bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman Study on Sol-Gel Derived Tungsten Oxides from Tungsten Ethoxide
Authors: Miyakawa Akira Takase
Published: February 2005

Tungsten oxide gels were prepared by a sol-gel process from a tungsten ethoxide/ethanol/water solution (sol). Tungstic hydrates were observed in high-viscosity sol by Raman spectroscopy. As the sol is reduced to the gel, Raman bands ascribed to amorphous tungsten oxide appeared. The result of the Raman measurement shows that the structure of the gel changes progressively during heat treatment and that the amorphous tungsten oxide becomes a crystalline solid at 410°C.
Electronic Transport Characteristics in GaAs Double-Sawtooth-Doping Superlattice Structure
Authors: Wen-Chau Liu Wen-Chau Liu , Chung-Yih Sun Chung-Yih Sun
Published: February 2005

In this paper, a new GaAs switching device, based on a double-sawtooth-doping superlattice (SDS) structure and a metal-semiconductor (M-S) Schottky contact, has been demonstrated. The distinct δ-doping sheets, i.e., 1×1012 and 1×1013 cm-2, were employed in the double-SDS structure. Holes, created by the avalanche breakdown process at the M-S junction, cause the potential redistribution when they are accumulated at the valence band maxima of zigzag quantum wells. Hence, an attractive S-shaped negative-differential-resistance (NDR) phenomenon is observed. In addition, an interesting intermediate state between the initial off-state and the final on-state appears at 77 K. Consequently, with appropriately designed parameters, the studied structure will provide a good potential for application in switching and multiple-valued logic circuits.
Trapping of Ca+ Ions and Optical Detection
Authors: Urabe Shinji , Imajo Hidetsuka , Kazuhiro Hayasaka Kazuhiro Hayasaka , Masayoshi Watanabe Masayoshi Watanabe
Published: February 2005

A medium-sized rf ion trap is developed, and stored Ca+ ions are optically detected. Weak fluorescence from Ca+ ions is detected using a frequency-doubled Ti:sapphire laser and the photon counting method. The temperature and number of stored ions are estimated from the measured spectrum of the ions and the spatial distribution of the ion cloud.
Real-Time Observation of AlAs/GaAs Superlattice Growth by Coaxial Impact Collision Ion Scattering Spectroscopy
Authors: Sugiyama Naoharu , Akihiro Hashimoto Akihiro Hashimoto , Masao Tamura Masao Tamura
Published: February 2005

Monitoring of the layer-by-layer growth of an AlAs/GaAs superlattice is performed using coaxial impact-collision ion-scattering spectroscopy. By exploiting high-frequency time-of-flight analysis, real-time observations of the intensity variation from Ga signals, which indicates the surface coverage of GaAs, are achieved. The intensity increases when GaAs is grown on AlAs, and the rise time of the intensity variation agrees well with the time for one-monolayer growth of GaAs.
Atomic Structure of Si(111)-(√3×√3)R30°-Al Studied by First Principle Molecular Dynamics
Authors: Tsuge Hiroshi , Masao Arai Masao Arai , Takeo Fujiwara Takeo Fujiwara
Published: February 2005

The atomic structure of Si(111)-(√3×√3)R30°-Al was studied without any symmetry restriction by using the first principle molecular dynamical simulation. The results are in good agreement with the experimental ones.
Characterization of Improved AlGaAs/GaAs Resonant Tunneling Heterostructure Bipolar Transistors
Authors: Wu Jenq-Shinn , Chang Chun-Yen , Lee Chien-Ping , Chang Kou-Hsiung , Don-Gey Liu Don-Gey Liu , Der-Cherng Liou Der-Cherng Liou
Published: February 2005

We report on the fabrication of AlGaAs/GaAs resonant tunneling heterostructure bipolar transistors (RTHBT's). The devices exhibit a current peak in the transfer characteristics, with peak-to-valley current ratios of 1.7 and 9 at 300 K and 77 K, respectively. The common-emitter small signal current gains at 300 K and 77 K reach 40 and 28, respectively. They are the best results to date for AlGaAs/GaAs resonant tunneling transistors. Because the double barriers are placed in the emitter and far from the emitter-base interface, and the heterostructure emitter suppresses the hole injection from the base to the emitter, the occurrence of the negative differential resistance (NDR) in the device characteristics is governed by the emitter current but not by the base current. The operation mechanism of the NDR behavior in the common-emitter output characteristics is discussed.
Dependence of Ga Desorption Rate upon the Step Density in Molecular Beam Epitaxy of GaAs
Authors: Suzuki Takashi , Ikuhisa Ichimura Ikuhisa Ichimura , Tatau Nishinaga Tatau Nishinaga
Published: February 2005

By using a single quantum well structure, the dependence of the Ga desorption rate upon the step density in the growth of GaAs by molecular beam epitaxy is studied. It is shown that the desorption rate has no dependence in the entire range of the growth temperature within the sensitivity of the experiments. By comparing the present theory with the experimental results, the upper limit of supersaturation possibly existing at the growth step is estimated and it is concluded that near equilibrium is established at the step edge at relatively high growth temperature where the evaporation of Ga occurs.
Dependence of Band Offsets on Elastic Strain in GaAs/GaAs1-xPx Strained-Layer Single Quantum Wells
Authors: Zhang Xiong , Onabe Kentaro , Nitta Yoshiki , Zhang Baoping , Fukatsu Susumu , Yasuhiro Shiraki Yasuhiro Shiraki , Ryoichi Ito Ryoichi Ito
Published: February 2005

