bluuebunny/crossref_metadata_2025 huggingface dataset:
Influences of Interchain Interaction on Exciton Dynamics in Poly(3-alkylthiophene)
Authors: Hidayat Rahmat , Fujii Akihiko , Ozaki Masanori , Yoshino Katsumi
Published: October 2002

Luminescent conjugated polymers, poly(3-alkylthiophene) (PAT) with alkyl side chains of different lengths have been studied using time-resolved photoluminescence (PL) spectroscopy. PL characteristics in polymer films of PAT with a long alkyl side chain are found to depend on the preparation methods of the films, namely spin coating and casting methods. The PL spectrum of the cast film is redshifted with respect to that of the spin-coated film. PL decays of both films follow single exponential function. However, it is found that the cast film has a longer PL lifetime with a lower PL efficiency in comparison to the spin-coated film. PL characteristics are also found to depend on the length of the side chains. In PAT with a short alkyl side chain, PL decay does not follow a simply single exponential function, but obeying a suppressed-exponential function. PL lifetime and quantum efficiency increase with increasing length of the side chains. The experimental results have been discussed by taking the interchain interaction as the result of the exciton dissociation at strongly interacted chains and the formation of nonemissive interchain species such as polaron pairs into consideration.
Phosphorus-Species-Induced Band-Gap Anomaly in InGaP Grown by Solid-Source Molecular-Beam Epitaxy
Authors: Cheng Yi-Cheng , Chi Sien , Huang Kai-Feng
Published: October 2002

We report on the growth of InGaP by solid-source molecular-beam epitaxy. It is revealed by photoluminescence (PL) that a lower effective band-gap energy appeared when a higher phosphorus cracker temperature was used. Temperature-dependent PL and polarized photoreflectance (PR) also exhibited a weaker atomic ordering effect when the phosphorus cracker temperature increased. Since the variation of the phosphorus cracker temperature significantly changed the P2/P4 ratio, we believe that a more chemically reactive P2 will not only incorporate more In atoms into the epilayer, but will also bring about a smaller composition fluctuation and weaker ordering effect. Therefore, InGaP grown under a more P2-rich condition probably has a higher In content which results in a lower band-gap energy instead of the ordering effect.
The Effects of Super-Steep-Retrograde Indium Channel Profile on Deep Submicron n-Channel Metal-Oxide-Semiconductor Field-Effect Transistor
Authors: Chen Coming , Chang Sun-Jay , Chou Jih-Wen , Lin Tony , Yeh Wen-Kuan , Chang Chun-Yen , Luo Wen-Zheng , Lee Yao-Jen , Chao Tien-Sheng , Huang Tiao-Yuan
Published: October 2002

A complete study on the effects of indium channel implant energy on transistor characteristics including carrier mobility, drain current, drain induce barrier lowering (DIBL), device breakdown, junction leakage, impact ionization rate and hot-carrier degradation were performed on 0.1 µm devices. It was found that devices with super-steep-retrograde (SSR) indium channel profile depict higher transconductance in linear region, albeit the saturation drive current is lower, compared to the conventional BF2-doped control. In addition, In-doped devices also depict improved DIBL, I
on–I
off current ratio and transistor breakdown voltage. Finally, by increasing the indium implant energy, devices depict an improved transconductance, reduced DIBL and hot-carrier degradation, while suffering larger junction leakage and capacitance.
Change of Surface Structures of Ba Deposited on Mo(110) Surface
Authors: Jo Sadaharu , Gotoh Yoshihiko
Published: October 2002

The change of the surface structures of barium (Ba) deposited on a Mo(110) surface has been investigated by means of a reflection high-energy electron diffraction (RHEED) apparatus. Based on our RHEED observation, it has been clarified that the surface atomic density of Ba increased continuously in proportion to the increase of the film thickness, and there are no critical film thicknesses related to the structural phase transition. This means that the surface structures which appear in the Ba/Mo(110) system do not exhibit any drastic phase transition at any film thickness. The change of the surface structures of the Ba/Mo(110) system occurs in two steps and results in the c(2×2), (1.6×2) and (1.5×1.8) structures that form a boundary. In either of the two steps, surface structures appear in the balance between the energetic stability of the coherency with the atomic arrangement of the Mo substrate and the energetic stability achieved by surface structures themselves forming triangle lattices.
Conductance in Breaking Nanocontacts of Some Transition Metals
Authors: Yuki Kenji , Kurokawa Shu , Sakai Akira
Published: October 2002

The conductance in breaking nanocontacts has been measured at room temperature for relay contacts of Pd, Pt, Rh, Ru and Ir. None of them showed well-defined quantized conductance peaks in their conductance histograms, but some metals exhibited short plateaus in conductance traces and broad peaks in conductance histograms. We found a general tendency that harder metals have lesser degree of conductance quantization, i.e., lesser chance of observing conductance plateaus and peaks. This correlation is, however, weak and can be explained by considering the deformation of nanocontacts as that of defect-free ideal crystals. No sign of quantized conductance were observed in Pd contacts.
Mechanism of the Production of Concentric Spread Plasma
Authors: Sumita Masahiro , Watanabe Seiichi
Published: October 2002

Concentric spread plasma (CSP) is a new type of surface-wave-excited plasma that is disc-shaped and that expands concentrically with increasing microwave power. This study compares the results obtained experimentally with those obtained by three-dimensional electromagnetic wave simulations taking into account the energy absorbed by the plasma. It is shown here that at pressures above 100 Pa, the plasma is produced and sustained by Joule heating.
Experimental Studies of 90° Bragg Reflection from a Sub-Micron InxGa1-xAs Single-Crystal Film Deposited on a GaAs Substrate
Authors: Nikulin Andrei Y. , Tamasaku Kenji , Usher Brian F. , Ishikawa Tetsuya
Published: October 2002

