bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-Band-Edge Photoluminescence of Sulfur-Doped GaAs Prepared by Liquid Phase Epitaxy
Authors: Jiang Gwo-Cherng , Chang Yih , Chang Liann-Be , Juang Yung-Der , Su Lu Su Lu
Published: October 2002

Photoluminescence measurement is used to characterize the sulfur-doped GaAs epitaxial layers grown on GaAs(100) substrates by liquid phase epitaxy. The dependences of spectral line shape on the doping levels ranged from 5×1017 to 1.8×1018 cm-3 as functions of excitation power and temperature have been investigated. Three main competing near-band-edge radiative transitions are identified as: direct conduction band to valence band transition, conduction band filling levels to valence band tail transition, and donor-related states to valence band tail or to acceptor transition. In order to explain the spectral shifting and broadening observed in heavily sulfur-doped GaAs, the luminescence peak emitted from the conduction band filling to valence band tail transition is also compared with theoretical calculations where the carrier concentration dependence of peak energy can be well described based on the heavy doping induced band-tail effect.
Estimation of Current Profile during Ion Cyclotron Range of Frequency Heated Discharges Characterized by Sawtooth Stabilization and Crash in JT-60U
Authors: Sato Masayasu , Kimura Haruyuki , Azumi Masafumi , Fujii Tuneyuki , Saigusa Mikio , Moriyama Shin-ichi , Isei Nobuaki , Kamada Yutaka , Shirai Hiroshi , Hirotaka Kubo Hirotaka Kubo
Published: October 2002

Sawteeth are stabilized by the second harmonic Ion Cyclotron Range of Frequency minority ion heating in JT-60U. In these discharges, time evolution of the current profile is studied by using a 1.5D transport code in order to understand the effect of sawtooth crash on the current profile and to determine whether the plasma conductivity is given by Spitzer or by neoclassical formulae. The computational results using resetqprofile at experimental sawtooth crash time and the neoclassical conductivity are in good agreement with experimental observations. The resistive diffusion of the current is neoclassical except at the crash and the current profile abruptly changes at the crash.
Radiation Level Measured by a Portable Geiger-Müller Counter at the Altitude of Commercial Air Routes
Authors: Takashi Araki Takashi Araki
Published: October 2002

The background intensities of naturally occurring radiation were measured aboard scheduled commercial airplanes using a newly developed Geiger-Müller counter with a pocket computer. The preliminary results show that the radiation at the cruising altitude of a commercial airplane on a transcontinental flight is 40 times higher than the ground-level.
Scattering-Matrix Formalism for Antidot Lattices
Authors: Seiji Uryu Seiji Uryu , Tsuneya Ando Tsuneya Ando
Published: October 2002

A method of full quantum mechanical calculation of energy bands of antidot lattices is developed based on a scattering (S) matrix which describes scattering at a junction of quantum wires. A comparison of calculated energy bands with results of diagonalization of the Hamiltonian in a lattice model shows that an S matrix including all traveling and a few evanescent modes gives a sufficiently accurate result.
Disappearance of the Breakdown of Quantum Hall Effects in Short Devices
Authors: Yasushi Kawaguchi Yasushi Kawaguchi , Fumio Hayashi Fumio Hayashi , Susumu Komiyama Susumu Komiyama , Toshihito Osada Toshihito Osada , Yasuhiro Shiraki Yasuhiro Shiraki , Ryoichi Itoh Ryoichi Itoh
Published: October 2002

Device-length dependence of the breakdown of the integer quantum Hall effects is studied by using devices with narrow constricted regions of different lengthsLatT=1.5 – 4.2 K and Landau-level filling factors of ν= 2, 4 and 6. Samples are fabricated from GaAs/AlGaAs heterostructures. Sharp increase in the diagonal resistanceRxat a critical current disappears, and is replaced by a continuous and gradual increase in short constricted regions ofL< 30 µm. The observedL-dependence supports an avalanche-type carrier multiplication mechanism triggered by electron-superheating.
Numerical Studies on Quantum Transport in Antidot Arrays in Magnetic Fields
Authors: Satoshi Ishizaka Satoshi Ishizaka , Fumiyuki Nihey Fumiyuki Nihey , Kazuo Nakamura Kazuo Nakamura , Jun'ichi Sone Jun'ichi Sone , Tsuneya Ando Tsuneya Ando
Published: October 2002

The density of states and the conductivity tensor in antidot arrays in magnetic fields are calculated numerically by the self-consistent Born approximation (SCBA). The peak positions of the density of states agree well with the quantization condition for several short-periodic orbits. The behavior of calculated magnetoresistivity agrees with that of experimental data. However, the behavior of the conductivity tensor is very complicated, and it is not explained simply by the periodic orbit expression for the conductivity tensor.
A Comparison of the Growth of GaAs and GaP from Trimethyl-Gallium
Authors: Weyers Markus , Michio Sato Michio Sato
Published: October 2002

In the growth of GaAs and GaP from trimethyl-gallium (TMG) significant differences are observed. At low growth temperatures, the GaP growth rate is lower than that of GaAs. Additionally, more carbon is incorporated into GaP than into GaAs. Mass spectrometric studies on methyl desorption from a substrate show that As and P differ in their ability to break the final Ga-carbon bond. The lower efficiency of P in breaking monomethyl-gallium (MMG) causes to the observed differences in the growth rates and carbon uptake. Based on the growth results and the mass spectrometric data on methyl desorption, a model of the reaction path leading to the decomposition of TMG and to the production of Ga is developed. This model includes the presence of dimethyl-gallium (DMG) in both a physi-sorbed (weakly bonded) state and a chemi-sorbed (strongly bonded) state as the first intermediate products in the decomposition of TMG.
The Magnetic Field Dependent Characteristics of Conductance Fluctuations in Ballistic Quantum Dots
Authors: Jonathan P. Bird Jonathan P. Bird , Koji Ishibashi Koji Ishibashi , Yuichi Ochiai Yuichi Ochiai , Yoshinobu Aoyagi Yoshinobu Aoyagi , Takuo Sugano Takuo Sugano
Published: October 2002