High-quality GaAs/GaAs1-x
P
x
(x=0.15, 0.20, 0.22) strained-layer single quantum well structures have been grown on GaAs1-y
P
y
(y=0.1, 0.2) substrates by metal organic vapor phase epitaxy (MOVPE) and characterized by the combination of the reflectance and photoluminescence measurements. Relying on the strong and highly resolved optical transitions between the energy subbands of electrons and holes (including heavy and light holes) in the spectra, we have accurately determined the conduction and valence band offsets in this strained system. The results obtained clarify for the first time that the band offsets are strongly dependent on elastic strain or composition.
Effect of Electronic States of Triphenylamine Derivatives on Their Charge Transport Properties
Authors: Aratani Sukekazu , Tsuneaki Kawanishi Tsuneaki Kawanishi , Atsushi Kakuta Atsushi Kakuta
Published: February 2005

The hole drift mobilities of polymers doped with triphenylamine derivatives have been measured and the effect of the electronic states of triphenylamine derivatives on the charge transport properties has been studied. The HOMO (highest occupied molecular orbital) distribution strongly affects the charge transport properties and it was found that when the triphenylamine part had more HOMO distribution, the mobility increased. Moreover, 2-[p-di(p-tolyl)aminostyryl]-4-methylthiazole was found as a new charge transport material having rather high drift mobility.
Si(111)(√3×√3)-Al Surface Studied by Angle-Resolved Electron-Energy-Loss Spectroscopy
Authors: Li Sung-Te , Hasegawa Shigehiko , Nakamura Shogo , Nakashima Hisao
Published: February 2005

The surface electronic structures of Si(111)(√3×√3)-Al are investigated with the use of angle-resolved electron-energy-loss spectroscopy. Three new surface one-electron transitions (in specular reflection) are found at 1.8, 7.2, and 13.1 eV. Compared with the surface state band structures calculated by Northrup and STM results by Hamers and Demuth, the loss peak at 1.8 eV is ascribed to the one-electron transition between the occupied and unoccupied surface state bands which originate from the Al adatoms. The other two peaks are considered to be due to the Si-Si strained back bonds.
As and P Desorption from III-V Semiconductor Surface in Metalorganic Chemical Vapor Deposition Studied by Surface Photo-Absorption
Authors: Naoki Kobayashi Naoki Kobayashi , Yasuyuki Kobayashi Yasuyuki Kobayashi
Published: February 2005

As and P desorption processes from (001) oriented GaAs, InAs, GaP, and InP surfaces during metalorganic chemical vapor deposition are investigated by surface photo-absorption. The reflectivity varies from that of a group V stabilized surfaces, formed by the supply of AsH3 or PH3, to that of a group III metal surface during the desorption of group V species in hydrogen carrier gas. This reflectivity change can be described by first-order kinetics. The rate equation including the activation energy can be obrained from the Arrhenius plot of the desorption rate constants. The desorption rate increases in the order of GaP, GaAs, InAs, and InP in the substrate temperature range of 400∼640°C. The observed desorption activation energies suggest that the desorption species are As2 for GaAs (450∼560°C) and InAs (400∼460°C), P2 for GaP (500∼620°C) and InP (below 390°C), and P for InP (above 390°C).
In Situ Monitoring of Surface Kinetics in GaAs Atomic Layer Epitaxy by Surface Photo-Absorption Method
Authors: Koukitu Akinori , Ikeda Hitoshi , Hiroshi Suzuki Hiroshi Suzuki , Hisashi Seki Hisashi Seki
Published: February 2005

The epitaxial growth reactions that proceed on the substrate surface during halogen transport atomic layer epitaxy (ALE) are observed directly with a surface photo-absorption method. The heat of desorption (48.5 kcal/mol) is obtained from the reflective intensity change. The value agrees well with the activation energy reported in classical halogen transport vapor-phase epitaxy. Based on the observation, a reaction mechanism is proposed. The self-limiting mechanism of halogen transport ALE is ascribed to the complete coverage of surface As sites by the adsorbed complex.
Observation of Interface Stress in Barrier/Y-Ba-Cu-O Structure by Laser Raman Scattering Spectroscopy
Authors: Matsubara Gensoh , Matsui Toshiyuki , Yoichi Okabe Yoichi Okabe
Published: February 2005

Stress at the interface between thin Y-Ba-Cu-O film and various insulating materials deposited on Y-Ba-Cu-O was investigated by laser Raman scattering spectroscopy. The shift of the phonon mode at 500 cm-1, which is the stretching vibration associated with O-Cu-O bonding parallel to the c-axis, indicates the existence of stress in the interface region of Y-Ba-Cu-O. As the penetration depth of the 514.5 nm incident light was estimated to be less than 40 nm, this method was found to be effective for the characterization of the junction interface.
Influence of Oxygen Content on the Superconductivity of Bi-Based Oxides Homologous to 2212 Phase
Authors: Deshimaru Yuichi , Otani Tetsuya , Shimizu Youichi , Norio Miura Norio Miura , Noboru Yamazoe Noboru Yamazoe
Published: February 2005

Thermal desorption of oxygen and its relevance to superconductivity were examined for a series of oxides Bi2Sr2-x
Ca1+x
Cu2O
y
(x=0, 0.25, 0.5, 0.8 and 1.0) isostructural to the 2212 phase. The total oxygen desorbed up to 600°C amounted to 2∼3×10-5 mol/g for each oxide. T
c was constant at about 80 K for all the as-prepared oxides but T
c decreased linearly with x from 97 K (x=0) to 67 K (x=1.0) for the oxygen-desorbed oxides. The total oxygen contents (y) were determined and correlated with T
c, which increased for x=0 and 0.25, whereas it went through a maximum at about y=8.15 for x=0.8.
Atomic-Scale Fluctuation of the Terrace Width on Vicinal (001) GaAs Surfaces
Authors: Shunsuke Ohkouchi Shunsuke Ohkouchi , Ichiro Tanaka Ichiro Tanaka
Published: February 2005

