrease of impurity concentration at the TiSi2/Si interface significantly degrades performance of metal oxide semiconductor field effect transistor (MOSFET). It is verified for the first time that this degradation is due to dopant redistribution from Si to TiSi2 during post-silicidation annealing. Dopant redistribution is strongly confirmed by evaluation of the contact resistance at the TiSi2/Si interface and analysis of impurity concentration by improved secondary ion mass spectroscopy (SIMS) technique and a two-dimensional process simulation dealing with a SALICIDE process. In order to overcome the dopant redistribution-induced degradation, a novel SALICIDE scheme, doubly source/drain-ion-implanted SALICIDE (DIS), is proposed and concluded to be an alternative to PJS scheme.
Structure of Polycrystalline Silicon Thin Film Fabricated from Fluorinated Precursors by Layer-by-Layer Technique
Authors: Ishihara Shun-ichi , Deyan He Deyan He , Isamu Shimizu Isamu Shimizu
Published: October 2002

We observed the structure of polycrystalline silicon (poly-Si) fabricated from fluorinated precursors, SiF

n

H

m

(n+m≤3), by repeated deposition of very thin layers, 10 nm thick, and atomic hydrogen treatment (H-treatment). The surface views and the cross-sectional views of poly-Si were observed using a field-emission scanning electron microscope (FE-SEM) and transmittance electron microscope (TEM), respectively. Poly-Si was made up of columnar crystalline grains of which diameters were 200 nm or more. These columnar crystalline grains grew perpendicularly on the amorphous layer grown directly on the glass substrate. Crystalline nuclei were formed within the amorphous layer and grew into crystalline grains with the aid of H-treatment. The thickness of this incubation layer was dramatically reduced by extending the period of H-treatment.
An Advanced NAND-Structure Cell Technology for Reliable 3.3 V 64 Mb Electrically Erasable and Programmable Read Only Memories (EEPROMs)
Authors: Aritome Seiichi , Hatakeyama Ikuo , Endoh Tetsuo , Yamaguchi Tetsuya , Shuto Susumu , Iizuka Hirohisa , Maruyama Tooru , Watanabe Hiroshi , Hemink Gertjan , Sakui Koji , Tanaka Tomoharu , Masaki Momodomi Masaki Momodomi , Riichiro Shirota Riichiro Shirota
Published: October 2002

An extremely small NAND-structure cell of 1.13 µm2 per bit, 80% of the smallest Flash memory cell reported so far [H. Kume et al.: IEEE Tech. Dig. IEDM (1992) p. 991], has been developed in 0.4 µm technology. The chip size of a 64 Mb NAND electrically erasable and programmable read only memory (EEPROM) using this cell is estimated to be 120 mm2, which is 60% that of a 64 Mb DRAM. In order to realize the small cell size, a 0.8 µm field isolation is used. A negative bias of -0.5 V to the P-well of the memory cell is applied during writing. In addition, a bit-by-bit intelligent writing technology allows a 3.3 V data sensing scheme which can suppress read disturb to 1/1000 in comparison with the conventional 5 V scheme. As a result, it is expected that with this technology, 106 write and erase cycles can be achieved and that the tunnel oxide can be scaled down from 10 nm to 8 nm.
Blue Light Emission from Rapid-Thermal-Oxidized Porous Silicon
Authors: Mimura Hidenori , Futagi Toshiro , Matsumoto Takahiro , Nakamura Takato , Kanemitsu Yoshihiko
Published: October 2002

We have converted the hydrogen-passivated surface of porous Si prepared by electrochemical etching into a stable oxidized one using a rapid thermal oxidation process. At a high oxidation temperature (T
ox) above about 800° C, blue photoluminescence (PL) with a peak wavelength of about 400 nm was clearly observed. On the other hand, at low T
ox below about 800° C, the PL peak remained at about 750 nm, which is similar to that of as-anodized porous Si. From Fourier transform infrared (ETIR) spectra, we found that the PL spectra are closely related to the structure of the oxygen-terminated surface on Si nanocrystallites. Spectroscopic data suggest that the red PL and the blue PL originate from a surface state and a quantum-confinement state, respectively.
Structural Dimension Effects of Plasma Hydrogenation on Low-Temperature Poly-Si Thin Film Transistors
Authors: Kim Yong-Sang , Choi Kwon-Young , Lee Seong-Kyu , Byung-Hyuk Min Byung-Hyuk Min , Min-Koo Han Min-Koo Han
Published: October 2002

