bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Large REBa2Cu3Oy (RE=Y, Yb) Film of 2 Inch Diameter by Liquid Phase Epitaxy
Authors: Nomura Katsumi , Hoshi Saburo , Nakamura Yuichi , Izumi Teruo , Shiohara Yuh
Published: October 2002

Processing parameters for liquid phase epitaxy (LPE) growth were investigated in order to grow a large REBa2Cu3O
y
film of high quality. In the case of large film growth, the liquid surface and growth interface temperatures can easily increase due to both the heat radiation shield and the forced convection effects of the substrate. The LPE growth temperature should be decreased to less than the peritectic temperature of the seed material while maintaining a reasonable supersaturation. It was confirmed that the growth of the (Y, Yb)Ba2Cu3O
y
system from the YBa2Cu3O
y
seed film could realize the above requirement. A large LPE film of 2-inch diameter was successfully grown into a quasi-single-crystalline film of Y0.9Yb0.1Ba2Cu3O
y
. The grown film had both high crystallinity and high in-plane uniformity. The film exhibited the critical temperature of 91 K.
Tunneling Spectroscopy of Non-Oxide Perovskite Superconductor MgCNi3
Authors: Go Kinoda Go Kinoda , Masato Nishiyama Masato Nishiyama , Yong Zhao Yong Zhao , Masato Murakami Masato Murakami , Naoki Koshizuka Naoki Koshizuka , Tetsuya Hasegawa Tetsuya Hasegawa
Published: October 2002

We report the tunneling spectroscopy of non-oxide perovskite superconductor MgCNi3 polycrystals using a low-temperature scanning tunneling microscope. The obtained tunneling spectra clearly show a superconducting energy gap structure, which can be well fitted by the BCS function with smearing parameter Γ. The value of the superconducting gap Δ is estimated to be 1.10–1.15 meV at 3 K, resulting in a ratio of 2Δ/k
B
T
c=3.3–3.4 for T
c of 7.8 K. This result suggests that MgCNi3 is a conventional BCS s-wave superconductor in the weak-coupling regime.
Influence of Zinc Co-Doping on Carbon Doped InGaAs
Authors: Keiper Dietmar , Sermage Bernard , Benchimol Jean-Louis
Published: October 2002

We have investigated the effect of Zn co-doping in metal-organic vapor-phase epitaxy (MOVPE) growth of highly carbon doped In0.53Ga0.47As/InP layers using nitrogen carrier gas. A Zn concentration of 3×1018 cm-3 for a C concentration of 1.8×1019 cm-3 leads to a significantly increased minority carrier lifetime, and also to slightly improved majority carrier characteristics. At this concentration the Zn diffusion is not crucial, and this technique may have important applications for InP based hetero bipolar transistors (HBTs).
New Concept of the Wide Viewing Angle Liquid Crystal Display without Grayscale Inversion
Authors: Shibazaki Minoru , Ishinabe Takahiro , Miyashita Tetsuya , Uchida Tatsuo , Sunata Tomihisa
Published: October 2002

We analyzed the grayscale inversion mechanism of birefringent-type liquid crystal displays (LCDs). As a result, we propose a new LCD that prevents grayscale inversion, without using the multidomain alignment method. In addition, using this new method, we established the design rules for a compensation film that can compensate for the retardation of the black state from any viewing angle. We call this new LCD the OCP cell, which is an abbreviation for optically compensated parallel cell. This OCP is very promising as a next-generation LCD, due to its wide range of viewing angles, simple fabrication process, which is almost the same as that for a twisted nematic (TN) cell, and large aperture ratio.
Physical and Chemical Contributions of Interfacial Impurities to Film Adhesion
Authors: Suk Kim Young , Yukihiro Shimogaki Yukihiro Shimogaki
Published: October 2002

Effects on adhesion strength of residual Cl and F impurities at the interface between a Cu film deposited by chemical vapor deposition and a TiN substrate were studied through experimental and computational methods. The adhesion strength of the Cu film on HCl treated TiN was enhanced compared with that on untreated TiN, whereas the adhesion strength on HF treated TiN was reduced. X-ray photoelectron spectroscopic (XPS) analysis of the near-interface region revealed that the adhesion differences in the presence or absence of the residual impurities were not due to the contribution of chemical interactions, but rather to physical contributions. Computational estimations suggest that incorporation of Cl in the TiN substrate improves the physical bonding strength by increasing the dispersion force.
Doping Effects of Tetra(amino)fullerene Epoxide in Conducting Polymer Thin Film
Authors: Akihiko Fujii Akihiko Fujii , Tokiyoshi Umeda Tokiyoshi Umeda , Hiroyuki Isobe Hiroyuki Isobe , Eiichi Nakamura Eiichi Nakamura , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

Optical properties and photoconduction of the composites of poly(3-octylthiophene) (PAT-8) and novel C60 derivatives, tetra(amino)fullerene epoxides (TAFEs) have been studied. TAFEs have high solubility, so heavy doping into conducting polymers is possible in the wet process. PL intensity of PAT-8 has been quenched and photocurrent intensity has been enhanced markedly with increasing the concentration of TAFEs, which can be explained as being due to the photoinduced charge transfer from PAT-8 to TAFEs. In the case of heavy doping of TAFEs into PAT-8, spectral changes in absorption and photoconduction spectra have been observed, which can be interpreted as being due to the charge transfer from PAT-8 to TAFEs in the ground state.
A Micromachined Millimeter-Wave Cavity Resonator on Silicon and Quartz Substrates
Authors: Ki-Jae Song Ki-Jae Song , Bup-Sang Yoon Bup-Sang Yoon , Jong-Chul Lee Jong-Chul Lee , Byungje Lee Byungje Lee , Jong-Heon Kim Jong-Heon Kim , Nam-Young Kim Nam-Young Kim , Jae-Yeong Park Jae-Yeong Park , Geun-Ho Kim Geun-Ho Kim , Jong-Uk Bu Jong-Uk Bu
Published: October 2002

