bluuebunny/crossref_metadata_2025 huggingface dataset:
Multidimensional Kinetic-Fluid Simulation of Inductive Discharges
Authors: M. M. Turner M. M. Turner
Published: October 2002

Inductive discharges for plasma processing (in particular for reactive ion etching) are preferably operated in a low-pressure regime in which collisionless heating of electrons is probably dominant. It is therefore desirable that efficient computer simulation techniques should be developed that are accurate under these conditions, where the ordinary fluid equations on which most current models are based are not valid. This paper discusses an approach based on “kinetic-fluid” equations: Fluid equations in which the closure assumptions are altered to enhance accuracy in the relevant regime. We show that this approach permits efficient three dimensional simulations, and that subtle features of the electron dynamics observed in recent experiments are reproduced by such simulations.
Two Dimensional Fluid Model of RF Plasmas in SiH4/Ar Mixtures
Authors: Nobuyasu Sato Nobuyasu Sato , Yutaka Shida Yutaka Shida
Published: October 2002

A self-consistent two dimensional numerical fluid model of rf plasmas under conditions close to those of the experiments for observing particle growth in silane rf plasmas has been developed. The geometry of the discharge chamber and the electrodes used in the model is cylindrically symmetric: two cylinders for the electrodes are surrounded by the grounded chamber. The rf plasmas are in SiH4(10%)/Ar(90%) at a pressure of 100 mTorr at 6.5 MHz. The results from the model, including the rf plasma structures and the generation rates for radicals, SiH, SiH2and SiH3, are presented. Effects of the applied rf voltage and the secondary electron emission coefficient on the generation rates of the radicals are discussed.
Convected Scheme Simulations of the Electron Distribution Function in a Positive Column Plasma
Authors: Hitchon Gregory J. Parker
Published: October 2002

A numerical procedure that provides an accurate and efficient solution of the Boltzmann equation in cylindrical geometry with coordinates (ρ, v) is discussed. The procedure, based primarily on the convected scheme, propagates the particle phase-space density on a computational mesh. A combination of the choice of independent variables, the design of the mesh structure and the use of a moving mesh can provide an exact solution of Vlasov's equation. A variant of the method is also presented which first iterates the scattering rate throughout phase space then finds the distribution function from the scattering rate. We describe the methods and apply them to a kinetic model of a dc positive column. Results are compared to Monte Carlo simulations.
Radical and Ion Compositions of BCl3/Cl2 Plasma and Their Relation to Aluminum Etch Characteristics
Authors: Kazumi Hideyuki , Hamasaki Ryoji , Kazutami Tago Kazutami Tago
Published: October 2002

Plasma compositions in BCl3/Cl2 were calculated using a molecular orbital method and a plasma kinetic method. The key factors for plasma compositions and their relations to the etch characteristics of Al-based multilayers were investigated. The etch rate of Al seemed to be correlated with the Cl density rather than the Cl2 density. The etch rates of TiN and the resist were also related to the Cl density and the ion density. Therefore the ion energy distribution (IED) impinging on the wafer was also calculated and the rf frequency dependence of the selectivity of the TiN/resist was evaluated using an etching model. Even if the rf frequency increased to 10 MHz, where the IED had a single peak, the predicted selectivity was slightly improved. A narrower IED was required.
Silicon Dry Etching in Hydrogen Iodide Plasmas: Surface Diagnostics and Technological Applications
Authors: Richter Harald H. , Aminpur Massud-A. , Erzgräber Heide B. , Wolff André , Krüger Dietmar , Dehoff Arnulf , Reetz Martin
Published: October 2002

We have investigated hydrogen iodide (HI) as an alternative to conventional chlorine or bromine chemistry for dry etching. Plasma exposed Si surfaces show damage, as revealed by photoluminescence studies. These defects can be annealed out by thermal treatment at 550° C. We have developed an anisotropic polysilicon gate etch process for 0.35 µ m MOS technology based on iodine chemistry. The selectivity between polysilicon and oxide is determined as a function of various process parameters. Decreasing the rf source power from 350 to 100 W increases the selectivity between polysilicon and SiO2 from approx. 30:1 to 180:1. Profiles with a degree of anisotropy close to unity can be obtained without trenching or other undesirable anomalies. Iodine-based plasmas are characterized by very low self-biased voltages, typically less than 70 V.
Resist Etching with Parallel-Plate RF Plasmas Enhanced by a Cusp Magnetic Field
Authors: Kawata Hiroaki , Kubo Takashi , Masaaki Yasuda Masaaki Yasuda , Kenji Murata Kenji Murata
Published: October 2002

Ring-shaped permanent magnets are placed on the back of both the cathode and the anode electrodes in a parallel-plate RF plasma device and magnetron plasmas with axial symmetry are produced. Positive photoresist films are etched using the magnetron plasma device. The S pole of the magnets faces the plasmas. Since the same poles face each other, the axial magnetic field is canceled and the cusp field is formed around the axis. An Al plate is placed on the cathode and its thickness is varied. Then, the sheath in front of the cathode is formed around the region where the axial magnetic field is canceled by the two magnets. The etch rate of 1.1 µm/min can be obtained. However, the region in which the etch rate is uniform is not large. The measured etching characteristics are discussed based on the spatial distributions of the magnetic field and the ion saturation current. Line-and-space of 0.25 µm patterns are etched although somewhat undercut profiles are observed.
Fast Deposition of Amorphous and Microcrystalline Silicon Films from SiH2Cl2–SiH4–H2 by Plasma-Enhanced Chemical Vapor Deposition
Authors: Arai Takeshi , Takuya Nakamura Takuya Nakamura , Hajime Shirai Hajime Shirai
Published: October 2002

