bluuebunny/crossref_metadata_2025 huggingface dataset:
Breakdown of the Phonon Bottleneck Effect in Self-Assembled Quantum Dots
Authors: V. Ignatiev Yasuaki Masumoto , E. Kozin Igol , G. Davydov Valentin , V. Nair Selvakumar , Hong-Wen Ren Hong-Wen Ren , Jeong-Sik Lee Jeong-Sik Lee , Shigeo Sugou Shigeo Sugou
Published: October 2002

Spectral and temporal behavior of photoluminescence of site-selectively excited InP self-assembled quantum dots were studied in external electric fields. External electric field accelerates the nonradiative relaxation and competing fast phonon mediated relaxation processes make prominent structures in the static spectra. The spectra agree with the time-resolved spectra around the time zero and reflect the phonon relaxation rate. Acoustic phonon mediated carrier relaxation is much faster than predicted theoretically. The increases of the excitation intensity, temperature, electric current and charging of quantum dots accelerate the relaxation of the carriers in quantum dots, indicating build-up of Auger-like processes. This observation demonstrates the breakdown of the predicted phonon bottleneck effect not only at the condition for the practical application of the quantum dots but also at low temperature and under weak excitation.
Transmission through a Quantum Dot with Two Orbitals
Authors: Wataru Izumida Wataru Izumida , Hiroshi Akera Hiroshi Akera
Published: October 2002

Transmission coefficient through a quantum dot, which contains two orbitals, is calculated in the weak-tunneling regime, taking into account the Coulomb interaction within the dot. Transmitted waves through these orbitals acquire phase shifts which differ by π from each other in the present model. The transmission coefficient as a function of gate voltage exhibits symmetric and asymmetric line shapes, depending on temperature T. A nearly symmetric line shape appears in the temperature region of 0.05 \lesssimk
B
T/δ\lesssim0.25, where δ is the single-particle energy level separation in the dot. This behavior is understood by a combined action of the above-mentioned phase difference and the Coulomb interaction. A possibility that this mechanism explains the recent experiment is suggested.
Photon-Assisted ac Transport through Quantum Dots
Authors: Jun-ichiro Ohe Jun-ichiro Ohe , Kousuke Yakubo Kousuke Yakubo
Published: October 2002

The ac currents through coherently driven quantum dots have been studied using a transfer-matrix method. This method enables us to calculate quantitatively the ac current of a nonequilibrium quantum system with realistic potential profiles. We show that the expected magnitude of the ac current induced by a time-varying potential is as large as that of the dc current and the photo-induced ac current can be observed by actual experiments. Amplitudes of ac current oscillate spatially, which means that the ac current depends on both frequency ω and wavenumber q. This is due to the fact that the ac current is induced by the interference between different sideband states. It has also been clarified that the quenching effect of ac current appears in a different manner from that of dc transport. Furthermore, we discuss a way of taking the thermal average of the ac current at a finite temperature under a finite dc-bias voltage.
Large Electron Addition Energy above 250 meV in a Silicon Quantum Dot in a Single-Electron Transistor
Authors: Saitoh Masumi , Takahashi Nobuyoshi , Ishikuro Hiroki , Hiramoto Toshiro
Published: October 2002

We demonstrate large Coulomb blockade oscillations in a silicon single-electron transistor (Si SET) whose peak-to-valley ratio is about 2 at room temperature. The device is fabricated in the form of a point-contact metal-oxide-semiconductor field-effect transistor (MOSFET) and the gate oxide is formed by chemical vapor deposition (CVD) instead of thermal oxidation. From the analysis of current-voltage characteristics, it is found that the single-electron addition energy is about 259 meV and the dot diameter is less than 4.4 nm. The mechanism of silicon dot formation is also discussed.
Charging and Retention Times in Silicon-Floating-Dot-Single-Electron Memory
Authors: Shin-ichi O'uchi Shin-ichi O'uchi , Takeshi Tsubokura Takeshi Tsubokura , Takuro Tajima Takuro Tajima , Shuhei Amakawa Shuhei Amakawa , Minoru Fujishima Minoru Fujishima , Koichiro Hoh Koichiro Hoh
Published: October 2002

The mechanism of electron storage was studied in a metal-oxide-silicon (MOS)-type single-electron memory which utilized the direct tunneling of electrons between a silicon floating dot and the conducting channel on the surface of silicon substrate. Time constants of charging and discharging were derived by a simple analysis of a single-electron box circuit, taking the structure of the energy band of silicon into consideration. It was shown that the features of the energy band were substantial for the memory function of the device and that a write time of the order of sub-microseconds was obtained; 1010 times longer retention time was also obtained with compatibility in the same device at room temperature.
Far-Infrared Magneto-Optical Absorption of Vertically Aligned Double Dot Array System
Authors: Ken-ichi Fujii Ken-ichi Fujii , Takeshi Yoshizawa Takeshi Yoshizawa , Tyuzi Ohyama Tyuzi Ohyama , Kenichi Oto Kenichi Oto , Sadao Takaoka Sadao Takaoka , Kazuo Murase Kazuo Murase , Kenji Gamo Kenji Gamo
Published: October 2002

We propose the optical control of the coupling between vertically aligned double dots. The coupling of the dots depends on the distance between the double dots and affects the strength of the electron-electron interaction in the dots. For this purpose, we fabricated a vertically aligned double dot array using a modulation-doped GaAs/AlGaAs single quantum well with two interfaces. Far-infrared magneto-optical absorption measurements of the double dot array system were carried out under photoexcitation. We observed a peak shift of the electron transition only in a dot located near the top interface. The peak shift includes the change in the coupling as well as the change in the confinement potential by the photoexcitation. This is evidence of the potential modulation by light which changes the coupling between the two dots. This indicates the possibility of the optical control of the coupling.
Hydrogen-Defect Shallow Donors in Si
Authors: Meng Xiang-Ti , Kang Ai-Guo , Bai Shou-Ren
Published: October 2002