In this letter, a Ka-band cavity resonator using micromachining process is presented. A two-port cavity resonator is designed using the three-dimensional (3-D) design software, HP HFSS. The cavity resonator is fabricated on a Si substrate and bonded with a Quartz wafer. The resonator shows the resonant frequency of 39 GHz, the insertion loss of 4.6 dB, and the loaded quality factor (Q
L) and unloaded quality factor (Q
U) of 44.3 and 107, respectively.
Fixed-in Variable-out Wavelength Vonversion Using LiNbO3 Quasiphase-Matched Wavelength Vonverter
Authors: Loy Lam Chang-Qing Xu , Shin Arahira Shin Arahira , Yoh Ogawa Yoh Ogawa , Hiromasa Ito Hiromasa Ito
Published: October 2002

Fixed-in variable-out wavelength conversion using a cascaded χ(2) based quasiphase matching (QPM) LiNbO3 waveguide is proposed and demonstrated for the first time. In this method, the QPM wavelength of the wavelength converter is set to be consistent with the fixed-wavelength of a pulse signal (λs), and a cw control signal with a moderate power (wavelength µm) is used to change the wavelength (λc) of the converted light. It is shown that fixed signal at λs can be converted to any wavelength in a range as broad as 80 nm by using a 4-cm-long device.
Electron Swarm Parameters in SF6and Krypton Gas Mixtures
Authors: Xiao Deng-Ming , Zhu Li-Li , Li Xu-Guang
Published: October 2002

The electron swarm growth processes in SF6-Kr gas mixtures have been studied using a pulsed Townsend method over the range 32.24≤E/N≤564.2Td(1Td=10-21V·m2), whereEis the electric field andNis the gas density of the mixture. The variation patterns as a function of the density-reduced electric field of the effective ionization coefficient α, electron drift velocityVeand longitudinal diffusion coefficientDLin SF6-Kr gas mixtures have been determined. The dielectric strength of SF6-Kr gas mixtures which varies linearly with the SF6concentration in the gas mixtures Has also been determined.
High-Quality Homoepitaxial Diamond Films Grown at Normal Deposition Rates
Authors: Wang Chunlei , Irie Masatake , Ito Toshimichi
Published: October 2002

High-quality homoepitaxial diamond films without any growth hillocks and abnormal particles have been successfully deposited at a reasonably high deposition speed of ∼0.5 µm/h by a 5 kW microwave plasma chemical vapor deposition system. These films show cathodoluminescence (CL) spectra predominated by strong free-exciton recombination radiation assisted by a transverse optical phonon and its replicas even at room temperature. The temperature dependence of the CL feature has been analyzed quantitatively. The results suggest that a considerable reduction of non-radiative relaxation paths is accomplished in the present case of high-quality diamond films.
Field Emission Properties of Carbon Tubule Nanocoils
Authors: Lujun Pan Lujun Pan , Taichi Hayashida Taichi Hayashida , Mei Zhang Mei Zhang , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

The first carbon nanocoil field emitter has been prepared by catalytic thermal chemical vapor deposition and its properties of field emission have been investigated. The carbon nanocoils grow selectively from the patterned iron film and maintain their self-organization well. The field emission measurement shows that the turn-on field is as low as 180 V at a 130 µm gap. High emission current density, excellent stability, especially uniformity of the field emission from carbon nanocoils have been observed. These properties suggest that the carbon nanocoils is an attractive candidate for the fabrication of flat panel field emission display.
Production of CW High-Density Non-Equilibrium Plasma in the Atmosphere Using Microgap Discharge Excited by Microwave
Authors: Akihiro Kono Akihiro Kono , Tomohiko Sugiyama Tomohiko Sugiyama , Toshio Goto Toshio Goto , Hideo Furuhashi Hideo Furuhashi , Yoshiyuki Uchida Yoshiyuki Uchida
Published: October 2002

A new technique for cw production of high-pressure, high-density, non-equilibrium plasma is presented. Using microwave excitation at 2.45 GHz, a stable atmospheric glow discharge was sustained between two knife-edge electrodes, having a length of 10 mm and facing each other across a ∼100 µm microgap. Laser Thomson scattering diagnostics indicates that the plasma density in the microgap is as high as 1.6×1015 cm-3 at a microwave power of 100 W. The optical emission of the N2 second positive band indicates that the gas temperature in the microgap is 1800 K, much lower than the electron temperature.
Vapor Phase Synthesis of Fluorescent Gallium Nitride Powders
Authors: Hara Kazuhiko , Matsuno Yuuki , Matsuo Yoshinori
Published: October 2002

GaN crystalline powders have been synthesized by the reaction of a Ga vapor with ammonia at the reaction temperatures (T
r) of 900–1100°C under the atmospheric pressure. The size of the crystalline particles ranges from 0.2 to 2 µm. The structural and the luminescent properties depend strongly on T
r. For T
r≥1050°C, the powders consist primarily of hexagonal GaN particles, whereas those synthesized at T
r≤1000°C contain cubic GaN particles. Photoluminescence (PL) spectra are dominated by band-edge emissions. For the powders synthesized at higher T
r, reduction in the PL intensity between 24 and 293 K indicates excellent luminescent quality. Thermal quenching is relatively significant for the powders synthesized at lower T
r. This is presumably due to enhanced nonradiative recombination at the surface because of their small particle size.
Donor and Acceptor Levels in Undoped β-FeSi2 Films Grown on Si (001) Substrates
Authors: Ken-ichiro Takakura Ken-ichiro Takakura , Takashi Suemasu Takashi Suemasu , Fumio Hasegawa Fumio Hasegawa
Published: October 2002