Fast deposition of hydrogenated chlorinated amorphous and microcrystalline silicon (a-Si:H(Cl), µ c-Si:H(Cl)) thin films is achieved without powder formation and deterioration of their optoelectronic properties by plasma-enhanced chemical vapor deposition (rf PECVD) from SiH2Cl2– SiH4– H2. The Si-network can be varied from microcrystalline to amorphous at high deposition rate of about 20 Å/s with addition of SiH4 under steady flow of SiH2Cl2– H2 plasma. The deposition rate strongly depends on the mixture ratio of SiH2Cl2 and SiH4 and the substrate temperature.
Roles of SiH3and SiH2Radicals in Particle Growth in rf Silane Plasmas
Authors: Kawasaki Hiroharu , Ohkura Hiroshi , Fukuzawa Tsuyoshi , Shiratani Masaharu , Watanabe Yukio , Yamamoto Yasuo , Suganuma Shinji , Hori Masaru , Goto Toshio
Published: October 2002

Temporal evolutions of spatial profiles of SiH3radicals, radical production rates, short-lifetime radicals and particle amount in rf silane plasmas are studied using various methods including infrared-diode-laser-spectroscopic and laser-light-scattering methods. Based on the results, contributions of SiH3and SiH2radicals to particle growth are discussed. Particles nucleate and grow, from beginning of their growth, principally around the plasma/sheath boundary near the powered electrode. The spatial profile of the particle amount is very similar to those of the densities and production rate of short-lifetime radicals. A density of SiH3radicals amounts to about 1012cm-3, and its spatial profile is fairly flat between the electrodes from the discharge initiation. These results suggest that the particle species responsible for the nucleation of particles is not SiH3but radicals such as SiH2, which is highly reactive and produced at a high rate. The SiH2radicals react quickly with SinH2n+2(n=1, 2,…) to form polymerized species. Among them, the higher-order polymerized species absorb the lower-order ones produced later, and consequently suppress further nucleation of particles. While the contribution of SiH3radicals to particle nucleation and subsequent initial growth is not so important, they may affect the deposition rate of film on the substrate when the particle radius increases to about 10 nm.
Spectroscopic Measurement of DC Plasma Jet in Diamond Synthesis
Authors: Sakiyama Satoshi , Fukumasa Osamu , Tomohide Murakami Tomohide Murakami , Tsuyoshi Kobayashi Tsuyoshi Kobayashi
Published: October 2002

In synthesis of diamond with a plasma jet under medium pressure, the morphology of the deposited particles depends strongly on the ratio of the methane gas flow rate to the hydrogen gas flow rate and the distance from the feed ring exit to the substrate. The relationship between the morphology of the deposited particles and the chemical species in the plasma jet is studied by means of emission spectroscopy, with a view toward achieving large-area deposition at a high rate. The intensity ratio of the CH to the Hα spectrum is strongly correlated with the quality of the diamond synthesized and the deposition area.
Kinetic Analysis of Non-Thermal Plasmas Used for Pollution Control
Authors: Penetrante Bernie M. , J. Norman Bardsley J. Norman Bardsley , Mark C. Hsiao Mark C. Hsiao
Published: October 2002

Non-thermal plasma techniques are being developed for the treatment of many gas-phase pollutants. In these methods electrical energy from electron beams or electrical discharges is directed selectively into the production of electrons, ions and radicals, or into molecular excitations that will result in the efficient destruction of the unwanted species. The processes by which this can be achieved are described. Kinetic analysis of the deposition of energy into contaminated air is illustrated by studies of the decomposition of nitrogen oxides, methylene chloride, carbon tetrachloride and methanol.
Electrical Stress Effect on Poly-Si Thin Film Transistors Fabricated by Metal Induced Lateral Crystallization
Authors: Ihn Tae-Hyung , Lee Byung-Il , Jeon Seung-Ki Joo
Published: October 2002

Electrical stress effects on polycrystalline silicon thin film transistors (poly-Si TFTs) fabricated by metal induced lateral crystallization at 500° C have been investigated. Leakage current decreased by four orders of magnitude after the electrical stress in both n-channel TFTs and p-channel TFTs. It turned out that the electrical stress between the drain and source was more effective than that between the gate and source. Polarity of the electrical stress turned out to be also important for depression of the leakage current.
A Multistate Switch with Double Delta-Doped Strained-Layer Quantum Wells
Authors: Der-Feng Guo Der-Feng Guo
Published: October 2002

A GaAs–InGaAs switching device, prepared by molecular beam epitaxy (MBE), has been investigated. A double delta-doped (δ-doped) strained-layer quantum-well structure is employed to produce the potential wells for the carrier confinement and the potential barriers for carriers thermionically emitted over them. Equipped with the different doping levels of the δ-doped sheets, the barriers are successively collapsed to form a double negative-differential-resistance (NDR) phenomenon in the current–voltage ( I–V ) characteristics when a sufficient external bias is applied to this device. Moreover, because the temperature variation changes the carrier confinement efficiency and carrier thermal energy, the NDR characteristics are sensitive to environmental temperature. The influence of temperature on the device performance is also discussed.
Monte Carlo Modeling of Transient Effects in Resonant-Tunneling Bipolar Transistors
Authors: Maxim Ryzhii Maxim Ryzhii
Published: October 2002

Transient behavior of bipolar transistors with a quantum-well base and a resonant-tunneling structure in the collector is studied using the ensemble Monte Carlo particle method. The switch on/off processes as a response to trigger pulses of the collector voltage and the base current are simulated. The amplitudes and duration of the pulses providing reliable switching are obtained.
Simultaneous Operation of Superconducting Field Effect Transistors
Authors: Nakamura Takao , Hiroshi Inada Hiroshi Inada , Michitomo Iiyama Michitomo Iiyama
Published: October 2002

A new process was developed for preparing four superconducting field effect transistors (SuFET's) on a substrate. This process yielded the gate structure of YBa2Cu3O7-
x

