bluuebunny/crossref_metadata_2025 huggingface dataset:
Molybdenum Film Technology For Power Metal Oxide Semiconductor Field Effect Transistor Gate Electrode Applications
Authors: Liu Ying-Kun , Liang Chun-Guang , Wang Zhan-Li , He Yu-Zhang , Lang Xiu-Lan , Zhou Ming-Hui
Published: October 2002

Molybdenum (Mo) film as a gate electrode for high-frequency power metal oxide
semiconductor field effect transistor (MOSFET) has been investigated. The Mo films
were deposited by sputtering in Ar ambient. The Mo films properties depend greatly on
the substrate temperature. An accurate pattern was realized for Mo film. Stability and
reliability of Mo gates for high-frequency power vertical double-diffused metal oxide
semiconductor field effect transistors (VDMOSFETs) are as good as those of polysilicon
gates. The shift of threshold voltage is below ±35 mV and the change of
gate-source leakage current is less than 5 nA under the stress condition of
±5 MV/cm for 100 h at 250°C. Power gain and drain efficiency
improvement of Mo gates for VDMOSFETs have been obtained.
Reactive Ion Pretreatment Technique to Improve the Ashing Resistance of Low Dielectric Constant High Carbon Content Polymer
Authors: Chang Kow-Ming , Yang Ji-Yi , Chang Yu-Hsun , Tsai Jung-Yu
Published: October 2002

The oxygen plasma via resist strip process causes significant
damage to organic spin on polymer (Allied Signal X-720); thus its
inter-level dielectric application is limited. A simple treatment
technology, reactive glass stabilization (RGS), using reactive ion
is proposed to reform the X-720 film surface. The reactive ion
modification of the X-720 film can improve the resistance against
oxygen plasma. The measurements of stress, thickness variation,
scanning electron microscope (SEM) micrographs of gap filling and
dielectric constant show that RGS can be practically used in the low
dielectric material application with non-etch-back process. The
measurements of fourier transform infrared (FTIR) spectroscopy, and
auger electron spectroscopy (AES) show that RGS can effectively
reform the surface of the X-720 film and increase the ashing
resistance even in high carbon content spin on polymer.
Optical Switching Due to Local Kerr Nonlinearity in Attenuated Total Reflection Geometry
Authors: Toshihiro Okamoto Toshihiro Okamoto , Masanobu Haraguchi Masanobu Haraguchi , Masuo Fukui Masuo Fukui
Published: October 2002

By employing attenuated total reflection geometries, we have numerically analyzed optical switching due to local Kerr nonlinearity by the coupled mode theory for a lossy polydiacetylene waveguide and explored the possibility of realizing the observation of optical attenuated total reflection (ATR) switching. We have adopted a Gaussian incident beam and have taken into account beam spread. It has been found that the choice of a proper beam spread of the incident Gaussian light leads to a considerable decrease of the critical light power and the critical light intensity required for the optical switching. Moreover, the effect of the incident beam width and guided layer thickness on the critical incident intensity and the critical incident power has been discussed.
Semiclassical Approach in the Analysis of Ring Laser: II. Mode Coupling due to Backscattering and Interference
Authors: Yoshiyuki Shimosako Yoshiyuki Shimosako , Takahiro Numai Takahiro Numai
Published: October 2002

In the research on ring lasers, the relationship between the lock-in phenomenon and backscattering was usually analyzed by treating the backscattered waves as phenomenological coupling terms. However, with these approaches, it is difficult to quantitatively estimate the relationship between lock-in phenomena and reflection due to backscattering. Also, the dependence of the coupling constant for a two-mode operation on backscattering reflection has not been described. To overcome these problems, rate equations, in which spatial distributions of the fields are expressed as superpositions of traveling wave and its backscattered wave, have been derived in our previous paper [Jpn. J. Appl. Phys. 39 (2000) 3983]. Based on these newly derived rate equations, this paper introduces a modified coupling constant, which includes backscattering reflectivity, the Doppler effect, linear mode pulling, and the interference between two modes. As a result, it is found that the Doppler effect plays an important role in the modified coupling constant which is related to lock-in phenomena. It is also shown that a weak coupling for all relative phase angles which leads to stable two-mode operations can be observed when the Doppler effect is significant. Moreover, an upper limit of reflectivity of backscattered waves to achieve stable two-mode operations is revealed quantitatively.
One-Equation, Two-Equation and Kinetic Theory: Laser Pulse Heating
Authors: Yilbas Bekir Sami , Shuja Shahzada Zaman
Published: October 2002