Donor and acceptor levels of undoped n- and p-type β-FeSi2 films were investigated in terms of temperature dependence of carrier density. β-FeSi2 films were formed from Si/Fe multilayers on Si (001) substrates. Two kinds of donor (E
D=0.075 eV and 0.21 eV) and acceptor levels (E
A=0.10 eV and 0.19 eV) were observed. The density of these levels was found to be about 1020 cm-3, suggesting that they originate from defects rather than impurities included in the 4N-Fe source. The energy gap of the β-FeSi2 film was determined to be about 0.80 eV. This value corresponded to the reported value of electroluminescence peak wavelength (1.6 µm) of the p-Si/β-FeSi2 balls/n-Si(001) diode we reported recently, and is slightly smaller than the reported energy gap estimated from the absorption edge.
Effects of Thermal Annealing on Ni/Ta/n-GaN Schottky Diodes
Authors: Gin-Liang Chen Gin-Liang Chen , Fu-Chin Chang Fu-Chin Chang , Wang-Cheng Chung Wang-Cheng Chung , Bohr-Ran Huang Bohr-Ran Huang , Wen-Hsiung Chen Wen-Hsiung Chen , Ming-Chih Lee Ming-Chih Lee , Wei-Kuo Chen Wei-Kuo Chen
Published: October 2002

The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800°C. Preliminary results indicate that when a Ta intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.
Optimal Temperature-Time Condition for the Post-Exposure Bake Process of Deep-UV Resists
Authors: Tsung-Lung Li Tsung-Lung Li , Jyh-Hua Ting Jyh-Hua Ting
Published: October 2002

A simulator is devised to investigate the effects of temperature-time history on the post-exposure bake of deep-UV resists based on a simple reaction-diffusion model whose reaction coefficients and diffusion coefficient are treated as temperature-dependent parameters over the entire course of the bake process. The temperature, in turn, is modeled by exponential functions with heating and cooling time constants. Because the reaction slows down as the bake process proceeds, the cooling stage has to be much longer than that for the heating. The optimal process condition determined from this simulation is the maintenance of the cooling/heating constant ratio between 20 and 30.
Magnetic-Relaxation Behavior of (Tl0.5Pb0.5)(Sr1.84Nd0.16)CaCu2O7 Superconducting Material
Authors: Sung Li-Ru , Huang Shin-Hau , Yao Yeong-Der , Lee Wun-Hsin
Published: October 2002

We report experimental studies of the time deacy of the nonequilibrium magnetization, a phenomenon known as magnetic relaxation, in a polycrystalline high-temperature superconductor (Tl0.5Pb0.5)(Sr1.84Nd0.16)CaCu2O7 with T
c=105 K. The temperature dependence of the relaxation rate defined as A=d[M(t)-M
eq]/dln
(t) has been sketched for this material at a wide range of temperatures for applied fields of 1, 2, 3 and 10 kOe. Analysis of Arrhenius plots yields two field-dependence avearge pinning energies in the temperature range 5–70 K, reflecting two regimes of relaxation behavior. The relaxation rate approaches zero at the irreversibility line which can be described by the scaling relation H(T
*)=H
o(1-T
*/T
c)
n
with n ∼2.0 for H ≦10 kOe.
Magnetic Promotion of Oxygen Reduction Reaction with Pt Catalyst in Sulfuric Acid Solutions
Authors: Wakayama Nobuko I. , Okada Tatsuhiro , Okano Jun-ichi , Ozawa Takeo
Published: October 2002

In cathode gas reactions of polymer electrolyte fuel cells, oxygen gas is reacted with H+ to produce water on platinum catalyst. The magnetic effect on this electrochemical oxygen reduction was studied. When a magnet field gradient was applied to the cathode by setting a permanent magnet behind it and oxygen gas was supplied toward a stronger magnetic field, electrochemical flux was enhanced. The current increased with increasing magnetic field strength. Magnetic promotion of the cathode reaction was explained by the magnetic attractive force toward paramagnetic O2 gas. The present study demonstrates how fuel cell performance can be improved.
Novel Nematic Liquid Crystal Device Associated with Hybrid Alignment Controlled by Fringe Field
Authors: Ho Hong Seung , Hak Jeong Yeon , Yul Kim Hyang , Hee Lee Seung
Published: October 2002

We propose a novel hybrid aligned liquid crystal (LC) cell with negative dielectric anisotropy of the nematic LC driven by fringe field, which is normally black mode. In the on-state, the dielectric torque between the LC director and horizontal component of the fringe field causes the LC director to rotate in the entire area, so that the cell appears to be white. The device, with a wedge-shaped pixel electrode and optical compensation film, also shows a wide viewing angle, high light efficiency and low driving voltage.
Thomson-Like Electron-Hole Recombination in Organic Light-Emitting Diodes
Authors: Kalinowski Jan , Cocchi Massimo , Fattori Valeria , Marco Piergiulio Di , Giro Gabriele
Published: October 2002

The quantum electroluminescence (EL) yield (ϕEL) of a single-layer light-emitting diode (LED) based on a mixture of an oligothiophene (T5Ohex), an aromatic diamine (TPD) and bisphenol A polycarbonate (PC), and of a double-layer LED with a (TPD:PC) hole-transporting layer and an 8-hydroxyquinoline (Alq3) electron-transporting layer, was measured as a function of electric field (F). The devices exhibit maximum ϕEL(F) atFmaxaround 106V·cm-1. This behavior can be explained by the carrier motion-controlled Langevin recombination in the low-field region, and the Thomson-like recombination, controlled by the carrier capture, dominating the high-field regime.
Artifact and Fact of Si(111)7×7 Surface Images Observed with a Low Temperature Noncontact Atomic Force Microscope (LT-NC-AFM)
Authors: Nobuhito Suehira Nobuhito Suehira , Yasuhiro Sugawara Yasuhiro Sugawara , Seizo Morita Seizo Morita
Published: October 2002

We investigate Si(111)7×7 surface by using a low temperature noncontact atomic force microscope (LT-NC-AFM). We obtain two types of AFM images with and without an additional structure between the corner and center adatoms. The distance between the corner adatom and additional structure is 7.0 Å±0.2 Å, which is not consistent with that (4.3 Å) between the corner adatom and the rest atom. This suggests that the additional structure observed is an artifact. We propose a model to explain these experimental results, which is based on atomic arrangement of the Si tip apex with an asymmetric ad-dimer and the Si(111)7×7 surface.
Electrical Breakdown Voltage In a Mixed Gas
Authors: Uhm Han S. , Choi Eun H. , Cho Guansup , Whang Ki W.
Published: October 2002