/SrTiO3/YBa2Cu3O7-
x

(YBCO/STO/YBCO) and the contact structure of buried YBCO electrodes. The average T
c of the YBCO (100 nm)/STO (200 nm)/ YBCO (5 nm) structures was 49.7 K and the I–V characteristics of gate STO were symmetric. The temperature dependence of transconductance was larger compared with other SuFET's reported to date. Furthermore, we confirmed the operation of all the SuFET's on one substrate and two adjacent SuFET's connected in series. This device fabrication process also led to improved T
c values of ultrathin YBCO channels.
High-Tc Josephson Junctions Fabricated Using a Focused Ion Beam Technique
Authors: Morohashi Shin'ichi , Wen Jianguo , Youichi Enomoto Youichi Enomoto , Naoki Koshizuka Naoki Koshizuka
Published: October 2002

The narrow-focused Ga-ion beam (FIB) technique has the two functions of etching and deposition. Using each of the functions (etching or deposition) of FIB independently, we have fabricated high-T
c Josephson junctions with structures of two types both on MgO and SrTiO3 substrates. We studied the current-voltage characteristics of these junctions and the interfaces of these junctions were observed by cross-sectional transmission electron microscopy. Both FIB junctions have been confirmed to be grain boundary junctions. The formation of the grain boundary in these junctions strongly depends on the crystal structures of NdBaCuO (perovskite-like), MgO (face centered cubic), SrTiO3 (perovskite-like) and tungstein (body centered cubic) deposited by a focused ion beam chemical vapor deposition, and the degree of the lattice mismatch between them.
Structural and Magnetic Anisotropy of Tb/Fe Multilayers
Authors: Fujiwara Yuji , Masaki Tsugihiko , Yu Xiangyou , Sakurai Masaki , Tsunashima Shigeru , Suzuki Satoshi Iwata
Published: October 2002

Local structural anisotropy of Tb/Fe multilayers (MLs) was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Quantitative analysis of Fe EXAFS signals was performed to estimate the coordination number related to the structural anisotropy. A difference in the Fourier-transformed Fe EXAFS spectra between two incident polarized light directions has indicated that considerable anisotropy of atomic pair ordering exists in the MLs prepared by sputtering. It was further found that the variation of the structural anisotropy well corresponds to the magnitude of the perpendicular magnetic anisotropy, which changes depending on the bilayer periods and the preparation condition.
Analysis of X-Intersecting Waveguide Switches with a Large Branching Angles Ranging from 2° to 12°
Authors: Feng Hao , Tada E. Herbert Li
Published: October 2002

This is a study on the analysis of the X-junction waveguide switches with a large branching angle ranging from 2° to 12°. The characteristics of the modeled are simulated by using the beam propagation method. We will show that, for an X-intersecting waveguide with a branching angle more than 2°, the eigenmodes interference remains and prevails even up to 12°. This produces a high unbiased crosstalk. In the analysis of the modulation efficiency of the switch, it is revealed that a large positive refractive index change will produce higher modulation efficiency than a negative refractive index change because of optical field re-distribution. In designing an X-intersecting waveguide switch using the coupled mode theory, a -40 dB crosstalk can be achieved for device smaller than 2 µ m. The interference X-intersecting waveguide switches will be more suitable for large scale switching arrays.
Dielectric Properties of SrTiO 3 Capacitor Using TiN Bottom Electrode and Effects of SrTiO 3 Film Thickness
Authors: Yoshio Abe Yoshio Abe , Midori Kawamura Midori Kawamura , Katsutaka Sasaki Katsutaka Sasaki
Published: October 2002

SrTiO3 thin films are prepared on TiN bottom electrodes by rf magnetron sputtering, and the effect of the oxidation of the TiN electrodes on dielectric properties of SrTiO3 capacitors is studied. At the substrate temperature of 400°C, a relative dielectric constant of 120 is obtained for SrTiO3 films with a thickness of 150 nm and the maximum capacitance of 15 nF/mm2 is obtained at the SrTiO3 film thickness of 12 nm. The TiN bottom electrode is found to be oxidized during SrTiO3 film deposition, and the oxidized layer is suggested to be rutile-TiO2, with a relative dielectric constant of 80, through comparisons with Au/SrTiO3/TiN and Au/SrTiO3/Pt capacitors. The thickness of oxidized TiN is found to grow logarithmically with increasing SrTiO3 thickness.
Steady-State Current due to Ionic Carriers in Polymethylphenylsilane Thin Films
Authors: Hironori Iga Hironori Iga , Hiroyoshi Naito Hiroyoshi Naito
Published: October 2002

Steady-state current in polymethylphenylsilane thin films has been studied. It is found that the steady-state current is proportional to the square root of the applied electric field at high applied electric fields. The temperature dependence of the steady-state current shows the thermally activated behavior with the activation energy of 0.33 eV and 0.95 eV below and above 9.0 ×104 V/cm, respectively. These experimental results can be explained in terms of the ion generation due to the Poole-Frenkel mechanism and the subsequent transport in this material.
Electrical Properties of Discotic Liquid Crystal Hexahexyloxytriphenylene
Authors: Katsumi Yoshino Katsumi Yoshino , Hiroaki Nakayama Hiroaki Nakayama , Masanori Ozaki Masanori Ozaki , Mitsuyoshi Onoda Mitsuyoshi Onoda , Maki Hamaguchi Maki Hamaguchi
Published: October 2002