We study magneto-resistance fluctuations in GaAs/AlGaAs, ballistic quantum dots. At low temperatures, and at sufficiently low magnetic fields, the fluctuations obscure any average features in the magneto-resistance. As the magnetic field is increased, such that the cyclotron orbit size becomes much smaller than the dot dimensions, however, a strong decay in their high frequency content is observed. We associate this behaviour with the formation of well defined edge states in the dot, and in order to account for our observations apply a simple model, which considers the flux enclosed by skipping orbits localised at the dot walls.
Anomalous Magnetoresistance near Superconducting Transition Temperature in a Mesoscopic Aluminum Wire
Authors: Seongjae Lee Seongjae Lee , Kyoung Wan Park Kyoung Wan Park , Mincheol Shin Mincheol Shin , El-Hang Lee El-Hang Lee , Hyuk Chan Kwon Hyuk Chan Kwon
Published: October 2002

We have observed an anomalous magnetoresistance (MR) in a mesoscopic aluminum wire near the superconducting transition temperature. The anomaly exists in a region of low magnetic field less than 12.5 G and within the narrow temperature region where the Ginzburg-Landau coherence length exceeds half the distance between the voltage probes. It consists of a “mesa” or “peak”-type MR centered around zero field (negative MR) with zero resistance outside the field region; in other words, the sample undergoes a normal-superconducting-normal transition as the magnetic field increases. Satellite peaks around the mesa MR were also observed for a very narrow range of temperature. We speculate that the sample size and dimensionality play an important role in these phenomena, but the origin is unclear.
Exchange Effects in Artificial Atoms
Authors: Marc A. Kastner Marc A. Kastner , Olivier Klein Olivier Klein , Claudio de C. Chamon Claudio de C. Chamon , David Tang David Tang , David M. Abusch-Magder David M. Abusch-Magder , Udi Meirav Udi Meirav , Xiao-Gang Wen Xiao-Gang Wen , Shalom J. Wind Shalom J. Wind
Published: October 2002

If a small region of electron gas is separated from its leads by tunnel junctions, the quantization of charge and energy gives rise to sharp peaks in the conductance as a function of electron density, one for each electron added to the isolated region. Because the charge and energy are quantized, we call this an artificial atom. The peaks in conductance occur when the Fermi energy in the leads is degenerate with one of the quantized energy levels of the artificial atom, thus providing a measure of the chemical potential µN of the artificial atom with a fixed number N of electrons. Detailed comparison of µN at high magnetic field with theory shows that exchange profoundly affects the ground state of electrons confined in this way. In particular, it stabilizes the singlet state to an unexpectedly high field, above which there is a gradual transition to the spin polarized state.
Formation of InGaAs Quantum Dots on GaAs Multi-Atomic Steps by Metalorganic Chemical Vapor Deposition Growth
Authors: Masatoshi Kitamura Masatoshi Kitamura , Masao Nishioka Masao Nishioka , John Oshinowo John Oshinowo , Yasuhiko Arakawa Yasuhiko Arakawa
Published: October 2002

Aligned InGaAs quantum dots as small as 20 nm were naturally formed at multi-atomic step edges by metalorganic chemical vapor deposition growth. In addition, it was found that anisotropic structure of InGaAs along the step edges toward the [110]A direction appears with the increase of growth time of InGaAs. This phenomenon may be useful in the formation of quantum wires.
Many-Body Effects in the Magnetoplasma of In 0.13Ga 0.87As/GaAs Quantum Wires
Authors: Forchel Manfred Bayer , Stefan Benner Stefan Benner , Hartmut Haug Hartmut Haug
Published: October 2002

We have performed photoluminescence experiments on modulated barrier In0.13Ga0.87As/GaAs quantum wires in normal magnetic fields up to B = 10.5 T. By using high excitation powers we observed emission from several lateral subbands. In comparison to low excitation spectra the emission features are shifted to lower energies due to band gap renormalization. Calculated luminescence spectra are in excellent agreement with the experimental spectra and have been used to study many-particle effects in these wires. We have found clear indications for an enhancement of the renormalization in quantum wires as expected due to the increase of the Coulomb interaction.
One-Dimensional Quantum Electron and Hole States in n-AlxGa 1-xAs/u-GaAs/u-AlxGa 1-xAs Corrugated Double-Heterojunctions
Authors: Karel Vacek Karel Vacek , Toshiyuki Usagawa Toshiyuki Usagawa
Published: October 2002

Quasi-one-dimensional quantum electron and hole states are suggested in modulation-doped n-AlxGa1-x
As/u-GaAs/u-AlxGa1-x
As corrugated double heterojunctions. The interfaces between n-AlxGa1-x
As/u-GaAs and u-GaAs/u-AlxGa1-x
As are saw-tooth corrugated by bends with period 850 Å and bending angle 90°. The thickness of the sandwiched GaAs layer is 150 Å. Quantum-mechanical simulations are performed for electrons and holes. The electrons are found to be densely packed in quasi-one-dimensional states located in the convex corner of the GaAs layer near the doped layer of n-AlxGa1-x
As. The hole states are also quasi-one-dimensional and are located in the convex corner of the GaAs layer near the undoped layer of u-AlxGa1-x
As. Consequently, spatial separation of ground level electron and hole quantum states can be achieved.
Multiple Negative Differential Resistance due to Quantum Interference of Hot Electron Waves in Metal (CoSi 2)/Insulator (CaF 2) Heterostructures and Influence of Parasitic Circuit Elements
Authors: Wataru Saitoh Wataru Saitoh , Takashi Suemasu Takashi Suemasu , Yoshifumi Kohno Yoshifumi Kohno , Masahiro Watanabe Masahiro Watanabe , Masahiro Asada Masahiro Asada
Published: October 2002