In the present study, comparisons of electron kinetic theory predictions with results of two-equation and one-equation models are made. The numerical solutions for all models employed are introduced for exponentially decaying and step input intensity pulses. The closed form solution for the electron kinetic theory approach is obtained for the exponentially decaying pulse. The study is extended to include comparisons of the closed form solution of the kinetic theory approach with the analytical solutions previously obtained according to the Fourier theory. It is found that all the models considered result in similar temperature profiles inside and at the surface of the substrate for laser pulses up to 10-9 s. As the pulse length reduces further (<10-9 s) and intensity increases (>1013 W/m2), the kinetic theory predictions deviate considerably from the Fourier theory results.
Pyroelectric Properties of Sol–Gel Derived (Pb,Ca)TiO3 Thin Film Detectors
Authors: Wang Chih-Ming , Huang Yao-Te , Chen Ying-Chung , Lee Maw-Shung , Cheng Chein-Chuan , Kao Ming-Cheng
Published: October 2002

Calcium-modified lead titanate (PCT) thin film pyroelectric infrared (IR) detectors were fabricated on Pt(111)/SiO2/Si(100) substrates using a diol-based sol–gel process. The randomly oriented PCT thin film, which has not undergone the poling treatment, exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric properties of PCT thin film point detectors with various Ca contents on modulation frequency are measured and compared. The optimized composition of PCT thin film IR detectors was found to be the PCT(25), which exhibits a large voltage responsivity of 4533 (V/W) at 20 Hz and a specific detectivity (D
*) of 6.45×107 cmHz1/2/W at 100 Hz. The results show that Pb1-x
Ca
x
TiO3 thin film with x = 0.25 [PCT(25)] was most suitable for application to the pyroelectric thin film IR detector.
Tin Oxide Films by Chemical Vapor Deposition Using a Monobutyltin Trichloride Source: The Effect of H2O on Deposition Behavior and Electrical Properties
Authors: Lee Si-Moo , Kim Dong-Lae , Youn Hyuk-Joon , Hong Kug Sun
Published: October 2002

Tin oxide films were produced by chemical vapor deposition using
monobutyltin trichloride and oxygen as reactants. The effect of
H2O addition on deposition behavior and electrical properties at
various deposition temperatures were investigated. The addition of
H2O significantly increased deposition rates and lowered
corresponding apparent activation energies at low temperatures. At
high temperatures, however, the addition of H2O decreased
electrical conductivity in films, which was attributed to a decrease
in carrier concentration, i.e. incorporated Cl content. It was
therefore unlikely that both the deposition rate and the conductivity,
in case of H2O addition, were controlled by the same reaction. It
could be suggested that while the deposition rate is enhanced by the
well known hydrolytic decomposition of the Sn–Cl bond, the electrical
conductivity (incorporated Cl amount) is determined by a reaction
involving the removal of surface Cl.
Maximization of Extinction Ratios of Thin-Metal-Clad Optical Waveguide Polarizers with Proper Dielectric-Cover-Layer Thickness
Authors: Chen Chyong-Hua , Wang Likarn
Published: October 2002

We theoretically analyze the performance of optical thin-metal-clad waveguide
polarizers with emphasis on the effect of dielectric-cover-layer (i.e., superstrate)
thickness. We show that the polarization extinction ratio can be theoretically made
infinite by selection of metal film thickness and polarizer length for a given
dielectric-cover-layer thickness. It is shown that the required metal film thickness
and polarizer length should be changed for reaching an infinite extinction ratio as
different cover layer thicknesses are to be used. However, an infinite extinction ratio
is not possible as the dielectric cover layer is thinner than some value. For fixed metal
film and buffer layer thicknesses, a certain discrete cover layer thicknesses are
required for reaching infinite extinction ratios.
Plasma Position Measurements in a Tokamak with an Iron Core Transformer
Authors: Gi-Chung Kwon Gi-Chung Kwon , W. Choe W. Choe , Jayhyun Kim Jayhyun Kim , Hyo-Suk Yi Hyo-Suk Yi , Sang-Jean Jeon Sang-Jean Jeon , Songwhe Huh Songwhe Huh , Hong-Young Chang Hong-Young Chang , Duk-In Choi Duk-In Choi
Published: October 2002