The influence of different original Si crystals and neutron fluence on the formation of hydrogen-defect shallow donors in neutron-irradiated floating-zone silicon grown in hydrogen atmosphere (FZ Si:H2) is studied. The annealing behavior of neutron-irradiated floating-zone silicon grown in argon atmosphere (FZ Si:Ar), neutron-irradiated FZ Si:H2 kept for three years at room temperature (RT) and only fast-neutron-irradiated FZ Si:H2 reveals that shallow donors are directly related to hydrogen and defects, especially to thermal-neutron-radiation point defects. The maximum concentration of the shallow donors approaches to a stable value with an increase in neutron fluence. Some characteristics of the shallow donors are discussed.
Simple Fabrication Technique of Symmetrical Emitter-Collector Zinc-doped Planar Ga1-xAlxAs/GaAs/Ga1-yAlyAs Double Heterojunction Bipolar Transistors
Authors: Deesirapipat Yuparwadee , Thainoi Supachok , Ratanathammaphan Somchai , Antarasena Choompol
Published: October 2002

Symmetrical emitter-collector planar Ga1-x
Al
x
As/GaAs/Ga1-y
Al
y
As double heterojunction bipolar transistors have been designed and fabricated. Crystal growth and doping are carried out using liquid phase epitaxy (LPE) technique. Five layers consisting of collector, base, emitter, emitter contact and mask layer, Ga0.6Al0.4As, have been grown consecutively by LPE on GaAs (n+) substrate. After etching the mask layer to open a region for base diffusion, the sample was carried back to the LPE furnace to grow the Zn-doped Ga0.6Al0.4As in order to diffuse Zn to the p-type base. After the process, both the diffusion layer and the mask layer were selectively etched. Ohmic contacts were then made. Finally, the DC characteristics of the transistors were measured to show their symmetrical behaviors.
Magnetic Disaccommodation in Ferrites with Nonmagnetic Divalent Substitutions
Authors: Francisco Óscar Alejos , María Muñoz José , Arias Pablo Hernández-Gómez
Published: October 2002

The after-effect processes in magnetite with nonmagnetic divalent substitutions are studied by means of disaccommodation techniques. We have recorded at room and high temperatures the time evolution of the initial magnetic susceptibility after sample demagnetization for polycrystalline specimens with nominal composition MxFe3-x
O4+δ, M being a divalent cation such as Zn2+, Mg2+, or Ca2+. These ions replace Fe2+ inside the spinel structure and, consequently, affect the original process III in magnetite. We have found that the presence of these ions involves the splitting of process III into similar processes, according to the position of the substituting ions. In addition, high-temperature processes are discussed on the basis of vacancy-mediated diffusion of nonmagnetic metallic ions.
Analysis of Processing Damage on a Ferroelectric SrBi2Ta2O9 Capacitor for Ferroelectric Random Access Memory Device Fabrication
Authors: Kawahara Jun , Matsuki Takeo , Hayashi Yoshihiro
Published: October 2002

For Ferroelectric random-access memory (FeRAM) device fabrication, it is important to control the processing ambience, especially the hydrogen in process, due to the reduction of ferroelectric oxides such as SrBi2Ta2O9 (SBT). We investigated processing damage to SBT capacitors during (1) the deposition of a cover film on SBT capacitors, (2) the fabrication of a contact hole by reactive ion etching (RIE), and (3) the photoresist mask removal. The O3-TEOS chemical vapor deposition (CVD) process for the deposition of a cover film causes less damage due to the presence of O3 a strong oxidizer. However, during the fabrication of contact holes in SBT capacitors, the plasma-gas species strongly affect the damage to the SBT capacitors. A less damaging process has been developed as follows: forming the contact hole by RIE with CF4 plasma gas instead of CHF3, and removing the photoresist by exposure to oxygen-radical downflow to eliminate hydrogen regeneration from the photoresist decomposition in the O2 plasma. After the process, the leakage current density and the remanent polarization are kept below 10-6 A/cm-2 and over 15 µC/cm2, respectively.
Enhanced Ferroelectric Properties of V-Doped BaBi4Ti4O15 Single Crystal
Authors: Irie Hiroshi , Miyayama Masaru , Kudo Tetsuichi
Published: October 2002

Single crystals of barium bismuth titanate (BaBi4Ti4O15) and BaBi4Ti4O15 partially substituted with V5+ and Ba2+ for Ti4+ and Bi3+ sites, respectively, at 5 at.% (Ba1.2Bi3.8Ti3.8V0.2O15), were grown using slow cooling. The incorporation of vanadium into the B-site of the layered pseudo-perovskite block resulted in a shift of the Curie point to a higher temperature, from 410°C to 425°C, and an increase in dielectric permittivity from 8000 to 9500 along the a(b)-axis direction and from 150 to 160 along the c-axis direction at 1 MHz and at their respective Curie points. The increase in Curie temperature brought about an increase in remanent polarization, and saturated remanent polarization was enhanced from 14.8 µC cm-2 to 15.5 µC cm-2.
Thermal Stability Enhancement of Cu Interconnects by Employing a Self-aligned MgO Layer Obtained From a Cu(Mg) Alloy Film
Authors: Lee Wonhee , Cho Heunglyul , Cho Bumseok , Yang Hee-Jung , Kim Jiyoung , Kim Yong-Suk , Jung Woo-Gwang , Kwon Hoon , Lee Jinhyung , Reucroft P. J. , Lee Chongmu , Lee Eungu , Lee Jaegab
Published: October 2002