Properties of electrical breakdown voltage in a mixed gas are investigated based on Townsend criterion. The breakdown temperature T

b
and voltage V

b
are obtained in terms of the gas mixture ratio χ. As an example, we investigate electrical breakdown properties in neon gas mixed with xenon. It is shown that the breakdown voltage decreases, reaches the minimum value at χ=0.02 and then increases again, as the mixture ratio χ increases from zero to unity. A preliminary experiment of AC-plasma display panel (PDP) is carried out for neon gas mixed with a few percent of xenon to verify some of the theoretical models. The experimental data agree qualitatively well with theoretical predictions.
High-Purity and Thick 4H– and 6H–SiC(0001) Epitaxial Growth by Cold-Wall Chemical Vapor Deposition and High-Voltage pin Diodes
Authors: Tamura Satoshi , Fujihira Keiko , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: October 2002

Thick (>30 µm) 4H– and 6H–SiC(0001) epilayers have been grown by cold-wall chemical vapor deposition. The increased thickness of a polycrystalline SiC film coated on a graphite susceptor has allowed growth time to be prolonged, enabling thick epitaxy in one growth run. The unintentionally doped epilayers grown with a C/Si ratio of 2 show low net donor concentrations of 2∼5×1014 cm-3. In low-temperature photoluminescence, very strong free-exciton peaks have been observed, indicating the high purity of the epilayers. A high breakdown voltage of 4200 V has been achieved for a 6H–SiC epitaxial pin diode with a thickness of 31 µm.
Complete Polarization Control of 12×8-Bit Matrix-Addressed Oxide-Confined Vertical-Cavity Surface-Emitting Laser Array
Authors: Ueki Nobuaki , Nakayama Hideo , Sakurai Jun , Murakami Akemi , Otoma Hiromi , Miyamoto Yasuaki , Yamamoto Masateru , Ishii Ryoji , Yoshikawa Masahiro , Nakamura Takeshi
Published: October 2002

The authors have shown complete polarization control of a 12×8-bit matrix-addressed oxide-confined vertical-cavity surface-emitting laser (VCSEL) array, which has an unstrained active region emitting at 780 nm. By using a combination of an elliptical-shaped post structure fabricated on misoriented substrate and upper p-side metal lines elongated in the substrate off-direction, we observed complete polarization pinning in an index-guide type array device. All of the VCSELs in this array lased in a fundamental transverse mode and linearly polarized along the <01-1> direction.
Stabilization of Ferromagnetic States by Electron Doping in Fe-, Co- or Ni-Doped ZnO
Authors: Kazunori Sato Kazunori Sato , Hiroshi Katayama-Yoshida Hiroshi Katayama-Yoshida
Published: October 2002

Detailed guidelines for controlling magnetic states in ZnO-based diluted magnetic semiconductors are given based on ab initio electronic structure calculations within the local spin density approximation using the Korringa-Kohn-Rostoker method. Effects of disorder were taken into account by the coherent potential approximation. It was found that the ferromagnetic state was stabilized by electron doping in the case of Fe-, Co- or Ni-doped ZnO. From the view point of practical applications, it is possible to realize a high-Curie-temperature ferromagnet, because n-type ZnO is easily available.
High Output Energy Quasi-Phase-Matched Optical Parametric Oscillator Using Diffusion-Bonded Periodically Poled and Single Domain LiNbO3
Authors: Nakamura Koichiro , Hatanaka Takaaki , Ito Hiromasa
Published: October 2002

We report a quasi-phase-matched optical parametric oscillator with diffusion-bonded stacks of periodically poled lithium niobate (PPLN) and single domain lithium niobate. In the experiment, a 500-µm-thick PPLN wafer was diffusion-bonded between 500-µm-thick single-domain LN wafers. With large aperture and the crystal length of 40 mm, a low-threshold, high-output-energy quasi-phase-matched optical parametric oscillator was realized. The quasi-phase-matched optical parametric oscillator generated 1.61-µm-signal output energy of 2.35 mJ at the pump energy of 6.35 mJ.
(Pb, La)(Zr, Ti)O3 Film Grain-Boundary Conduction with SrRuO3 Top Electrodes
Authors: Cross Jeffrey S. , Tomotani Miki , Kotaka Yasutoshi
Published: October 2002

The relationship between Sr interdiffusion from a Pt/SrRuO3 [SRO] top electrode into (Pb, La)(Zr, Ti)O3 [PLZT] ferroelectric thin films with different excess Pb contents (2–10%) and leakage properties was studied. Secondary ion mass spectrometry and energy dispersive X-ray spectroscopy revealed significant Sr diffusion into the PLZT film after annealing, which increased with increasing excess Pb content. The diffused Sr existed in the PLZT crystalline grain boundaries, but not in the grains. The high leakage was attributed to a low resistance compound Sr–Pb–O in the PLZT grain boundaries. To obtain low leakage SRO/PLZT capacitors, it is necessary to eliminate the Sr–Pb–O grain boundary phase by lowering the excess Pb content to 7% or less.
Strong Liquid Crystal Anchoring on Photo-Alignment Copolymer Films Containing ω-(4-chalconyloxy)alkyl Side Groups
Authors: Kimura Masayuki , Nakata Shoichi , Makita Yutaka , Matsuki Yasuo , Kumano Atsushi , Takeuchi Yasumasa , Yokoyama Hiroshi
Published: October 2002

One order of magnitude enhancement of the liquid crystal anchoring strength can be realized on photo-aligned copolymer films containing ω-(4-chalconyloxy)alkyl side groups, when the photo-dimerization of chalconyl units by linearly polarized near ultraviolet light is carried out at a temperature above the glass transition of the start polymer. Under the optimal condition, the polar anchoring strength was found to become comparable with that of rubbed polyimide alignment films, thereby allowing a stable electro-optical performance. Based on the behavior of the photo-induced optical anisotropy, we argue that the enhanced anchoring results from a cooperative relaxation of polymer main chains that assists further photo-crosslinking of chalconyl units via a “zipper-closing” mechanism.
Viscosity of Porous Low-Dielectric Glass Composite
Authors: Jean Jau-Ho , Fang Yu-Ching
Published: October 2002