Two simple methods of estimating the plasma position in a large-aspect-ratio, low-βptokamak with an iron core transformer are demonstrated: a magnetic diagnostic method and an optical method. The magnetic diagnostic method utilizes an array of magnetic pickup coils to measure the poloidal magnetic field produced by the plasma current. To include the effects of toroidicity and an iron core transformer, the correction factor was calculated with the magnetic material (or iron core) inside the calculation domain and incorporated in the analysis. The evolution of horizontal and vertical displacement of the plasma center obtained in this way is used to control the KAIST-Tokamak plasmas. To compare the plasma position estimated using the magnetic pickup coils, a simple optical method is also demonstrated on KAIST-TOKAMAK using a composite video signal from a charge-coupled device (CCD) camera. The two results are in good agreement.
Negative Resist Material Based on Polysilanes for Electron Beam and X-Ray Lithographies
Authors: Seki Shu , Sakurai Yusuke , Maeda Kensaku , Kunimi Yoshihisa , Tagawa Seiichi
Published: October 2002

In the present paper, we describe the mechanisms of photo- and radiation-induced reactions in silicon based resist materials, polysilanes with Si-branchings and Si–H bondings, candidates for future resist materials. Polysilanes have been previously confirmed to show positive-type resist properties for ultra violet (UV) light, electron beams (EB), and X-rays under all conditions. However, the cross-linking reaction of the polymer became dominant in the polysilane with Si-branchings, upon irradiation with UV light, EB, and ion beams. The efficiency of the cross-linking reaction strongly depended on the ratio of Si-branching producing polymer gels in the polysilane with a higher amount of Si-branching than 5%, even with γ-ray irradiation. Polyhydrosilanes containing vinyl groups were revealed to cause efficient cross-linking reactions in the presence of catalysts for hydrosilylation upon exposure to deep UV or X-rays, leading to high-sensitive negative resist materials for extreme UV lithography.
Effect of Radiative Losses on the Parabolic Two-Step Heat Conduction Model
Authors: Kiwan Suhail , Al-Nimr Moh'd Ahmad
Published: October 2002

The effects of radiative thermal losses on the thermal behavior of thin metal films, as described by the parabolic two-step heat conduction model, are investigated. Different criteria, which determine the ranges within which thermal losses are significant, are derived. The effects of these criteria on the thermal losses from the thin film are investigated. It is found that radiative losses from metal films are significant when the ratio of the diffused energy within the electron gas to the exchanged energy between the electron gas and the solid lattice is larger than one. Also, it is found that radiative losses are significant when the ratio of the radiative lost energy to the exchanged energy between the electron gas and the solid lattice is larger than 10-5.
Effect of Atomic Hydrogen on GaAs Growth on GaAs(311)A Substrate in Molecular Beam Epitaxy
Authors: Jang Kee-Youn , Okada Yoshitaka , Kawabe Mitsuo
Published: October 2002

The uniform corrugated structures along [1\overline12] direction have been found in the GaAs layers grown on GaAs (311)A substrates by atomic hydrogen-assisted molecular beam epitaxy (H-MBE). On the other hand, no corrugated structures were observed in the growth by conventional MBE. The differences in the surface morphology between H-MBE and conventional MBE samples were analyzed by using an atomic force microscope. In H-MBE, atomic H was continuously supplied during the growth, and hence the dangling bonds on the surface would be terminated by the H atoms. Thus, the [1\overline12] azimuth-oriented corrugations observed in H-MBE samples is thought to be due to the presence and interation of atomic H with the migrating Ga atoms, and preference of growth along the the steps where Ga atoms are terminated by H atoms.
First-Principle Calculation of Migration Processes of As during Growth on GaAs(001)
Authors: Kaori Seino Kaori Seino , Akira Ishii Akira Ishii , Takaaki Kawamura Takaaki Kawamura
Published: October 2002

The microscopic migration of an As adatom on a
Ga-terminated GaAs(001) surface is investigated by
performing first-principle calculations using
density functional theory and a slab model of the
surface, because the importance of As adatom
migration has been reported. The obtained values
of barrier energy are compared with those to
hopping in the kinetic Monte Carlo simulation. The
anisotropic migration of the As adatom is
clarified, which agrees with the result of the
kinetic Monte Carlo simulation as well as the
properties obtained by the scanning tunneling
microscopy observation. It is
shown that an As adatom is more mobile than a Ga
adatom, and the kinetics of both As and Ga atoms
on the growing surface are important during
molecular beam epitaxial growth.
Quantum Size Effects in Metallic Overlayer Epitaxy
Authors: Sinnott Susan B. , Wood Richard F. , Cho Jun-Hyung , Zhang Zhenyu
Published: October 2002