Experimental studies of a 90° Bragg reflection from a thin surface In
x
Ga1-x
As layer grown on a GaAs substrate are reported and discussed. The experiment was performed on the undulator beamline BL29XU at the SPring-8. Two-dimensional (angular deviation from 90° position versus incident synchrotron radiation energy) diffraction intensity profiles were collected from six samples with different In contents (x=0.2–1.5%) and different layer thicknesses (0.5–1.5 µm). Observation of the layer performing as a thin-film optical interferometer (filter) and a discrepancy between layer-substrate lattice mismatch values obtained from standard (400) and extreme 90° reflection measurements (using the same radiation energy) are discussed.
Aberration Monitoring toward Wavefront Matching with Device Patterns
Authors: Nomura Hiroshi , Konomi Kenji , Takakuwa Manabu
Published: October 2002

Wavefront matching is a new technique for compensating uncontrollable aberration effects on a certain reticle design which involves moving controllable aberrations. Such a compensation concept is crucial for producing system-on-chip devices using photolithography. A high-precision wavefront monitor is an essential item for the wavefront matching. The resist-based aberration measurement technique based on the three-beam interference theory is a candidate for monitoring. In the present work, the wavefront in the lithography lens was driven by the lens controller, and then the slight change from the initial state was measured using the technique. For the experiment, a krypton fluoride excimer laser scanner with a numerical aperture (NA) of 0.68 was used. The measurement results verified that the technique has sufficient sensitivity to monitor the wavefront matching.
Generation of Sub-picosecond GeV Electron Bunches by Laser Acceleration in Vacuum
Authors: Wang Ping-Xiao , Ho Yu-Kun , Kong Qing , Yuan Xiang-Qun , Nishida Yasushi , Yugami Noboru , Ito Hiroaki
Published: October 2002

The interaction of free electrons with intense laser beams in vacuum was studied using 3D test particle simulation instead of analytically solving the relativistic Newton-Lorentz equation of motions. We found a group of solutions for the equation, which reveal very interesting and unusual characteristics different from any previously reported. The fundamental characteristics of those trajectories are that an electron can be captured into the high-intensity region, rather than expelled from it and that the captured electron can be accelerated to GeV energy with an acceleration gradient of 1–50 GeV/cm. These solutions emerges only when the laser intensity is a
0\gtrsim100, where a
0≡e
E
0/m
eωc is a measure of the laser intensity. The accelerated GeV electron bunch is a macropulse composed of multiple micropulses, which is analogous to the structure of bunches produced by conventional linacs. The paraxial approximation equations for the Gaussian laser beam used in the simulation are highly accurate and the contribution of the high-order correction is almost negligible when the laser beam width is w
0\geqslant60.
Performance Simulation for Dye-Sensitized Solar Cells: Toward High Efficiency and Solid State
Authors: Tanaka Shigenori
Published: October 2002

We have carried out performance simulations for the dye-sensitized solar cells which consist of a mesoporous TiO2 semiconductor film coated with photosensitizing dyes and a charge transport layer which is either a liquid electrolyte or a solid hole conductor. The calculations for the current–voltage characteristics and the energy conversion efficiency have been made, and the dependence of the efficiency on the material parameters has been discussed. In the case of liquid-state cells, the improvement in the sunlight absorption ability through the enhancement of molar extinction coefficient of the dye sensitizer or of roughness factor of the nanocrystalline TiO2 is essential for achieving very high efficiencies. The effects on the efficiency caused by other factors such as the resistance of transparent conducting oxide electrode, the cell area and the diffusion constants of redox ions are also investigated. In the case of solid-state cells, some specific factors such as the detachment of the hole transport layer from the TiO2 electrode and the decrease of the shunt resistance associated with internal leakages are suggested as possible causes of the significant suppression of the efficiency.
Self-Consistent Calculations of Performance Parameters in Highly Doped Silicon-on-Insulator Metal-Oxide-Semiconductor Field-Effect Transistors
Authors: Iwata Hideyuki
Published: October 2002

The inversion-layer mobility, gate capacitance, transconductance and threshold voltage in highly doped silicon-on-insulator (SOI) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) have been investigated for various SOI layer thicknesses (t
SOI) using self-consistent calculations. It has been found for SOI MOSFETs with highly doped channels that, whenever t
SOI (\gtrsim2 nm) is reduced under the full-depletion condition, the current drive of SOI MOSFETs becomes higher than that of bulk MOSFETs because of the increase in the inversion-layer mobility. In such SOI MOSFETs, the total scattering rate of phonon and ionized impurity scatterings becomes lower with decreasing t
SOI. These results are different from those of the previous work for SOI MOSFETs with low channel impurity concentration.
A Delta-Sigma Analog-to-Digital Converter Using Resonant Tunneling Diodes
Authors: Yokoyama Yuji , Ohno Yutaka , Kishimoto Shigeru , Maezawa Koichi , Mizutani Takashi
Published: October 2002

A novel delta-sigma (ΔΣ) analog-to-digital converter (ADC) using resonant tunneling diodes (RTDs) is proposed. A ΔΣ modulator circuit, which is the key element of the ΔΣ ADC, can be designed in a very simple form using a monostable-bistable transition logic element (MOBILE). The operation of this ΔΣ modulator circuit is confirmed by numerical simulation.
Absorption Saturation of Intersubband Transition in InGaAs/AlAsSb Quantum Well Characterized by Absorption Spectral Analysis
Authors: Gopal Achanta Venu , Yoshida Haruhiko , Neogi Arup , Mozume Teruo , Georgiev Nikolai , Wada Osamu , Ishikawa Hiroshi
Published: October 2002