Self-aligned surface and interfacial MgO layers were formed by pre-annealing Cu(Mg)/SiO2/Si and Cu(Mg)/TiN/Si multilayer films at 500°C in an oxygen ambient, resulting in the structures of MgO/Cu/MgO/SiO2/Si and MgO/Cu/MgO/TiN/Si, respectively. During pre-annealing, Mg segregates preferentially to the Cu surface until a dense, uniform MgO layer of 150 Å thickness is formed. Substantial Mg segregation to the SiO2 or TiN surface also takes place to form an interfacial MgO layer. Diffusion barrier characteristics of the surface MgO layer were investigated by vacuum-annealing the Si/MgO/Cu(Mg)/MgO/SiO2/Si multilayer structure. It was shown that self-aligned surface MgO produced by the annealing process prevents interdiffusion of Cu and Si up to 700°C. Furthermore, interfacial MgO between Cu and SiO2 or TiN reduces diffusion of Cu into the Si substrate at temperatures up to 700–800°C, indicating that self-aligned interfacial MgO plays an important role in suppressing interdiffusion between the Cu and TiN or SiO2. Consequently, the thermal stability of Cu/SiO2/Si and Cu/TiN/Si multilayer systems is significantly enhanced by introducing self-aligned surface and interfacial layers of MgO from Cu(Mg) alloy films.
NOx Removal Process in Pulsed Corona Discharge Combined with TiO2 Photocatalyst
Authors: Daito Shigeo , Tochikubo Fumiyoshi , Watanabe Tsuneo
Published: October 2002

The NOx removal process was studied experimentally in the pulsed corona discharge combined with the TiO2 photocatalytic reaction. First, the adsorption and desorption properties of NOx on the photocatalyst were investigated using UV irradiation from a black light without gas discharge. We found that NO2 was easily adsorbed on the photocatalyst surface, whereas NO was hardly adsorbed. Addition of water vapor enhanced the NO2 adsorption. Next, the relationship between the plasma-enhanced chemical reaction and the photocatalytic reaction was investigated using pulsed corona discharge with wire-plate-type electrodes positioned between two photocatalysts. The TiO2 photocatalyst efficiently assisted the increase of the NOx removal rate. The main role of the plasma-chemical reaction in this system is the oxidation of NO into NO2. A considerable part of NO2 is adsorbed on the photocatalyst surface, and is transformed to HNO3 through photocatalytic reaction with OH. HNO3 on the photocatalyst is hardly desorbed from the catalyst surface.
Overdense Plasma Production in a Low-power Microwave Discharge Electron Source
Authors: Ikkoh Funaki Ikkoh Funaki , Hitoshi Kuninaka Hitoshi Kuninaka
Published: October 2002

Plasma characterization of a low-power microwave discharge electron source was conducted. The electron source, which was developed for the neutralization of the 150 mA-class ion beam exhausted from an ion thruster, consists of a small discharge chamber of 18 mm diameter, into which an L-shape antenna is directly inserted into the magnetic circuit comprised of permanent magnets and iron yokes. An overdense plasma production for the 4.2 GHz microwave was observed for an input power range from 3 to 26 W and for the mass flow rate of 0.5–2.0 sccm. In such a wide range, the plasma density inside the discharge chamber can be proportionally increased as the microwave input power. This is because the direct insertion of the microwave antenna into the ECR magnetic field removes the accessibility difficulty of the microwave, and enables energy transmission from the antenna to the plasma even in the overdense mode. In addition, high-energy electrons above the ionization energy were observed for the large microwave input power above 10 W, and these electrons from the antenna also contribute to plasma production.
Characteristics of Nucleation Using the Bias-Enhanced Nucleation Method at Low Pressure
Authors: Kudo Kouichi , Aoki Kousuke , Toyofuku Masaharu , Ogi Sukeomi
Published: October 2002

The bias-enhanced nucleation (BEN) method is well known as a pretreatment method for nucleation, and the nucleus is generated in the plasma sheath region during the BEN process. To utilize high-density nucleation at low pressure and to expand the nucleation region in hot-filament chemical vapor deposition (HFCVD), the BEN method was applied under a low-pressure condition in which the plasma and plasma sheath expanded. Some substrates were treated in hydrogen plasma or activated hydrogen before nucleation. The purpose of this study is to confirm the characteristics of nucleation at low pressure and to determine the condition for realizing uniform, high-density and large-area nucleation. By using emitted electrons, bias voltage and current were controlled to be steady at the low pressure of 0.1 Torr. The nucleation density increased and the width of the nucleation area expanded when the substrate surface was treated in hydrogen plasma or activated hydrogen before nucleation. It was proposed that the nucleation mechanism is as follows. (1) A substrate surface was treated by H ions and H radicals, (2) a nucleation site was formed on the treated position and (3) nucleation occurred on the nucleation site. To achieve high-density and large-area nucleation, it is necessary to obtain the treated substrate surface and to generate carbon-containing cations, H ions and H radicals with appropriate ratios and density distributions in the nucleation phase.
Measurement of Optical Absorption in InAs/InAlAs Quantum Dots using a Photoluminescence Technique
Authors: Dao Lap V. , Gal Mike , Koo B. H. , Makino Hisao , Yao Takafumi
Published: October 2002

We describe a simple method based on photoluminescence which allowed us to determine theabsorption spectra of InAs/InAlAs quantum dots at low temperatures. The method is applicable to any luminescing layer structure, such as quantum dots, wires or wells, and only requires standard photoluminescence equipment.
Field Analysis of Two-Dimensional Dynamics of Non-neutral Plasma by Imaging Diagnostics and Examination by Sector Probing
Authors: Ito Kiyokazu , Kiwamoto Yasuhito , Sanpei Akio
Published: October 2002