Ab-initio total energy calculations have been performed to study
the stability and electronic structure of epitaxial Sb and
close-packed Ag films on GaAs(110) surfaces. These are model
metal-semiconductor systems that have been studied extensively
experimentally. The method used is density functional theory within
the pseudopotential approximation. These calculations provide
information on the relaxation and structure of the Sb and Ag surface
layers and the stability of the metal films as a function of the
number of metal layers.
Silver-Induced 3×3 Phase on 6H-SiC(0001)√3×√3 Surface
Authors: Kubo Osamu , Harada Toru , Kobayashi Tadashi , Ryu Jeong-Tak , Katayama Mitsuhiro , Oura Kenjiro
Published: October 2002

The processes of structural and morphological change of a 6H-SiC(0001)√3×√3
surface induced by Ag deposition and annealing have been studied by scanning tunneling microscopy
(STM). A surface phase with 3×3 periodicity was found for Ag adsorption onto the √3×√3
surface at 500°C. STM images of this surface revealed one round protrusion per 3×3 unit
cell in the empty state, and this round protrusion demonstrated a trimer like appearance in the filled
state. We also observed the presence of 2D-island-like areas with no periodicity, which were surrounded
by the 3×3-Ag surface phase. These structures disappeared and the original √3×√3
surface phase was recovered by annealing at 600°C.
GaSb(001) 4×2-In Surface Structure Studied by Core-Level Photoelectron Spectroscopy and X-Ray Standing-Wave Analysis
Authors: Maeda Fumihiko , Sugiyama Munehiro , Watanabe Yoshio
Published: October 2002

The surface structure of GaSb(001) 4×2-In was investigated by core-level photoelectron spectroscopy (CLPES) using synchrotron radiation and X-ray standing-wave (XSW) analysis. From the CLPES measurement, we found that the 4×2 surface was mainly composed of single chemical bondings, which could be assigned to In–Sb bonding. This indicated that an In–Sb molecular layer terminated this 4×2 surface. In addition, the In atom position was analyzed by XSW using two different asymmetric (111) and (1-11) reflections. The coherent position values of 0.684 for (111) and 0.015 for (1-11) that were obtained indicated that the In atom position was higher than the top Sb atom position of Sb-double-layer. From these results, we propose a surface local bonding model for GaSb(001) 4×2-In, in which the Sb-double layer remains and In atoms terminate the surface.
Formation of Ordered Rod-like Clusters of Iodine on H-Terminated Si(111) Surfaces During Immersion in Concentrated HI Solutions
Authors: Imanishi Akihito , Ishida Masaki , Zhou Xiaowen , Nakato Yoshihiro
Published: October 2002

Iodine adsorption (or reaction) on atomically-flat H-terminated Si(111) surfaces in 7.1 M HI and 7.1 M HI+0.05 M I2 was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS measurements showed that iodine was adsorbed gradually with time when immersed in 7.1 M HI, and rapidly and in a larger quantity when immersed in 7.1 M HI/0.05 M I2. AFM inspection showed that circular dot-like clusters were formed initially in both the HI and HI/I2 solutions. However, for the case of 7.1 M HI solution, dot-like clusters, located near steps, grew with time only in particular directions of threefold symmetry of Si(111), resulting in ordered wire-like clusters. For the case of HI/I2 solution, the circular dot-like clusters were distributed randomly on terraces and steps even after prolonged immersion, with no formation of any ordered clusters.
Molecular Dynamics Studies of Surface Difference Effect on Gas Separation by Zeolite Membranes
Authors: Mizukami Koichi , Kobayashi Yasunori , Morito Hideaki , Takami Seiichi , Kubo Momoji , Belosludov Rodion , Miyamoto Akira
Published: October 2002

The permeation of CO2/N2 gas mixture through zeolite
membranes was investigated by molecular dynamics (MD) study. MD
calculation successfully reproduced the experimental results of
CO2/N2 separation by NaY membrane. Furthermore, the
surface difference effect on gas separation was examined using the
NaA zeolite (100) surface and its (111) surface. The
CO2/N2 separation factor of the (111) surface was much
lower than that of the (100) surface. This was caused by the
difference in surface structure, since the pore structures of both
models were the same.
Work Function and Surface Segregation Study on Nb/Ti/Cu Multilayer Films
Authors: Reddy Aparna Yarrama , Yoshitake Michiko , Yoshihara Kazuhiro
Published: October 2002

