bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Characterization of Thick GaN by Sublimation Method and Homoepitaxial Growth by Metalorganic Chemical Vapor Deposition
Authors: Satoshi Kurai Satoshi Kurai , Toshimitsu Abe Toshimitsu Abe , Yoshiki Naoi Yoshiki Naoi , Shiro Sakai Shiro Sakai
Published: October 2002

Thick GaN, 10-30 µm, was grown on sapphire substrate by a sublimation method for the first time. GaN was homoepitaxially grown on this thick layer by metalorganic chemical vapor deposition to obtain a high-quality layer. Stimulated emission from a photopumped homoepitaxial GaN grown on thick GaN prepared by the sublimation method at room temperature was demonstrated. The threshold of the stimulated emission was estimated to be 1.04 MW/cm2.
Multiple-Phonon Resonant Raman Scattering in CuGaS2
Authors: Susaki Masami , Yamamoto Nobuyuki , Prevot Bernard , Schwab Claude
Published: October 2002

Resonant enhancements of multiple-phonon Raman scattering in CuGaS2 excited by a wide range of laser energy are studied. At 8.6 K, the intensities of the multiple-phonon modes show a sharp resonance maximum at the scattered-photon energy just below that of the free exciton. Polarization characteristics of these modes have the same selection rule as the free exciton. The behavior is attributed to the intraband Fröhlich interaction for longitudinal E modes of polar phonons. The resonant scattering by this mechanism exhibits a temperature-dependent enhancement correlated with the thermal shift and broadening of the free exciton energy. On the other hand, the temperature dependence of the resonance is greatly decreased for the nonpolar A1 mode which has a large deformation potential.
Dependence of Electrical Properties on Work Functions of Metals Contacting to p-type ZnSe
Authors: Tadanaga Osamu , Koide Yasuo , Hashimoto Kazuya , Oku Takeo , Teraguchi Nobuaki , Tomomura Yoshitaka , Suzuki Akira , Masanori Murakami Masanori Murakami
Published: October 2002

In order to search a possibility to prepare Ohmic contacts to p-ZnSe by depositing a single metal element, the electrical properties and thermal stability were studied by a current–voltage (I–V) method for a variety of metals (In, Cd, Nb, W, Cu, Ag, Au, Ni, Pt, and Se) contacting to nitrogen-doped ZnSe layers grown by the molecular beam epitaxy technique. All the metals were deposited on the ZnSe substrates which were chemically cleaned prior to metal deposition in order to remove the native oxide layers. The turn-on voltages (V
T) and differential resistances were determined by the I–V curves for these contacts before and after annealing. The contacts were divided into three groups by the V
T values: (1) In, Cd, Nb, and W contacts with V
T∼16 V, (2) Au and Pt contacts with V
T larger than 9 V, and (3) Cu, Ag, Ni, and Se contacts with V
T∼3 V. The lowest V
T value of 2 V was achieved by the Cu contact. However, this Cu contact deteriorated during storage at ambient temperature. The V
T value of ∼3 V was routinely obtained for the Ag and Ni contacts. The Ni contact is the most promising materials for the device application among the contact materials studied in the present experiment, although the linear relation in the I–V behavior was not obtained. The electrical properties of these contacts during annealing at temperatures below 300° C were studied, and no significant reduction of the V
T value was obtained in the present contacts. The present study suggests that the deposition of a single metal element to p-ZnSe with doping level of 1×1018 cm-3 would not provide low resistance Ohmic contact.
The Influence of Surface Treatment on the Quality of Pd/Au Contacts to p-type ZnSe
Authors: Rennie John , Onomura Masaaki , Nishikawa Yukie , Saito Shinji , Masayuki Ishikawa Masayuki Ishikawa , Gen-ichi Hatakoshi Gen-ichi Hatakoshi
Published: October 2002

The influence of surface treatment prior to the deposition of Pd/Au metallic contacts to p-type ZnSe is discussed. The methods studied being a sulphur based treatment and a CuSe

x

contact treatment. The results show that both of these form better quality contacts, with lower applied voltages for set current densities, in comparison to an untreated sample. Although, the barrier height increased for the sulphur treated sample, by 0.11 eV to 0.69 eV, the active contact area was increased by an order of magnitude. The CuSe

x

treatment is shown to reduce the Schottky barrier height to 0.50 eV but the active contact area was severely reduced in this case.
Ge:Ga Far-Infrared Photoconductors for Space Applications
Authors: Hiromoto Norihisa , Fujiwara Mikio , Shibai Hiroshi , Okuda Haruyuki
Published: October 2002

We have fabricated 0.5×0.5×0.5-mm3 Ge:Ga photoconductors for the [OI] 63-µm line channel of the Far-Infrared Line Mapper (FILM) on the Infrared Telescope in Space (IRTS). These photoconductors have a high responsivity of 10–20 A/W (ηG of 0.13–0.25) and a good noise equivalent power (N
E
P) of about 2×10-17 W/√ Hz for step change in photon influx at a bias field of 1.8 V/cm and operational temperature of 2 K under a low background photon influx of 1.1 to 2.2×106 photons/s. The photoconductors show slow transient response with a time constant of about 10 s at low temperature under low background conditions, but they have almost no hook response. The responsivity to chopped light decreases as the chopping frequency increases from 7.5 to 210 Hz. We infer that this is due to what we call the “moderately fast response”. Two time constants, τ a∼10 s and τ m∼0.23 s, derived from the two-region model of a Ge:Ga photoconductor, correspond to the slow transient response and the “moderately fast response”, respectively.
Solar Cells Based on CuInS2 Thin Films through Sulfurization of Precursors Prepared by Reactive Sputtering with H 2S Gas
Authors: Takayuki Watanabe Takayuki Watanabe , Masahiro Matsui Masahiro Matsui
Published: October 2002