The viscosity of a low-dielectric glass composite containing a low-softening-point borosilicate glass and a high-softening-point high silica glass as a function of porosity has been measured by an isothermal beam-bending technique using a commercial thermal mechanical analyzer. Results reveal that the apparent viscosity of the glass composite decreases with increasing porosity for porosity in the range of 0–40 vol%.
Capacitively Coupled Microplasma Source on a Chip at Atmospheric Pressure
Authors: Yoshiki Hiroyuki , Horiike Yasuhiro
Published: October 2002

A small-scale and low-power 13.56 MHz capacitively coupled plasma is generated in a capillary, whose cross section is 65–500×500–5000 µm, on a quartz chip of 20×20 mm at atmospheric pressure. The capillary is sandwiched between parallel-plate electrodes which are externally located on a chip. A π-type matching network is miniaturized and appropriately designed to satisfy the resonance condition with the excitation frequency, so that helium plasma ignites at an incident power of1–3 W. The atomic excitation temperature measured from the intensity distribution of He I lines is about 1900 K at atmospheric pressure. This result suggests that a low-electronic-temperature plasma is obtained.
The Effects of In Flow during Growth Interruption on the Optical Properties of InGaN Multiple Quantum Wells Grown by Low Pressure Metalorganic Chemical Vapor Deposition
Authors: Leem Shi-Jong , Kim Min Hong , Shin Johngoen , Choi Yoonho , Jeong Jichai
Published: October 2002

In0.2Ga0.8N/In0.03Ga0.97N 3-period multiple quantum wells (MQWs) were grown by low pressure metalorganic chemical vapor deposition and the effects of pre-In flow prior to QW growth on its overall optical property were investigated. Pre-In flow did not change the structural property of the MQW structure such as In composition and period but strongly influenced its optical properties. MQW samples grown with pre-In flow exhibited longer peak wavelength and stronger peak intensity. CL measurement revealed more uniform and smaller emission centers in pre-In flow samples, implying a reduction of non-radiative defective regions and more In-rich regions. These results indicate that the In source introduced prior to QW growth preferentially gets incorporated around defect sites such as threading dislocations to inhibit their propagation while forming seeds for In-rich regions.
Fast Epitaxial Growth of 4H–SiC by Chimney-Type Vertical Hot-Wall Chemical Vapor Deposition
Authors: Kimoto Tsunenobu , Tamura Satoshi , Chen Yi , Fujihira Keiko , Matsunami Hiroyuki
Published: October 2002

4H–SiC has been homoepitaxially grown on off-axis 4H–SiC(0001) at 1700°C by chimney-type vertical hot-wall chemical vapor deposition. Mirror-like surface morphology can be obtained with high growth rates up to 21 µm/h. Epitaxial growth under C-rich conditions at growth rates of 10–14 µm/h leads to enhanced macrostep formation but reduced doping and deep trap concentrations of 7.2×1014 cm-3 and 1.3×1013 cm-3, respectively. Good thickness and doping uniformities of 4% and 6%, respectively, are achieved with this growth technique.
Low-Temperature Microscopic Photoluminescence Images of Epitaxially Laterally Overgrown GaN
Authors: Masahiro Yoshimoto Masahiro Yoshimoto , Junji Saraie Junji Saraie , Shuji Nakamura Shuji Nakamura
Published: October 2002

Microscopic photoluminescence (PL) measurement has been carried out on epitaxially laterally overgrown (ELO) GaN with a spatial resolution of 0.3 µm at 15 K. PL emissions ascribed to free excitons (E
XA) and excitons bound to donors (D
0
X) were clearly discriminated. In a plan-view observation, these band-edge emissions from a region above a SiO2 mask are twice as large as those from a region above the opening between masks. In a cross-sectional observation, the emission intensity at 3.494 eV ascribed to E
XA increased along the growth direction. An intense emission at 3.487 eV ascribed to D
0
X was observed above the SiO2 mask within a distance of 8 µm from the SiO2 mask.
Chiral-Doped Optically Compensated Bend Nematic Liquid Crystal Cell with Continuous Deformation from Twist to Twisted Bend State
Authors: Lee Seung Hee , Hong Seung Ho , Noh Jeong Dong , Kim Hyang Yul , Seo Dae-Shik
Published: October 2002

We have fabricated a nematic liquid crystal (LC) cell associated with the transition of the liquid crystal director from a twist to a twisted bend alignment, where an initial transition voltage is not required unlike in the case of the conventional optically compensated bend (OCB) cell. For the device which is initially in the twist state, the molecular deformation occurs continuously from twist to bend alignment without forming nucleations with increasing voltage and initial setting voltage for transition. The device exhibits a wide viewing angle with compensated films and a fast response time of less than 10 ms.
Growth of Preferentially Oriented Microcrystalline Silicon Film Using Pulse-Modulated Ultrahigh-Frequency Plasma
Authors: Kazuya Murata Kazuya Murata , Yuko Mizutani Yuko Mizutani , Emi Iwasaka Emi Iwasaka , Seigou Takashima Seigou Takashima , Masaru Hori Masaru Hori , Toshio Goto Toshio Goto , Seiji Samukawa Seiji Samukawa , Tsutomu Tsukada Tsutomu Tsukada
Published: October 2002