GaAs (001) vicinal surfaces which were tilted 2 degrees toward the [010] direction were observed with a scanning tunneling microscope equipped with a molecular beam epitaxy facility. The surface of 30 monolayers of GaAs grown on a substrate consisted of both large flat and narrow terraces. On the other hand, the surface of a 1.5-µm-thick GaAs layer grown on a substrate consisted of relatively uniform-width terraces which reflected the off-angle. However, their terrace edges showed a large atomic-scale fluctuation.
The Effects of Reverse Injection Current on High a Quality InSb Photovoltaic Detector
Authors: Chen Liang Po , Luo Jiunn Jye , Liu Tai Hwa , Yen Ming Pang Yen Ming Pang , Sheng Jenn Yang Sheng Jenn Yang
Published: February 2005

This paper presents the fabrication and characterization of high-quality InSb p+-n photovoltaic detectors. The reverse dark current of the detector at small reverse bias is dominated by the generation-recombination current and shunt current. We also present, for the first time, the effects of the reverse injection current on the detector. The breakdown voltage of the detector increases after the injection process. However, the dark current at small reverse bias (-200 mV) increases and then decreases with increase of the reverse injection current. This result may be due to the hole trapping in the passivation layer during the injection process.
Effect of Ultraviolet Light Irradiation on Noncontact Laser Microwave Lifetime Measurement
Authors: Katayama Ken-ichi , Kirino Yoshio , Kunio Iba Kunio Iba , Fumio SHimura Fumio SHimura
Published: February 2005

An ultraviolet (UV) irradiation effect on minority-carrier recombination lifetime measured by a noncontact laser/microwave (LM) method is investigated for silicon wafers with native oxide. After UV irradiation, the surface recombination velocity greatly decreased resulting in the increase in the effective recombination lifetime (τeff). The effect disappears rapidly with time after the irradiation, and τeff recovers to the initial value after several minutes at room temperature. Since the UV irradiation process is noncontact and nondestructive, the irradiation is proposed to minimize the surface effect of sample, in turn, to obtain the bulk lifetime (τb) with a noncontact LM lifetime measurement method.
Preparation of Glass-Conducting Polymer Composite by Sol-Gel Method and Its Property
Authors: Ohsawa Toshiyuki , Onoda Mitsuyoshi , Morita Shigenori , Yoshino Katsumi
Published: February 2005

Simple methods to obtain composite glass with conducting polymers by the sol-gel method have been developed. Poly(2,5-diethoxy aniline)-glass composite is prepared by gelation of a sol containing a polymer. Polypyrrole-glass composite is made by polymerization of pyrrole in the premade glassy medium with FeCl3 as a catalyst. Electrical and optical properties of the obtained composites have been studied.
Point Group Determination of Calcium Tartrate by Etch Figure
Authors: Noriyuki Nakatani Noriyuki Nakatani
Published: February 2005

Etch figures of gel-grown orthorhombic calcium tartrate tetrahydrate crystals have been examined in order to determine the point group symmetry. Making a thorough investigation of etch-figure characters on natural surfaces of rhombic dodecahedron crystals, we reached the firm conclusion that the point group is nonpolar 222.
Thermodynamical Calculation and Experimental Confirmation of the Density of Hole Traps in SiO2 Films
Authors: Ohmameuda Toshiaki , Miki Hiroshi , Asada Kunihiro , Ohji Takuo Sugano
Published: February 2005

Assuming the oxygen vacancy as a point defect, the density of oxygen vacancies in SiO2 films thermally grown on Si substrates is calculated thermodynamically, taking into account the strain incorporated into SiO2 films, and the calculated density of oxygen vacancies has been found to be in good agreement with the measured density of hole traps. The density of oxygen vacancies is thermodynamically predicted to decrease at lower oxidation temperature, and, consistently, it is experimentally shown that the density of hole traps is decreased from 2×1012 cm-2 to 1×1012 cm-2 by lowering the oxidation temperature from 1000°C to 900°C.
X-Ray Chemical Analysis of an YBa2Cu3OxThin Film by Scanning Electron Microscopy and Total-Reflection-Angle X-Ray Spectroscopy (SEM-TRAXS)
Authors: Usui Toshio , Aoki Yuji , Kamei Masayuki , Takahashi Hiromi , Tadataka Morishita Tadataka Morishita , Shoji Tanaka Shoji Tanaka
Published: February 2005

Scanning electron microscopy and total-reflection-angle X-ray spectroscopy (SEM-TRAXS) were applied to X-ray chemical analysis of a 1000 Å-thick YBa2Cu3Ox(YBCO) film on an MgO substrate. The intensity of the characteristic X-rays emitted from the YBCO thin film varied as a function of the take-off angle (θt) with respect to the film surface. The intensity of higher-energy X-rays of BaL lines and CuK lines was almost constant against the θtover the wide range of 0°-30°, but that of lower-energy X-rays of YLα, CuLαand OKαlines depends strongly on the θtup to 10°, and then slightly increases with the θt.
Lasers without Inversion in Microcavities
Authors: Björk Yoshihisa Yamamoto
Published: February 2005

The lasing characteristics of microcavity lasers with high coupling efficiency of spontaneous emission into the lasing mode are studied. Output power, population inversion, spectral linewidth and intensity noise are calculated as functions of pumping rate. When the spontaneous emission coupling efficiency into the lasing mode is close to one, a lasing threshold characterized by a sharp increase in an output power, a clamping of population inversion, a decrease in spectral linewidth and a peak in intensity noise, are observed at a pump rate in which a population inversion is not created yet. A physical interpretation for lasing without inversion in a microcavity is given on the basis of a photon recycling picture consisting of dissipation-free stimulated emission and re-absorption.
Real-Time Ultrashort Pulse Shaping and Pulse-Shape Measurement Using a Dynamic Grating
Authors: Kazuhiro Ema Kazuhiro Ema
Published: February 2005

We report a new technique for shaping an ultrashort pulse and measuring a pulse shape in real time using an optically induced dynamic grating in a nonlinear material. The technique is all optically controllable, not limited by electronic switching time, and works over a wide range of wavelengths. We demonstrate the technique by using three kinds of nonlinear materials: a Bi12SiO20 (BSO) crystal, a DODCI solution and a ZnSe film.
Relationship between Thermally Grown SiO2 and the As-Dried Physical Surface Characteristic
Authors: Yukihiro Murakami Yukihiro Murakami
Published: February 2005