CuInS2 films were prepared using a two-stage process in which Cu–In–S precursors were sputtered in H2S/Ar with metal targets (Cu and In) and then annealed in H2S atmosphere. Control of S content in the precursor is essential for fabricating high-quality CuInS2 films and achieving high-efficiency solar cells. When S/(Cu+In) ratio in the precursor was about 0.3, CuInS2 films with good crystallinity and smooth surface were obtained, and consequently a CuInS2 solar cell with an efficiency of 6.3% has been achieved without KCN treatment.
Determination of Built-In Electric Field Strength in InP/n+-InP Structures Using Photoellipsometry
Authors: Saitoh Tadashi , Nakamura Kensaku , Hasegawa Hideki , Yi-Ming Xiong Yi-Ming Xiong
Published: October 2002

Photoellipsometry, a nondestructive and contactless optical method, was applied to InP/ n+-InP structures. Three InP/ n+-InP samples were studied, each containing an undoped InP layer of thickness L (L=40, 100, and 150 nm, respectively) epitaxially grown on top of a heavily doped n-InP substrate. The measured spectra were analyzed using the Franz-Keldysh theory, in which the effects of broadening and contributions from the heavy and light holes were included. Our main objective was to determine the built-in electric field strength in the top layer of each given sample. The results of our analysis not only verify that a uniform built-in field was present in the top layer but also suggest that the surface Fermi level was pinned at a fixed position for each sample studied. In addition, a small downward shift of the band-gap energy was observed in the three InP samples. We believe that this type of shift is due to the field-induced effect on the sample materials.
Crystalline Alignment of Tl2Ba2CaCu2Oδ Thin Films Annealed in a Sealed Capsule
Authors: Nemoto Masaaki , Yoshikawa Shuichi , Yuasa Ryokan , Yoshida Isao , Yorinobu Yoshisato Yorinobu Yoshisato , Shigeru Maekawa Shigeru Maekawa
Published: October 2002

C-axis oriented Tl2Ba2CaCu2Oδ thin films have been prepared on MgO with good reproducibility by annealing them in an alumina capsule sealed with a gold gasket. The crystalline alignment of the thin films depends on the annealing temperature, the Tl content of the pellets used for Tl compensation, and the film thickness. The electric properties of the thin films depend on their alignment. The critical temperature T
c of c-axis oriented thin films is above 90 K, whereas that of randomly oriented thin films is below 85 K. The highest T
c is 108 K and the highest critical current density J
c is 4.5×105 A/cm2.
Pressure Effect of Fe–29 wt% Ni Alloy Ultrafine Particles
Authors: Yunhong Chen , Qingliu Chen , Fang Fang , Huaixian Lu , Youwei Du
Published: October 2002

Fe–29 wt% Ni alloy ultrafine particles with various average sizes are prepared by the evaporation-condensation method. They are compressed into disks or small rings under different pressures. As the pressure increases, martensitic volume fraction and specific saturation magnetization σ s increase markedly, while coercivity H
c exhibits a linear decrease. The complex permeability varies with the pressure. Its high-frequency characteristic is far superior to that of bulk. The effect of pressure depends on the average size *BAR*d*BAR*.
Analysis of Mark Formation Mode in Exchange-Coupled Double-Layer Magneto-Optical Disk
Authors: Kubogata Masayuki , Hidaka Yasuharu , Hasegawa Motoko , Ogawa Masatsugu , Masafumi Nakada Masafumi Nakada , Mitsuya Okada Mitsuya Okada
Published: October 2002

The contribution of Co concentration in the writing layer to the read/write characteristics of our novel magneto-optical disk structure with an exchange-coupled double-layer (ECDL) is investigated. Raising the Co concentration of the TbFeCo writing layer increases the Curie temperature from 170° C to 210° C and changes the recorded mark formation process from the regular magnetization copying mode to the inverse magnetization copying mode. Computer simulation based on the Landau-Lifshitz-Gilbert equation confirms that the GdFeCo readout layer does not contribute to the mark formation process near the Curie temperature (∼210° C) for an ECDL disk comprising the writing layer with higher Co concentration. This is because the effective magnetic anisotropy field (H
k-4πM
s) for the GdFeCo readout layer at around 210° C becomes negative and the easy axis lies in-plane.
High-Performance Strain-Compensated Multiple Quantum Well Planar Buried Heterostructure Laser Diodes with Low Leakage Current
Authors: Cho Ho Sung , Jang Dong Hoon , Lee Jung Kee , Park Kyung Hyun , Kim Jeong Soo , Lee Seung Won , Hong Man Kim Hong Man Kim , Hyung-Moo Park Hyung-Moo Park
Published: October 2002

The dependence of leakage current in a planar buried heterostructure laser diode (PBH-LD) on the operating temperature was analyzed by taking the effects of the connection width between a p-InP clad layer and a p-InP blocking layer into account. A two-step etching process comprising nonselective mesa etching followed by InP selective etching is proposed for obtaining a narrow connection width and high controllability of an active layer width. The performance was compared for LDs fabricated using the two-step etching process and those fabricated using conventional nonselective etching process. The average threshold current and the slope efficiency of the 1.3 µ m strain-compensated multiple quamtum well (MQW) PBH-LD fabricated using the two-step etching process were 5.6 mA and 0.27 mW/mA, respectively, for a cavity length of 400 µ m. However, using the nonselective etching process, the average threshold current was 14.5 mA and the slope efficiency was 0.22 mW/mA, given the same cavity length. A higher differential gain and characteristic temperature were also obtained due to the lower leakage currents and strain-compensated multiple quantum well active layers.
1/f Fluctuations in LiCl Solution
Authors: Tohei Takehisa , Nakagawa Keisuke , Takada Koji , Musha Toshimitsu
Published: October 2002