A lineshape analysis is carried out to deduce the homogeneous linewidth from temperature dependent absorption spectra on the intersubband transitions in InGaAs/AlAsSb quantum wells. Using this linewidth and the pump-probe relaxation time (≈ 2.1 ps) at room temperature, we estimate the saturation intensity to be 52±5 MW/cm2 which shows an agreement with the value obtained from a saturation measurement using a femtosecond laser.
Simplified Magnetically Shielded Cylinder Using Flexible Magnetic Sheets for High-Tc Superconducting Quantum Interference Device Magnetocardiogram Systems
Authors: Suzuki Daisuke , Yokosawa Koichi , Miyashita Tsuyoshi , Kandori Akihiko , Tsukada Keiji , Tsukamoto Akira , Arakawa Shunsuke
Published: October 2002

A small and simple magnetic-shielding cylinder using a new high-permeability sheet, developed for magnetic shielding, can reduce the amount of effort expended on taking magnetocardiogram (MCG) measurements. This sheet is made of a nanocrystalline soft-magnetic material (an Fe–Cu–Nb–Si–B alloy) and is flexible and easy to handle. Moreover, magnetostriction of the material is nearly zero, unlike that of the materials used in conventional magnetic shielding. The shielding cylinder is made up of three tubes of various diameters (but having the same length), placed one inside the other. The shielding cylinder is 1.0 m in diameter and 2.0 m long, and it has a shielding factor of about 35 dB at 1 Hz. The shielding cylinder was tested by measuring MCGs using a high-T
c superconducting quantum interference device (SQUID) gradiometer.
Levitation Experiment Using a High-Temperature Superconductor Coil for a Plasma Confinement Device
Authors: Morikawa Junji , Ozawa Daisaku , Ogawa Yuichi , Yanagi Nagato , Hamaguchi Sinji , Mito Toshiyuki
Published: October 2002

Levitation experiments using a high-temperature superconductor coil have been carried out. A coil with a minor radius of 42 mm was fabricated with a Bi-2223 tape conductor, and immersed in the liquid nitrogen. The coil current was induced by the field-cooling method up to the critical current value. The current decay of the coil can be accounted for by the flux flow resistance and the normal resistance at the lap joint. The high-temperature superconductor coil can be levitated for 4 min or more within an accuracy of 25–30 µm.
Complex Phase Encoding Method for Phase-Code Multiplexed Holographic Memory
Authors: Cho Byung-Chul , Kim Eun-Soo
Published: October 2002

A new complex phase code (CPC) is proposed as a practical orthogonal phase encoding method for volume hologram multiplexing. Through comparative performance analysis of the proposed CPC with the conventional phase codes, the CPC is found to have the lowest cross-correlation mean value of 0.019 and the lowest standard deviation value of 0.0102.
Millimeter-Wave Deflection Properties of Liquid Crystal Prism Cells with Stack-Layered Structure
Authors: Tanaka Masaki , Sato Susumu
Published: October 2002

The liquid crystal (LC) prism with a stack-layered structure is prepared using wedge-shaped metal substrates and nematic LC with a positive dielectric anisotropy. The millimeter-wave deflection properties of the LC prism are measured at 94 GHz and changes in the deflection angle of 3° induced by the external applied voltage can be obtained. The deflection effect is also studied by the finite-difference time-domain (FDTD) method, and the experimental results are consistent with those estimated by the FDTD method.
Photorefractivity and Optical Transmittance of Hybrid Liquid Crystal Cell with Homeotropically Photoaligned Layer and Fullerene Initiation
Authors: Kim Hyun-Wuk , Yoon Choon-Sup , Kim Jin-Yool , Kim Tae-Min , Kim Jong-Duk
Published: October 2002

A hybrid photorefractive liquid crystal cell was prepared with poly(9-vinylcarbazole) as a photoconduction layer and with a photocrosslinkable polymer of the pendant cinnamoyl group as a vertical photoalignment layer. The hybrid structure could increase the diffraction efficiency and transmittance by eliminating light loss by undesirable scattering of the incident beam through the liquid crystal cell. The use of the photoalignment layer in the hybrid liquid crystal structure resulted in a gain coefficient over 900 cm-1, diffraction efficiency over 13%, and transmittance over 85%. These results indicate that the hybrid cell design provides high efficiency for many applications in real-time holography and data storage devices.
Electrooptical Performance of the Vertical-Alignment-1/4π Cell Photoaligned on a Homeotropic Photopolymer Surface
Authors: Hwang Jeoung-Yeon , Kim Jae-Hyung , Seo Dae-Shik
Published: October 2002

Electrooptical (EO) performance of the vertical-alignment (VA)-1/4π cell photoaligned on a homeotropic photopolymer surfaces by polarized UV exposure was studied. Excellent voltage–transmittance (V–T) curves of the VA-1/4π cell photoaligned on the photopolymer containing a cholesteryl moiety of 8% were obtained by polarized UV exposure for 3 min. The V–T and response time characteristics can be improved by high the presence of a cholesteryl moiety in the photopolymer.
Effects of Pyrogenic Reoxidation Annealing on Inversion Channel Mobility of 4H–SiC Metal-Oxide-Semiconductor Field-Effect Transistor Fabricated on (112̄0) Face
Authors: Senzaki Junji , Kojima Kazutoshi , Harada Shinsuke , Kosugi Ryoji , Suzuki Seiji , Suzuki Takaya , Fukuda Kenji
Published: October 2002