The linear response of the luminosity of the charge-coupled-device (CCD) camera image to the electron-flux distribution on the phosphor screen is demonstrated as the basis of two dimensional (2D) analyses of non-neutral plasma dynamics. We present a fast and sufficiently accurate procedure to construct the potential and the electric field distribution from the observed 2D images. Such field analyses are essential for deep and extensive studies of vortex dynamics or turbulence. Using this procedure, we quantitatively compare the image diagnostics by sector probing for the first time to show that core dynamics which is observed clearly by imaging is severely obscured by probing; thus, its application should be limited to simple dynamics of a small number of discrete distributions of particles.
Impurity Measurement in Specialty Gases Using an Atmospheric Pressure Ionization Mass Spectrometer with a Two-Compartment Ion Source
Authors: Kitano Masafumi , Shirai Yasuyuki , Ohki Atsushi , Babasaki Shinichi , Ohmi Tadahiro
Published: October 2002

Using an atmospheric pressure ionization mass spectrometer (APIMS) with a two-compartment ion source, impurity in specialty gases (CH4, SiH4, GeH4) is measured due to a stable ionization reaction with a detection limit of approximately 0.1 to 1 parts per billion (ppb). The form in which the impurity exists in these gases has been clarified. In the case of SiH4, the main impurity is disiloxane (SiH3–O–SiH3). We have also established a method for obtaining the SiH3–O–SiH3 calibration curve standardized for a known concentration of SiH3–O–SiH3 generated from the reaction of SiH4 with H2O. In the case of CH4 and GeH4, the main impurity is moisture (H2O) and it is quantified from the plotted H2O calibration curve.
Formation of High-Temperature Stable Co-Silicide from Co0.92Ta0.08/Si Systems
Authors: Lee Deok-Hyung , Ko Dae-Hong , Ku Ja-Hum , Choi Siyoung , Fujihara Kazuyuki , Kang Ho-Kyu , Oh Sang-Ho , Park Chan-Gyung , Lee Hoo-Jeung
Published: October 2002

We investigated the formation and thermal stability of Co-silicide films using Co–Ta alloy films on (100) Si substrates. Co–Ta alloy films were deposited by direct current (DC) magnetron sputtering using Co and Ta targets. The content of Ta in the films was controlled at 8 at.%. The Co-silicide films were formed through a rapid thermal annealing (RTA) process in N2 ambient. Compared with the Co/Si systems, the formation of CoSi2 occurs at higher temperatures in Co0.92Ta0.08/Si systems. X-Ray diffractometry (XRD) analyses showed the presence of strong (200)-preferred orientation in the Co-silicide films formed from Co0.92Ta0.08/Si systems. We observed that Co-silicide films formed from Co0.92Ta0.08/Si systems maintained low sheet resistance values upon annealing at 950°C, while those of Co-silicide from Co/Si systems increased significantly. The improvement of the thermal stability of the Co-silicide films from Co0.92Ta0.08/Si systems is due to the formation of Ta-compounds such as the TaSi2 phase at the grain boundaries or at the surface of the CoSi2 films.
Velocity-Mismatching Effect on Extinction Characteristics of Traveling Wave Electroabsorption Modulator
Authors: Lim Jiyoun , Shin Myunghun , Kim Jeha , Kim Jeong Soo , Pyun Kwang Eui , Hong Songcheol
Published: October 2002

The velocity-mismatching effect of the traveling wave electroabsorption modulator (TWEAM) is investigated. A model is proposed to design the length of the modulator. Optical transmission through the device is simulated and the degradation of extinction ratio with velocity mismatch is analyzed.
Highly Sensitive Metal-Insulator-Semiconductor Field-Effect Transistor Sensors for Detecting Carbon Monoxide Gas Using Porous Platinum and Tungsten Oxide Thin Films
Authors: Fukuda Hisashi , Zohnishi Ryuji , Nomura Shigeru
Published: October 2002

A novel device based on a porous Pt–WO3 metal-insulator-semiconductor field-effect transistor (MISFET) for carbon monoxide (CO) gas sensing has been fabricated. The structure integrates the catalytic properties of porous Pt as a thin catalytic layer, and the spillover effect onto WO3 film as a gas adsorptive oxide layer, with surface-sensitive MISFET. The operation characteristics of the device for the detection of CO gas are presented as a function of CO gas concentration. The drain current increased rapidly with time depending on the CO gas concentration. It was possible to detect 54 ppm of CO gas with a response time of less than 1 min at 75°C. A model was proposed to explain the operation. The sensing mechanism of the device is supported well by experimental data.
Effect of Yttria-Stabilized Zirconia Thickness on Crystal Structure and Electric Property of Epitaxial CeO2/Yttria-Stabilized Zirconia Buffer Layer in Metal/Ferroelectric/Insulator/Semiconductor Structure
Authors: Tomoaki Yamada Tomoaki Yamada , Naoki Wakiya Naoki Wakiya , Kazuo Shinozaki Kazuo Shinozaki , Nobuyasu Mizutani Nobuyasu Mizutani
Published: October 2002