Intensity fluctuations of scattered light of an Ar+ laser incident on a LiCl solution are measured. Power spectral density of the ratio of outputs of two photomultipliers shows a 1/f-like dependence in the lower-frequency region. Dissolved LiCl raises the level of 1/f fluctuations from that for pure water. Above the molar ratio 0.2 of Li ions to water molecules the fluctuation rapidly decreases. The 1/f level dependence on the concentration of Li ions is semiquantitatively explained by taking the cluster structure into account.
Quantitative Deconvolution of Photomodulated Thermoreflectance Signals from Si and Ge Semiconducting Samples
Authors: Andreas Mandelis Andreas Mandelis , Robert E. Wagner Robert E. Wagner
Published: October 2002

A variety of photomodulated thermoreflectance (PMTR) data have been obtained for two germanium wafer samples (one crystalline and the other ion-implanted and unannealed), and three silicon wafer samples (one crystalline, unimplanted; the other implanted and flash-annealed; and the third an amorphous thin layer). Physically different mechanisms contributing to the PMTR signals have been formulated theoretically for these materials. For the crystalline and implanted-annealed samples it was found that the PMTR signal has two main components, one due to temperature modulation (thermal wave); the other due to the free-carrier density modulation (the Drude effect). For the ion-implanted-unannealed and amorphous materials two components were found to be dominant: one due to the thermal wave; the other due to the band-filling of localized gap states. The two component mechanisms were validated in a quantitative manner by curve-fitting experimental PMTR frequency-response data, while taking into account the photocurrent (PC) responses of the samples. As a result, unambiguous deconvolution of the electron-hole plasma or trapped-carrier contribution and the thermal-wave component to the PMTR signal were obtained throughout the frequency range 1 kHz–1.6 MHz.
Atmospheric Pressure Dependence of Rotation Speeds of a Motor Composed of Resonating Crystalline Quartz
Authors: Takashi Aoki Takashi Aoki
Published: October 2002

Changes in rotation speeds of quartz rectangular parallelepipeds cut perpendicular to the X, Y and Z axes were determined as a function of atmospheric pressure from 1 to 760 Torr. The rotation speed increased with decreasing pressure down to a certain pressure which initiated a discharge, then gradually decreased, and finally became zero at lower pressures. This rotation increase is ascribable to a resonance current increase caused by a decrease in friction between air molecules and a vibrating quartz crystal. The stopping of the rotation seems to be ascribable to a decrease in the resonance current resulting from the discharge.
Growth and Characterization of Gadolinium Vanadate GdVO4 Single Crystals for Laser Applications
Authors: Shimamura Kiyoshi , Uda Satoshi , Kochurikhin Vladimir V. , Tetsuo Taniuchi Tetsuo Taniuchi , Tsuguo Fukuda Tsuguo Fukuda
Published: October 2002

We have successfully grown Nd3+-doped gadolinium vanadate ( Nd:GdVO4) single crystals by a modified Czochralski method in which a high temperature gradient was maintained at the interface during growth. Step faceting occurred during crystal growth and the cause of the faceting is discussed in relation to the growth conditions. Laser diode (LD) pumped laser oscillations were demonstrated. The Nd:GdVO4 single crystal showed superior lasing properties to Nd:YVO4 and Nd:YAG single crystals.
Materialistic Difference in Macroscopic Friction Coefficients of Sputtered Metal Oxide Thin Films Deposited on Glass
Authors: Suzuki Susumu , Hisashi Ohsaki Hisashi Ohsaki , Eiichi Ando Eiichi Ando
Published: October 2002

The origin of the difference in macroscopic friction coefficients of various metal oxide thin films sputtered on glass substrates was investigated from viewpoints of surface roughness and adhesion. Surface roughness and adhesive force were evaluated by atomic force microscopy (AFM). Thin films of the ZrO2–SiO2 system showed a minimum friction coefficient at 50 mol% SiO2–ZrO2. This could be explained by an increase in the number of smooth areas on the film surface. ZnO, Al2O3, SnO2, TiO2 and Ta2O5 thin films showed friction coefficients which varied from material to material. Oxide films with weaker metal-oxygen (M-O) bond were found to become highly frictive. This could be understood by the difference in the number of bonds formed between the film surface and the opponent material.
Morphology and Structure of Aluminum Nitride Thin Films on Glass Substrates
Authors: Cheng Chien-Chuan , Chen Ying-Chung , Horng-Jwo Wang Horng-Jwo Wang , Wen-Rong Chen Wen-Rong Chen
Published: October 2002

Aluminum nitride (AlN) thin films are deposited on Corning 7059 glass at low substrate temperature by reactive RF magnetron sputtering. The structural and morphological characterizations are found to be sensitive to deposition conditions such as sputtering pressure, RF power, substrate temperature and N2 concentration. A highly oriented AlN (002) plane parallel to the substrate surface is identified by X-ray diffraction (XRD) measurement and a dense pebble-like surface texture is observed by scanning electron microscopy (SEM). The cross-sectional SEM micrograph shows that well-aligned columnar structures with preferred orientation along the c-axis exist in the AlN thin film. However, a selected-area diffraction (SAD) pattern shows that some other planes exist in the deposited film, though only a hexagonal AlN (002) plane is obtained by XRD.
Neutral-Beam-Assisted Etching System for Low-Damage SiO2 Etching of 8-Inch Wafers
Authors: Yokogawa Ken'etsu , Yunogami Takasi , Mizutani Tatsumi
Published: October 2002