The interface properties of 4H-silicon carbide (SiC) metal-oxide-semiconductor (MOS) capacitors and the electrical properties of MOS field-effect transistors (MOSFETs) on the (112̄0) face fabricated using pyrogenic reoxidation annealing (pyrogenic ROA) have been characterized. Pyrogenic ROA reduces the interface-state density near the conduction band, resulting in an increase in the inversion channel mobility and a decrease of the threshold voltage for the MOSFETs with both dry and wet gate-oxides. Eventually, a high channel mobility of 68 cm2/(V·s) was successfully achieved in a MOSFET with wet gate-oxide using the pyrogenic ROA. On the (112̄0) face, the channel mobility of MOSFETs strongly depends on the interface-state density near the conduction band.
Nonlinear Polarization Interferometer for Photon-Number Squeezed Light Generation
Authors: Junichi Higuchi Junichi Higuchi , Norihiko Nishizawa Norihiko Nishizawa , Masakazu Mori Masakazu Mori , Kazuo Yamane Kazuo Yamane , Toshio Goto Toshio Goto
Published: October 2002

We propose a new scheme of photon-number squeezed light generation using a nonlinear polarization interferometer which is constructed by the cascade connection of two polarization-maintaining fibers. Since it is possible to generate photon-number squeezed light by only passing an optical pulse through an optical fiber without spatial alignment, it is expected that the squeezed light can easily and stably be generated in this scheme. The magnitude of maximum squeezing in the numerical analysis is estimated to be about -13 dB. Since the arbitrary dividing ratio and two outputs can be obtained by merely turning the half-wave plates on the input and output side, photon-number squeezed light can be generated for the broad input and output power ranges.
Fabrication of Silicon Utilizing Mechanochemical Local Oxidation by Diamond Tip Sliding
Authors: Miyake Shojiro , Kim Jongduk
Published: October 2002

Nanoprotuberances and grooves were fabricated on a silicon surface by approximately 100-nm-radius diamond tip sliding using an atomic force microscope in atmosphere. To clarify the mechanical and chemical properties of these processed parts, changes in the protuberance and groove profiles due to additional diamond tip sliding and potassium hydroxide (KOH) solution etching were evaluated. Processed protuberances were negligibly removed, and processed grooves were easily removed by additional diamond tip sliding. The KOH solution selectively etched the unprocessed silicon area, while the protuberances, grooves and flat surfaces processed by diamond tip sliding were negligibly etched. Three-dimensional nanofabrication is performed in this study by utilizing these mechanochemically processed parts as a protective etching mask.
Numerical Simulation of a Sessile Bubble beneath a Horizontal Solid Wall in Liquid
Authors: Peng Guoyi , Ishizuka Masaru , Cao Shuliang , Hayama Shinji
Published: October 2002

This paper presents a numerical method to predict the shape and size of a sessile bubble beneath a horizontal solid wall in liquid. A set of mathematical equations describing the interface of a gas bubble with the surrounding liquid is derived by considering the effects of gravity, surface tension and contact angle with the solid wall. The method is applied to the numerical simulation of an air bubble in silicone oil. The results of computation show good agreement with the experimental ones for a real bubble; thus, the present method is shown to be valid. Numerical simulations reveal that the shape of a sessile bubble in liquid is dependent on its size and the temperature has a great effect on bubble size. With the increase in circumference temperature, the mean diameter of the bubble increases, but its shape remains almost the same.
Observation of Micro-Oxygen Precipitates in the Vicinity of the Oxidation-Induced Stacking Fault Ring and Their Effects on Thin Gate Oxide Breakdown
Authors: Kim Hyun-Soo , Lee Ki-Sang , Lee Bo-Young , Yoo Hak-Do , Pyi Seung-Ho , Koh Chung-Geun , Hong Byung-Sub , Kim Yil-Wook
Published: October 2002

Micro-oxygen precipitates and their effects on thin gate oxide breakdown have been investigated using a crystal-originated-particle (COP)-free wafer and a low COP wafer. After two-step annealing and subsequent repolishing, regions containing micro-oxygen precipitates were observed inside and outside the oxidation-induced stacking fault (OSF) ring. Delta [Oi] and near-surface microdefects (NSMDs) in those regions showed a reverse trend. It appears that micro-oxygen precipitates show a different precipitation behavior from the anomalous oxygen precipitation (AOP) behavior in the conventional Czochralski (CZ) silicon wafer with the OSF ring. The oxide breakdown electrical field was degraded in almost the same region as that where micro-oxygen precipitates were revealed. This indicates that micro-oxygen precipitates can affect the degradation of gate oxide integrity (GOI).
Properties of Freestanding GaN Substrates Grown by Hydride Vapor Phase Epitaxy
Authors: Lee Kyoyeol , Auh Keunho
Published: October 2002

We report on freestanding GaN thick films with a thickness of 300 µm grown on 2-inch sapphire (0001) substrates by hydride vapor phase epitaxy. In order to improve the surface morphology of GaN with hillocks, we polished its surface with diamond abrasives and investigated the photoluminescence properties of the polished GaN. Transmission electron microscopy measurement was used to observe the subsurface damage layers. We used the dry etching method, chemically assisted ion-beam etching (CAIBE), for the removal of the damage layer and identified the recovery of photoluminescence properties. As a result, the morphology of the homoepitaxial GaN regrown layer was improved by ion-beam etching compared to that of the not-etched layer.
Effectiveness of NH3 Plasma Treatment in Preventing Wet Stripper Damage to Low-K Hydrogen Silsesquioxane (HSQ)
Authors: Chang Ting-Chang , Mor Yi-Shien , Liu Po-Tsun , Tsai Tsung-Ming , Chen Chi-Wen , Mei Yu-Jen , Sze Simon-M.
Published: October 2002

Wet stripper is commonly used to remove photoresist in IC integration processing. However, the high alkalinity of the wet stripper solution often leads to the hydrolysis of hydrogen silsesquioxane (HSQ) film and induces water uptake. As a result, both the leakage current and dielectric constant of HSQ increase. In this study, NH3 plasma treatment was applied to the HSQ film to form a thin nitrogen-containing layer on the HSQ surface and prevents the hydrolysis of HSQ during photoresist stripping. Dielectric degradation can be prevented by NH3 plasma treatment.
Hydrogenated Polycrystalline GaN Surface Light-Emitting Devices on Transparent Conductive Glass
Authors: Yagi Shigeru , Suzuki Seiji , Iwanaga Takeshi
Published: October 2002