Carrier transport of 2,3,6,7,10,11-hexahexyloxytriphenylene (HHOTP) in the discotic phase and the effects of C60doping and shear stress have been studied by a time-of-flight method. The relatively high mobility of positive carriers insensitive to temperature and also C60doping are interpreted to be the hole mobility. The hole mobility decreases on applying shear stress which deforms the columnar structure in the discotic phase. Small and temperature-dependent mobility (with activation energy of 0.3 eV) of negative carriers which are influenced by C60doping is interpreted to be that of ionic carriers. Electronic band schemes of HHOTP in various phases (solid, discotic and isotropic) have been evaluated by absorption and photoelectron emission spectra measurements.
Preparation of Epitaxial Pb(Zr, Ti)O3 Thin Films on Nb-Doped SrTiO3 (100) Substrates by Dipping-Pyrolysis Process
Authors: Hwang Kyu-Seog , Manabe Takaaki , Yamaguchi Iwao , Toshiya Kumagai Toshiya Kumagai , Susumu Mizuta Susumu Mizuta
Published: October 2002

Epitaxially grown Pb(Zr, Ti)O3 (PZT, Pb:Zr:Ti=1:0.52:0.48) thin films were prepared on Nb-doped SrTiO3 (100) substrates by dipping-pyrolysis process with metal naphthenates used as starting materials. The alignments of the films were investigated based on X-ray diffraction (XRD) θ–2θ scans, β scans (pole figures), and asymmetric ω–2θ scans (reciprocal-space maps). Epitaxial films with smooth surfaces were obtained by heat treatment of prefired films at 600°–750° C; a film heat-treated at 750° C showed the strongest peak intensities in the XRD θ–2θ scans. These PZT films were found by reciprocal-space map analysis to consist of the c-axis-oriented tetragonal phase.
Time-Dependent X-Ray Photoelectron Spectroscopy Observed for Dimethylaluminum Hydride Adsorbed on S i O2
Authors: Hidetaka Koya Hidetaka Koya , Mitsugu Hanabusa Mitsugu Hanabusa
Published: October 2002

Time-dependent X-ray photoelectron spectroscopy (XPS) was observed for adsorbates of dimethylaluminum hydride formed on SiO2surfaces. The peak intensity of the C 1s spectra decreased slowly under 1847-eV Al Kα X-ray irradiation, while the binding energy of the Al 2p spectra increased. The time dependence of the XPS spectra varied for the adsorbates formed over a range of temperatures from room temperature up to 200° C. The time dependent XPS spectra was explained by the decomposition of the adsorbates. However decomposition was not complete enough to produce Al or Al2O3. Indirect decomposition by secondary electrons was suggested from X-ray induced electron emission measurements.
Initial Stage and Growth Process of Ceria, Yttria-Stabilized-Zirconia and Ceria-Zirconia Mixture Thin Films on Si(100) Surfaces
Authors: Hirai Tadahiko , Teramoto Kazuhiro , Koike Hiroshi , Kazuhito Nagashima Kazuhito Nagashima , Yasuo Tarui Yasuo Tarui
Published: October 2002

Initial stages and growth processes of ceria ( CeO2), yttria-stabilized-zirconia (YSZ) and ceria-zirconia mixture ( Ce·ZrO2) thin films on Si(100) surfaces were studied in conjunction with O2 pressure. We showed that (110)-oriented films of CeO2, YSZ and Ce·ZrO2 grew obeying the arrangements of Si atoms in (2×1) or (1×2) structures on a Si(100) surface under about 5×10-7 Torr O2 gas at about 900° C. On the other hand, under 1×10-5 Torr O2 gas, (111)-oriented CeO2 polycrystal films grew because of formation of Ce2O3 and Si O2 layers at the interface between CeO2 and Si(100). Furthermore, the (100)-epitaxial YSZ and Ce·ZrO2 films grew, reducing the SiO2 layer on Si(100) under 1×10-5 Torr O2 gas. We attempted to explain these processes in terms of standard formation enthalpies of CeO2, Ce2O3, ZrO2 and SiO2.
Ab Initio Molecular Orbital Study of Suppression of Water Absorption and Hydrolysis (F-Removal) of Chemical-Vapor-Deposited SiOF Films by Nitrogen Doping
Authors: Nakasaki Yasushi , Miyajima Hideshi , Hayasaka Ryota Katsumata
Published: October 2002

We investigated the mechanism of the nitrogen-doping effect on the suppression of water absorption and hydrolysis (F-removal) of fluorine-doped SiO2 (SiOF) films, using the ab initio molecular orbital method with model clusters of three-membered-rings of Si–O bonds with and without N atoms in the siloxane rings ( Si3O3-
n

(NH)

n

F(OH)5 ( n=0, 1)). We focused on the changes in the reactivity of these clusters with OH- in the presence of N in the rings. The calculations revealed the following. Three-membered SiOF rings of Si–O bonds are more stabilized by the OH- coordination and more easily form metastable pentacoordinated-Si intermediates than the unconstrained small SiOF clusters we examined elsewhere. The N-incorporated SiOF ring becomes less reactive with OH- due to the increase in the reaction barrier for HF formation. The incorporated N atoms suppressed the back-bond deformations by forming Si–N–Si linkages.
Bending of a Rectangular Cantilever of an Atomic Force Microscope as a Function of Position along Length
Authors: Tatsuya Miyatani Tatsuya Miyatani , Masamichi Fujihira Masamichi Fujihira
Published: October 2002

In order to measure quantitatively the surface stress change of a cantilever for an atomic force microscope, we studied the bending of a rectangular cantilever pushed ca. 50 nm against a hard surface as a function of the laser spot position on the cantilever and compared the result with the bending caused by the surface stress change.
Characteristics of 1 MHz Discharge in SF 6/O 2 Mixture in a Parallel-Plate System
Authors: Kenji Aoyagi Kenji Aoyagi , Yuuji Hirose Yuuji Hirose , Itsuo Ishikawa Itsuo Ishikawa , Yukinori Saito Yukinori Saito , Shinji Suganomata Shinji Suganomata
Published: October 2002