A novel neutral-beam-assisted etching apparatus has been developed for large-diameter etching. Neutral radicals from halide molecules and energetic neutral beams are irradiated on the specimen surface. The etching reaction of these neutral radicals is enhanced by neutral-beam bombardment. The neutral-beam source and the neutral-radical source are produced from a magneto-microwave plasma source. These plasmas are arranged in tandem in front of the specimen. This arrangement enables highly uniform supply of neutral radicals over a large area. This etching system was applied to SiO2 etching using Ar and CHF3 mixed gas. The SiO2 etch rate was 76 nm/min, and the etch rate uniformity was within ±7.4% for an 8-inch-diameter specimen and ±3.4% for a 6-inch-diameter specimen. In addition, highly anisotropic etching shapes of submicron patterns were obtained.
Increase of Lifetime of Thallium Zeolite Ion Source for Single-Ended Accelerator
Authors: Nishizawa Akimitsu , Hamada Yasuji , Yoshiaki Kawasumi Yoshiaki Kawasumi , Harukazu Iguchi Harukazu Iguchi
Published: October 2002

By multiple sintering, we have significantly increased the lifetime of the thallium (Tl) zeolite ion source used in single-ended electrostatic accelerators. The obtained lifetime of a small ion source (6.4 mm in diameter and 10 mm long) was about 4400 µ Ah (70 µ Ah/mm3 for Tl zeolite).
Preparation of a Polyacetylene Derivative Monolayer for Molecular Wire
Authors: Soga Mamoru , Ogawa Tohru Nakagawa
Published: October 2002

A polyacetylene derivative monolayer was investigated for application as a molecular wire. First, an acetylene derivative monolayer was prepared by chemically adsorbing (self-assembling) 19-trimethylsilyl-18-nonadecynyl- trichlorosilane on a silica substrate. Then, the monolayer was polymerized in the presence of Ziegler-Natta catalyst of triethyl aluminum and tetra-n-butoxy titanium. The polyacetylene derivative monolayer thus synthesized was covalently bonded to the silica substrate and showed conductivity as high as 1×10-4 S/cm after being doped with iodine. The method of preparing a conductive polymer monolayer by combination of chemical adsorption and catalytic polymerization leads to a molecular wire which is one of the key technologies for molecular devices.
Influence of Optical Parameters of Synchrotron Radiation Lithography Beamline on Pattern Replication
Authors: Shimano Hiroki , Ozaki Yoshihiko , Kenji Marumoto Kenji Marumoto
Published: October 2002

The influence of the angular divergence of X-rays incident on an X-ray mask and the exposure spectrum, which are the optical parameters determined by the geometric and band-pass properties of beamline optics and the synchrotron radiation (SR) spectrum, on resist pattern replication on various substrates was investigated. Using a compact storage ring as the SR source, we confirmed that there is no problem in 0.15-µm-feature pattern replication on Si substrate, regardless of the type of beamline optics. However, we found that an undercut or undeveloped portion inevitably occurs on a substrate which is covered with high atomic number material film, but this overexposure of resist can be reduced in a beamline with a broad band exposure spectrum.
Frequency Shift of X-Band Free Electron Laser
Authors: Toshiyuki Ozaki Toshiyuki Ozaki
Published: October 2002

A frequency shift occurring at the rise part of the pulsed output was observed in a free electron laser amplifier. This is explained as being due to a change in the phase movement as the power increases.
Resistivity Correction Factor for the Four-Point Probe Method on Cylindrical Materials
Authors: Masato Yamashita Masato Yamashita , Toshifumi Nishii Toshifumi Nishii , Hiroshi Kurihara Hiroshi Kurihara
Published: October 2002

The correction factor F which is necessary to obtain resistivity by means of the four-point probe array located on the convex surface of a cylindrical material is investigated. Electric potential in a finite-length cylindrical material having a current source and a current sink is derived by solving Poisson's equation under various boundary conditions. The correction factor F is obtained using the potential. The resistance measurements are performed for isotropic graphite rods with different radius or different length. It is found from the experimental results that the correction factor F revises data accurately and yields a reasonable resistivity.
The Stability of the Rotation of a Magnetized Gyro with a Fixed Point
Authors: Zheng-Ming Ge Zheng-Ming Ge , Hsien-Keng Chen Hsien-Keng Chen
Published: October 2002

In conventional studies about the gyro motion the gyroscopic forces which are produced by the Lorentz action of the magnetic field on the electrical charges moving in space have not been considered. Euler gyro, Lagrange gyro and Kovalveskaya gyro are three representative gyros. In this paper, the stability and instability conditions of the rotation of the three representative gyros under the action of the Lorentz forces both in a uniform force field and in a central force field are obtained by using Liapunov's direct method.
Effects of Stimulus Waveform on Magnetic Nerve Stimulation
Authors: Wada Shigeru , Kubota Hiroshi , Maita Soichiro , Yamamoto Isao , Yamaguchi Masuhiro , Andoh Tomio , Kawakami Tadashi , Okumura Fukuichiro , Takenaka Toshifumi
Published: October 2002

The dependence of nerve excitability on the waveform of a magnetic stimulus was experimentally and analytically studied. In the experiment frog sciatic nerves were stimulated by pulsed magnetic fields which had damped sinusoidal waveforms with different numbers of cycles. In the analysis a neuroelectric model of the myelinated nerve fiber was assumed to be stimulated by pulsed magnetic fields with various waveforms which were produced in an LCR series circuit. Both the experiment and the analysis show that the excitation threshold of the nerve depends strongly on the number of oscillating cycles. The magnetic stimulus with one-cycle oscillation is useful to excite the nerve in practice.
Al-Induced Crystallization of an Amorphous Si Thin Film in a Polycrystalline Al/Native SiO2/Amorphous Si Structure
Authors: Jin Hyeok Kim Jin Hyeok Kim , Jeong Yong Lee Jeong Yong Lee
Published: October 2002