We report the observation of multiple negative differential resistance (NDR) in a metal (CoSi2)/insulator (CaF2) resonant tunneling hot electron transistor structure. Multiple NDR observed here can be attributed to the modulation of the transmission probability of hot electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers. By reducing the influence of the Schottky diode at the CoSi2/Si interface, relatively clear and low-voltage NDR is observed. It is found, by a simulation including parasitic elements, that the collector resistance and leakage current greatly influence the current voltage characteristics.
Silicon-Based Single-Electron-Tunneling Transistor Operated at 4.2 K
Authors: Akiko Ohata Akiko Ohata , Hiromi Niiyama Hiromi Niiyama , Toru Shibata Toru Shibata , Kazuaki Nakajima Kazuaki Nakajima , Akira Toriumi Akira Toriumi
Published: October 2002

We have fabricated single-electron-tunneling transistors using silicon which is a useful material for device applications. The device is composed of thin polycrystalline silicon film patterned by electron-beam lithography and its thermally grown oxidized film. We have observed, in this device, periodic conductance oscillations as a function of gate voltage and nonlinear resistances as a function of drain voltage at 4.2 K. These experimental results are in agreement with the theory of Coulomb blockade. We conclude that the observed behavior results from the charging energy of single-electron tunneling.
Surface Morphology and Crystallite Size during Growth of Hydrogenated Microcrystalline Silicon by Plasma-Enhanced Chemical Vapor Deposition
Authors: Hajime Shirai Hajime Shirai
Published: October 2002

The correlation between the surface morphology and the crystallite size during growth of hydrogenated microcrystalline silicon (µ c-Si:H) has been discussed using spectroscopic UV-visible phase-modulated ellipsometry, Raman spectroscopy and atomic force microscope (AFM). Through the deposition study of µ c-Si:H on Corning 7059 glass and Cr substrates from SiH4 highly diluted in H2 and layer-by-layer (LbL) technique by plasma-enhanced chemical-vapor deposition (PECVD), we found that the surface roughness during µ c-Si:H growth strongly influenced the creation of the crystallite phase and the relaxation of Si network. The ion bombardment induces surface roughness and decreases the crystallinity in µ c-Si:H growth. The LbL technique using H2 plasma promotes the nucleation and coalescence processes in the early stage of µ c-Si:H growth.
Study of Inelastic Scattering Effect in Unstrained and Strain-Compensated GaInAs/GaInP Multiquantum Barriers
Authors: Terhoe Loh Terhoe Loh , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga , Kazuhito Furuya Kazuhito Furuya
Published: October 2002

The effect of inelastic scattering on electron reflection in multiquantum barriers has been examined for the first time by using the damped resonant tunneling model. The electron reflectivity exhibits marked deterioration to values below unity at discrete energies in the virtual barrier. The largest dip in reflectivity is about 15% for an intraband relaxation time of 0.16 ps. It is also shown that this deterioration can be reduced by utilizing a strain-compensated superlattice in the multiquantum barriers.
Picosecond Photoluminescence Study of Relaxation Phenomena of Hot Electrons in a Quasi-One-Dimensional Structure
Authors: Shoko Niwa Shoko Niwa , Takamasa Suzuki Takamasa Suzuki , Nobuhiko Sawaki Nobuhiko Sawaki
Published: October 2002

The energy relaxation phenomena of photoexcited hot carriers in a quasi-one-dimensional (quasi-1D) structure are investigated using the photoluminescence intensity correlation method. It was found for the first time that the anti-correlation dip appears on application of the external electric field, if the kinetic energy of electrons is nearly equal to the GaAs LO phonon energy. Results are discussed in terms of the imbalance between the cooling effect due to the electron-phonon interaction and the heating effect due to the external field. It is suggested that the energy relaxation time and/or the electron mobility is enhanced in quasi-1D structure.
Behavior of Oxide Precipitates in Czochralski Silicon during Crystal Growth
Authors: Sueoka Koji , Ikeda Naoki , Yamamoto Toshiro , Sumio Kobayashi Sumio Kobayashi
Published: October 2002

During Czochralski silicon (CZ-Si) crystal growth, polyhedral oxide precipitates are formed in the high temperature range (>1000° C). In order to clarify the behavior of polyhedral precipitates in the low temperature range (<1000° C) during crystal growth, a series of simulation annealing was carried out as follows. Polyhedral precipitates were intentionally created in CZ-Si wafers by annealing at 1100° C for 16 h and then subjected to low-temperature annealing at 900° C or 700° C from 1 h to 64 h. The stress state and growth process of polyhedral precipitates in the wafers were studied by transmission electron microscopy (TEM) observations. It was found that (1) the strain around the precipitates increases considerably with annealing at 900° C within 1 h, and the precipitates generate dislocations during annealing at 900° C for between 4 h and 16 h, and (2) the growth rate of polyhedral precipitates is very low in the low temperature range. From these results, it is concluded that the polyhedral precipitates grow with very low growth rate in the low temperature range (<1000° C), and the lattice strain increases considerably around 900° C during CZ-Si crystal growth.
Comparison of Planar to Columnar Transformation of PtSi Layers on Si(001) and Si(111) Substrates in the Si Capping Layer Growth Process
Authors: Kumagai Yoshinao , Ishimoto Kouichi , Hashimoto Satoshi , Park Kyung-ho , Fumio Hasegawa Fumio Hasegawa
Published: October 2002