Microcrystalline silicon films were formed on glass substrate at 300°C using pulse-modulated ultrahigh-frequency plasma, with variation of the pulse duty ratio (10–100%) and the pulse frequency (2–50 kHz). We found that the ratio of (111) to (220) crystalline orientation of films can be precisely controlled by changing the duty ratio or frequency. Variation in crystalline orientation closely correlated with the ratio of silicon atom density to hydrogen atom density in the plasma. Strongly preferential (111) growth was achieved, and we propose that the mechanism for this involves the ratio between silicon species and hydrogen atoms in the pulse-modulated plasma.
Deep Level Transient Spectroscopy Analysis of an Anatase Epitaxial Film Grown by Metal Organic Chemical Vapor Deposition
Authors: Miyagi Takahira , Ogawa Tomoyuki , Kamei Masayuki , Wada Yoshiki , Mitsuhashi Takefumi , Yamazaki Atsushi , Ohta Eiji , Sato Tetsuya
Published: October 2002

The deep level transient spectroscopy (DLTS) study of anatase-type TiO2 material was performed for the first time. The anatase film was epitaxialy grown on a conductive Nb-doped single-crystalline SrTiO3 (100) substrate by metal organic chemical vapor deposition. The photoluminescence characteristics of this anatase film were identical to those in previous reports, where they were attributed to the radiative recombination of self-trapped excitons. According to the DLTS analysis, it was revealed that this anatase film had a characteristic deep level located at 0.96 eV below the bottom of the conduction band with large concentration (6.5×1016/cm3) and capture cross section (8.3×10-13 cm2). Since the capture cross section of this level appeared to be too large to be caused by point defects, the origin of this deep level was attributed to line defects such as dislocations.
Formation of Two-Dimensional Network Structure of DNA Molecules on Si Substrate
Authors: Tanaka Shin-ichi , Cai Lin-Tao , Tabata Hitoshi , Kawai Tomoji
Published: October 2002

We have succeeded in attaching deoxyribo nucleic acid (DNA) molecules to a semiconducting Si substrate by adding MgCl2 to the DNA solution. The optimum concentration of MgCl2 solution to form the DNA network structure is 0.05 to 0.5 mM. Furthermore, it is found that DNA molecules attach to a hydrophilic SiO2 surface but not to a hydrophobic SiH surface. This result indicates that it is possible to fabricate micropatterning on a Si surface by using a DNA template and photolithography.
Laser Ablation of Silicone Rubber for Fabricating SiO2 Thin Films
Authors: Okoshi Masayuki , Kuramatsu Masaaki , Inoue Narumi
Published: October 2002

We deposited SiO2 thin films at room temperature by 193-nm ArF excimer laser ablation of silicone rubber in oxygen atmosphere. (Si–O)
n
chains were selectively ejected from silicone rubber targets by ablation in high laser fluence at about 10 J/cm2. Oxygen gas worked to oxidize the ejected (Si–O)
n
chains to form SiO2 thin films at the gas pressure of 4.4×10-2 Torr, in addition to reducing the isolated carbon mixed into the films. The transmittance of the 400-nm-thick films was 95% at a 500 nm wavelength. The refractive index of the films was defined as 1.4 to 1.5.
Pore Characteristics of Low-Dielectric-Constant Films Grown by Plasma-Enhanced Chemical Vapor Deposition Studied by Positron Annihilation Lifetime Spectroscopy
Authors: Suzuki Ryoichi , Ohdaira Toshiyuki , Shioya Yoshimi , Ishimaru Tomomi
Published: October 2002

The pore characteristics of plasma-enhanced chemical-vapor-deposition (PECVD)-grown low-dielectric-constant (low-k) porous films, grown with dual-frequency power sources and with a source gas of hexamethyldisiloxane, have been studied by positron annihilation lifetime spectroscopy. Six low-k films of different dielectric constants (2.66–4.13) were prepared by changing the low frequency (380 kHz) power of the PECVD process. The long-lived component due to pick-off annihilation of ortho-positronium strongly depends on the low frequency power. Based on the empirical relationship between the ortho-positronium lifetime and the cavity volume, average pore volumes were estimated to be 0.23–0.85 nm3. The correlation between the pore size and dielectric constant was discussed.
Beryllium-Implanted P-Type GaN with High Carrier Concentration
Authors: Yu Chang-Chin , Chu Chen-Fu , Tsai Juen-Yen , Lin Chia-Feng , Lan Wen-How , Chiang Chung-I. , Wang Shing-Chung
Published: October 2002

We report the results of beryllium implantation in Mg-doped GaN to obtain a high hole concentration and lower activation energy for Mg. The metal organic chemical vapor deposition (MOCVD)-grown Mg-doped GaN samples were implanted with Be ions at two different energies of 50 keV and 150 keV and a dose of 1014cm-2. The implemented samples were subsequently annealed at 1100°C for 60 s. The annealed samples showed an increase of hole concentration by three orders of magnitude from the non-implanted value of 5.5×1016to 8.1×1019cm-3as determined by Hall measurement. The activation energy of Mg dopants for the implanted annealed samples estimated from the temperature dependence of the photoluminescence data is about 170 meV, which is nearly 30% lower than that for the as-grown samples.
High-Temperature Hardness of Bulk Single-Crystal AlN
Authors: Yonenaga Ichiro , Nikolaev Andrey , Melnik Yuriy , Dmitriev Vladimir
Published: October 2002

The hardness of single-crystal aluminum nitride (AlN) 0.5-mm-thick wafers was measured at elevated temperatures and compared with that of other semiconductors. A Vickers indentation method was used to determine the hardness under an applied load of 0.5–5 N in the temperature range 20–1400°C. The average hardness was measured as 17.7 GPa at room temperature. AlN exhibits a hardness higher than that of GaN in the entire temperature range investigated. A high mechanical stability for AlN at high temperatures is deduced.
Electrical Properties and Thermal Stability of Cu/6H-SiC Junctions
Authors: Takashi Suezaki Takashi Suezaki , Kazuaki Kawahito Kazuaki Kawahito , Tomoaki Hatayama Tomoaki Hatayama , Yukiharu Uraoka Yukiharu Uraoka , Takashi Fuyuki Takashi Fuyuki
Published: October 2002