Al-induced crystallization of an amorphous Si (a-Si) thin film in a polycrystalline Al/native SiO2/a-Si structure has been investigated on an atomic level using cross-sectional high-resolution transmission electron microscopy. A 7-nm polycrystalline Al layer was thermally deposited onto a 50-nm a-Si thin film, deposited by low-pressure chemical vapor deposition and covered with a 2.2-nm layer of native SiO2. The a-Si thin film in this structure was partially crystallized at 250°Cand completely crystallized at 500°C after 30 min. Lattice fringes of Si(111) were observed in the original Al layer and interfacial native SiO2 layer after the annealing process. From the above results, it was concluded that Al-induced crystallization of the a-Si thin film occurred by interdiffusion of Al and Si atoms through the native oxide layer even though the 2.2-nm native SiO2 layer was not removed completely at the Al/a-Si interface. A possible model, that can be used to explain the Al-induced crystallization phenomena by taking into account the changes that take place within or near the native SiO2 layer during the annealing process, was proposed.
Study of Zinc-Delta-Doped Strained Quantum Well InGaAs/GaAs p-Channel Heterostructure Field-Effect Transistors
Authors: Hsu Rong Tay , Hsu Wei Chou , Wang Jiann Shiun , Kao Ming Jer , Yu Huei Wu Yu Huei Wu , Jan Shing Su Jan Shing Su
Published: October 2002

Zinc-delta-doped strained quantum well InGaAs/GaAs p-channel heterostructure field-effect transistor (HFET) grown by low-pressure metalorganic chemical vapor deposition has been realized. In terms of using the zinc-delta-doping technique by interrupting the growth, high concentration is carried out. The influence of spacer layer thickness on two-dimensional hole gas concentration and hole mobility is also studied. The delta-doped p-type strained InGaAs/GaAs HFET with 8 nm spacer layer thickness exhibits extrinsic transconductances of 15 mS/mm at 300 K and 24 mS/mm at 77 K. Secondary-ion mass spectrometry (SIMS) is carried out to confirm the film quality, zinc diffusion profile and sharpness of the proposed structures. Due to the smaller mobility difference in InGaAs/GaAs than in using AlGaAs barriers, the gate voltage swing in the p-channel delta-doped InGaAs/GaAs HFET exhibits a value about 1.7 V. Consequently, a wider linear amplifier application is expected in the present device.
Theoretical Consideration of a New Nanometer Transistor Using Metal/Insulator Tunnel-Junction
Authors: Kouji Fujimaru Kouji Fujimaru , Hideki Matsumura Hideki Matsumura
Published: October 2002

A new metal/insulator tunnel transistor (MITT) is proposed as a nanometer switching device. In the transistor, metal/insulator/metal tunnel currents are controlled by a gate electrode placed above the insulator, as in a metal/oxide/semi-conductor field-effect transistor. The characteristics of this MITT are theoretically studied using a computer simulation. It is confirmed that this new device operates in the same way as conventional semiconductor devices. The currents flowing through an insulator between two metals can be controlled in the ranges from 10-16 A to 10-5 A at 77 K and from 10-11 A to 10-6 A at room temperature, for a variation in gate voltage of 2 V, when the channel length, i.e. the thickness of the sandwiched insulator, is between 15 nm and 20 nm and the relative dielectric constant of the channel is assumed 5. The switching speed is estimated to be of the order of picoseconds (ps) for operation at 77 K and about 100 ps for operation at room temperature.
Post-Stress Interface-Trap Generation in P-Channel Metal-Oxide-Semicondutor Field-Effect-Transistors after Hot-Electron Stress
Authors: Ang Man-Siu Tse
Published: October 2002

Post-stress electron discharging and interface trap generation in p-channel Metal Oxide Semiconductor Field-Effect-Transistors (MOSFETs) after drain avalanche hot-electron stress (DAHE) are investigated. It was found that the effect of electron discharging must be taken into account for the interpretation of charge-pumping characteristics after DAHE stress. To clarify the physical mechanism underlying post-stress interface trap generation, the effect of hot-electron injection and post-stress gate bias are studied. electron discharging and post-stress interface trap generation are strongly dependent on the gate bias polarity and magnitude. A physical model is proposed which is based on mechanisms involving carrier injection, recombination and the breaking of Si–H bonds at the Si/SiO2 interface.
Excellent Au/Ge/Pd Ohmic Contacts to n-type GaAs Using Mo/Ti as the Diffusion Barrier
Authors: Chai Chun-Yi , Huang Jung-A , Lai Yong-Lin , Wu Janne-Wha , Chang Chun-Yen , Chan Yi-Jen , Huang-Chung Cheng Huang-Chung Cheng
Published: October 2002

Au/Ge/Pd metallization system using Mo/Ti as the diffusion barrier between the Au overlayer and the Ge/Pd underlayer has been performed for the first time to achieve excellent ohmic contacts to n+-GaAs with the Si-doping concentration of about 2×1018 cm-3. The minimum specific contact resistivity as low as 1.2×10-7 Ω·cm2 can be obtained after the rapid thermal annealing at 325°C for 60 s, which is much lower than those of the conventional Au/Ge/Pd metallization systems. Furthermore, the available annealing temperature range for such low specific contact resistivities is also significantly extended from 325°C to 400°C. The improvement is attributed to the effective retardation of As-outdiffusion by the Mo/Ti barrier.
Transport Equations for Homogeneous and Variable-Composition Semiconductor Devices at Low Temperatures
Authors: Hideyuki Iwata Hideyuki Iwata , Takashi Ohzone Takashi Ohzone
Published: October 2002

Transport equations for use in the analysis of homogeneous and variable composition semiconductor devices at low temperatures are reviewed. In these equations, Fermi-Dirac statistics and position-dependent band structure are taken into account. The general transport models developed previously by other workers are recast into a simple form so as to be convenient for use in numerical device simulation of semiconductors at low temperatures.
Investigation of YBCO Single Crystals Grown under 1 atm Oxygen Pressure and Air Atmosphere
Authors: Yao Xin , Mizukoshi Takanobu , Egami Masahiro , Zama Hideaki , Masaru Nakamura Masaru Nakamura , Yuh Shiohara Yuh Shiohara
Published: October 2002