Highly oriented PtSi layers were grown on both (001) and (111) Si substrates heated to 500° C by codeposition of Pt and Si with a stoichiometric ratio (Pt/Si=1/1) in an ultrahigh vacuum (UHV). On Si(001) substrates, the PtSi layer consists of two types of grains, PtSi(110)łSi(001) with azimuthal orientation of PtSi[001]łSi<110>, whereas it consists of three types of grains on Si(111) substrates, PtSi(010)łSi(111) with PtSi[001]łSi<1\bar10>. When Si was subsequently grown on the PtSi layer at temperatures lower than 400° C for Si(001) and lower than 500° C for Si(111), Si/PtSi/Si double heterostructures were obtained. However, above these temperatures, each grain forming the PtSi layer transformed into a columnar shape in the process of Si growth so as to minimize the contact area between PtSi and Si, and the space between the PtSi columns was filled epitaxially by Si.
Alternate Sign Reversal in Magnetic Flux-Induced Persistent Current in an Isolated Mesoscopic Ring by Half-the-Ring Electrostatic Potential
Authors: Ohta Kuniichi , Daisuke Takai Daisuke Takai
Published: October 2002

We calculate the energy spectrum for an electron in an isolated ideal one-dimensional mesoscopic ring subject to magnetic flux threading the ring and electrostatic potential applied to one half of the ring. The problem is reduced to that of Kronig-Penney potential with Beyers and Yang boundary condition around the ring. The energy bandEis periodic in magnetic phase shift θ and approximately periodic in electrostatic phase shift φ. At low electrostatic potential,E(θ) bands are shifted in half the potential. Where theE(θ) bands are degenerate, band gaps are formed by electrostatic potential. Above some critical strength of electrostatic potential, narrow energy bands with wide gap are formed that are propagating in one half of the ring and decaying in the other half. From theE(θ) band, magnetic-flux-induced persistent current is calculated. Possibility of its alternate sign reversal by increasing the strength of the electrostatic potential is discussed.
Semi-Insulating Polycrystalline Silicon by Low Pressure Chemical Vapour Deposition from Disilane and Nitrous Oxide
Authors: Dehan Eric , Pedroviejo Juan Jose , Scheid Emmanuel , Morante Joan Ramon
Published: October 2002

Usually, semi-insulating polycrystalline silicon films SiO

x

are obtained from the chemical decomposition of silane and nitrous oxide. In this paper we describe the study of semi-insulating polycrystalline silicon (SIPOS) films from disilane and nitrous oxide by low pressure chemical vapour deposition. The kinetics of growth and the variation of oxygen content have been investigated relatively to deposition parameters such as temperature, total pressure and gas flow ratio. The oxygen content is assessed by X-ray photoelectron spectroscopy (XPS) and by differential thickness method. We show that the growth rate is higher for “disilane SIPOS films” than “silane SIPOS films” and we explain this behaviour by the strong difference in growth rate of silylene species. We also show that the inhibition effect of nitrous oxide on the growth rate is very low in the case of SIPOS films obtained with disilane. The electrical resistivity depends on the oxygen content and is ranged between 109 and 1013 Ω· cm.
Substrate-Dependent Growth of Polycrystalline Silicon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Using SiF 4 and H 2 Gases
Authors: Kwang-Yeol Choi Kwang-Yeol Choi , Chang Woo Lee Chang Woo Lee , Choochon Lee Choochon Lee
Published: October 2002

The growth of polycrystalline silicon films deposited on two different types of substrates by rf plasma-enhanced chemical vapor deposition using SiF4 and H2 gases was investigated. We observed that on the glass substrates, small grains grew and grain boundaries were not clear at the early stage of deposition (≤100 nm) before the growth of a columnar crystalline layer. However, on the SiO2 substrates, after the growth of a thin amorphous layer (∼10 nm), direct growth of a columnar crystalline layer was observed. Surface roughness of the films increases with the film thickness on both substrates and is larger on glass substrate than on SiO2 substrate. The growth mechanism of the poly-Si films deposited on these two types of substrates was also discussed.
Fabrication and Characterization of Metal-Semiconductor Field-Effect Transistor Utilizing Diamond Surface-Conductive Layer
Authors: Itoh Masahiro , Hiroshi Kawarada Hiroshi Kawarada
Published: October 2002

Metal-semiconductor field-effect transistors (MESFETs) have been fabricated using the p-type surface-conductive layer of undoped homoepitaxial diamond film on the surface. The layers have been employed as the channel of MESFETs. Since the surface-conductive layer is ultrathin, the depletion region has already closed the surface-conductive channel at the gate voltage of 0 V, i.e., these MESFETs exhibit the enhancement mode (normally off-mode). The threshold voltages are -1.6 V and -0.7 V in the case of Al and Pb gate respectively. These MESFETs also exhibit channel pinch-off and complete saturation of drain current, and high transconductance of 2.5 mS/mm at room temperature. This value is the highest of all diamond FETs at present. enhancement/resistor (E/R) inverters with the enhancement mode transistor and resistor, and direct coupled enhancement/enhancement (E/E) inverters with the two enhancement mode transistors have been also fabricated. This E/R inverter exhibits high voltage gain. For a E/E inverter, the voltage gain has also been measured as a function of frequency. The high 3-dB frequency (f
H) is above 2 MHz. The voltage gain at frequency=f
H (Hz) is equal to 1/√ 2 the voltage gain at frequency=0 (Hz).
Infrared Spectroscopy of Hg1-xZnxTe Alloys
Authors: Wu Ching-Cherng , Chu Dong-Yuan , Sun Cherng-Yuan , Yang Tzuen-Rong
Published: October 2002

Infrared spectra, including transmission and reflection, have been used to characterize Hg1-
x

Zn

x

Te crystals with various compositions x from cryostat temperature to room temperature. The energy band gap of the crystals were determined from the transmission spectra and their temperature dependence was observed. The reflection spectra of Hg1-
x

Zn

x

Te crystals have been measured in the wave-number region of 60 to 450 cm-1. The frequencies of optical mode lattice vibrations are determined and their temperature dependence is discussed. A correlation between the HgTe lattice vibration TO mode and the electronic band structure of Hg1-
x