The influence that mixing SF6 with O2 has on the discharge characteristics varies with the pressure. At the total pressure of 0.5 Torr, the discharge structure changes remarkably and becomes almost the same as that of SF6 discharge by mixing only 5% SF6 with O2. At the total pressure of 0.1 Torr, the discharge-sustaining voltage, the discharge current and the spatiotemporal profile of optical emission do not vary noticeably by mixing only 5% SF6, though the radial distribution of plasma density changes clearly. In this case, the electronegativity of SF6 influences obviously on the discharge characteristics of SF6/O2 mixture at SF6 ratios greater than 50%.
Optimum Recording Conditions of Direct Overwrite Magneto-Optical Disk Drive for the Widest Power Margin
Authors: Kurita Shinichi , Saito Jun , Ishii Kohichiro , Horikawa Masashi , Akasaka Hideki
Published: October 2002

The write laser power margin of magneto-optical (MO) disks is determined by, for example, the disk sensitivity and various conditions of MO drive. Especially when the multipulse writing method is used for mark edge recording, the drive conditions influence the writing power margin. The drive conditions include both the write channel conditions, such as the writing waveform and the writing power, and the read channel conditions, such as the readout equalizer. When these conditions are optimal, the drive has the widest power margin possible for the object disk. We used the multipulse writing method on direct overwrite (DOW) MO disks and examined the optimum write power condition and the optimum readout equalizer condition. As a result, the correlation between those parameters has been clarified.
Investigations on the Loading of a Two-Color Vapor-Cell Magneto-Optic Trap for Sodium Atoms
Authors: Zilio Sérgio C. , Flemming Júlio , Luis G. Marcassa Luis G. Marcassa , Vanderlei S. Bagnato Vanderlei S. Bagnato
Published: October 2002

We investigate the loading of a two-color vapor-cell magneto-optical trap for sodium atoms as a function of several operational parameters of the trap. We use two laser frequencies acting in different spatial regions to obtain either enhancement or inhibition of the capture mechanism. We demonstrate that the best enhancement is achieved when the trap operates on a combination of atomic transitions, known as type I tuning, by using a second laser beam to capture atoms through a different combination of transitions (type II tuning).
Low-Temperature Si Oxidation Using Inductively Coupled Oxygen-Argon Mixed Plasma
Authors: Masato Tabakomori Masato Tabakomori , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

N- and p-type Si were oxidized using an inductively coupled oxygen–argon mixed plasma at about 60°C and 300°C. The flow-rate ratio of O2 (O2(O2 + Ar)) was fixed at 80%. Capacitance–voltage (C–V) characteristics were improved by a combination of substrate heating at 300°C and post-thermal annealing at 500°C for 30 min in an oxygen ambient as compared with those reported previously. However, the interface-state density was about 1 ×1012 eV-1cm-2, still higher than that in the device-grade thermal SiO2/Si interface. The conductance–voltage (G–V) characteristics showed rather large conductance in the accumulation region for both oxide samples grown on p- and n-Si substrates as compared with thermal oxides. The X-ray photoelectron spectroscopic (XPS) measurements revealed that a fairly uniform SiO2 layer was formed in the upper portion of the film using this technique although the transition region was observed at the interface between oxide and Si, which was composed of the Si suboxides such as Si2O3 and SiO. The thickness of this “transition” region was roughly 13–15 nm which was larger than that for the thermal oxide/Si interface. Current–voltage (I–V) characteristics showed that the leakage current was mainly Fowler–Nordheim (F–N) tunneling current and much smaller for the oxide on p-Si than for the oxide on n-Si. The breakdown voltage was also higher for the oxide/p-Si than for the oxide/n-Si. The reason for these findings was discussed on the basis of the F–N current mechanism.
Heteroepitaxial Growth of InGaP on Si with InGaP/GaP Step-graded Buffer Layers
Authors: Yuji Komatsu Yuji Komatsu , Keiji Hosotani Keiji Hosotani , Takashi Fuyuki Takashi Fuyuki , Hiroyuki Matsunami Hiroyuki Matsunami
Published: October 2002

Heteroepitaxial growth of indium gallium phosphide (In1-x
Ga
x
P) with x ∼0.7 was successfully achieved on a silicon (Si) substrate by introducing step-graded buffer layers which consist of a gallium phosphide (GaP) buffer layer and In1-x
Ga
x
P layers whose gallium (Ga) composition x decreases in steps toward the direction of the growth. For the GaP buffer layer, the effects of thermal cycle annealing (TCA) were studied using a Rutherford back scattering channeling (RBS-C) measurement. The layer was shown to be improved greatly and a high-quality heteroepitaxial GaP layer could be obtained in the region close to the surface by introducing TCA. For the In1-x
Ga
x
P step-graded layers, the lattice strain, investigated using X-ray diffraction, was shown to be more relaxed using a Si substrate than using a GaP substrate. The growth of InGaP on a Si substrate with the step-graded layers is an effective method to reduce the strain in the InGaP layer.
Purely Intrinsic Poly-silicon Films for n-i-p Solar Cells
Authors: Rath Jatindra Kumar , Hans Meiling Hans Meiling , Ruud E. I. Schropp Ruud E. I. Schropp
Published: October 2002

Polycrystalline silicon films have been prepared by hot wire chemical vapor deposition (HWCVD) at a relatively low substrate temperature of 430° C at a high growth rate (>5 Å/s) by optimizing the hydrogen dilution of the silane feedstock gas, the gas pressure and the wire temperature. The optimized material has 95% crystalline volume fraction with complete coalescence of grains. The grains with an average size of 70 nm have a preferential orientation along the (220) direction. Large structures up to 0.5 µ m could be observed by atomic force microscopy (AFM). An activation energy of 0.54 eV for the electrical transport and a low carrier concentration (<1011 cm-3) confirmed the intrinsic nature of the films. A white light photoconductivity of 1.9×10-5 Ω-1 cm-1, a high minority carrier diffusion length of 334 nm and a low (<1017 cm-3) defect density ensure that the poly-Si:H films possess device quality. A very small temperature dependence of the Hall mobility (0.012 eV) indicates negligible barrier to carrier transport at the grain boundaries. A single junction n-i-p cell incorporating HWCVD poly-Si:H in the configuration n+-c-Si/i-poly-Si:H/p-µc-Si:H/ITO yielded 3.15% efficiency under 100 mW/cm2 AM1.5 illumination and a current density of 18.2 mA/cm2 was achieved for only 1.5 µ m thick i-layer.
Evaluation of Effective Gate Length of Gallium Arsenide Metal-Semiconductor Field Effect Transistors
Authors: Tamotsu Kimura Tamotsu Kimura , Tomoyuki Ohshima Tomoyuki Ohshima
Published: October 2002