The effects of oxygen partial pressure on Y123 single-crystal growth, morphology and properties were investigated. YBCO (Y123) single crystals were fabricated using the crystal pulling method under 1 atm oxygen pressure. Compared with crystals fabricated under air atmosphere, it was found that this high oxygen partial pressure played a significant role in increasing growth rate, which was 1.5–2.5 times higher than that of crystals fabricated under air atmosphere. A large crystal with size of 19.8×19.5 mm2 in the a–b plane and 16.5 mm in the c-axis direction was successfully obtained using a crucible 50 mm in diameter. In the YBCO system, critical temperature T
c was not sensitive to the growth atmosphere.
Magnetic and Structural Studies of Ni(OH)2 Monolayered Nanoclusters
Authors: Kimishima Yuko Ichiyanagi
Published: October 2002

Chemical, magnetic and structural analysis have been carried out for the precipitates obtained by mixing NiCl2·6H2O and Na2SiO3· mH2O (m=0 or 9) aqueous solutions. The formation of Ni(OH)2 monolayered clusters with diameter of 2–3 nm was confirmed in the above precipitates. The exchange interaction in these Ni(OH)2 monolayered nanoclusters was also discussed on the basis of molecular field approximation.
Polarization-Independent Tunable Liquid-Crystal Fabry-Perot Interferometer Filters
Authors: Tsuda Hiroyuki , Yoshizawa Tetsuo , Hirabayashi Katsuhiko , Kurokawa Takashi
Published: October 2002

Two methods are studied for reducing the polarization dependence of a tunable liquid-crystal Fabry-Perot interferometer filter (LC-FPI). One uses a twisted nematic (TN) liquid-crystal in a Fabry-Perot cavity. We have theoretically explained that the twist angle should be π/2+mπ (m=0, 1, 2,···) to eliminate the polarization dependency. An approximate 5 nm polarization-independent tuning with a π/2 TN LC-FPI cell was achieved. The other uses a polarization diversity configuration. We have fabricated a polarization-independent LC-FPI filter module with a Faraday rotator using polarization diversity double-pass configuration. This filter module has a 3 dB bandwidth of less than 0.5 nm, a 15 dB bandwidth of 1.7 nm, and a polarization-dependent loss (PDL) of 0.8 dB. The filter module was utilized in 10 Gbit/s transmission experiments to confirm its feasibility.
Effect of CO2 Addition on Diamond Growth by DC Arc Plasma Jet Chemical Vapour Deposition
Authors: Akira Higa Akira Higa , Akimitsu Hatta Akimitsu Hatta , Toshimichi Ito Toshimichi Ito , Minoru Toguchi Minoru Toguchi , Akio Hiraki Akio Hiraki
Published: October 2002

The effect of adding carbon dioxide ( CO2) to the reactant gases was studied in a dc arc plasma jet chemical vapour deposition (CVD) for the synthesis of diamond films. The fabricated films were characterized by Raman scattering spectroscopy and scanning electron microscopy. Without CO2, Raman spectra of these films display only graphitic peaks. As CO2 is added, faceted diamond crystal is observed in micrographs from scanning electron microscopy and a sharp diamond peak in the Raman spectrum appears. At a CO2/ CH4 ratio of 2.0, diamond films exhibit a pure diamond Raman peak at 1333 cm-1 with small nondiamond carbon peaks. In addition, plasma diagnosis was performed using optical emission spectroscopy.
Theoretical Comparison of (111) and (100) GaAs/AlGaAs p-Type Quantum Well Infrared Photodetectors
Authors: Taehee Cho Taehee Cho , Hyungsuk Kim Hyungsuk Kim , Youngse Kwon Youngse Kwon , Songcheol Hong Songcheol Hong
Published: October 2002

Intersubband absorptions in p-type GaAs/Al0.3Ga0.7As quantum wells (QWs) grown on (111) substrates are theoretically investigated using the multiband effective mass model. Because of the stronger band mixing of (100) QW, the peak absorption coefficient of the (100) QW is about twice as large as that of (111) QW. Nevertheless, the detectivity of (111) Quantum Well Infrared Photodetector (QWIP) is found to be ∼30% larger than that of (100) QWIP because of the smaller dark current of (111) QWIP. This is due to the smaller heavy-hole confinement energy in (111) QW.
A Simple Graphical Method for Evaluating Dipole Relaxation Time in Dielectric
Authors: Hideharu Matsuura Hideharu Matsuura
Published: October 2002

A simple graphical method for evaluating the dipole relaxation times (τ) in a dielectric is proposed. From isothermal measurements of the transient discharge current due to dipole relaxation, τ can be obtained graphically by means of discharge current transient spectroscopy (DCTS). In other words, the time at which the DCTS signal is a maximum corresponds to τ. Since τ and the steady-state polarization (P
s) in dielectrics at electric field (F
p) and temperature (T) can be obtained using DCTS, the dependencies of τ and P
s on F
p or T can be investigated in detail.
Nearly Homeotropically Aligned Four-Domain Liquid Crystal Display with Wide Viewing Angle
Authors: Vithana Hemasiri , Johnson David , Bos Philip , Herke Richard , Y. K. Fung Y. K. Fung , S. Jamal S. Jamal
Published: October 2002