Zn

x

Te alloys was found and the temperature dependence of electronic states for Hg1-
x

Zn

x

Te can be explained well by a clustering effect in crystals.
Influence of the Seed Face Polarity on the Sublimation Growth of α-SiC
Authors: Takahashi Jun , Ohtani Noboru , Masatoshi Kanaya Masatoshi Kanaya
Published: October 2002

The influence of the face polarity of the seed crystal on the α-SiC sublimation growth has been investigated. Optical and electrical measurements were carried out for undoped and nitrogen-doped crystals grown on the (0001̄)C and the (0001)Si faces. The undoped crystal grown on the (0001̄)C face showed n-type conduction and high optical transmittance in the visible light region. In contract, the undoped crystal grown on the (0001)Si face was highly resistive p-type. It was dark in color and showed low optical transmittance. The differences between the two crystals are explained in terms of impurity incorporation during growth, which has different kinetics on the (0001̄)C and the (0001)Si faces.
Thermal Analysis of Chemical Reaction Process Forming CuInSe 2 Crystal
Authors: Hiroaki Matsushita Hiroaki Matsushita , Takeo Takizawa Takeo Takizawa
Published: October 2002

In order to establish the preparation method of high-quality CuInSe2 single crystals, we have investigated the chemical reaction process of CuInSe2 by differential thermal analysis and by powder X-ray diffraction measurements. It is confirmed that CuInSe2 compound undergoes a phase transition from chalcopyrite to sphalerite structure at 815°C and melts at 996°C. In the chemical reaction process of a Cu+In+2Se mixture, an explosive exothermic reaction occurs at 250°C, which is ascribed to the formation of intermediate products of the In-Se system. In the chemical reaction process of a CuIn+2Se mixture, an explosive selenization reaction forming CuInSe2 compound occurs at 575°C. It is concluded that the selenization of CuIn alloy at temperatures higher than 600°C suppresses the formation of lattice defects and heterogeneous products.
Transient Measurements of Heat Distribution in Devices Fabricated on Silicon-On-Diamond Material
Authors: Edholm Bengt , Söderbärg Anders , Olsson Jörgen , Johansson Erik
Published: October 2002

Thermal properties of devices fabricated on different silicon-on-diamond (SOD) and silicon-on-insulator (SOI) structures have been investigated. A new method for transient measurements of temperature distributions in the SOI/SOD materials has been developed and demonstrated. The heat is detected as a shift in avalanche voltage in p-n diodes fabricated on these materials. Devices on diamond/copper were found to be more than two times cooler than devices on oxide/silicon structures. The measured results were also compared with results from computer simulations in order to estimate the thermal coefficients of the silicon device layer, the buried silicon dioxide, and the diamond material. The thermal conductivity of the polycrystalline diamond film in this work was estimated to be 2 W·cm-1·K-1, which is about 140 times higher than the value of the buried silicon dioxide layer.
A Simple Model for Substrate Current Characteristics in Short-Channel Ultrathin-Film Metal-Oxide-Semiconductor Field-Effect Transistors by Separation by Implanted Oxygen
Authors: Yasuhisa Omura Yasuhisa Omura
Published: October 2002

In this paper a simple and analytical closed-form expression is proposed for the substrate current of ultrathin-film metal-oxide-semiconductor field-effect transistors by separation by implanted oxygen (MOSFETs/SIMOX) to assist physical understanding and rapid SOI device design. The expression is based on an empirical consideration of the impact ionization phenomenon and the energy balance equation assisted by a two-dimensional simulation. The expression includes nonstationary energy transfer effects. The model successfully explains the experimental substrate current characteristics.
SiO2/InP Structure Prepared by Direct Photo-Chemical Vapor Deposition Using Deuterium Lamp and Its Applications to Metal-Oxide-Semiconductor Field-Effect Transistor
Authors: Shei Shih-Chang , Su Yan-Kuin , Hwang Chih-Jen , Meiso Yokoyama Meiso Yokoyama
Published: October 2002

Silicon dioxide ( SiO2) films have been successfully deposited on indium phosphide (InP) substrate at low temperature and low pressure by direct photo-enhanced chemical vapor deposition (photo-CVD) under irradiation by a deuterium lamp. Silane ( SiH4) and oxygen ( O2) are used as reactant sources. The measurements of Fourier transform infrared (FTIR), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) show that the dominant components of the oxide are silicon and oxygen and the film is SiO2. Metal-oxide-semiconductor (MOS) capacitors show sharp interfaces with densities of states in the range of 1.2×1011 cm-2 eV-1. N-channel depletion-mode InP metal-oxide-semiconductor field-effect transistors (MOSFETs) have been fabricated with a transconductance of 63 mS/mm for 2 µ m gate length and an effective channel mobility as high as 1140 cm2 V-1 s-1. High-frequency S-parameter measurements of microwave characteristics for the devices indicate a current-gain cutoff frequency f
t=6.3 GHz.
Transport Properties of Bi2Sr2Ca1Cu2Ox/Ag Multifilamentary Tape
Authors: Okada Michiya , Tanaka Kazuhide , Sato Junichi , Awaji Satoshi , Watanabe Kazuo
Published: October 2002

Ag-sheathed Bi2Sr2Ca1Cu2O

x

multifilamentary tapes with 19 and 55 cores were successfully fabricated by a powder-in-tube process. The multifilamentary tapes showed critical current densities J
c of 1800 A/mm2 (Bł tape surface), 1070 A/mm2 (B⊥ tape surface) at 4.2 K and 23 T, and 1710 A/mm2 (Bł tape surface) at 4.2 K and 30 T, showing a practical range of current carrying capacities. The maximum J
c, 4900 A/mm2 (critical current I
c=550 A) was observed for a 55-filament tape at 4.2 K and 0 T.
A single pancake coil fabricated using 3.5 m-long tape with 19 filaments carried 751 A, generating a maximum magnetic field of 1.9 T.
Magnetic Relaxation in K3C60 Superconductors Prepared with Potassium Hydride
Authors: Lee Ming-Way , Tai Ming-Fong , Shyh-Chyu Luo Shyh-Chyu Luo
Published: October 2002