To improve the performance of field-effect transistors (FETs), it is necessary to reduce the gate length. However the gate length, which affects the characteristics of FETs, is generally not the same as the metallurgical gate length, and is referred to as the effective gate length, which depends on the device structure. This paper describes a method of evaluating the effective gate length of GaAs MESFETs using I–V measurement under the bias condition, then discusses the relationship between the effective gate length and the structural parameters of the device, such as the distance between the gate metal and the n+ region, which is controlled by the sidewall thickness for n+ self-alignment ion implantation. From the results of a two-dimensional device simulation, it is observed that the effective gate length is related to the depletion layer extending around the gate electrode.
Optically Controlled Plasma Resonances in Induced-Base Hot-Electron Transistors
Authors: Victor Ryzhii Victor Ryzhii , Irina Khmyrova Irina Khmyrova , Maxim Ryzhii Maxim Ryzhii
Published: October 2002

We study theoretically the influence of the optical generation of electrons and holes in the base of an induced-base hot-electron transistor (IBHET) on its high-frequency operation. High electron mobility is assumed in the IBHET base, so that the standing plasma waves in the base can substantially affect the induced-base IBHET performance. It is shown that the photogeneration leads to marked transformation of the resonant peaks in the IBHET frequency-dependent transconductance. This is due to the dependence of the resonant frequencies and the electron scattering time on the concentration of the photogenerated electrons and holes. The latter results in the shift of the resonant peaks to higher frequencies and their broadening. This effect can be used for an effective optical control of IBHETs operation in the terahertz range of signal frequencies.
Real-Time Monitoring System of Pulse Durations of Picosecond Ti:Sapphire Laser
Authors: Sasaki Motonobu , Lin Shujie , Tsukakoshi Motowo , Shimizu Tadao , Takanori Suzuki Takanori Suzuki
Published: October 2002

Real-time monitoring of picosecond pulse duration of a Gaussian pulse has been demonstrated by the single-shot second-harmonic spatial distribution method. By taking into account the contribution of the actual incident beam profile, the duration of the picosecond pulses from a regeneratively amplified Ti:sapphire laser has been measured at a 10 Hz repetition rate with a pulse energy of 10 µ J.
Photovoltaic Effect in Titanium Dioxide/Polythiophene Cell
Authors: Koichi Kajihara Koichi Kajihara , Katsuhisa Tanaka Katsuhisa Tanaka , Kazuyuki Hirao Kazuyuki Hirao , Naohiro Soga Naohiro Soga
Published: October 2002

The photovoltaic effect has been observed in a titanium dioxide (TiO2) and polythiophene (PT) composite cell, ITO/TiO2/PT/Au. The TiO2/PT junction forms a rectifying contact and the ideality is better than that of the TiO2/ZnPc junction reported previously. There exists a good correlation between the optical absorption spectrum of the PT layer and collection efficiency of the cell with illumination from the ITO side. This indicates that the TiO2 layer effectively works as a wide-gap window material. Photovoltaic and electrical properties of the cell are varied considerably by changing the undoping potential of the PT layer. These phenomena are interpreted in terms of the band theory taking into consideration the contribution from surface states.
Far-Infrared Reflectance Study of Coupled Longitudinal-Optical Phonon-Hole Plasmon Modes and Transport Properties in Heavily Doped p-Type GaAs
Authors: Fukasawa Ryoichi , Perkowitz Kiyomi Sakai
Published: October 2002

We measured room-temperature far-infrared reflectance spectra of ten p-type, Be-doped, molecular-beam-epitaxy-grown GaAs films with hole densities from 6.3×1017 to 2.9×1019 cm-3 and examined the frequency-dependent dielectric function of coupled phonon-heavily damped hole plasmon modes in these samples without the complications that arise in Raman scattering experiments. Both a two-oscillator dielectric function ε(ω), and Kukharskii's factorized form ε

K
(ω) for the dielectric function, reproduce the data well. The plasmon-like modes clearly appear in the reflectance spectra, although they are suppressed in the Raman spectra, and we find that their frequencies are best given by finding the solutions of ε(ω)=0 in the complex ω-plane. The infrared data also accurately yield the hole drift mobilities when we consider values for the Hall scattering factor in p-type GaAs.
Properties of CdS/CdTe Solar Cells with Cu2Te–Au Contacts
Authors: Uda Hiroshi , Ikegami Seiji , Hajimu Sonomura Hajimu Sonomura
Published: October 2002

Cu2Te-based contact layers are annealed onto CdTe films of CdS/CdTe solar cells. The photovoltaic properties of cells with Cu2Te–Au contacts are greatly improved when the annealing temperature was increased. The V
oc and J
sc of the cells reached a maximum value at around 250° C. An increase in the spectral response of the short wavelength region was observed for cells with thinner CdS films. CdS/CdTe solar cells with Cu2Te–Au contacts had a conversion efficiency of 10.5%.
Anomalous Dielectric Relaxation in Reduced LiNbO3 Single Crystals
Authors: Kim Chong-Don , Joo Gi-Tae , Ho-Gi Kim Ho-Gi Kim
Published: October 2002