A new type of nearly homeotropically aligned four-domain liquid crystal display has been developed using nematic liquid crystals with negative dielectric anisotropy. In this display a pixel is divided into four domains which have different and optically compensating molecular alignment properties. This molecular arrangement gives much improved electro optic characteristics over the conventional mono-domain liquid crystal displays and there are no disclinations between the domains. We have found that the director configurations in these domains produces something closer to an electrically controlled birefringence mode than a twisted nematic mode, hence the effective optical retardation is lower at the brightest state. Therefore, this display gives a much wider viewing angle than other types of multi-domain liquid crystal displays.
Evaluation of Low-Temperature Specific Heats and Thermal Conductivities of Er–Ag Alloys as Regenerator Materials
Authors: Biwa Tetsushi , Yagi Wataru , Uichiro Mizutani Uichiro Mizutani
Published: October 2002

The low-temperature specific heat for a series of Er

x

Ag100-
x

(x=40, 50, 60 and 70) alloys has been measured over the temperature range 1.6–30 K to evaluate their applicability as regenerator materials. In the temperature range 10–20 K, the volumetric specific heat for the x=50–70 samples exceeds that for Er3Ni, which is currently known as the most efficient regenerator material. The x=40 sample is superior to Er3Ni below 6 K. In addition, we found that the thermal conductivity for the present Er–Ag alloys is 5–10 times that for Er3Ni below 25 K. We conclude that the present Er–Ag alloys are suitable as regenerator materials, particularly if a composition-gradient composite regenerator material, in which the Er concentration varies from 70 to 40 along the direction of the gas flow, is fabricated.
A Modeling of Smoothing of Nonuniform Pressure in Laser Driven Ablative Plasmas
Authors: Yasushi Shimuta Yasushi Shimuta , Katunobu Nishihara Katunobu Nishihara
Published: October 2002

A theoretical model that studies smoothing of non-uniform ablation pressure is presented. The “cloudy day” model that is widely used to estimate the smoothing considers only thermal waves in homogeneous plasmas. However, sound waves caused by temperature perturbation, and steep ablation structure are considered in the present model. The work of [Manheimer et al..: Phys. Fluids 25 (1982) 1644] attempted to include these. However, we newly 1) consider an ablation structure with a finite density ratio between sonic point and ablation surface; 2) solve eigenvalue problem to initialize the variables consistently with fluid equations in the shock compression region; 3) impose different boundary condition at the sonic point; and 4) consider higher mode (k

y

x
0≥30). A nonlinear relation between the perturbed ablation pressure ratio between sonic point and ablation surface, and transverse wave number of perturbation k

y

x
0 is shown. As k

y

x
0 becomes larger, the smoothing becomes more efficient.
Plasma Characteristics of a Large RF-Driven Negative Hydrogen Ion Source
Authors: Takanashi Toshihiko , Takeiri Yasuhiko , Kaneko Osamu , Oka Yoshihide , Tsumori Katsuyoshi , Tsutomu Kuroda Tsutomu Kuroda
Published: October 2002

A large rf-driven negative hydrogen ion source has been developed for a neutral beam injection (NBI) system in future experimental fusion devices. Dimensions of the rf plasma generator are 30×30×20 cm3. An induction coil antenna is fully immersed into the plasma generator. The rf-driven plasma with an electron density of 1.5×1012 cm-3 was generated at 28 kW rf power at a frequency of 2 MHz. The electron temperature in the extraction region decreases as the line-integrated magnetic filter field strength increases. An electron temperature in the extraction region of 1 eV, which is suitable for generating negative ions, was obtained at a line-integrated filter field strength of 1030 G cm. Negative hydrogen ions are extracted from a single aperture of 13 mm in diameter in a pure-volume operation. An extracted negative ion current of 5.5 mA was obtained at 13.1 mTorr gas pressure and 15 kW rf power. This negativeion current corresponds to a power efficiency of 5.0 ( mA/cm2)/( W/cm3), which is superior to that in filament-arc negative ion sources.
Influence of Pattern Displacement Error Caused by Film Deposition on Overlay Accuracy in LSI Fabrication
Authors: Toshiyuki Horiuchi Toshiyuki Horiuchi , Kimiyoshi Deguchi Kimiyoshi Deguchi
Published: October 2002

Overlay accuracy is influenced by wafer distortion that occurs during the LSI fabrication process. The effect of film deposition can be especially harmful when fabricating highly miniaturized devices. For this reason, we have investigated pattern displacement error caused by film deposition. The error was measured using a laser interferometric measuring system, and it was collated with the calculation results by the theory on the strength of materials. It was clarified that pattern displacement error arose even if bends in the wafer were corrected by vacuum chucking. The displacement error is proportional to the product of film stress and thickness. Accordingly, the film stress should be kept as low as possible. However, it is quite difficult to achieve large reductions in film stress for all materials in the LSI process. Therefore, countermeasures such as magnification control will be needed hereafter.
Experimental Evaluation of Phase Contrast Lithography
Authors: Fujisawa Tadahito , Satoshi Tanaka Satoshi Tanaka , Soichi Inoue Soichi Inoue
Published: October 2002

Phase contrast lithography (PCL) using an annular-phase-only filter on a pupil plane of a projection optics was evaluated experimentally for lines and spaces and hole patterns. A g-line exposure tool was fabricated so that a spatial frequency filter can be inserted in the pupil of the projection optics for a feasibility study. Using a common annular-phase-only filter, depth of focus (DOF) was 40% and 14% better than that without the filter for 0.6 µ m lines and spaces and 0.6 µ m hole patterns, respectively. In addition, it was confirmed that combination of PCL with low contrast imaging process is more effective in DOF enhancement.
Phonon Number Fluctuations in One-Dimensional Fermi-Pasta-Ulam Lattices
Authors: Hisanori Kawamura Hisanori Kawamura , Nobuko Fuchikami Nobuko Fuchikami , Donghak Choi Donghak Choi , Shunya Ishioka Shunya Ishioka
Published: October 2002