Two conditions are used to dry Si wafers: (A) for 5 minutes at 800 r.p.m. and (B) for 3 minutes at 800 r.p.m. This drying with a centrifugal effect in a clean air environment was done after immersion into diluted HF (1:200) at R.T. and sufficient rinsing with DIW at R.T. We observed the physical surface characteristics (or adsorbent state) for each wafer by the cold chuck method at 5°C. The breakdown voltage characteristic, V
bd, was measured for each sample. It is found that there is a relationship between the physical surface characteristic seen in the cold chuck image and the V
bd.
Effect of Twinning Caused by Thermal Annealing on Etched Tracks in Synthetic Quartz
Authors: Sawamura Teruko , Satoshi Baba Satoshi Baba , Hatsuo Yamazaki Hatsuo Yamazaki
Published: February 2005

Synthetic quartz crystal –x-, y- and z-cut plates– irradiated with fission fragments were heated to temperatures above 573°C and cooled to room temperature before etching in 65% NaOH. The crystals displayed twinning caused by the heating. The openings of etched tracks in twinned areas showed differences in shape in the x-cut plates and in orientation for the y- and z-cut plates (no differences in shape). The bulk etching rates of the twinned areas were also different for twins on the x-cut plates, but were the same for the y- and z-cut plates.
Modification of E-Beam Latent Images in Negative Resist by Exposure to Monochromatic Deep UV Flood Light
Authors: Ban Hiroshi , Moriya Shigeru , Jiro Nakamura Jiro Nakamura , Akinobu Tanaka Akinobu Tanaka
Published: February 2005

1.7-µm-thick SAL601 single-layer resist was post-exposed to monochromatic deep UV flood light after e-beam delineation to enhance its resolution. Substantially improved pattern shape and pattern size controllability were obtained by exposing the resist to 254- and 248-nm light where SAL601 has absorption coefficients of 0.46 and 0.88 µm-1, respectively. Monte Carlo simulation of the deposition energy profile indicates that the incident light reaches considerable depth in the resist and modifies the whole preexisting latent image formed by e-beam delineation.
GaInAs/InP Quantum Wells and Strained-Layer Superlattices Grown by Chemical Beam Epitaxy
Authors: Uchida Toshi K. , Uchida Takashi , Yokouchi Noriyuki , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: February 2005

Ga
x
In1-x
As/InP (0.2≤x≤0.47) quantum wells were grown by chemical beam epitaxy. The thinnest well of two monolayers was obtained and confirmed by transmission electron microscope. Room temperature photoluminescence emission was observed from two-monolayer quantum wells which peaked at 1.0 µm. Strained quantum wells were grown with successive well thickness from 9 Å to 60 Å. By optimizing the growth sequence, we obtained a photoluminescence linewidth of 15 meV from 20 Å to 60 Å wells at 77 K.
Selective Epitaxial Growth on (100) Vicinal GaAs Surfaces by Atmospheric Pressure-Metalorganic Chemical Vapor Deposition Using Diethylgalliumchloride
Authors: Ko-ichi Yamaguchi Ko-ichi Yamaguchi , Kotaro Okamoto Kotaro Okamoto
Published: February 2005

Selective epitaxial growth of the step-flow mode is observed on (100) vicinal GaAs surfaces by atmospheric-pressure metalorganic chemical vapor deposition (MOCVD) using diethylgalliumchloride (DEGaCl). The extremely flat surface obtained is identified as an exactly (100)-oriented plane and extends from one side of the mask edge (upstream edge of step flow) toward the downstream region of the step flow. The step-flow-mode growth was observed in a wide range of growth conditions, and it is suggested that the enhancement of the reevaporation of GaCl species suppresses two-dimensional nucleation on the terrace surfaces.
InP/InGaAs Heterostructure Bipolar Transistors Grown at Low Temperature by Metalorganic Chemical Vapor Deposition
Authors: Kurishima Kenji , Makimoto Toshiki , Takashi Kobayashi Takashi Kobayashi , Tadao Ishibashi Tadao Ishibashi
Published: February 2005

We describe the performance of InP/InGaAs heterostructure bipolar transistors (HBTs) grown at low temperature by metalorganic chemical vapor deposition (MOCVD). HBTs with a base thickness of 70 nm and doping level of 1×1019 cm-3 show excellent current gain characteristics (current gains h
FE>300, ideality factors n
B<1.25) at growth temperatures ranging from 500 to 575°C. In addition, Zn out-diffusion from the base layers into the undoped spacer layers is well suppressed to as low as 5×1017 cm-3.
Structural Change of Al-Cu-Co Decagonal Quasicrystal Studied by High-Resolution Electron Microscopy
Authors: Hiraga Kenji , Wei Sun Wei Sun , Francis John Lincoln Francis John Lincoln
Published: February 2005

We found that the stable decagonal quasicrystal of Al-Cu-Co undergoes a structural change at low temperatures. The Al65Cu15Co20 alloy quenched from 800°C shows diffraction patterns with sharp spots placed at nearly perfect decagonal symmetry positions, but by annealing at 550°C the diffraction patterns show a remarkable change in the appearance of diffuse scatterings. High-resolution electron microscopy shows the transformation, at low temperatures, into a partially crystalline structure of a monoclinic unit cell with a=b=2 nm, c=0.4 nm and γ=108°.
Pyrolysis of Trimethylgallium on (001) GaAs Surface Investigated by Surface Photo-Absorption
Authors: Naoki Kobayashi Naoki Kobayashi , Yoshiji Horikoshi Yoshiji Horikoshi
Published: February 2005