The effect of yttria-stabilized zirconia (YSZ) film thickness on crystal structure and electric properties of epitaxial CeO2/YSZ films was investigated. The CeO2/YSZ films were prepared on Si(001) substrates by pulsed laser deposition (PLD). X-ray diffraction measurements and reflection high energy electron diffraction (RHEED) observation indicated that heteroepitaxial growths of CeO2 and YSZ were achieved with a cube-on-cube relation (CeO2[100] ∥YSZ[100] ∥Si[100]) regardless of the YSZ film thickness. Measurement of C–V characteristics showed ion drift; this ion drift decreased with the decrease of YSZ film thickness. Measurement of I–V characteristics indicated that the leakage-current for all films was low enough for the insulating layer in the metal/ferroelectric/insulator/semiconductor (MFIS) structure, however for the films with a thicker YSZ layer, a difference in current was observed at various measurement positions. The reason for this was ascribed to the differences in the microstructure.
X-Ray Radiation Response of Epitaxial and Nonepitaxial n-6H–SiC Metal-Oxide-Semiconductor Capacitors
Authors: Vasconcelos Elder Alpes de , Jr. Eronides Felisberto da Silva, , Katsube Teruaki , Yoshida Sadafumi , Nishioka Yasushiro
Published: October 2002

We investigated total interface trap generation in epitaxial and nonepitaxial n-type 6H–SiC metal-oxide-semiconductor (MOS) capacitors by the photo-capacitance–voltage method (Jenq technique) for doses of low energy X-rays up to 20 Mrad (Si). Interface trap generation is low for both epitaxial and nonepitaxial SiC MOS capacitors and they show considerable radiation hardness, even without being specially processed to be radiation-hard. Characteristic features of the photo-capacitance–voltage curves and trapped charge are briefly discussed.
Terahertz Emission due to Miniband Transport in GaAs/AlGaAs Superlattices
Authors: Shimada Yozo , Matsuno Tetsuya , Hirakawa Kazuhiko
Published: October 2002

We have investigated terahertz (THz) emission due to miniband transport of electrons in biased GaAs/AlGaAs superlattice diodes by time-resolved THz spectroscopy. Quasi-autocorrelation measurements were performed on the emitted THz electromagnetic wave using a bolometer as a wideband detector. We found that the THz emission due to miniband transport is strongly dependent on the photon energy of the pump laser pulses. A clear oscillation in the THz autocorrelation signal due to Bloch oscillation has been observed by exciting the sample at a photon energy slightly lower than the center of the Wannier-Stark ladder even for a superlattice with a miniband width larger than the longitudinal optical (LO) phonon energy. Furthermore, transient velocities of electrons in the miniband have been estimated from the measured THz autocorrelation signal.
Phase-Breaking Effect Appearing in the Current–Voltage Characteristics of Double-Barrier Resonant Tunneling Diodes –Theoretical Fitting Over Four Orders of Magnitude–
Authors: Nagase Masanori , Furuya Kazuhito , Machida Nobuya
Published: October 2002

We analyzed current–voltage (I–V) characteristics of double-barrier resonant tunneling diodes (DBRTDs), taking into account the phase-breaking effect and the structural inhomogeneity by using the correlation function theory of phase breaking to fit the experimental data over four orders of magnitude. The phase-breaking effect appears in the current region of less than one-hundredth of the peak in I–V characteristics, in addition to the peak of the second derivative curve. The well width fluctuation, if any, influences the latter but not the former. Using the theory, the phase-coherent length and the well width fluctuation are estimated separately.
Characterization of Si wafer Surfaces after Wet Chemical Treatment by the Microwave Reflectance Photconductivity Decay Method with Surface Electric Field
Authors: Tada Atsushi , Hirano Masashi , Ichimura Masaya , Arai Eisuke , Takamatsu Hiroyuki , Sumie Shingo
Published: October 2002

Voltage is applied between an external electrode and a Si wafer to control surface recombination, and carrier lifetime is measured by the microwave reflectance photconductivity decay (µ-PCD) method. The voltage dependence of the lifetime changes depending on the surface Fermi level and the surface state density. We apply this method to Si wafers with various chemical treatments, and qualitatively characterize the surface properies from the dependence of lifetime on applied voltage. The change in the surface properties with time after the treatment is also investigated.
Scattering Mechanisms of Carriers in Natural Diamond
Authors: Tsukioka Kunio
Published: October 2002

The scattering mechanisms of carriers in natural diamond are investigated theoretically, based on the experimental low-field mobility data. The calculated values of low-field mobility are compared with published experimental data. Three types of intervalley phonon scatterings (zero-order) and acoustic phonon scattering are considered for electrons in the conduction band (c.b.), and acoustic and nonpolar-optical phonon scatterings are taken into account for holes in the valence band (v.b.). A procedure for fitting the theoretical mobility to the experimental mobility yields deformation potential constants and coupling constants of the intervalley and the nonpolar-optical phonons as follows: for electrons, E
1(c.b.)=8.8 eV, D
iv1=D
iv2=D
iv3=9.0×1010 eV/m, and for holes, E
1(v.b.)=14.5 eV and D
npo=5.5×1011 eV/m.
Fabrication of Schottky Junction Between Au and SrTiO3
Authors: Inoue Akira , Izumisawa Kei , Uwe Hiromoto
Published: October 2002

A Schottky junction with a high rectification ratio between Au and La-doped SrTiO3 has been fabricated using a simple surface treatment. Highly La-doped (5%) SrTiO3 single crystals are annealed in O2 atmosphere at about 1000°C for 1 h and etched in HNO3 for more than five min. The HNO3 etching is performed in a globe box containing N2 to prevent pollution from the air. After the treatment, Au is deposited on the SrTiO3 surface in a vacuum (∼10-7 Torr) with an e-gun evaporator. The current voltage characteristics of the junction have shown excellent rectification properties, although junctions using neither annealed nor etched SrTiO3 exhibit high leak current in reverse voltage. The rectification ratio of the junction at 1 V is more than six orders of magnitude and there is no hysteresis in the current voltage spectra. The logarithm of the current is linear with the forward bias voltage. The ideal factor of the junction is estimated to be about 1.68. These results suggest that, if prevented from being pollution by the air, a good Schottky junction can be obtained by easy processes such as annealing in oxygen atmosphere and surface etching with acid.
Conductivity at Each Layer of a Spin Valve System
Authors: Satoshi Kokado Satoshi Kokado
Published: October 2002