Reduced black LiNbO3 single crystals were prepared by heat treatment at 1000° C for 3 h in H2–N2 atmosphere. The dependence of their dielectric properties on frequency and temperature was investigated from 1kHz to 100kHz in the temperature range 400° C<T<800° C. A dielectric anomaly was found within 500° C<T<680° C. The position of the maximum dielectric constant depends on heating rates in air. At a constant heating rate, intensity of dielectric constant depends on the frequency but its position does not change. The anomalous dielectric relaxation resulted from the oxygen vacancies in reduced LiNbO3.
Diffusion Process of Interstitial Atoms in an Electron Irradiated InP Studied by Transmission Electron Microscopy
Authors: Ohno Yutaka , Saitoh Nagahito , Seiji Takeda Seiji Takeda , Mitsuji Hirata Mitsuji Hirata
Published: October 2002

Growth of interstitial agglomerates, that are formed in InP by post-annealing above 700 K following 200 keV electron irradiation, has been systematically examined by transmission electron microscopy to understand the migration of point defects in InP. The nucleation and growth of the agglomerates stopped at an early stage of post-annealing. The number density of interstitial atoms in agglomerates, estimated after the growth of all agglomerates stops, did not depend on annealing temperature but on electron dose, and it increased quadratically with electron dose up to 2.5×1022 cm-2. These results were well explained by a model in which the agglomerates were formed through the migration of In
i
–P
i
interstitial-pairs. The migration energy for the pairs was estimated as 1.52 eV.
Controlling the Orientation of Purple Membrane Fragments on an Air/Water Interface by a New Method of Direct Electric Field Application during Purple Membrane Spreading
Authors: Sugiyama Yukihiro , Inoue Takakazu , Ikematsu Mineo , Iseki Masahiro , Tatsuhiko Sekiguchi Tatsuhiko Sekiguchi
Published: October 2002

The orientation of purple membrane (PM) fragments on an air/water interface was controlled by a direct electric field applied across the interface during spreading of a PM solution. We call this the direct electric field application Langmuir-Blodgett (LB) technique, and found it effective in increasing the population of preferentially oriented PM fragments at the interface. Using this technique with an electric field exceeding 4 kV/cm and an initial coverage C
i of 0.2 (i.e., the ratio of the surface area of the air/water interface covered by PM fragments to the total surface area of the interface before the PM was spread over the interface), we produced a PM LB film in which all the constituent PM fragments were preferentially oriented. We successfully demonstrated that this technique is a powerful tool for producing LB films in which proteins are perfectly oriented (i.e., all the constituent PM fragments are preferentially oriented).
A Self-Sensitive Probe Composed of a Piezoelectric Tuning Fork and a Bent Optical Fiber Tip for Scanning Near-field Optical/Atomic Force Microscopy
Authors: Muramatsu Hiroshi , Yamamoto Noritaka , Umemoto Takeshi , Homma Katsunori , Fujihira Norio Chiba
Published: October 2002

A self sensitive probe was composed of a piezoelectric tuning fork and a bent optical fiber tip for scanning near-field optical/atomic force microscopy. The topography, optical image and fluorescent spectrograph were successfully derived using the combined probe. The probe showed 1.1 nm vertical resolution at the tip-sample distance regulation. The combined probe showed single or twin resonant frequency peaks while the original tuning fork has only one resonant frequency of 32.7 kHz. In the twin peaks-case, results for various combination patterns suggested that one of the peaks is the response for a free arm of the tuning fork and the other is the response for the combined arm. The near-field acoustic effect was detected in the tuning fork probe as a small effect, but the effect was not detected in the combined probe.
An X-Ray Stress Measurement Method for Very Small Areas on Single Crystals
Authors: Yoshiike Takahisa , Fujii Nobuyuki , Kozaki Shigeru
Published: October 2002

We realized measurement of stresses existing in very small areas on single crystals using an X-ray beam 60 µm in diameter. No such stress measurement has been feasible in the past because conventional measurement methods customarily use a polycrystalline powder material as a reference sample. Diffracted X-rays from a powder sample are weak and a long exposure time is required to obtain a diffraction pattern. Moreover, if the diameter of the X-ray beam is reduced, it is difficult to obtain a continuous diffraction ring. We thought of using a single crystal as a reference sample and eventually succeeded in measuring stresses in very small areas. We also examined the measurement precision of this method. As for the medium of recording X-ray diffraction patterns, we employed an imaging plate and tried to shorten the measurement time. We also clarified that high-precision stress measurements can be performed, even with the imaging plate. As a result, we were able to measure stresses in a silicon single crystal with an X-ray beam of 60 µm diameter in 16 min of exposure time.
Method for Normalizing the Write Laser Power of Magneto-Optical Disk Drives by Using a Calibration Disk
Authors: Shigeji Hara Shigeji Hara , Fumiaki Yamada Fumiaki Yamada , Shuuji Sasaki Shuuji Sasaki , Kan-ichi Oishi Kan-ichi Oishi
Published: October 2002

Normalization of write laser power is important for facilitating the device-independent use of optical disks in optical disk drives produced by different manufacturers. In this paper, we describe methods for normalizing laser power by using a calibration disk, for maintaining the guaranteed characteristics of the calibration disk, and for maintaining the performance of a measurement system used to evaluate the calibration disk. We also give test results relating to the methods for a long period of over 3 years.
Life Time Test of Rewritable Mini Disc (MD) Media
Authors: Okino Yoshihiro , Hashimoto Hidehiko , Mizumoto Kunihiko , Kubo Takahiro , Kikawa Hayami
Published: October 2002