We directly observe the process of CH3 desorption from a GaAs surface reacted with trimethylgallium (TMG), using the surface photo-absorption method. After supply of TMG onto the As-stabilized (001) GaAs surface in H2 carrier gas, the reflectivity increases and saturates during H2 purging at substrate temperatures below 500°C. The observed reflectivity change corresponds to the formation of the Ga metal surface caused by CH3 desorption from the CH3-terminated surface. The CH3 desorption can be described by first-order kinetics, and the desorption rate constant is 2×10-2 s-1, i.e., a lifetime of 50 s at 485°C. This is long enough to support the well-accepted mechanism of atomic layer epitaxy, i.e., the inability of the excess TMG to adsorb when supplied to the CH3-terminated surface.
Characteristic of a Microwave Strip Line Made from YBa2Cu3O7-x Superconductor on Alumina Substrate
Authors: Ohashi Yoshiko H. , Kawabata Keisuke , Minoru Niwa Minoru Niwa , Mitsuru Fukuchi Mitsuru Fukuchi
Published: February 2005

Strip lines of high T
c (HTC) superconductor material are made on alumina substrates. Films with a sharp transition temperature of YBaCuO superconductor have been prepared by a printing method with buffer treatment. The attenuation of microwaves travelling on the HTC strip lines was examined by means of the time domain method at 77 K, and the value of the attenuation per meter was found to be 5.5 dB/m around 10 GHz.
In Situ Preparation of Pb-Based Superconducting Thin Films at Low Temperature and Low Oxidizing Atmosphere
Authors: Adachi Hideaki , Adachi Seiji , Ichikawa Yo , Kentaro Setsune Kentaro Setsune , Kiyotaka Wasa Kiyotaka Wasa
Published: February 2005

Thin films of Pb-based superconductor have been epitaxially grown in situ on MgO (100) substrates by rf-magnetron sputtering. The growth temperature was 550°C, which is relatively low compared to that of conventional oxide-superconducting films. The reducing atmosphere was preferable for the formation of films with Pb-3212 structure, and no oxygen was required in the sputtering gas. The film showed a superconductive transition at 75 K, and zero-resistivity was realized below 60 K without post-heat treatment.
Optimization of Nitridation and Reoxidation Conditions for an EEPROM* Tunneling Dielectric
Authors: Arima Hideaki , Ajika Natsuo , Ohi Makoto , Sakamoto Osamu , Takayuki Matsukawa Takayuki Matsukawa , Natsuro Tsubouchi Natsuro Tsubouchi
Published: February 2005

We show that the maximum reoxidation time is one of the useful parameters for determining the optimum processing condition of reoxidized nitrided oxide (RONO) film. The maximum reoxidation time is defined as the time in which the thickness of a nitrided oxide film increases 10%. Since many RONO process parameters have a close relationship to this parameter, it is easy to determine an optimum RONO condition. Using such an optimized condition of RONO film formation, that is, performing the nitridation of oxide in 50% NH3 ambient at 1050°C for 30 s and following it with reoxidation in O2 ambient at 1100°C for 120 s, we formed 9-nm-thick RONO film as the EEPROM tunnel dielectric. The film is found effective not only in improving the endurance to more than 106 cycles, but also in causing no degradation at all to the characteristics of the 1M-bit EEPROM devices actually fabricated.
Low-Temperature Cleaning of GaAs Substrate by Atomic Hydrogen Irradiation
Authors: Takeyoshi Sugaya Takeyoshi Sugaya , Mitsuo Kawabe Mitsuo Kawabe
Published: February 2005

Low-temperature cleaning of GaAs substrate by atomic hydrogen irradiation has been demonstrated. Atomic hydrogen was provided by dissociation of hydrogen gas, which was carried out in a simple cracking cell with a 1500°C tungsten filament. Auger electron spectroscopy showed that carbon was removed at 200°C and oxygen was removed at 400°C by 30-min atomic hydrogen irradiation. The surface cleaning of GaAs was confirmed by the change of RHEED pattern from halo to streak after the hydrogen irradiation.
New Light Modulator Using GaSe Layered Crystal
Authors: Iwamura Yasuo , Makoto Moriyama Makoto Moriyama , Naozo Watanabe Naozo Watanabe
Published: February 2005

Layered crystals of GaSe are grown by the Bridgman method. Transmission spectra are measured for various sample configurations with respect to the c-axis, applied electric field, direction of incident light and polarization. Absorption edge shifts toward longer wavelength by 20 nm under an electric field of 1 kV/cm, the shift of which is two orders larger than estimated on the Franz-Keldysh mechanism. Switching time is measured to be 53 ns or less.
Crystallization Behavior and Curie Temperature for Melt-Spun Amorphous Fe100-XGdX(18≤X≤70) Alloys
Authors: Yano Kazuo , Tokumitsu Kazuto , Kita Eiji , Ino Hiromitsu , Akira Tasaki Akira Tasaki
Published: February 2005

The crystallization behavior and Curie temperature, T
c, for the amorphous Fe100-X
Gd
X
alloys prepared with a melt quenching method with wide range concentration (18≤X≤70) were studied by means of a thermomagnetization measurement. Final stable phases were determined from the measurement in the cooling process from 800°C. They are (i) α-Fe, Fe23Gd6 and Fe2Gd for X=22, (ii) α-Fe, Fe2Gd and α-Gd for 33.3≤X≤58, and (iii) Fe2Gd and α-Gd for X=70. The concentration dependence of T
c has a maximum value of 320°C around X=40. T
c in the present melt-spun ribbons is higher than that of thin films by about 100 degrees.
Observation of Photoinduced Alkyl Group Elimination from Precursors in Organometallic Vapor-Phase Epitaxy of Zn-Based II-VI Semiconductors
Authors: Fujita Shizuo , Shin-ya Hirata Shin-ya Hirata , Shigeo Fujita Shigeo Fujita
Published: February 2005