The effects of plasma hydrogenation on various N- and P-channel polycrystalline-silicon (poly-Si) thin film transistors (TFT's) fabricated at a maximum temperature of 600° C were analyzed systematically. Device characteristics, such as threshold voltage and field-effect mobility, were improved significantly with hydrogenation time as the channel length of poly-Si TFT's was decreased from 20 µm and 2.5 µm. However, hydrogenation effects on the characteristics of poly-Si TFT's, of which channel width was varied from 2.5 µm to 20 µm, were almost identical. In thin active layer (50 nm) TFT's, the device performance was improved significantly compared with thick (100 nm and 150 nm) devices with hydrogenation time while the thickness of gate poly-Si may not be directly related with hydrogenation effects, probably due to the fact that the hydrogen atoms may diffuse along the channel region while the diffusion of hydrogen atoms through gate poly-Si may be negligible.
As Preamorphization of the Predeposited Amorphous Si Layer for the Formation of the Silicided Ultra Shallow p+-n Junction
Authors: Kwon Sang Jik , Kim Yeo Hwan , Chun Kuk Jin , Lee Jong Duk
Published: October 2002

Major limiting factors in the linear scaling down of the shallow source/drain junction are the boron channeling effect and the Si consumption phenomenon during silicidation. We can solve these problems by As preamorphization of the predeposited amorphous Si layer. The predeposited amorphous Si layer made the junction depth decrease to nearly the thickness value of the layer and was effectively utilized as the consumed Si source during Ti silicidation. This method was applied to the actual fabrication of the PMOSFET (p-channel metal oxide semiconductor field effect transistor) through the SES (selectively etched Si) technology.
A Static Random Access Memory Cell Using a Double-Emitter Resonant-Tunneling Hot Electron Transistor for Gigabit-Plus Memory Applications
Authors: Mori Toshihiko , Muto Shunichi , Hirotaka Tamura Hirotaka Tamura , Naoki Yokoyama Naoki Yokoyama
Published: October 2002

This paper describes our research on quantum memory devices having a single transistor structure similar to that of a double-emitter resonant-tunneling hot electron transistor (RHET). Its prototype 2×2 bit cell array was fabricated and operated at room temperature. The device used in the prototype cell had no current gain, however, and required other active devices to build static random access memory (SRAM) peripheral circuits such as a decoder and senseamplifier. We also report recent advances in the memory cell made using a double-emitter RHET which has a current gain of 8 at 77 K–suitable for logic circuits peripheral to our memory cell array. The cell's small size shows promise for use in large scale memory application.
Spectral Linewidth and Linewidth Enhancement Factor in 1.5-µ m Modulation-Doped Strained Multiple-Quantum-Well Lasers
Authors: Mawatari Hiroyasu , Kano Fumiyoshi , Yamamoto Norio , Kondo Yasuhiro , Yuichi Tohmori Yuichi Tohmori , Yuzo Yoshikuni Yuzo Yoshikuni
Published: October 2002

A study of the linewidth enhancement factor ( α-parameter) of 1.5-µm modulation-doped strained multiple-quantum-well (MQW) lasers is reported. The α-parameter was effectively decreased with increasing negative detuning. At a detuning of -30 nm, the α-parameter can be reduced to less than 1 by 1×1018 cm-3 p-type modulation doping and 1.4% compressive strain in a Fabry-Perot laser. Applying this structure to a distributed feedback (DFB) laser, we investigate the dependence of the linewidth characteristics on the α-parameter. Finally, in the DFB laser with the cavity length of 1500 µm, the minimum spectral linewidth is lowered to 80 kHz at an output power of 40 mW.
Hydrogenated Amorphous Silicon Carbide P-I-N Thin-Film Light-Emitting Diodes with Barrier Layers Inserted at P-I Interface
Authors: Jen Tean-Sen , Pan Jen-Wei , Shin Nerng-Fu , Tsay Wen-Chin , Chang Jyh-Wong Hong
Published: October 2002