Electroluminescence (EL) from hydrogenated polycrystalline GaN surface light-emitting devices is reported for the first time. The devices consist of a simple sandwich-type cell of films grown at 380°C on indium-tin-oxide coated glass and Al substrates with an Au electrode. Pale yellow EL is observed at room temperature in a lighted room at wavelengths ranging from 450 nm to 700 nm with a peak at 570 nm. Luminance is 7 cd/m2 at an applied DC voltage of 7 V and a current of 35 mA.
Local Magnetic Properties of Underdoped La2-xSrxCuO4 Single Crystal Probed by Scanning Superconducting Quantum Interference Device Microscopy
Authors: Junpei Kasai Junpei Kasai , Yoshihiko Togawa Yoshihiko Togawa , Takao Sasagawa Takao Sasagawa , Jun-ichi Shimoyama Jun-ichi Shimoyama , Kohji Kishio Kohji Kishio , Hideomi Koinuma Hideomi Koinuma , Tetsuya Hasegawa Tetsuya Hasegawa
Published: October 2002

In order to investigate the local magnetic properties of high-T
c superconductors, we have performed scanning superconducting quantum interference device (SQUID) microscopy (SSM) on the ab-surfaces of an underdoped La1.9Sr0.1CuO4 (LSCO) single crystal (T
c=26 K) at various temperatures. The obtained magnetic images below T
c clearly demonstrated diamagnetic behavior together with trapped vortices in units of Φ0 (= hc/2e). Above T
c up to 97 K, on the other hand, we did not observe any magnetic structures within an experimental error of ≤0.2 µT, contrary to the recent SSM results of LSCO thin films exhibiting diamagnetic regions of over-micron scales. From the present SSM observations, it can be safely said that local diamagnetism of such scales is unique to thin film specimens.
All-Optical Variable-In Variable-Out Wavelength Conversions by Using MgO:LiNbO3 Quasiphase Matched Wavelength Converters
Authors: Bo Chen Bo Chen , Chang-Qing Xu Chang-Qing Xu , Bing Zhou Bing Zhou , Yasukazu Nihei Yasukazu Nihei , Akinori Harada Akinori Harada
Published: October 2002

A novel method of all-optical variable-in variable-out wavelength conversions is, for the first time, proposed and demonstrated by using MgO:LiNbO3 quasiphase matched (QPM) waveguides. It is shown that input signal in a wavelength range of 60 nm can be converted to any output signal in a wavelength range of 30 nm with almost the same efficiency (-26 dB with a pump power of -0.5 dBm) by changing device temperature and pump wavelength.
Preparation of Large Freestanding GaN Substrates by Hydride Vapor Phase Epitaxy Using GaAs as a Starting Substrate
Authors: Kensaku Motoki Kensaku Motoki , Takuji Okahisa Takuji Okahisa , Naoki Matsumoto Naoki Matsumoto , Masato Matsushima Masato Matsushima , Hiroya Kimura Hiroya Kimura , Hitoshi Kasai Hitoshi Kasai , Kikurou Takemoto Kikurou Takemoto , Koji Uematsu Koji Uematsu , Tetsuya Hirano Tetsuya Hirano , Masahiro Nakayama Masahiro Nakayama , Seiji Nakahata Seiji Nakahata , Masaki Ueno Masaki Ueno , Daijirou Hara Daijirou Hara , Yoshinao Kumagai Yoshinao Kumagai , Akinori Koukitu Akinori Koukitu , Hisashi Seki Hisashi Seki
Published: October 2002

A freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate. In the experiment, a GaAs (111)A substrate with a SiO2 mask pattern on its surface was used. A thick GaN layer was grown on the GaAs substrate at 1030°C through the openings in the SiO2 mask. By dissolving the GaAs substrate in aqua regia, a freestanding GaN substrate about 500 µm thick was obtained. The full-width at half maximum (FWHM) in the ω-mode X-ray diffraction (XRD) profile of GaN (0002) plane was 106 arcsec. The dislocation density of the GaN substrate obtained was determined to be as low as 2×105 cm-2 by plan-view transmission electron microscopy (TEM). Hall measurements revealed the n-type conductivity of the GaN substrate with typical carrier concentration and carrier mobility of 5×1018 cm-3 and 170 cm2·V-1·s-1, respectively.
Analysis of the Photocurrent in Quantum Dot Infrared Photodetectors
Authors: Victor Ryzhii Victor Ryzhii
Published: October 2002

We calculate the photocurrent in realistic quantum dot infrared photodetectors (QDIPs) using a developed device model. This model takes into account the space charge and the self-consistent electric potential in the QDIP active region, the activation character of the electron capture and its limitation by the Pauli principle, the thermionic electron emission from QDs and thermionic injection of electrons from the emitter contact into the QDIP active region, and the existence of the punctures between QDs. The developed model yields the photocurrent in a QDIP as a function of its structural parameters, applied voltage, and intensity. The calculated dependences are in agreement with available experimental data. The obtained results point the way for the optimization of QDIPs in order to realize their potential advantages.
Ordered Growth and Crystal Structure of Alq3 on Alkali Halide Surfaces
Authors: Hisashi Ichikawa Hisashi Ichikawa , Toshihiro Shimada Toshihiro Shimada , Atsushi Koma Atsushi Koma
Published: October 2002