The conductivity at each layer of a spin valve system consisting of a ferromagnet, a spacer, and a ferromagnet was investigated using the tight binding model and the Kubo formula. The interfacial roughness was treated by the coherent locator approximation, in which the coherent potential approximation was extended to enable application to alloys with various transfer integrals. In this system, the giant magnetoresistance (GMR) effect appears to originate from the dependence of conductivity in the spacer on the magnetization configuration. Furthermore, the atom-dependent transfer integral and the atom- and spin-dependent relaxation time strongly affect the conductivity and the GMR effect.
Critical Power of Stimulated Brillouin Scattering in Multimode Optical Fibers
Authors: Tei Kazuyoku , Tsuruoka Yasuhiko , Uchiyama Taro , Fujioka Tomoo
Published: October 2002

A set of coupled-wave equations for stimulated Brillouin scattering (SBS) in multimode optical fibers excited by single-mode laser light is derived. The analytical solution of the critical pump power is also derived. The solution explains the experimental results well.
Luminescence Characteristics of Eu-doped Strontium Halophosphate Phosphor Particles Prepared by Spray Pyrolysis
Authors: Lee Jong Ho , Kang Yun Chan , Park Seung Bin , Park Hee Dong
Published: October 2002

Eu-doped strontium halophosphate phosphor particles were first prepared by spray pyrolysis from various types of precursor sources and their luminescence characteristics were investigated. Phase-pure halophosphate particles were obtained when ammonium phosphate and ammonium dihydrogen phosphate were used as phosphorous source, while halophosphate particles were not obtained using phosphoric acid. Spherical and nonaggregated particles were obtained when ammonium phosphate and ammonium dihydrogen phosphate were used. However, the particles prepared from phosphoric acid were strongly aggregated. The particles prepared from the mixture of strontium nitrate and strontium chloride as strontium and chlorine sources, had a spherical shape and are nonaggregated. The particles prepared from strontium nitrate, strontium chloride and ammonium dihydrogen phosphate had the highest PL intensity among halophosphates due to their phase purity and spherical morphology.
Electronic Structure Calculations for Au-doped Ge and Si with a Possible High Thermoelectric Power
Authors: Fukushima Kimichika , Kondo Naruhito
Published: October 2002

Molecular orbital calculations were performed to investigate electronic structures of gold-doped germanium and silicon with consideration about the possibility of achieving high thermoelectric power. Calculational results show that in the case of Ge, the top of valence states is higher and the bottom of conduction states is rather lower compared to those in the case of Si. For Ge doped with Au, the atomic orbitals of Au contribute to energy levels just below the conduction states and above the valence states for Ge. A similar electronic structure is seen for Si doped with Au. In amorphous semiconductors, where Ge and Si are in contact with each other and doped with Au, ambiguous energy levels are usually formed near the bottom of the conduction states and the top of the valence states. Then, charge carriers may be introduced in the Si and Ge regions and may possibly enter the Ge and precipitated Au regions with a high energy. In addition, the energy levels of the conduction and valence states are lifted and lowered, respectively, when the interatomic distance becomes shorter. Since the Seebeck coefficient for amorphous semiconductors is a function of electron energy and electric conductivity which depend on the electron energy, the enhanced carrier energy will enhance thermoelectric power.
Thermoelectric Properties of β-Fe1-xCoxSi2 Semiconductors
Authors: Tani Jun-ichi , Kido Hiroyasu
Published: October 2002

The thermoelectric properties of Co-substituted β-FeSi2 (Fe1-x
Co
x
Si2, 0.00≦x≦0.10) have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 1150 K. Fe1-x
Co
x
Si2 samples are n-type in the measured temperature range. The electrical resistivity, Seebeck coefficient, and thermal conductivity are strongly affected by the Co substituting concentration (x). For the composition 0.00≦x≦0.05, κ decreases with increasing temperature, reaches a minimum, and increases. At x=0.10, the κ increases monotonically with increasing temperature. From the composition and temperature dependences of κ, it was found that the thermal conductivity of the lattice component κph is dominant in Fe1-x
Co
x
Si2 semiconductors. At low temperatures, κph can be explained by the presence of small polarons. At x=0.05, the power factor (P=S
2/ρ) as well as the dimensionless figure of merit (ZT) shows a maximum value of 1.1×10-5 W/cm K2 and 0.25 at 940 K.
Electrical Properties of the Free-Standing Diamond Film at High Voltages
Authors: Huang Bohr-Ran , Ke Wen-Cheng , Chen Wei-Kuo
Published: October 2002