Copper (Cu)/6H-SiC Schottky rectifiers were analyzed in detail for the first time. The barrier height of the as-deposited Cu contact on the 6H-SiC(0001) Si-face was determined to be 1.26 eV by internal photoemission spectroscopy. To obtain thermally stable electrical properties, the as-deposited Cu contacts were annealed. Cu/6H-SiC Schottky rectifiers had good electrical properties with the ideality factor below 1.1 even after thermal annealing at 500°C. However, the electrical properties of annealed Cu contacts over 500°C were deteriorated, which is caused by the formation of copper silicides at the Cu/6H-SiC interface.
Properties of High Tc Superconducting Quantum Interference Device Microscope with High µ-Metal Needle
Authors: Tanaka Saburo , Matsuda Kazuka , Yamazaki Osamu , Natsume Miyuki , Ota Hajime , Mizoguchi Takahiro
Published: October 2002

A new type of superconducting interference device (SQUID) microscope was designed and fabricated. A direct-coupled SQUID magnetometer with a high µ-metal needle was used and the substrate was machined to create a dimple for the needle at the center of the pick-up loop. One end of the needle penetrated through the superconducting pick-up loop in a vacuum; the needle was fixed in the vacuum window with the other end at room temperature in the outside atmosphere. As a demonstration, a laser printed output was scanned by the microscope. Line bars with a line width of 100 µm and a spacing between lines of 200 µm were clearly imaged.
1×8 Channel Power Splitter Using a Multimode Interference Coupler in InP/InGaAsP
Authors: Hyun Kyung-Sook , Yoo Byueng-Su , Kim Jeong-Soo , Yun Ilgu
Published: October 2002

InP/InGaAsP eight-channel multimode interference (MMI) power splitters were successfully demonstrated. Optical transmission characteristics were measured on a 1×8 splitter, by means of near-field images with varying wavelength or output power measurement for transverse electrical/transverse magnetic (TE/TM) modes. On the basis of our results, a 1×8 MMI power splitter is considered to have good power balance at each channel within a ±1 dB imbalance in the wavelength range of 60 nm at the centered wavelength of 1540 nm for all incident modes.
Write and Read-Out Operations of Novel 1T2C-Type Ferroelectric Memory Cells with an Array Structure
Authors: Sung-Min Yoon Sung-Min Yoon , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

We fabricated a 1T2C-type ferroelectric memory array structure with 2×3 cells on a silicon-on-insulator (SOI) substrate. Each cell in the array is composed of a metal-oxide-semiconductor field-effect transistor (MOSFET) and two ferroelectric capacitors with the same area. This type of memory has unique features such as nonvolatile data storage, nondestructive data read-out, and high-density integration based on the scaling rule. It was found that binary data could be correctly stored into a selected cell of the memory array after optimizing the gate SiO2 thickness of the MOSFET.
It was also found that the written data could be correctly read out with a current ratio as large as 10 for “0” and “1” data.
Oxygenation Process of Ti–O Films Formed by Reactive Ion Plating
Authors: Oumi Kenichi , Kashiwagi Kunihiro , Kokai Hideki , Murayama Youichi
Published: October 2002

Ti–O films were deposited under various conditions by RF reactive ion plating. The structures of the TiO2 films were controlled using various parameters such as substrate temperature, RF power, deposition rate, and pressure of reactive gas. By changing the deposition rate at the substrate temperature of 250°C, the crystal structure could be changed from an anatase phase to a rutile phase. In other words, a rutile structure could be deposited even at a low substrate temperature. The emission spectra of ions and excited species in the plasma were measured by optical emission spectroscopy (OES). Relative spectral intensities of these species were studied. The resulting relative relationship of emission intensities of Ti* and O2
+ was found to influence reactions in Ti–O film formation.
Temperature Compensation with AlN Film on Y-128° LiNbO3
Authors: Wu Sean , Wu Long , Chang Feng-Chih , Chang Jia-Hua
Published: October 2002

Y-128° LiNbO3 is a well-known high-electromechanical-coupling Surface Acoustic Wave (SAW) material, but its usefulness is limited because of its poor temperature-stablility property. AlN films have some excellent characteristics, such as high SAW velocity, stable chemical properties, and high-temperature stability. In this research, the c-axis-oriented AlN films were successfully prepared on Y-128° LiNbO3 by the sputtering method and a SAW delay line oscillator under various temperatures was used to measure the temperature coefficient of frequency (TCF) value of this structure. For Y-128° LiNbO3 with an AlN layer, the TCF value was from -76.32 (ppm/°C) to -39.04 (ppm/°C) and the improved quantity was 48.8%. The oscillator frequency at 25°C also increased from 40.0909 MHz up to 41.6221 MHz. It exhibited Y-128° LiNbO3 with an AlN layer that will effectively improve the poor temperature stability and enhance the SAW velocity.
Quantum-Dot Semiconductor Optical Amplifiers for High Bit-Rate Signal Processing over 40 Gbit/s
Authors: Sugawara Mitsuru , Hatori Nobuyuki , Akiyama Tomoyuki , Nakata Yoshiaki , Ishikawa Hiroshi
Published: October 2002

This paper provides a theory and simulation of traveling-type semiconductor optical amplifiers (SOAs) with self-assembled quantum dots in their active region. We calculated their continuous-wave and 40-Gbit/s dynamic performance, and compared them with 1.55-µm SOAs with bulk InGaAsP active layers. The results demonstrate that quantum-dot SOAs can process multiple-wavelength high bit-rate optical pulse trains over 40 Gbit/s under gain saturation. This promises diverse functions like regeneration, reshaping, multiple-wavelength processing, wavelength conversion, and demultiplexing of high-bit-rate patterned optical signals, which meet with the demand of next-generation broadband all-optical photonic networks.
Activation of p-Type GaN in a Pure Oxygen Ambient
Authors: Wen Tzu-Chi , Lee Shih-Chang , Lee Wei-I , Chen Tsung-Yu , Chan Shin-Hsiung , Tsang Jian-Shihn
Published: October 2002