We study the long-term behavior of one-dimensional Fermi-Pasta-Ulam lattices by varying the system size and the degree of nonlinearity. The power spectral density of the lowest mode energy obeys the power law P(f)∝1/f
α over a wide range of frequencies: f
S\lesssimf\lesssimf
1, where f
1 is the lowest mode frequency. In the low frequency region f\lesssimf
S, white spectra are observed. The shoulder frequency f
S first increases and then decreases as the system size increases, which can be qualitatively explained in terms of two competing factors. If the system is not very small, the spectrum is Lorentzian at low frequencies, i.e., the spectral exponent α is closer to 2 than 1.
Phase Transition of Contact-Electrified Negative Charges on a Thin Silicon Oxide in Air
Authors: Fukano Yoshinobu , Sugawara Yasuhiro , Uchihashi Takayuki , Okusako Takahiro , Morita Seizo , Yamanishi Yoshiki , Oasa Takahiko
Published: October 2002

We investigated the dense contact-electrified negative charges on a thin silicon oxide surface by the reproducible and controllable contact electrification technique using an atomic force microscope (AFM). Time evolution of the contact-electrified negative charges, which was observed as electrostatic force, showed three dissipation processes. First, the contact-electrified negative charges dissipate slowly, then rapidly and finally, slowly again. It was found by comparison between attractive and repulsive force measurements that the first dissipation process was stable for the applied electric field, whereas the second one was unstable. Analysis of contact voltage dependence and time evolution of the spatial integral of the contact-electrified negative charges revealed the charge sites of silicon oxide for the negative charge. Furthermore, it was found that the time evolution from the first stable dissipation process to the second unstable one was a phase transition from a solid phase to a liquid or gas phase of the contact-electrified negative charges, which was investigated in terms of the nondimensional parameter Γ. By comparison between the spatial distributions of the electrostatic forces measured repulsively and attractively, it was found that the contact-electrified negative charges were very dense and stable in the central region (i.e., solid phase), whereas they were sparse and unstable in the surrounding region (i.e., liquid or gas phase).
S i O2Etching Using M= 0 Helicon Wave Plasma
Authors: Nogami Hiroshi , Nakagawa Yukito , Mashimo Kimiko , Yoneichi Ogahara Yoneichi Ogahara , Tsutomu Tsukada Tsutomu Tsukada
Published: October 2002

When applying high-density plasma to SiO2etching, the ability to control the degree of dissociation is critical. In this study, two methods for controlling the degree of dissociation were evaluated usingM=0 helicon wave plasma. One method was time-modulated discharge and the other adjusting the source power in the conventional continuous discharge. It was concluded that almost identical etching characteristics could be obtained, at least inM=0 helicon wave plasma, if and only if the applied source power in the continuous discharge was equal to the net source power in the time-modulated discharge. The probe measurement revealed that the electron temperature did not change with increasing source power; however, the emission spectroscopic study indicated that the high-energy tail of the electron-energy distribution function grew with increasing source power. This is considered to be the cause of the high degree of dissociation.
Control of Etch Slope during Etching of Pt in Ar/Cl2/O2 Plasmas
Authors: Yoo Won Jong , Hahm Jin Hwan , Kim Hyoun Woo , Jung Chan Ouk , Young Bum Koh Young Bum Koh , Moon Yong Lee Moon Yong Lee
Published: October 2002

Pt patterns of the 0.25 µ m design rule were etched at 20° C using a magnetically enhanced reactive ion etcher. The main problem of this device integration process is the redeposition of the etch products onto the pattern sidewall, making it difficult to reduce the pattern size. In both cases using a photoresist mask and an oxide mask, the redeposits of the etch products onto the sidewall were reduced by the addition of Cl2 to Ar, although the etch slope was lowered to 45°. Using the oxide mask, by adding O2 to the Cl-containing gas, the etch slope was increased up to 70°, and the redeposits were removed by an HCl cleaning process.
Investigation of Discharge Phenomena in a Cell of Color Plasma Display Panel I. One-Dimensional Model and Numerical Method
Authors: Takahashi Kazuo , Hashiguchi Seishiro , Murakami Yukio , Takei Makoto , Itoh Kazuhiro , Tachibana Kunihide , Sakai Tetsuo
Published: October 2002

A numerical simulation method using a one-dimensional fluid model under the local field approximation is presented in order to understand pulsed-dc discharge in He–Xe gas mixture in a cell of a full-color plasma display panel. Spatiotemporal behaviors of the electric field and number densities of twelve independent particles, including electrons and four kinds of ions, were calculated self-consistently at a gas pressure of 200 Torr (27 kPa) and an electrode distance of 0.02 cm. The imprisonment of 147-nm-resonance radiation, the excitation source of phosphors, was also taken into account. Calculated results of the discharge current and voltage are consistent with those of experiment. The waveform of 147-nm-resonance radiation agreed well with experiment, although that of the discharge current showed some difference, probably due to the local field approximation.
High-Rate and Smooth Surface Etching of Al 2O 3-TiC Employing Inductively Coupled Plasma (ICP)
Authors: Fukushima Nobuto , Katai Hiroaki , Wada Toshiaki , Horiike Yasuhiro
Published: October 2002

High-rate and smooth surface etching of Al2O3-TiC, which is widely used as a slider material for magnetic recording heads, has been developed employing inductively coupled plasma (ICP). The etching rate of 200 nm/min was obtained with Cl2/BCl3 mixture. However the etched morphology exhibited roughness around 40 nm Ra (arithmetic average deviation from center line) because of different etching rates for Al2O3 and TiC grains in the substrate. The addition of Ar to the Cl2/BCl3 improved both the etching rate and roughness of the etched surface considerably. As a result the high etching rate of more than 350 nm/min, which is more than ten times that of conventional Ar+ ion etching, and relatively smooth surface roughness around 20 nm Ra were achieved with Ar/Cl2/BCl3 mixture using 1.2 kW RF power and -500 V V
dc.