To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), a barrier-layer (BL) structure had been inserted at its p-i interface and used to enhance the hole injection efficiency of TFLED under forward-bias operation. Two TFLEDs with different BL structures were studied. The device I had a 25 Å i-type single-barrier structure and the device II had an i-type double-barrier structure of barrier(10 Å)/well(10 Å)/barrier(10 Å). The obtainable brightness of device I was 342 cd/m2 at an injection current density of 600 mA/cm2. On the other hand, the device II had a brightness of 256 cd/m2 at 800 mA/cm2. These brightnesses were about 3 orders of magnitude higher than that of a basic a-SiC:H p-i-n TFLED.
Magnetotransport in Two Parallel Two-Dimensional Electron Gases Formed by a Delta-Doped Layer and a Heterojunction in GaAs
Authors: Klaus-Jürgen Friedland Klaus-Jürgen Friedland , Klaus Ploog Klaus Ploog
Published: October 2002

Magnetotransport measurements in a two-layer electron system with large spacing between the layers are reported. The application of differential methods allows us to investigate each of the two conducting layers separately. At low magnetic fields we observe additional high-mobility carriers located between the two conducting layers forming an extended electronic state. With increasing magnetic field these electrons are frozen out. The spin-split integer quantum Hall states and the fractional quantum Hall states with the filling factors 1/3 and 2/3 of the high-mobility electron gas are found in this two-layer system by differential magnetotransport studies.
Single and Double δ-Doped Al0.25Ga0.75As/In0.25Ga0.75As Pseudomorphic Heterostructures Grown by Molecular-Beam Epitaxy
Authors: Kudo Makoto , Mishima Tomoyoshi , Washima Takuma Tanimoto
Published: October 2002

Single and double δ-doped Al0.25Ga0.75As/In0.25Ga0.75As pseudomorphic heterostructures grown by molecular-beam epitaxy are examined to improve the performance of high-electron-mobility transistors (HEMTs). Double δ-doped layers, which are inserted in uniformly-doped AlGaAs carrier supply layers, can reduce the distance between the surface and the channel down to 19 nm without degrading the electrical properties. The mobility and sheet electron concentration at room temperature are 6050 cm2/(V·s) and 2.32×1012 cm-2, respectively ( 16270 cm2/(V·s) and 2.30×1012 cm-2 at 77 K). Shubnikov-de Haas oscillations confirm that the parallel conduction in the carrier supply layer is negligible. This work indicates that δ-doping in uniformly-doped carrier supply layers can be a key factor in improving the performance of HEMTs.
Low-Temperature Epitaxy of GaAs by Metalorganic Chemical Vapor Deposition
Authors: Chen Wei-Kuo , Chang Chen-Shiung , Chen Wen-Chun
Published: October 2002

The low-temperature (LT) epitaxial growth of high quality GaAs films is achieved by using triethylgallium and tertiarybutylarsine as the precursors. Without any external work, the deposition can be conducted at a temperature as low as 350° C in a conventional metalorganic chemical vapor deposition system. The full width at half-maximum of 77 K photoluminescence and X-ray rocking curve for a sample grown at 425° C are 8.2 meV and 14 arcsec, respectively. Materials with good electrical properties were also obtained. A Schottky diode formed on the LT CaAs epilayer shows a barrier height of 0.83 eV, and a reverse saturation current of 1.1×10-7A/cm2, comparable to that of a normal GaAs Schottky diode.
Method for Determination of Rotational Viscosity in Nematic Liquid Crystals
Authors: Masahiro Imai Masahiro Imai , Hiroyoshi Naito Hiroyoshi Naito , Masahiro Okuda Masahiro Okuda , Akihiko Sugimura Akihiko Sugimura
Published: October 2002

A simple method is proposed for the determination of the rotational viscosity of nematic liquid crystals. Theoretical expressions for the rotational viscosity from transient displacement current in nematic liquid crystals are derived. It is demonstrated that the values of the rotational viscosity measured with this method are in excellent agreement with the Merck data.
Initial Plasma Density Dependence of Kinetic Energy of Ions Collected on Electrode
Authors: Koichi Ogura Koichi Ogura , Takemasa Shibata Takemasa Shibata
Published: October 2002