In this study, we activated p-type GaN in a pure oxygen ambient by rapid thermal annealing. The sheet resistance of p-type GaN was greatly reduced from > 107 Ω/\Box to 7.06 ×104 Ω/\Box after annealing in oxygen ambient at 500°C. The photoluminescence intensity of blue emission increased by one order of magnitude compared to the as-grown sample. Moreover, the sheet resistance of p-type GaN annealed in pure oxygen ambient is lower than that of p-type GaN annealed in nitrogen ambient. The carrier concentrations of the samples annealed in oxygen ambient are higher than those annealed in nitrogen ambient. The better activation of p-type GaN in oxygen ambient is due to the higher activity of oxygen than that of nitrogen. Oxygen would remove hydrogen that passivates Mg atoms by forming H2O at a lower temperature.
Photoresponse and Defect Levels of AlGaN/GaN Heterobipolar Phototransistor Grown on Low-Temperature AlN Interlayer
Authors: Mouillet Robert , Hirano Akira , Iwaya Motoaki , Detchprohm Theeradetch , Amano Hiroshi , Akasaki Isamu
Published: October 2002

We report on a visible-blind AlGaN/GaN heterobipolar phototransistor with low threading dislocation density, fabricated by organometallic vapor phase epitaxy using the low-temperature interlayer technique. The dark current at room temperature was as low as 34.6 pA/mm2 at 3 V and the responsivity was 160 A/W under 0.78 nW/cm2 illumination. The high-temperature device performance up to 200°C was marked by the exponential evolution of the dark current under the influence of a deep defect near 459 meV. Also, photoinduced transient spectroscopy between 50°C and 175°C yielded evidence of defects at about 93 meV, 137 meV and 205 meV energies, which caused a long-lasting photocurrent after weak-intensity illumination.
Fabrication of InGaN Multiple Quantum Wells Grown by Hydrogen Flux Modulation in RF Molecular Beam Epitaxy
Authors: Takahashi Kazuya , Okada Yoshitaka , Kawabe Mitsuo
Published: October 2002

We have investigated the effect of atomic hydrogen on In incorporation during InGaN growth, and that of hydrogen flux modulation on the fabrication of InGaN multiquantum wells (MQWs) by RF molecular beam epitaxy (MBE). The In incorporation in InGaN was increased with increasing atomic hydrogen flow rate, and InGaN MQW structures were successfully formed solely by only modulating the hydrogen flux during growth. The InGaN MQW structures have been fabricated without changing other growth conditions such as Ga and In cell temperatures, substrate temperature and the RF nitrogen plasma condition.
It was also found that the average In composition and period of superlattice increased with increasing hydrogen flow rate.
A Passively Q-Switched Laser Constructed by a Two-Mirror Reentrant Ring Cavity
Authors: Huang Pi-Ling , Weng Chun-Ren , Cheng Huy-Zu , Huang Sheng-Lung
Published: October 2002

A passively Q-switched laser is demonstrated by a two-mirror reentrant and unidirectional ring cavity. Due to the cavity configuration, the pulse-to-pulse timing jitter is effectively reduced to less than 3% over 40,000 shots. As indicated in our simulation on photon dynamics in the cavity, spontaneous noise from the gain medium is the major cause of large timing jitter in passively Q-switched lasers, and it is eliminated in this laser.
Striation Mechanism and Triggered Striation in Dielectric Microdischarge Plasma
Authors: Koo Lee Jae , Hwa Shon Sheikh Dastgeer , Sup Hur Min , Chul Kim Hyun , Suwon Cho Suwon Cho
Published: October 2002

The striation mechanism of dielectric microdischarges, as in many plasma devices, is extensively explored by collisional kinetic and fluid simulations. Striation in a typical dielectric microdischarge device predominantly occurs near the anode region and is basically governed by the ionization-dominated α-processes, wherein surface and space charges collectively dictate the phenomenon in a complex manner. A novel type of striation has been investigated by us near the cathode region, which is dominated by γ-processes and is driven by the secondary-electron emission mechanism.
Magnetic Flux Quanta in YBa2Cu3O7-δ Thin-Film Loops Controlled by Femtosecond Optical Pulses
Authors: Tonouchi Masayoshi
Published: October 2002

The optical control of magnetic flux in superconducting thin-film loops is studied by terahertz radiation imaging. The magnetic flux quanta φ are generated in the loop by illuminating it with femtosecond optical pulses under the bias current I
B. The optically generated φ are semiqualitatively evaluated by estimating the amount of the persistent supercurrent circulating along the loop. The threshold and hysteretic characteristics are found in the φ-I
B curves, which strongly depend on optical excitation conditions such as laser power and bias current.
The Control of Cluster-Glass Transition Temperature in Spinel-Type ZnFe2O4-δ Thin Film
Authors: Yamamoto Youhei , Tanaka Hidekazu , Kawai Tomoji
Published: October 2002

The room-temperature cluster glass state has been realized in zinc ferrite (ZnFe2O4-δ) thin films using the pulsed-laser-deposition (PLD) method. When the deposition rate was slow about 7 Å/min, the thin film showed antiferromagnetism similar to the bulk zinc ferrite whose Néel temperature was about 20 K. However, by increasing the deposition rate, the magnetization-temperature curve behaved the same as that of cluster glass, and hysteresis between zero-field-cooled and field-cooled magnetization processes was also observed. At higher than 30 Å/min, the cluster glass transition temperature (T
G) reached approximately room temperature. There are two possibilities for the origin of high-T
G cluster glass: 1) spin frustration resulting from the competition of antiferromagnetic interaction between A-B and B-B site iron ions, and 2) random oxygen deficiency. These two factors induced the high-temperature cluster-glass state in zinc ferrite thin films.
Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping
Authors: Morikawa Takeshi , Asahi Ryoji , Ohwaki Takeshi , Aoki Koyu , Taga Yasunori
Published: October 2002

TiO2-based powder, including 0.1 at% of N doped in the rutile lattice, has been synthesized by oxidation of TiN. As a result, a significant shift of the absorption edge to a lower energy in the visible-light region has been observed. The substitutional doping of N into the TiO2 lattice is found to be effective; its 2p states contribute to the band-gap narrowing by mixing with O 2p as shown in ab initio electronic structure calculations.