We observed, from mass analysis, enhancement of alkyl group elimination from alkylzinc (dimethyl- and diethylzinc) under photoirradiation of energy higher than the band gaps of the underlying II-VI semiconductors, where the growth rates in organometallic vapor-phase epitaxy (OMVPE) of these materials are remarkably enhanced. This result suggests the association of carriers generated at the growth surface for the alkyl group elimination, and this phenomenon seems to be one of the fundamental chemical processes contributing to the growth rate enhancement of Zn-based II-VI semiconductors.
Optically Pumped Blue-Green Laser Operation Above Room-Temperature in Zn0.80Cd0.20Se-ZnS0.08Se0.92 Multiple Quantum Well Structures Grown by Metalorganic Molecular Beam Epitaxy
Authors: Kawakami Yoichi , Yamaguchi Shigeo , Wu Yi-hong , Ichino Kunio , Shizuo Fujita Shizuo Fujita , Shigeo Fujita Shigeo Fujita
Published: February 2005

We report the characteristics of optically pumped stimulated emission in Zn0.80Cd0.20Se-ZnS0.08Se0.92 multiple quantum well (MQW) structures fabricated by metalorganic molecular beam epitaxy (MOMBE). At room-temperature (290 K), laser operation at 504 nm was achieved with the threshold excitation intensity (I
th) of 66 kW/cm2 under pulsed excitation condition. Laser operation up to 400 K has been observed in this MQW structure.
Study on Annealing Treatment and Sr/Ca Ratio for Pb-Sr-Y-Ca-Cu-O Ceramics with “1212” Structure
Authors: Adachi Seiji , Adachi Hideaki , Kentaro Setsune Kentaro Setsune , Kiyotaka Wasa Kiyotaka Wasa
Published: February 2005

The annealing effects of “1212” lead cuprate in a Pb-Sr-Y-Ca-Cu-O system were investigated. Samples with a nominal composition of (Pb0.7Cu0.3)Sr2(Y1-x
Ca
x
)Cu2O
y
(x=0.4-0.7) were annealed at various temperatures in oxygen. The x=0.5 sample, which was annealed at 800°C and then quenched, exhibited the highest T
c(zero resistivity) of 48 K. It was found that there were three different types, two tetragonal phases and one orthorhombic phase, in the “1212” of x=0.5. It was considered that the phase transformation was caused by different oxygen contents. Samples with a nominal composition of (Pb0.7Cu0.3)Sr2+z
(Y0.5Ca0.5-z
)Cu2O
y
(z=±0.3) were also prepared. Deviation from z=0.0 in the composition induced degradation of the superconductivity.
Influence of Nitrogen Incorporation in Hydrogenated Amorphous Silicon Films Prepared by Photochemical Vapor Deposition
Authors: Hiramatsu Masato , Kamimura Takaaki , Mitsuo Nakajima Mitsuo Nakajima , Hiroshi Ito Hiroshi Ito
Published: February 2005

The influence of nitrogen incorporation in a-Si:H films by mercury-photosensitized decomposition of a silaneammonia gas mixture was investigated. It was found that there are two different film structures of a-Si:H films. In a high nitrogen concentration, nitrogen is one of the elements of the a-SiN
x
alloy. On the other hand, in a low nitrogen concentration, nitrogen plays the role of a dopant in a-Si:H, and nitrogen-induced localized states are created at around 0.5 eV above the valence band edge.
Coherent Electron Devices
Authors: Kazuhito Furuya Kazuhito Furuya
Published: February 2005

In conventional transistors, the transport of the electron is controlled using the incoherent interaction between the electron and fixed charges. This paper points out that the coherent interaction between the electron and fixed charges can provide more efficient control of the transport. To attain the coherent interaction, a systematic placement of impurity atoms in the crystal lattice is required. Atomic planes and atomic wires consisting of the impurity atoms will act as building elements for the coherent electron devices.
Direct Determination of Interface Trapped Charges
Authors: Yang Cary Y. , Hiroshi Inokawa Hiroshi Inokawa , Felicia E. Pagaduan Felicia E. Pagaduan
Published: February 2005

A technique to determine the interface trapped charge, Q
it, from C-V and I-V measurements is introduced. This Q
it technique is free from the assumptions used in the conventional methods for determining the density of interface traps, D
it. The technique is applied to current-stressed metal-oxide-semiconductor (MOS) capacitors with different oxide thicknesses and found to be useful in revealing donor- and acceptor-type characteristics of interface traps.
Temperature Dependence of Lattice Parameters of YBa2Cu3Ox Superconductor at Low Temperature
Authors: Usami Katsuhisa , Norio Kobayasi Norio Kobayasi , Toshiya Doi Toshiya Doi
Published: February 2005

The temperature dependence of lattice parameters of YBa2Cu3O
x
(x=6.95) was studied by X-ray diffraction in the range of 300-20 K. All three lattice parameters decreased linearly with decreasing temperature in the range of 300-130 K, and anisotropies in the thermal expansion coefficients were observed. The expansion coefficients along the a, b and c axes were 5.2×10-6, 9.2×10-6 and 1.57×10-5 (K-1), respectively. There was only a slight difference in their temperature dependencies in the region below 130 K, and lattice parameters a and b were nearly constant below the superconducting transition temperature.
Partial Melting of Solution-Spun Y1Ba2Cu3Ox Filament
Authors: Sugishita Tomoko Goto
Published: February 2005

A partial-melt growth process is used to enhance the J
c of solution-spun Y1Ba2Cu3O
x
filaments. The filaments have been prepared by dry spinning through a homogeneous aqueous solution containing mixed acetates of Y, Ba and Cu, polyvinyl alcohol, and organic acids. By controlling the melt growth process of the filaments, dense and highly oriented textures are produced, and a transport critical current density of more than 1×104 A/cm2 at 77 K and 0 T is achieved for the filaments, each with a diameter of 60 µm.
Enhancement of Third-Order Optical Nonlinearities of Soluble Vanadyl Phthalocyanines in Doped Polymer Films
Authors: Hosoda Masahiro , Wada Tatsuo , Yamamoto Tomihiro , Kaneko Akimasa , Anthony F. Garito Anthony F. Garito , Hiroyuki Sasabe Hiroyuki Sasabe
Published: February 2005