Polycrystalline diamond films were deposited on p-type (100) silicon substrates by the microwave plasma chemical vapor deposition system. The free-standing diamond film was then obtained by etching the silicon substrate with a KOH solution. It was found that more non-diamond components, i.e., SiC and amorphous carbon, existed on the bottom surface of the free-standing diamond film. Two different contact geometries, coplanar contact and sandwich contact geometries, were used to characterize the in-plane and transverse high-voltage electrical properties of the free-standing diamond film, respectively. The transverse electrical property of the free-standing diamond film showed the asymmetric current–voltage (I–V) characteristic and lower breakdown voltage at -220 V and 850 V. However, the in-plane electrical property exhibited the symmetric I–V characteristic in the range of -1100 V to 1100 V. The electrical properties were successfully represented by the Frenkel-Poole conduction mechanism at high voltages (>200 V). The simulated results indicated that the breakdown field was strongly related to the Coulombic center density of the free-standing diamond film.
Time and Energy Responses of Liquid-Xenon Scintillation Chamber for 20Ne Ion Beam at 135A MeV
Authors: Toshiyuki Kato Toshiyuki Kato , Tadayoshi Doke Tadayoshi Doke , Jun Kikuchi Jun Kikuchi , Fumihiko Nishikido Fumihiko Nishikido , Hiroyuki Okada Hiroyuki Okada , Kouji Morimoto Kouji Morimoto , Isao Tanihata Isao Tanihata
Published: October 2002

The time and energy responses of a liquid-xenon (LXe) scintillation chamber to heavy-ion beams were studied using 20Ne ions at an energy of 135A MeV. The scintillation light in LXe was observed by two photomultipliers (PMTs). The intrinsic time resolution by one PMT was confirmed to be approximately 30 ps in sigma up to a beam intensity of 1.3 ×105 counts per second (cps). The energy output was observed to be also constant for the increase in the beam intensity. The energy resolution was 1.2–1.4% in sigma. The possibilities of LXe as a detector medium for an energy spectrometer and a timing detector for heavy-ion beams were described.
Production of Highly Charged Xe Ions from Liquid He Free Super Conducting Electron Cyclotron Resonance Ion Source
Authors: Kurita Tetsuro , Imanaka Masashi , Nakagawa Takahide , Kidera Masanori , Lee Sang-Moo
Published: October 2002

We successfully produced an intense beam of highly charged xenon ions using a liquid He free superconducting electron cyclotron resonance ion source. The best results of 10 eµA for Xe30+ ions was obtained at an injected microwave power of 650 W and an extraction voltage of 15 kV.
Properties of the Electrical-Discharge Plasma-Density in a High Pressure Gas Mixture
Authors: Uhm Han S. , Choi Eun H. , Cho Guansup
Published: October 2002

Electrical breakdown in a mixed gas is investigated. The plasma at breakdown is evaluated in terms of the mole fraction χ. The optimum condition for the highest plasma density is described in terms of ionization energy and collisional cross-section of the mixed gas. The optimum mole fraction for highest plasma density is found to be χ=0.03 for the case ofplasma generation in neon gas mixed with xenon for a typical plasma display panel.
Spatial Distribution of H Atom Density in High-Density, Helicon-Wave H2 Plasmas Measured by Laser-Induced Fluorescence
Authors: Masahiko Nakamoto Masahiko Nakamoto , Koichi Sasaki Koichi Sasaki , Kiyoshi Kadota Kiyoshi Kadota
Published: October 2002

Spatial distributions of H atom density in high-density, helicon-wave H2 plasmas were measured by (2+1)-photon laser-induced fluorescence spectroscopy. In low-power, high-pressure discharges, hill-type distributions, i.e., the H atom density in the plasma column was higher than that in the outside region, were observed. The hill-type density distribution can be explained by known mechanisms of gas-phase reactions, diffusion, and surface loss of H atoms. On the other hand, in high-power, low-pressure discharges, deep dips were observed in the spatial distribution of the H atom density. The dip region corresponded to the location of the plasma column, suggesting significant heating of H atoms.
Elastic Constant Determinations of SiC/NiP Composite Coating by Surface Acoustic Wave and Nano-indentation
Authors: Ihara Ikuo , Sawa Takeshi , Tanaka Kohichi
Published: October 2002

Elastic constant determinations of coatings deposited on a substrate are performed using a surface acoustic wave technique, and the ultrasonically determined elastic constants are compared with mechanically determined ones using a nano-indentation technique in order to examine the present ultrasonic technique for its validity. The experimental results for a NiP coating have shown that the Young's moduli determined ultrasonically and mechanically coincide with each other within an error range of 2%. This demonstrates that the present ultrasonic technique has been successfully applied to the elastic constant determination of such coating. Based on this result, SiC/NiP composite coating (SiC particle reinforced NiP coating) of 10 µm thickness was examined. The result using the surface acoustic wave indicated a 32% increase in Young's modulus due to the randomly dispersed SiC particles. The validity of this result is also discussed in comparison with mechanically and theoretically estimated results.
Quartz Resonators vs Their Environment: Time Base or Sensor?
Authors: EerNisse Errol P.
Published: October 2002

This work discusses the effects of temperature, force, and acceleration on the frequency of quartz thickness shear mode resonators. Historically, workers in the frequency control industry have tried to reduce these effects. Some of the physical principles will be discussed. Turning the problem around, sensitivity to these effects can be maximized to develop sensors for temperature and pressure. Advantages of such sensors include inherently digital format, high resolution, high accuracy, and long-term stability. This work reviews the physical principles involved in the operation of some devices used down-hole in the oil and gas service industry.
New Functions of Scanning Nonlinear Dielectric Microscopy –Higher-Order Measurement and Vertical Resolution–
Authors: Yasuo Cho Yasuo Cho , Koya Ohara Koya Ohara , Atsushi Koike Atsushi Koike , Hiroyuki Odagawa Hiroyuki Odagawa
Published: October 2002

We investigated new features (functions) of scanning nonlinear dielectric microscopy (SNDM), namely, higher-order nonlinear dielectric imaging and the very high vertical resolution. The resolution of the higher-order nonlinear dielectric imaging is higher than that of the conventional nonlinear dielectric imaging which detects the lowest order of the nonlinear dielectric constant. The very high vertical resolution of SNDM is also reported. These features of the SNDM enable us to obtain a new microscopy for measuring the topography or a new displacement sensor with extremely high sensitivity.
Consideration of Figure of Merit of Piezoelectric Vibratory Gyroscope Using Charge Sensitivity
Authors: Kudo Subaru
Published: October 2002