We report an alternative method for preparing K3C60 fullerene superconductors. Potassium hydride (KH) is used to dope potassium into C60 powder. AC susceptibility and DC field-cooling susceptibility measurements show reasonably large diamagnetic signals in the prepared sample. Magnetic relaxation was measured on the sample and compared to that of a second K3C60 sample prepared by doping with pure potassium. The apparent pinning potential, U
0, of the first K3C60 is found to be about 10 meV at 5 K and shows little temperature dependence up to 13 K; in contrast, U
0 of the second sample increases with temperature. The relaxation rate vs temperature curve of the first sample shows a peak at 9 K.
U
0 of the KH-prepared sample is smaller than that of the second sample for most temperatures. We attribute this to a more homogeneous distribution of the potassium atoms in the KH-prepared sample than that of the second sample.
Design and Fabrication of Monolithically Integrated Lateral-Electrode Etched-Mirror Laser with Y-Branch Single-Mode Waveguide in GaAs/AlGaAs
Authors: Okamoto Kazuya , Yamada Atsushi , Nakano Yoshiaki , Tada Kunio
Published: October 2002

Design and fabrication of a monolithically integrated lateral-electrode laser with a Y-branch single-mode waveguide are described. The ridge-guided Fabry-Perot laser and strip-loaded waveguide are coupled with the evanescent field, and are fabricated simply without resorting to complicated regrowth procedures. The laser has planar lateral electrodes with a dry-etched cavity. Furthermore, the waveguide is of the strip-loaded type, consisting of two cladding layers having different carrier concentrations to reduce the impurity absorption. The growth structure is optimized theoretically, and the coupled beams from the waveguide are observed experimentally.
Optical Propagation Loss Increase of (GdBi)3Fe5O12 Films Caused by Sputter Etching
Authors: Yokoi Hideki , Mizumoto Tetsuya , Yoshiyuki Naito Yoshiyuki Naito
Published: October 2002

Rib waveguides, which are made of magnetic garnet films of composition (GdBi)3Fe5O12 and are fabricated by Ar sputter etching, have large optical propagation loss when Ti is used as the etch mask. The loss increase is alleviated by using a SiO2 mask. X-ray photoelectron spectroscopy analysis reveals that Fe chemical shift due to Ar+ ion bombardment causes increase in the optical absorption loss, and hence the propagation loss.
Effect of Gallium Addition on Density Variation of Molten Silicon
Authors: Kawanishi Soroku , Sasaki Hitoshi , Takeda Susumu , Terashima Kazutaka , Shigeyuki Kimura Shigeyuki Kimura
Published: October 2002

Density measurement of molten silicon added with gallium has been performed in a temperature range from the melting point to 1650° C by using an improved Archimedian method. No deviation from calculation was found with gallium introduction except when 25 at.% was added. Precise density measurement with 0.1 at.%Ga-doping near the melting temperature shows no sign of the “density anomaly” observed for pure silicon.
Large Verdet Constant of 30Tb2O3·70B2O3 Glass
Authors: Tanaka Katsuhisa , Hirao Kazuyuki , Naohiro Soga Naohiro Soga
Published: October 2002

Faraday effect measurement has been carried out for 30Tb2O3·70B2O3 glass at room temperature. The magnitude of the Verdet constant is 0.838 min/cm·Oe at the wavelength of 450 nm. This value is large compared with those reported for other glasses containing trivalent rare-earth ions. The wavelength dependence of the Verdet constant is analyzed in terms of Van Vleck-Hebb theory.
Dependence of Electron Mobility on Doped Impurities
Authors: Chen Yung-Fu , Kwei Cheng-May , Su Pin , Tung Chuan-Jong
Published: October 2002

The dependence of electron mobility on doped impurities was investigated. Analytical expressions of the momentum relaxation cross section and the electron mobility in n- and p-doped silicon for electron-impurity scatterings have been derived. Our approach involved the application of a screened scattering potential based on a charge density distribution for impurity ions in the semiconductor. This distribution was determined by the variational statistical method. Calculated results showed that ionized acceptor impurities in silicon scattered electron carriers less strongly than did ionized donor impurities. They also showed that majority electron mobility in n-type silicon was less than minority electron mobility in p-type silicon. These were consistent with experimental observations.
Influence of Native Oxide on Oxygen Concentration in Czochralski-Grown Silicon Wafers Determined by p-Polarized Brewster Angle Incidence Infrared Spectroscopy
Authors: Hiroshi Shirai Hiroshi Shirai
Published: October 2002

The influence of native oxide on the oxygen concentration in Czochralski-grown silicon (CZ-Si) wafers has been studied by p-polarized Brewster angle incidence infrared spectroscopy (PPBIR). It was found that the oxygen concentration changed only slightly (within 1%) by observation of the vibration bands of the native oxide which are located near the oxygen vibration band at 1106 cm-1.
Photolithographic Pattern Transformation by Backside Exposure in a-Si:H Thin-Film Transistor Liquid Crystal Displays
Authors: Uchikoga Shuichi , Hiromasu Yasunobu , Onozuka Yutaka , Koizumi Takashi , Akiyama Masahiko , Ikeda Mitsushi , Kouji Suzuki Kouji Suzuki
Published: October 2002

Resist pattern transformation by backside exposure, which is a key process for a self-alignment technique is investigated. The light intensity and a-Si:H thickness markedly affect the pattern transformation, while the effect of gate insulator thickness is small. Numerical simulations based on Fresnel diffraction showed fairly good agreement with the experimental results.
Influence of Microstructure and Grain Boundary Potential Barrier Layer on the Electrical Breakdown of Positive Temperature Coefficient BaTiO3 Ceramics
Authors: Kim Duk-Hee , Park In-Kil , Um Woo-Sik , Ho-Gi Kim Ho-Gi Kim
Published: October 2002