Gadolinium plasma was produced between parallel-plate electrodes by resonance photoionization. The kinetic energy of the ions, which were extracted from the plasma and collected on the electrode by means of an electric field, was measured by the time-of-flight method. At the applied potential of V
0, the kinetic energy of ions increased continuously from 0.5e
V
0 to e
V
0 with increasing initial plasma density. The initial plasma density which was required to change the kinetic energy of ions from 0.5e
V
0 to e
V
0 or to maintain the quasi-neutral plasma was estimated using a simple one-dimensional model.
Local Peeling of Photoresist Film during Ultraviolet Light Exposure
Authors: Kawai Akira , Nagata Hitoshi , Takata Hiroaki Morimoto
Published: October 2002

Circular peels are formed during exposure of the photoresist film to ultraviolet (UV) light. Dependency of peel formation in photoresist film on adhesion energy is investigated. The value of adhesion energy is derived from the measurement value of surface free energy. The surface free energy of inorganic substrates used for the investigation is between the values of 46.5 and 62.6 dyn/cm. It is found that the number of peels decreases as the adhesion energy increases. Peel formation can be explained by using the adhesion energy.
Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) Characterization of Sublimed C60 Solid
Authors: Maniwa Yutaka , Nagasaka Masayuki , Ohi Atushi , Kume Kiyoshi , Kikuchi Koichi , Saito Kazuya , Ikemoto Isao , Suzuki Shinzou , Achiba Yohji
Published: October 2002

Two kinds of electron spin resonance (ESR) signals were found in sublimed carbon-sixty ( C60) solid, one of which is extremely sensitive to air while the other is relatively stable. Although the origin of these signals could not be clarified, it was found that successive sublimation leads to a C60 solid which does not show any detectable ESR signal. 13C-nuclear magnetic resonance (NMR) study showed that the sublimed solid is much more homogeneous than the solution-grown solids, and that C60 orientational ordering transition around 262 K is a first-order phase transition.
Room-Temperature Operation of Fast-Axial-Flow Radio-Frequency-Discharge-Excited CO Laser
Authors: Kouki Shimizu Kouki Shimizu , Shunichi Sato Shunichi Sato
Published: October 2002

Room-temperature operation of a fast-axial-flow radio-frequency-discharge-excited CO laser is described. With a Xe-free N2-rich mixture ( CO/N2/He/O2=11.5/26.4/62.1/0.23), steady-state laser output of 163 W has been obtained from a 1.9-cm-diameter, 30-cm-long discharge at an entrance gas temperature of 289 K. The corresponding electrical conversion efficiency is 8.2%. The temperature dependence of output has also been measured in the range of 289–313 K, which gives a change of 0.94 W/K or 0.011 W/K per cm3 of discharge volume.
Synthesis of Sc15C19 Crystallites Encapsulated in Carbon Nanocapsules by Arc Evaporation of Sc-C Composite
Authors: Saito Yahachi , Okuda Mitsumasa , Yoshikawa Tadanobu , Bandow Shunji , Yamamuro Saeki , Wakoh Kimio , Sumiyama Kenji , Suzuki Kenji
Published: October 2002

Crystallites of scandium carbides nesting in multilayered, polyhedral graphitic cages (nanocapsules) were produced by evaporating a scandium-graphite composite rod by electric arc discharge in helium gas. The composite particles were characterized by analytical electron microscopy and X-ray diffraction. The encapsulated scandium carbide was identified to be Sc15C19, instead of dicarbide RC2 (R represents rare-earth elements) which was the form of carbide commonly found for other rare-earth elements entrapped in nanocapsules. The size of the capsules ranged from about 10 to 100 nm. Morphological features of the outer graphitic carbon, multilayered and polyhedral, were quite similar to those previously discovered for the capsules protecting RC2 (R=Y, La, Ce,…, Lu).
Magnetic Properties of Iron in Nanocapsules
Authors: Hihara Takehiko , Onodera Hideya , Sumiyama Kenji , Suzuki Kenji , Kasuya Atsuo , Nishina Yuichiro , Saito Yahachi , Yoshikawa Tadanobu , Okuda Mitsumasa
Published: October 2002

We have studied the magnetic properties of fine particles of iron and iron carbide nested in carbon cages (nanocapsules), which were synthesized by arc discharge of carbon rods. It is clarified by Mössbauer spectroscopy and thermomagnetic ( M-T ) curve that these particles consist of α-Fe, γ-Fe and Fe3C. Their coercive force is larger than that of bulk α-iron, being ascribed to the small particle size observed by high-resolution (HR) transmission electron microscopy (TEM).
Dry Etching Damage and Activation Ratio Degradation in δ-Doped AlGaAs/InGaAs High Electron Mobility Transistors
Authors: Tanimoto Takuma , Kudo Makoto , Kodera Mitsuhiro Mori
Published: October 2002