The third-order optical susceptibilities χ1111
(3)(-3ω; ω, ω, ω)s of a soluble vanadyl phthalocyanine derivative ((t-Bu)1.1VOPc) are studied for thin films and doped polymethylmathacrylate films by optical third-harmonic generation measurements at wavelengths of 1543 nm and 1907 nm. The χ(3) values are enhanced by a factor of 2-7 at resonant and
nonresonant wavelengths, concurrent with an absorption change induced by exposure to solvent vapor. The red-shifted phase (phase II), obtained by the treatment, has larger χ(3) values than the as-prepared phase (phase I). The enhancement of third-order optical nonlinear susceptibilities in phthalocyanine thin films is discussed in terms of electronic transition and molecular packing.
Observation of Photochromic Reactions in Spiropyran Monolayers by Surface Potential Measurement
Authors: Yamaguchi Takashi , Kajikawa Kotaro , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: February 2005

The monolayer films of photochromic spiropyran have been investigated by means of surface potential and optical absorption measurements. We found that UV light irradiation isomerises the spiropyran chromophore to zwitterionic photomerocyanine at the air-water interface and induces not only an optical absorption increase but a surface potential (ΔV) increase of about 500 mV. The thermal reversion process was also observed, using these techniques, to be fairly slow in the dark. In the ΔV-A (area) isotherm of the photomerocyanine monolayer, there exist three regions. In two of them, no detectable surface pressure is observed, while ΔV changes. The change in ΔV in the other region is mutually related to the surface pressure change and is caused by molecular orientational change.
Step Structure Transformation of Si(001) Surface Induced by Current
Authors: Natori Akiko , Hiroki Fujimura Hiroki Fujimura , Hitoshi Yasunaga Hitoshi Yasunaga
Published: February 2005

The domain conversion mechanism on a Si(001) surface induced by DC current is investigated, and the origin of the critical step spacing is clarified. The conversion between 2×1 and 1×2 domains on the Si(001) surface proceeds with the movement of each step, caused by the transport of adatoms across the terrace. The uniform driving force on adatoms is assumed to be induced by the supply of DC current. The step kinetics is treated by developing the BCF (Burton, Cabrera and Frank) theory to take account of the three effects: contribution of the drift flux of adatoms, anisotropy of a diffusion constant, and repulsive interaction between steps. The domain conversion is induced by the coupling of the first and second effects. The balance condition between the drift flux and the backward diffusion flux caused by the repulsive step-step interaction determines the critical spacing. The time evolution of step configuration is calculated numerically, and it explains well the observed behaviour.
Flow Orientation in Langmuir-Blodgett Films of a Charge-Transfer Complex (TMTTF)3(C14TCNQ)2
Authors: Ikegami Keiichi , Kuroda Shin-ichi , Tabe Yuka , Saito Kazuhiro , Sugi Michio , Matsumoto Mutsuyoshi , Nakamura Takayoshi , Kawabata Yasujiro
Published: February 2005

The occurrence of flow orientation during the deposition of Langmuir-Blodgett films of (TMTTF)3(C14TCNQ)2 is shown through studies of in-plane molecular orientation in films deposited by two types of the vertical dipping method, with the substrates parallel and perpendicular to the barrier, using ESR and polarized UV-visible spectroscopies. Larger in-plane anisotropy is observed toward the edge of the substrates, which is consistent with the prediction of the recent theory of flow orientation during the deposition process. Furthermore, in-plane anisotropy in the films deposited by the horizontal lifting method is detected, suggesting the existence of a compression orientation at the air-water interface.
Study of Sensitization Processes in Superionic Conductor α-AgI by Photoacoustic Spectroscopy (I)
Authors: Kurita Mitsufumi , Minomura Fumio Akao
Published: February 2005

The change in the photoacoustic (PA) spectrum of α-AgI has been measured by exposing an above-band-gap light as a function of time from 0 to 20 min at 443 K. It has been found that the PA signal below the band gap of α-AgI increases monotonically up to a factor of 4 with increasing lapse of exposure time. The behavior seems to be attributable to a photoinduced clustering of Ag+ ions.
Self-Scanning Light-Emitting Device (SLED) Using pnpn Thyristor Structure
Authors: Kusuda Yukihisa , Tone Kiyosi , Shuhei Tanaka Shuhei Tanaka , Ken Yamashita Ken Yamashita
Published: February 2005

We propose and demonstrate a new functional optoelectronic device, the “self-scanning light-emitting device (SLED).” The SLED consists of light-emitting thyristors whose turn-on voltages interact with each other through the resistor network. The SLED acts as an optical shift register, and the light-emitting element is automatically transferred by input clock pulses. We successfully demonstrated GaAs SLED operation using three-phase transfer clock pulses, and obtained 3 MHz as the maximum transfer rate. Moreover, we propose here the diode-coupled SLED, where the turn-on voltages of the thyristors interact through the pn diode in order to obtain the transfer operation driven by a two-phase clock pulse. The SLED has several unique functions and will become a new key device in the optoelectronic field and in optical information processing.
Phase-Modulated Grating Lenses for Two-Dimensional Optical Branching
Authors: Gen-ichi Hatakoshi Gen-ichi Hatakoshi , Masaru Nakamura Masaru Nakamura
Published: February 2005

Phase-modulated grating lenses, which have composite functions of focusing and branching, have been investigated. Grating lenses for two-dimensional optical branching were designed by introducing a phase-modulation function. The phase-modulation function was optimized, so as to balance the optical intensity values for the required branchings and to suppress those for undesirable branchings. The grating lens has an advantage, wherein the branching characteristics can be precisely controlled by the two-dimensional grating pattern.
A Liquid Crystal Microlens with Hole-Patterned Electrodes on Both Substrates
Authors: Nose Toshiaki , Shin Masuda Shin Masuda , Susumu Sato Susumu Sato
Published: February 2005