Ordered films of tris-8-hydroxyquionolate-aluminum (Alq3) were grown by molecular beam deposition on cleaved KCl and KBr surfaces. The local molecular arrangements in the films were characterized by two-dimensional analysis of multiazimuth reflection medium energy electron diffraction (RMEED). A new type of curved one-dimensional crystallographic ordering was observed on KBr while a continuous point-on-line-type ordering was observed on KCl. Growth of the crystals consisting of mer isomers is suggested from the observed triple period superstructure.
Current Density Enhancement at Active Layer Edges in Polycrystalline Silicon Thin-Film Transistors
Authors: Kimura Mutsumi , Nozawa Ryoichi , Inoue Satoshi , Shimoda Tatsuya
Published: October 2002

In polycrystalline silicon thin-film transistors, the electric field is concentrated, the carrier density is increased, and the current density is enhanced at active layer edges. This phenomenon is confirmed using the two-dimensional (2-D) device simulation. Because of this phenomenon, the on-current is not proportional to the gate width. This dependence of the on-current on the gate width is confirmed using the 2-D device simulation and experiment.
Effects of Substrate Surface Morphology on Microcrystalline Silicon Solar Cells
Authors: Nasuno Yoshiyuki , Kondo Michio , Matsuda Akihisa
Published: October 2002

The relationship between µc-Si:H solar cell performance and surface morphology of substrate is studied systematically using textured-ZnO substrate which is formed by wet etching process in order to clarify the optimum morphology of substrate for high efficiency. An average slope, tan
θ, of substrate surface textures is obtained by analysis of atomic force microscopy (AFM) images, and solar cell performance is correlated with the value os tan
θ. As a result, because of the balance between the optical confinement and the grain boundary formation, a conversion efficiency shows a maximum at a tan
θ of 0.08 which is 3 times smaller as compared to that used for a-Si:H. An efficiency of 9.4% (V
oc=0.526 V, J
sc=25.3 mA/cm2, F
F=0.710) is obtained at a deposition temperature of 140°C using the optimized morphology.
Comparative Study of Pore Size of Low-Dielectric-Constant Porous Spin-on-Glass Films Using Different Methods of Nondestructive Instrumentation
Authors: Eiichi Kondoh Eiichi Kondoh , Mikhail R. Baklanov Mikhail R. Baklanov , Eric Lin Eric Lin , David Gidley David Gidley , Akira Nakashima Akira Nakashima
Published: October 2002

The pore sizes of hydrogen-methyl-siloxane-based porous spin-on-glass (SOG) thin films having different k values (k=1.8–2.5) are comparatively studied using different nondestructive instrumental ways and also with reference to sorption porosimetry. The pore size and its spread are found to increase with increasing porosity, or with decreasing dielectric constant.
Characterization of GaN-Based Schottky Barrier Ultraviolet (UV) Detectors in the UV and Vacuum Ultraviolet (VUV) Region Using Synchrotron Radiation
Authors: Motogaito Atsushi , Yamaguchi Motoo , Hiramatsu Kazumasa , Kotoh Masahiro , Ohuchi Youichiro , Tadatomo Kazuyuki , Hamamura Yutaka , Fukui Kazutoshi
Published: October 2002

Characterization of GaN-based Schottky barrier ultraviolet (UV) detectors with a comb-shaped electrode using synchrotron radiation (hν=2.2–30 eV, λ=41–563 nm) is described. Below hν=8.0 eV (λ>155 nm), the detectors are available without any photoemission of GaN and Au electrode. Under application of reverse bias, the responsivity is increased to 0.05 A/W at -0.4 V. The photocurrent is controlled by reverse bias. On the other hand, above hν=8.0 eV (λ<155 nm), the responsivity spectra are dominated by photoemissions of Au and GaN. These results show that these Schottky type detectors with mesa structures are effective to detect vacuum ultraviolet (VUV)-UV light (155<λ<360 nm).
Observation of Thermomagnetically Recorded Magnetic Domains in TbFeCo Films with Soft X-Ray Microscopy
Authors: Takagi Naoyuki , Fischer Peter , Tsunashima Shigeru , Kumazawa Masayuki , Ishida Hiroki , Yamaguchi Atsushi , Noguchi Hitoshi , Kume Minoru
Published: October 2002

We observed thermomagnetically recorded domains of various sizes with magnetic transmission X-ray microscopy (M-TXM) in order to clarify the recording characteristics. The domains were recorded on TbFeCo films by laser-pumped magnetic field modulation (LP-MFM) using a 635 nm laser diode. Typical images of magnetic domains in TbFeCo films were taken at the Fe L3-edge, and it was confirmed that the crescent-shaped domains could be recorded with high quality for mark lengths down to 100 nm.
The Growth of K2Al2B2O7 (KAB) Crystal by Modified Middle Seeded Solution Growth (MSSG) Method
Authors: Hu Zhang-Gui , Ushiyama Naoki , Yap Yoke Khin , Yoshimura Masashi , Mori Yusuke , Sasaki Takatomo
Published: October 2002

Among many nonlinear optical (NLO) crystals, Sr2Be2B2O7 (SBBO) and structurally related crystals is promising for the generation of UV and vacuum-UV (VUV) light. However, high viscosity, volatility and the platy growth habit have limited the growth of thick crystals for actual NLO applications. The growth of these crystals to a significant thickness has perplexed researchers in the past decade. The K2Al2B2O7 (KAB) is a new NLO borate crystal discovered in our laboratory. KAB possesses a layered structure similar to SBBO and thus is another potential UV NLO crystals. We adopted a modified middle-seeded solution growth (MSSG) method to grow KAB crystals. We were able to grow high-quality, bulk KAB crystal with dimensions of 12×10×6.5 t mm3. As our knowledge, among NLO borate crystals that have similar structure like the SBBO crystal, KAB is the first one that can be grown to such dimension to meet the requirement for proper measurement of linear and nonlinear optical properties.
Evaluation of Numerical Aperture and Focusing Characteristics of Planar Microlens for Optical Interconnects
Authors: Aoki Yasuhiko , Shimada Yuji , Iga Kenichi
Published: October 2002