Damage caused by selective dry etching was examined for δ-doped AlGaAs/InGaAs HEMT structures by using Hall measurements of two-dimensional-electron-gas (2DEG) at room temperature. The penetration depth of the damage caused by Reactive Ion Etching (RIE) was found to be 25 nm. It was also found that δ-doped AlGaAs is more sensitive to damage than uniformly doped AlGaAs. The damage depth derived from mobility degradation agrees with the damage depth characterized by the reduction in the carrier activation ratio in the δ-doped AlGaAs layer.
Study of Sputtering Mechanism of Silicon with Hydrogen Plasma Controlled by Magnetic Field
Authors: Sun Yong , Nishitani Ryusuke , Miyasato Tatsuro
Published: October 2002

The sputtering mechanism of silicon in rf hydrogen plasma has been studied by controlling plasma density at silicon surface. The amounts of ionic and neutral species have been measured as functions of the magnetic field. We have observed that the amount of each neutral species shows a different dependence on the magnetic field. It is found that the silicon target is sputtered by mainly forming neutral SiH2 and SiH3 species into plasma. The amount of ionic species changes linearly with increase in the magnetic field. There is no direct relationship between the amount of ionic species and the corresponding neutral species.
InAlGaAs Staircase Avalanche Photodiodes
Authors: Tsuji Masayoshi , Watanabe Isao , Kikuo Makita Kikuo Makita , Kenko Taguchi Kenko Taguchi
Published: October 2002

Metal-organic vapor phase epitaxy (MOVPE)-grown InAlGaAs staircase avalanche photodiodes (APDs) with sawtooth graded-gap multiplication regions are demonstrated for the first time. Extremely high multiplication factors M of over 100, low dark currents of 550 nA at M=20, and high-gain-bandwidth products exceeding 100 GHz were confirmed in 10×200- Å sawtooth multilayer APDs.
Preparation of a BaF2/CaF2 Slab Optical Waveguide by Chemical Vapor Deposition
Authors: Hirotsugu Sato Hirotsugu Sato
Published: October 2002

Single crystal BaF2 films 0.6–3.8 µ m thick were grown on CaF2 substrates by chemical vapor deposition. Fluorinated Barium β-diketone chelates; Ba(ofhd)2 or Ba(dfhd)2 were used as the source material and oxygen was introduced to complete the fluorination of the barium precursor. The BaF2/CaF2 structure functioned as a slab optical waveguide and the losses were mainly dependent on the film thickness and the surface morphologies. The minimum loss was about 1 dB/cm at 633 nm.
Fabrication of Two Tesla Magnet Using Bi-2212 Ag-Sheathed Tapes
Authors: Yoshida Masashi , Akihiko Endo Akihiko Endo , Naoki Hara Naoki Hara
Published: October 2002

Pancake-type superconducting coils were fabricated using Ag-sheathed Bi-2212 tapes. The conventional powder-in-tube method was used where the metal composition of powders are Bi:Sr:Ca:Cu=2:2.3:0.85:2, different from the stoichiometric 2212 composition. Heat treatment was performed in the reduced oxygen partial pressure of 0.01 atm. The superconducting magnet assembled from pancake coils generated a field of 2.0 T at 4.2 K using the 1×10-13 Ω· m criterion. The J
c was 3.9×104 A/cm2.
Bidirectional Orientation and Size Distribution of Copper Phthalocyanine (CuPc) Microcrystals Doped in Polyurea Film
Authors: Tsukagoshi Kiyomi , Sakakibara Youichi , Masayuki Iijima Masayuki Iijima , Yoshikazu Takahashi Yoshikazu Takahashi
Published: October 2002

Bidirectional orientation of needle-like CuPc microcrystals was observed in CuPc-doped polyurea films prepared by vapor deposition on KCl(100). We postulate that this orientation of the microcrystals is due to the orientation of the crystalline polyurea matrix. The bell-shaped size distribution of the microcrystals indicates that the CuPc microcrystals are formed during sublimation in the source.
Scanning Shearing-Stress Microscopy of Gold Thin Films
Authors: Sasaki Akira , Katsumata Akira , Futoshi Iwata Futoshi Iwata , Hisayuki Aoyama Hisayuki Aoyama
Published: October 2002