Electrically controlled lens properties (liquid crystal microlens) can be obtained by utilizing molecular orientation effects in an axially symmetric nonuniform electric field. Excellent lens properties can be obtained using a symmetric electrode structure with hole-patterned electrodes on both substrates. Several kinds of optical properties have been investigated and characteristic phenomena of the liquid crystal microlens are discussed in terms of a molecular orientation model.
Optical Cosine Transform Using Microlens Array and Phase-Conjugate Mirror
Authors: K. W. Wong K. W. Wong , L. M. Cheng L. M. Cheng
Published: February 2005

An optical cosine transform system is designed using microlens array and phase-conjugate mirror. It can perform segmented cosine transform fulfilling the specification laid down by the CCITT H.261 recommendation on video audiovisual services. Design considerations and system sensitivity analysis will be presented.
Comparative Equilibrium Analysis of Metalorganic Chemical Vapor Deposition (MOCVD) GaAs Growth Using Trimethylgallium (TMGa) with Arsine or Trimethylarsine (TMAs)
Authors: Abril Evaristo José , Alonso Alonso , Lopez Miguel , Miguel Aguilar Miguel Aguilar
Published: February 2005

A thermodynamic equilibrium model has been employed to determine the equilibrium estate of Trimethylgallium (TMGa)-AsH3-H2 and TMGa-Trimethylarsine (TMAs)-H2 systems in vapor phase. The analysis has been made for pressure, hydrogen/trimethyl (H2/TM) ratio, V/III ratio and various temperature ranges, and includes, in both cases, 33 selected gas-phase species in the presence of solid GaAs. A study of the substitution of arsine for TMAs has been carried out, with regard to relative stabilities of the species and the changes in carbon incorporation. Dependence of carbon impurities on the growth parameters has been analyzed in order to postulate the factors that can influence carbon incorporation.
Vacuum Bakeout Effect on Ambient Gas in a High Pressure LEC Puller
Authors: Johji Nishio Johji Nishio
Published: February 2005

H2 and CO generation from graphite furnace components in a high-pressure liquid-encapsulated Czochralski (LEC) puller was studied in detail from the standpoint of reproducible contamination to the LEC charge (B2O3 encapsulant/GaAs melt). It has been found that H2 and CO contamination from the graphite furnace components varies widely according to the vacuum level as well as to the high-temperature duration time of the vacuum bakeout process. It has been concluded that controlling the vacuum bakeout condition is the key to achieving reproducible generation of H2 and CO during LEC GaAs single-crystal growth.
Torque Measurements of Ferromagnetic Mn-Al Multilayered Films
Authors: Hirayama Yoshiyuki , Teruaki Takeuchi Teruaki Takeuchi , Masaaki Futamoto Masaaki Futamoto
Published: February 2005

Magnetic torque curves are measured for Mn-Al multilayered films, while changing the number of layers or the layer thickness, to investigate the magnetic anisotropy. A seven-layer film with layer thickness of 10 nm shows two-fold symmetry, while the eight-layer film shows a unique four-fold symmetry in the torque curves measured with the magnetic field rotated in the normal plane. The torque amplitude of four-fold symmetry component decreases as the layer thickness increases. The results suggest that the four-fold symmetry in the torque curves of the Mn-Al multilayered films is due to the magnetic interactions between the ferromagnetic regions near the Mn-Al interfaces.
Evaluation of a Pre-Objective Scan System for the Laser Recrystallization of Silicon on Insulator Material
Authors: Geert Willems Geert Willems , Herman Maes Herman Maes
Published: February 2005

A quantitative description of the optical performance of a pre-objective scan system for the laser recrystallization of silicon on insulator (SOI) material is given. The thermal effects induced by the high power argon-ion laser beam in the transmitting optical components making up the optical path of the laser beam are discussed extensively. Thermal lensing in plan-parallel optics and heating of the flat field scan lens by the laser beam leads to a recrystallization condition dependent beam waist position of the focused laser beam. A model is presented to calculate the beam waist position as a function of the recrystallization parameters. Using this model it is possible to predict the thermal defocusing and compensate for it by adjusting the wafer position. In this way a recrystallization parameter independent spot size can be obtained on the wafer. A critical evaluation of the pre-objective scan technique is given.
Dependence of the X-Ray Photoacoustic Signal Intensity of Brass on Sample Thickness and Modulation Frequency
Authors: Toyoda Taro , Masujima Tsutomu , Shiwaku Hideaki , Ando M.
Published: February 2005

Hard X-ray photoacoustic signal intensities of brass have been measured in the Cu K-edge region as functions of sample thickness d (from 10 µm to 300 µm) and modulation frequency f (from 5 Hz to 50 Hz). The photoacoustic signal intensities are proportional to d-1 for each modulation frequency. The X-ray photoacoustic signal varies as f
-1.0 up to a sample thickness of 20 µm, whereas it varies as f
-0.5 beyond the sample thickness of 20 µm.
Advantage of Strained Quantum Wire Lasers
Authors: Ueno Shin-ichi , Yasunari Miyake Yasunari Miyake , Masahiro Asada Masahiro Asada
Published: February 2005

It is shown theoretically that the strained quantum wire (QW) lasers have gain and differential gain much larger than those of unstrained QW lasers. Application of the strain effect to quantum wire structure leads to small hole effective mass which induces a large separation between quantized energy levels in the valence band. Thus holes concentrate efficiently into fundamental level, giving rise to increase of gain and differntial gain. The wire width at which the energy separation is comparable to the thermal energy and the relaxation broadening is 2.5 times that of the unstrained case. Broadening of energy levels due to wire width fluctuation can be reduced 1/2 times that of the unstrained case.