The influence of the microstructure and the grain boundary potential barrier layer on the electrical breakdown of barium titanate positive temperature coefficient (PTC) ceramics was studied. Samples of various grain sizes were prepared by adjusting the amount of Sb substitution into Ba sites in barium titanate PTC ceramics. Samples exhibiting large PTC effect (R
max/R
min) and fine grain size withstand high applied voltage. It is clarified that grain size effect is related to the number of grain boundaries per unit thickness of the samples because the applied voltage drop is mainly across the potential barriers at grain boundaries. However, the voltage dependence of a single grain boundary potential barrier was more important in determining breakdown voltage in our study. The voltage dependence of the grain boundary potential barrier layer was due to the grain boundary built-in potential.
Anisotropic Dispersion Force Effects for Alignment of Liquid Crystals on Rubbed Polystyrene Surfaces
Authors: Seo Dae-Shik , Yoshida Norihiro , Kobayashi Shunsuke , Nishikawa Michinori , Yabe Yoshikazu
Published: October 2002

We have studied the anisotropic dispersion force effects for alignment of liquid crystals (LCs) on rubbed polystyrene (PS) surfaces. We previously demonstrated that the nematic (N) LCs are shown to align in the direction perpendicular to the rubbing and polar anchoring strength is very weak compared to rubbed polyimide (PI) surfaces [D.-S. Seo et al.: Jpn. J. Appl. Phys. 31 (1992) 2165]. In microphotographs of the textures, we obtained the NLCs are shown to align in both direction parallel and perpendicular to the rubbing for region up to medium rubbing, however to align in the direction perpendicular to the rubbing for strong rubbing region. We suggest that the anisotropic dispersion force is very important rather than macro-surface groove effect to uniform alignment of LCs. We also observed the surface ordering of the NLCs on rubbed PS surfaces for strong rubbing is disordered. We suggest that the low polarization of the orientation surfaces is attributed to weak anchoring strength.
Effect of Postcombustion Denitration Treatment in Pb-Bi-Sr-Ca-Cu-O Ceramic Superconductors
Authors: Develos Katherine D. , Villaflor Antonio B. , Roland V. Sarmago Roland V. Sarmago
Published: October 2002

Lead-substituted Bi-Sr-Ca-Cu-O ceramic superconductors were prepared using the combustion method. Differential thermal analysis (DTA) of the postcombusted powder showed the presence of residual nitrates. Subsequent modifications to effectively reduce the amount of nitrates required the prolonged exposure of the combustion product to further heat treatment. The denitration treatment was found to raise the volume fraction of the 2223 phase in the samples, but also lowered the T
c
onset values when performed at higher temperatures.
Texture Development in Bi-Sr-Ca-Cu-O (BPSCCO) and Ag-BPSCCO Superconductor through Zone Melting-Refining
Authors: Mani Themanam Veettil , Damodaran Alathoor Damodaran , Krishna Gopakumara Warrier Krishna Gopakumara Warrier
Published: October 2002

A horizontal sample holding novel zone melting refining technique for incorporating grain orientation in sintered Bi-based superconductor (BPSCCO) strips is presented. A three zone furnace having independent temperature controls and a rate of zone movement of 30 mm/h was used. While a-b plane oriented grains appear in BPSCCO samples, in Ag-BPSCCO composites the ductile silver is seen to flow along the intergranular boundaries of BPSCCO grains.
A New Apparatus for Impact Collision Ion Scattering Spectroscopy
Authors: Kawamoto Kiyoshi , Inari Kei , Mori Tatsuo , Kenjiro Oura Kenjiro Oura
Published: October 2002

A new type of time-of-flight impact collision ion scattering spectroscopy apparatus is presented. The system mainly consists of a 20 kV Penning ion source, a beam chopper and an annular-type micro-channel plate. Ion beam energy can be changed in the range from 2 to 20 keV. Since the shadow cone radius can be varied meaningfully by selecting suitable acceleration voltage, it becomes possible to determine structures of subsurfaces or buried regions as well as of the topmost layer. We show that this apparatus enables us to observe layers as much as 10 layers below the topmost layer. In addition, we measured the shadow cone radius of 10 keV4He+incident on the Si(001) surface, and the result is compared with a calculated value.
Magnetoresistance and Interlayer Coupling in Co-Pt/Cu/Permalloy Sandwiches
Authors: Kato Kazuteru , Kitakami Osamu , Yutaka Shimada Yutaka Shimada
Published: October 2002

Addition of a small amount of Pt greatly enhances the magnetic hardness of Co films. By combining this hard Co94.5Pt5.5 film with a soft permalloy film, we prepared Co-Pt/Cu/permalloy sandwiches, and investigated their magnetoresistance and the interlayer coupling between the two magnetic layers. The sandwiches exhibited large magnetoresistance of up to 4.4% without any buffer underlayers, although the magnetization reversal field of the permalloy layer was increased due to the ferromagnetic interlayer coupling with a Co-Pt layer. In order to reduce the coupling, the interfacial roughness in the sandwiches and the magnetization fluctuations in each magnetic layer must be reduced.
Intracavity Second-Harmonic Generation and Influence of Optical Loss of Organic Nonlinear Optical Materials
Authors: Minemoto Hisashi , Ozaki Yusuke , Wakita Katsuya , Sonoda Nobuo , Sasaki Takatomo
Published: October 2002