Gold thin films have been observed using scanning shearing-stress microscopy (SSSM), which is a new scanning probe microscopy based on a scanning tunneling microscope (STM) and a frequency shift of an AT-cut quartz resonator. The quartz resonator coupled to an STM sample is oscillated at its resonance frequency. The resonance frequency shift corresponds to the shearing-stress changes in the sample under tip scanning. Images of STM and SSSM topographies of gold thin films can be observed simultaneously. The shearing-stress distribution is caused by scanning-direction slope changes in STM profiles; therefore these stresses are caused by frictional force between the STM tip and sample.
Corner Rounding of Crystals Growing at High Pressure
Authors: Takano Kaoru J. , Kenichi Harigae Kenichi Harigae , Masao Wakatsuki Masao Wakatsuki
Published: October 2002

The benzene crystal growing at high pressure was visually observed using the optical liquid high pressure cell. The octahedral single crystals, surrounded by {111} faces of the orthorhombic lattice, were observed. The sharp corners in the particular direction abruptly rounded beyond a critical temperature that depended on pressure and concentration. Such pressure, temperature and concentration dependence of the corner shape was observed for the first time. It is possible that the corner rounding originates from the effect of surface free energy, and the transition-like change of the corner shape arises from the thermal roughening transition of the minor singular face at the corners.
Mesoscopic Roughness Characterization of Grown Surfaces by Atomic Force Microscopy
Authors: Yoshinobu Tatsuo , Atsushi Iwamoto Atsushi Iwamoto , Hiroshi Iwasaki Hiroshi Iwasaki
Published: October 2002

Mesoscopic roughness of material surfaces grown on (or dissolved from) flat substrates is described in terms of its scale dependence. It is demonstrated that three parameters, including the characteristic correlation length and the anisotropy exponent of scaling, in addition to the scale independent rms roughness on long length scales, describe well the scaling behavior of roughness. A procedure to derive these parameters from atomic force microscopy data is also discussed.
Preservation of the Phase Boundary of Si(111)7×7 Structure in Air Studied by Force Microscopy
Authors: Tsuneo Fukuda Tsuneo Fukuda
Published: October 2002

Si(111) surfaces cleaned under ultrahigh vacuum were studied by force microscopy in air. 7×7 domain boundaries associated with the phase transition from 1×1 to 7×7 during cooling were imaged as 1.0∼1.5 Å high protrusions. The morphology was quite consistent with results from in situ techniques. For rapidly quenched surfaces, disordered 1×1 triangles were also seen in the middle of terraces. These structures may be related to the difference in surface atom densities and the difference in reaction to oxygen.
Numerical Simulation of Backgating Suppression in High Electron Mobility Transistors (HEMTs) with a Low Temperature Molecular Beam Epitaxy (MBE)-Grown Gallium Arsenide Buffer Layer between the Substrate and Active Layers
Authors: Tan Leng Seow , Lau Wai Shing , Samudra Ganesh Shankar , Kin Man Lee Kin Man Lee , Boon Yong Ang Boon Yong Ang
Published: October 2002

Numerical simulations were carried out for a high electron mobility transistor (HEMT) in which the active device was separated from the hole-trap-rich substrate by a gallium arsenide buffer layer, grown by molecular beam epitaxy at low temperature, which contains the EL3 electron trap. The results show, for the first time, that the interface between the substrate and the buffer layer behaves like a reverse biased p-n junction when a negative backgate voltage is applied. By sustaining the backgate voltage across it, this junction effectively isolates the active channel of the HEMT from the substrate bias and thus eliminates backgating in the device.
Giant Magnetoresistance with Low Saturation Field in Ni14Fe13Co73/Cu Multilayers
Authors: Jimbo Mutsuko , Hirano Seishi , Meguro Kenichi , Tsunashima Shigeru , Uchiyama Susumu
Published: October 2002

The giant magnetoresistance effect has been investigated for Ni14Fe13Co73/Cu multilayers prepared by the rf magnetron sputtering method, where the NiFeCo alloy has a saturation magnetostriction constant as small as 1×10-6. A magnetoresistance ratio of 22% is obtained at room temperature for a Cu thickness of 2.1 nm. About 80% of the magnetoresistance change occurs in the range of magnetic fields within 50 Oe.