The lifetime test of optical media is discussed on the rewritable Mini Disc media for consumer use. The experiments were applying the method conventionally used for the data storage optical disc. Judging from some respects of the experimental results, the lifetime of the recording layer of rewritable MD media presently available in the market is deemed to be sufficiently long. In order to establish a measurement method to determine the reliability or lifetime of rewritable MD media, it is necessary to discuss the issues from view points except degradation of recording layer.
Effect of Film Thickness on Ferroelectric Properties of Sol-Gel-Derived Pb(Ti, Al)O3 Thin Films
Authors: Iijima Takashi , Kudo Setuko , Norio Sanada Norio Sanada
Published: October 2002

Degradation of ferroelectric properties with decreasing film thickness is a common
problem of PbTiO3 type ferroelectric thin films. We suspected that this degradation was caused
mainly by oxygen vacancies that diffused from the film surface through the grain boundaries
during firing. Thus we have attempted to substitute Al3+ for Ti4+ in PbTiO3 using a sol-gel
method. In this study, the effect of the film thickness on the ferroelectric properties of
Pb(Ti0.9Al0.1)O3-
x

thin films ranging from thickness of 637 to 169 nm was investigated, and the
dielectric constant and leakage current were compared to those of PbTiO3. The ferroelectric
properties of Pb(Ti0.9Al0.1)O3-
x

thin films did not change much when the film thickness was
decreased, and good ferroelectric properties were maintained. The values of ε
r and tan
δ for
a 169-nm-thick Pb(Ti0.9Al0.1)O3-
x

film were 365 and 0.0127, and the values of P
r and E
c were 15 µ C/cm2 and 86 kV/cm, respectively.
Asymmetric Ferroelectricity and Anomalous Current Conduction in Heteroepitaxial BaTiO3 Thin Films
Authors: Abe Kazuhide , Komatsu Shuichi , Yanase Naoko , Kenya Sano Kenya Sano , Takashi Kawakubo Takashi Kawakubo
Published: October 2002

Asymmetric ferroelectricity and conduction of anomalous leakage current were observed in
heteroepitaxial BaTiO3 thin films grown by rf magnetron sputtering at 600° C on three different
electrode/substrate combinations: SrRuO3/SrTiO3, Pt/MgO and Nb doped SrTiO3. The voltage
shift of hysteresis loops of the capacitance was a linear function of the thickness of the BaTiO3
films and became as large as 10 V in the film with a thickness of 410 nm. The asymmetry did not
disappear even after a heat treatment carried out at 800° C in air. On the other hand, a steep
increase in the leakage current was observed in the heteroepitaxial films when a positive voltage
was applied. The origin of both the asymmetric hysteresis and the anomalous conduction is
discussed in terms of asymmetric crystal structure caused by misfit dislocations introduced in
heteroepitaxial growth.
Dielectric Properties of Electron-Cyclotron-Resonance-Sputtered (Ba, Sr)TiO3 Films
Authors: Ohfuji Shin-ichi , Manabu Itsumi Manabu Itsumi , Hideo Akiya Hideo Akiya
Published: October 2002

Structural and electrical properties of Ba0.55Sr0.45TiO3 thin films
are investigated. Electron-cyclotron-resonance sputtering was used to
deposit the 200-nm-thick films in Pt/Ba0.55Sr0.45TiO3/Pt/Ti/SiO2/Si
structures. A dielectric constant of 250 is obtained for the films
deposited at 450° C, and that of 350 after annealing at 650° C for 30 min
in O2 gas. Although in literature the Curie temperature of the ceramics
with this composition is -15° C, a broad peak extended across 0° C is
observed in the dielectric constant versus measurement temperature
relationship. This result coincides with an increase in the width of (200)
diffraction peak after the annealing, suggesting that some peak splitting
to (200) and (002) due to tetragonality may occur at room temperature.
The polarization versus electric field curves for the annealed films also
showed hysteresis before and after dc-bias stress tests without
correlation with an increase in leakage current. These experimental
results suggest that the hysteresis does not result only from instability
due to charge trapping. The tetragonality caused by tensile stress is
thought to be one of the origins for the hysteresis.
Recording and Readout of a Cholesteric Liquid Crystal Based Multilayer Disk
Authors: Schlichting Wolfgang , Faris Sadeg , Fan Bunsen , Haag John , Lu Zhijian , Kane Steven , Li Le , Milster Tom , Luo Hui
Published: October 2002

A novel approach to optical storage based on layering of cholesteric liquid crystal (CLC) media is being investigated. CLC media have been chosen due to their unique property of selective reflection, whereby a CLC film reflects light of a characteristic wavelength and polarization handedness with near-zero loss while transmitting all other light. This new technology has the potential of enabling terabyte storage on a single optical disk. A two-layer disk with 5 µm data marks was recorded and crosstalk-free readout was demonstrated by selecting the correct circular polarization state of a 514 nm laser.
Preparation and Dielectric Properties of the Multilayer Capacitor with (Ba, Sr)TiO3 Thin Layers by Metalorganic Chemical Vapor Deposition
Authors: Takeshima Yutaka , Shiratsuyu Kosuke , Hiroshi Takagi Hiroshi Takagi , Yukio Sakabe Yukio Sakabe
Published: October 2002

Barium strontium titanate ( (Ba, Sr)TiO3; BST) thin films were prepared on Pt-coated magnesium oxide single-crystal substrates (Pt(111)/MgO(100) and
Pt(100)/MgO(100)) at 650° C by metalorganic chemical vapor deposition (MOCVD). The
BST films with a perovskite single phase were obtained. Their room-temperature
dielectric constant was 400–590 measured at 100 mV and 1 kHz. The leakage current
density was below the order of 10-7 A/cm2 at 3 V, and the breakdown field was above
500 kV/cm. In addition, the multilayer capacitor with five layers of BST was prepared.
The room-temperature capacitance with an effective electrode area of 0.16 mm2 was
20 nF at 100 mV and 1 kHz. The leakage current was on the order of 10-8 A at 1V, and on
order of 10-5 A at 3 V.