We evaluated the numerical aperture (NA) and focusing characteristics of a planar microlens (PML) for parallel optical interconnect systems. The NA of a PML of 250 µm in diameter was measured to be 0.07 using a 125 µm mask aperture to clean the beam profile. By stacking two PMLs, the NA was raised to 0.17 due to the elliptical index profile of the stacked PML. The spot diameter was 11 µm, which is nearly equal to the diffraction limit and is usable for single-mode application.
A Functionally Graded Piezoelectric Material Created by an Internal Temperature Gradient
Authors: Ken Yamada Ken Yamada , Daisuke Yamazaki Daisuke Yamazaki , Kiyoshi Nakamura Kiyoshi Nakamura
Published: October 2002

Ultrasound transducers will have a broadband frequency characteristic if relevant piezoelectric parameters can be graded in the thickness direction of the plate. As is well known, piezoelectric properties will gradually fade away if the material temperature approaches the Curie point. From this viewpoint, we present in this letter a functionally graded piezoelectric material for broadband ultrasound transducers created by forming a temperature variation across a piezoelectric ceramic plate that has a relatively low Curie temperature. The distribution of the piezoelectric constant is estimated using an equivalent network model specially derived by the authors for plates with a graded piezoelectric constant.
Synthesis of Carbon Nanochaplets by Catalytic Thermal Chemical Vapor Deposition
Authors: Yoshikazu Nakayama Yoshikazu Nakayama , Mei Zhang Mei Zhang
Published: October 2002

We have synthesized carbon chaplets in nanometer-scale size consisting of a nanotube bearing beads by catalytic thermal chemical vapor deposition. The catalyst is a patterned, layered thin film of iron and indium (Fe/In) that is coated indium tin oxide. The bushlike chaplets grow on both Fe/In-coated and Fe/In-uncoated regions by feeding acetylene at temperatures from 680 to 725°C. It is found that the Fe/In film changes to compound particles to be seeds of the chaplets. Some particles migrate into the Fe/In-uncoated region to grow the chaplets bearing the beads with a variety of shapes depending on the seed.
Fluorinated Polymer Alignment Layers Formed at Low Temperature for Plastic-Substrate-Based Liquid Crystal Devices
Authors: Sato Hiroto , Fujikake Hideo , Kikuchi Hiroshi , Iino Yoshiki , Kawakita Masahiro , Tsuchiya Yuzuru
Published: October 2002

In this paper, we describe an alignment layer of chemically and mechanically stable fluorinated polymer for light-weight flexible liquid crystal display devices. Since the fluorinated polymer can be formed on plastic substrates at room temperature, unlike conventional polyimide, thermal distortion of the substrate does not occur. Uniform 70-nm-thick polymer thin films were obtained by spin-coating using a hydrofluoroether solvent. The orientation of the liquid crystal molecules was perpendicular to the rubbing direction of the fluorinated polymer, and the anchoring strength of the rubbed polymer was approximately 10-4 N/m. Twisted nematic liquid crystal devices using plastic substrates coated with the polymer showed good spatial uniformity and a high contrast ratio of more than 100:1.
Interface Roughness Produced by Nitrogen Atom Incorporation at a SiO2/Si(100) Interface
Authors: Inoue Kouta , Furuno Keita , Kato Hirohisa , Tamura Naoyoshi , Hikazutani Kenichi , Sano Seiji , Hattori Takeo
Published: October 2002

The critical amount of nitrogen atoms at the interface, above which the roughness of the oxynitride/Si(100) interface increases, was studied using noncontact-mode atomic force microscopy and X-ray photoelectron spectroscopy. The interface roughness was found to increase upon increasing the amount of nitrogen atoms at and near the interface if the amount of nitrogen atoms is greater than 0.37 monolayers. This increase in interface roughness was found to be reflected in an increase in surface roughness of almost the same amount.
Three-Dimensional Imaging of Carbon Nanotubes
Authors: Kizuka Tokushi , Sumi Takao , Bansho Satoshi , Saito Toyofumi
Published: October 2002

A computer tomography technique for nanometer-sized materials was developed based on transmission electron microscopy imaging with a 360° specimen rotation system and numerical convolution by a rotation-axis compensation method. The three-dimensional structures of carbon nanotubes were analyzed.
Photoluminescence Analysis of {311} Interstitial Defects in Wafers Synthesized by Separation by Implanted Oxygen
Authors: Jun-ichi Takiguchi Jun-ichi Takiguchi , Michio Tajima Michio Tajima , Atsushi Ogura Atsushi Ogura , Shigeo Ibuka Shigeo Ibuka , Yozo Tokumaru Yozo Tokumaru
Published: October 2002

The interstitial-type {311} planar defects introduced in wafers synthesized by separation by implanted oxygen (SIMOX) have been investigated by photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Deep-level PL of low-dose SIMOX wafers with doses of 2, 4, and 6×1017 cm-2 were analyzed under various excitations
with different penetration depths. In as-implanted wafers, the 0.903 eV line associated with the {311} defects appeared in the region below the oxygen implanted layer. Correspondingly, TEM observation revealed rod-like defects due to the {311} defects in the same region. After annealing, the 0.903 eV line disappeared and dislocation-related lines became visible. These results indicate that the {311} defects are generated below the implanted layer and are extended to dislocations after annealing.
High Output Power InGaN Ultraviolet Light-Emitting Diodes Fabricated on Patterned Substrates Using Metalorganic Vapor Phase Epitaxy
Authors: Tadatomo Kazuyuki , Okagawa Hiroaki , Ohuchi Youichiro , Tsunekawa Takashi , Imada Yoshiyuki , Kato Munehiro , Taguchi Tsunemasa
Published: October 2002