We propose two different methods to estimate the optical loss of organic nonlinear optical (NLO) materials, which significantly reduces the efficiency of intracavity second-harmonic generation. One method is the estimation of the optical loss from the intracavity optical power at 1064 nm. The optical loss of the 4-nitrophenol sodium (:Na) salt dihydrate (NPNa) crystal was 1.3 dB/cm, and that of the DNPNa crystal, in which the water of crystallization of NPNa was deuterated, was 0.15 dB/cm. Another method is the estimation of the optical absorption loss from a liquid, the molecular structure of which has the same particular structural groups as those of the organic NLO materials. This latter method is very useful when new organic NLO materials are designed. The optical absorption losses at 1064 nm for the particular structural groups of the benzene ring were found to increase in the following order: -Cl<-NO2<-CH3=-OCH3<-OC2H5<-NH2.
Origin of Extra Diffraction Spots in C60/C70 Epitaxial Films Sublimed on Mica Substrates
Authors: Takahashi Yutaka , Shigeo Kotake Shigeo Kotake
Published: October 2002

Anomalous diffraction spots in (111) C60/C70 epitaxial films were investigated by high-resolution electron microscopy. It was revealed that the hcp phase existed in a very thin film while the fcc phase became dominant with increasing film thickness. The origin of extra spots and their thickness dependence were explainable by assuming that the hcp phase was stabilized by the interaction produced by the substrate.
Time-Resolved Plasma Expansion Measurements in a Formed Ferrite Plasma Cathode X-Ray Diode
Authors: Kashiwabara Shigeru , Fujimoto Ryozo , Watanabe Kazuhiro
Published: October 2002

Time-resolved measurements of plasma expansion in a plasma cathode X-ray and electron-beam generator using a formed ferrite plasma source have been made by means of streak-camera photography. The obtained streak images were analyzed in detail by a high-resolution image processing system (spatial resolution: 67 µ m/ pixel, time resolution: 6.5 ns/pixel) to derive the time-dependent expansion velocities. Time-averaged expansion velocities over periods (0.4-1.2 µ s) for plasma growth were 1-1.5 cm/µ s and ∼0.5 cm/µ s for the cathode plasma and for the secondary plasma from the anode, respectively. Measurements also show the influence of the cathode driving voltage and the acceleration field intensity upon the plasma expansion.
Preparation of Lead Magnesium Niobate Titanate Thin Films by Chemical Vapor Deposition
Authors: Takeshima Yutaka , Shiratsuyu Kosuke , Takagi Hiroshi , Kunisaburo Tomono Kunisaburo Tomono
Published: October 2002

Lead magnesium niobate titanate (PMN-PT) thin films were prepared on Pt-coated magnesium oxide single-crystal substrate (Pt(100)/MgO(100)) and Pt- and Ti-coated oxidized Si wafer (Pt(111)/Ti/SiO2/Si(100)) at 680-780° C by metalorganic chemical vapor deposition (MOCVD). The PMN-PT thin films comprising perovskite structure as a main phase were obtained in the composition of Ti/(Mg+Nb+Ti)≥25 mol%. Their room-temperature dielectric constant was 1000-1500 measured at 100 mV and 1 kHz.
Direct Bonding between InP and Gd3Ga5O12 for Integrating Semiconductor and Magnetooptic Devices
Authors: Totoki Machiko , Mizumoto Tetsuya , Nakamura Toshihiko , Maru Kouichi , Yoshiyuki Naito Yoshiyuki Naito
Published: October 2002

The bonding of InP/Gd3Ga5O12 and InP/GaInSb on Gd3Ga5O12 without glue is demonstrated. After chemical treatment, heat treatment in H2 ambient results in bonding of the samples. We have investigated the bonding conditions, mechanisms and the bonding durability against device fabrication processes. The bonding durability depends on the crystal orientation of the wafer, the heat-treatment temperature and GaInSb layer thickness. The samples bonded at higher temperature maintained bonding after typical device fabrication processes. The (111)-oriented InP is more susceptible to bonding than the (100)-oriented InP.
The heat-treatment temperature is reduced by using appropriate chemical treatment and by applying pressure.
Preparation and Dielectric Properties of SrTiO3/BaTiO3 Multilayer Thin Films by Sol-Gel Method
Authors: Hayashi Takashi , Takashi Tanaka Takashi Tanaka
Published: October 2002

SrTiO3/BaTiO3 multilayer thin films were prepared at 650° C on Pt(111)/SiO2/Si(100) substrates by the dip-coating method using metal alkoxides. No formation of (Ba, Sr)TiO3 solid solution between BaTiO3 layers and SrTiO3 layers was detected in X-ray diffraction analysis. The SrTiO3/BaTiO3 multilayer thin films consisted of grain structure with grain size of about 30 nm. A film thickness of about 20 nm was obtained by one cycle of the dip-coating/heating process. The SrTiO3/BaTiO3 multilayer thin films with a thickness of 400 nm exhibited dielectric constants of about 400 and loss tangent of 0.03. By reheating the multilayer thin films at temperatures up to 1000° C, (Ba1-
x

Sr

x

)TiO3 solid solution with the composition gradient between Ba and Sr was formed.
Electrical Properties of LiNbO 3 Thin Films by RF Magnetron Sputtering and Bias Sputtering
Authors: Nishida Takashi , Shimizu Masaru , Horiuchi Toshihisa , Tadashi Shiosaki Tadashi Shiosaki , Kazumi Matsushige Kazumi Matsushige
Published: October 2002

C-axis-oriented LiNbO3 thin films were prepared on Pt(111)/ SiO2 /Si substrates by rf magnetron sputtering. The LiNbO3 films grown showed pyroelectricity and piezoelectricity. The pyroelectric coefficient of the film was 71×10-6 C/(m2K) , which was 86% of the value of a LiNbO3 bulk crystal. The surface acoustic wave (SAW) velocity measured was 3980m/s. In order to control the polarization, bias sputtering was applied. When bias voltage was applied to the substrates during film growth, polarization reversal was observed. From these experimental results, it was found that bias sputtering effectively controls the polarization of LiNbO3 films.