In this paper, charge sensitivity has been considered as a figure of merit of piezoelectric vibratory gyroscope. First, an approximate equation for charge sensitivity is derived based on an equivalent circuit of the gyroscope. Second, the charge sensitivity characteristics have been discussed in terms of the effects of frequency deviation and load capacitance. The difference between charge sensitivity and voltage sensitivity is quantitatively clarified. Charge sensitivity is effective as a figure of merit for applying a piezoelectric single crystal to the gyroscope.
Very Small-Sized Resonator Filter Using Shear Horizontal Wave on Quartz
Authors: Michio Kadota Michio Kadota , Toshimaro Yoneda Toshimaro Yoneda , Koji Fujimoto Koji Fujimoto , Takeshi Nakao Takeshi Nakao , Eiichi Takata Eiichi Takata
Published: October 2002

By composing interdigital transducers (IDTs) and reflectors consisting of films made of a heavy metal such as Au, Ta or W on an ST cut 90°X propagation (direction perpendicular to X-axis) quartz substrate, the authors realized a new type of shear horizontal (SH) wave. This wave has an excellent temperature characteristic, a large electromechanical coupling factor (k), and a large reflection coefficient at reflector electrodes. The square of this electromechanical coupling factor (k
2=0.28∼0.34%) and the reflection coefficient at reflector electrodes are 2.2∼2.6 times and 30∼35 times, respectively, as large as those of a Rayleigh wave on an ST cut X propagation quartz substrate. The authors applied this technology to filters for the first intermediate frequency (first IF) stage of a global system for mobile communications (GSM) in the nominal center frequency from 200 to 400 MHz. As a result, we succeeded in developing the first IF filter having a low insertion loss, an excellent temperature characteristic (frequency shift: 1 ppm/°C) and a small package size (3×3 mm2), which is as small as a radio frequency (RF) surface acoustic wave (SAW) filter, for the first time.
High-Speed Nonreciprocal Optical Switching Using Phase Shift Induced by Magnetostatic Surface Waves
Authors: Rakesh Bhandari Rakesh Bhandari , Yasumitsu Miyazaki Yasumitsu Miyazaki
Published: October 2002

Interaction between optical guided waves and magnetostatic waves (MSW) has great potential for wideband optical signal processing directly at microwave signal frequencies. However, till now, all theoretical and experimental investigation has focused on optical mode conversion involving a change in polarization induced by magnetostatic waves. So far, the efficiency of this mode conversion has been low. Here, we propose and analyze, for the first time, the feasibility of obtaining an optical phase shift induced by magnetostatic surface waves in thin film waveguides. We show that with proper selection of the waveguide parameters, it is possible to obtain a phase shift which is sufficient for design of efficient optical-MSW signal processing devices. Further, we propose and analyze a device structure for an optical switch based upon this phase shift and demonstrate the design feasibilty through a numerical example.
Experimental Investigation of Acoustic Scattering and Reflection of Marine Sediments by the High-Speed Visualization Method
Authors: Koide Naotaka , Derbesse Laurent , Pernod Philippe , Otani Takahiko
Published: October 2002

Acoustic scattering and reflection phenomena at the surface of marine sediment models were visualized by the shadowgraph method with an impulse source realized by a small spark gap. Water saturated glass beads were used as a sediment model. Lateral wave was clearly observed for fine sediments (small grain size compared with wavelength). Scattered waves and multiple reflected waves were observed for coarse sediments (larger or equivalent grain size compared with wavelength).
Fundamental Study of a Stacked Lithium Niobate Transducer
Authors: Morita Takeshi , Niino Toshiki , Asama Hajime , Tashiro Hideo
Published: October 2002

Generally, a lead zirconate titanate ceramic is utilized for a high-power transducer such as an ultrasonic motor drive. However, it is difficult to realize an ultrasonic motor that can withstand a high temperature, above 500°C. We focused on lithium niobate because it has a high Curie temperature (1210°C) and high quality factor. The electromechanical coupling factor of lithium niobate is large, although the permittivity is one hundred times smaller compared to that of hard-type lead zirconate titanate (PZT)-8. Hence a stacked structure is required to generate high output power. Dimensions of the fabricated actuator were 10 mm square and 18.5 mm long. The number of lithium niobate layers was 18. The calculated force factor of this transducer was 0.28 N/V, a value comparable to that of the bolted Langevin transducer using PZT, though the vibration velocity was saturated at 0.12 m/s. To realize improved transducer performance, we are attempting to fabricate a new transducer that can generate high vibration velocity.
Discrimination of Underwater Materials Located on a Declined Seabed
Authors: Tao Liang , Hoshino Tomofumi , Motooka Seiichi
Published: October 2002

A circular six-receiver array centered around the transmitter and a compensation method
are proposed in order to improve the discrimination ratio of underwater materials located on a declined seabed. The signal intensity reflected from the seabed is employed as data for neural network processing. Compared to the distribution of the intensities of the original data acquired from the declined seabed, the compensated values approach those acquired from a planar seabed, which are employed as the standard learning data for neural network discrimination. A comparison of the results of discrimination of the underwater materials with and without compensation verifies the efficiency of the method. However, the intensity of the echo signal decreases with increasing angle of decline, and the discrimination ratio is reduced accordingly. The valid limitation of the angle of decline for the compensation method is about 9°, according to the discrimination results obtained under the conditions of different angles of decline.