Ultraviolet (UV) light-emitting diodes (LEDs) with an InGaN multi-quantum-well (MQW) structure were fabricated on a patterned sapphire substrate (PSS) using a single growth process of metalorganic vapor phase epitaxy. In this study, the PSS with parallel grooves along the <1120>sapphire direction was fabricated by standard photolithography and subsequent reactive ion etching (RIE). The GaN layer grown by lateral epitaxy on a patterned substrate (LEPS) has a dislocation density of 1.5×108 cm-2. The LEPS-UV-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-UV-LED was operated at a forward-bias current of 20 mA at room temperature, the emission wavelength, the output power and the external quantum efficiency were estimated to be 382 nm, 15.6 mW and 24%, respectively. With increasing forward-bias current, the output power increased linearly and was estimated to be approximately 38 mW at 50 mA.
Formation of Vertically Aligned Carbon Nanotubes by Dual-RF-Plasma Chemical Vapor Deposition
Authors: Khin Yap Takashi Hirao , Takashi Ikuno Takashi Ikuno , Shin-ichi Honda Shin-ichi Honda , Yusuke Mori Yusuke Mori , Takatomo Sasaki Takatomo Sasaki , Kenjiro Oura Kenjiro Oura
Published: October 2002

The dual-RF-plasma chemical vapor deposition (dual-RF CVD) technique was examined for the formation of large areas of vertically aligned multiwalled carbon nanotubes (MWNTs). Two RF powers, Pdischarge (P
dis) and Psubstrate (P
sub), were used for the dissociation of methane gas and control of the energy of positive ions impinging on the substrates, respectively. The P
sub is necessary for the formation of MWNTs, without which a foil-like carbon nanostructured film was deposited. The positive ion bombardment works to suppress the deposition of amorphous carbon films and foil-like carbon nanostructures. Formation of MWNTs was observed within an area of 25 cm2 under the experimental setup. A threshold temperature between 500 to 540°C was defined for the formation of vertically aligned MWNTs.
High-Power CW Operation of GaInAsP/InP Superluminescent Light-Emitting Diode with Tapered Active Region
Authors: Yamatoya Takeshi , Sekiguchi Shigeaki , Koyama Fumio , Iga Kenichi
Published: October 2002

We have developed a 1.55 µm superluminescent light-emitting diode (SLD) with a tapered active region. We achieved high power and broadband operation demonstrating an output power of 330 mW under cw operation at 7°C. We examined the beam profile of output light by measuring its near field and far field patterns. It was found that the output light shows a fundamental transversal mode profile in both horizontal and vertical directions. This device will be applicable to spectrum-sliced multiwavelength light sources for use in wavelength division multiplexing optical communication systems as well as in lightwave sensing.
Amplitude and Phase Characterization of 5.0 fs Optical Pulses Using Spectral Phase Interferometry for Direct Electric-Field Reconstruction
Authors: Liming Li Liming Li , Satoru Kusaka Satoru Kusaka , Naoki Karasawa Naoki Karasawa , Ryuji Morita Ryuji Morita , Hidemi Shigekawa Hidemi Shigekawa , Mikio Yamashita Mikio Yamashita
Published: October 2002

The amplitude and phase of 5.0 fs optical pulses with an ultrabroad bandwidth from 480 to 835 nm were rapidly characterized by the spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. To our knowledge, this is the shortest pulse ever measured by the SPIDER technique. To solve the problems of dispersion, bandwidth, sensitivity and wavelength resolution, which are essential for few-optical-cycle pulse characterization, we developed a SPIDER apparatus equipped with ultrabroad-band (450–850 nm) beam splitters, a thin (25 µm) β-BaB2O4 crystal, a 0.5 m spectrometer capable of the automatic and fast control of two gratings (1200 and 150 lines/mm) and a highly sensitive intensified charge-coupled device.
Hollow Optical Waveguide for Temperature-Insensitive Photonic Integrated Circuits
Authors: Miura Toru , Koyama Fumio , Aoki Yasuhiko , Matsutani Akihiro , Iga Kenichi
Published: October 2002

We propose a hollow optical waveguide with metal coating or dielectric multilayer coating to achieve sufficient reflectivity at guiding walls. Low-loss and polarization-insensitive propagation characteristics are predicted. The propagation constant is independent of the temperature, resulting in temperature-insensitive photonic waveguide devices, such as optical filters and grating optical demultiplexers. We demonstrate a hollow optical waveguide with metal-coated walls on a GaAs substrate, which was fabricated using dry etching. The propagation loss including the coupling loss with an input fiber was 2.6 dB/cm and 7.3 dB/cm for transverse electric (TE) mode and transverse magnetic (TM) mode, respectively.
Study of the Si(111) “5×5”-Cu Surface Structure by X-Ray Diffraction and Scanning Tunneling Microscopy
Authors: Nakatani Shinichiro , Kuwahara Yuji , Kuramochi Hiromi , Takahashi Toshio , Aono Masakazu
Published: October 2002

The quasi-“5×5” structure on the Cu/Si(111) surface was investigated by surface X-ray diffraction that utilized anomalous X-ray scattering by Cu atoms in part and scanning tunneling microscopy (STM). The X-ray reflectivity curve along the 00 rod was analyzed in the absolute scale to determine not only the vertical heights of the atomic layers of Cu but also the coverage of Cu atoms. The average interatomic distance of Cu–Cu was estimated by the measurement of the anomalous X-ray scattering. Clear STM topographs that are probably able to explain the origin of the “5×5” structure were taken. The topograph images also support the results of the X-ray diffraction.