Work function variation with surface segregation of underlayer elements was studied to enable the utilization of saturation behavior in segregation phenomena for work function control. Surface composition of Nb film/Ti film/Cu substrate was monitored by X-ray photoelectron spectroscopy (XPS) at elevated temperatures. Cu and Ti segregated after a certain period of time; the surface concentration of Cu saturated first followed by that of Ti. Both Cu and Ti were observed only at the surface region less than 1nm thick. Using a Kelvin probe, a monotonous work function decrease with increasing Cu and Ti concentration was observed. The amount of decrease at Cu saturation (Cu: 5 at.%, Ti: 20 at.%) was 0.2 eV and that at Ti saturation (Cu: 5 at.%, Ti: 30 at.%) was 0.3 eV. It was determined that the sample worked as a getter for residual gas and the work function on the surface with saturated segregation was stable.
Determination of Reactive Species for Alumina-Supported Molybdenum Carbide Catalysts for Methane Reforming Using Temperature-Programmed Reaction Methods
Authors: Oshikawa Katsuhiko , Nagai Masatoshi , Omi Shinzo
Published: October 2002

The activities and surface properties of alumina-supported molybdenum carbide catalysts used in methane reforming were studied. Hydrogen, ethane, ethylene, and benzene were detected as the main products. The addition of oxygen effectively regenerated the catalyst. Temperature-programmed reaction (TPR) experiments revealed that the surface molybdenum carbide species changes from β-Mo2C to η-Mo3C2. The addition of CO2 to the feedstream reduced the formation of graphitic carbon on the catalyst surface, increasing the catalyst lifetime for benzene formation.
Generalized Grazing Incidence-Angle X-Ray Diffraction Studies on InAs Quantum Dots on Si (100) Substrates
Authors: Uragami Takeshi , Fujioka Hiroshi , Waki Ichitaro , Mano Takaaki , Ono Kanta , Oshima Masaharu , Takagi Yasuo , Kimura Masao , Suzuki Tamaki
Published: October 2002

We have investigated structural properties of InAs quantum dots grown on a Si (100) substrate using Generalized Grazing Incidence-angle X-ray Diffraction (G-GIXD). Strong diffraction spots from the InAs dots were observed in spite of their small volume (37 nm in diameter) and small surface coverage (about 11%). It has been found that the InAs dots are dilated by 1.2% along the perpendicular direction to the surface and compressed by 0.8% in the lateral direction. This finding indicates that the density of the misfit dislocations introduced during the growth is not large enough to relax the lattice mismatch perfectly. We have found that the lateral strain in the InAs dots is smaller than that expected from the macroscopic strain model for flat epitaxial films.
X-Ray Photoelectron Spectroscopy Study of Hetero-Interface between Manganese Pnictide and Mn–Zn Ferrite
Authors: Ikeda Takeshi , Fujioka Hiroshi , Ono Kanta , Oshima Masaharu , Yoshimoto Mamoru , Koinuma Hideomi
Published: October 2002

We have investigated the hetero-interface between MnSb thin
films and Mn–Zn ferrite substrates using reflection high-energy
electron diffraction (RHEED) and X-ray photoelectron spectroscopy
(XPS). The RHEED observations have shown that the mismatch between
the MnSb and the Mn–Zn ferrite is fully relaxed at a film thickness
of less than 4.3 MLs. XPS analyses have revealed that MnSb grows
two-dimensionally from an early stage. We have observed a slight
outdiffusion of oxygen from the substrate. The diffusion length of
oxygen has turned out to be 50 Å. However, it has also been
found that the outdiffusion of Zn and Fe from the Mn–Zn ferrite
substrate are negligible.
Stabilization of ZrSixOy Films by Irradiation with an ArF Excimer Laser
Authors: Keisuke Nakazawa Keisuke Nakazawa , Takahiro Matsuo Takahiro Matsuo , Toshio Onodera Toshio Onodera , Tohru Ogawa Tohru Ogawa , Hiroaki Morimoto Hiroaki Morimoto
Published: October 2002

ZrSixOy is a candidate material for fabricating attenuated phase-shift masks used in ArF excimer laser lithography. To investigate the durability mechanism of ZrSixOy films following irradiation with an ArF excimer laser, we analyzed the films chemically and physically. The phase shift and the transmittance of a transmissive film with a high oxygen concentration increases and decreases, respectively, with irradiation. This is because of an increase of Si-O-Zr bond structures. The phase shift and the transmittance of an absorptive film with a low oxygen concentration decreases and increases, respectively, with irradiation because of photooxidation at the surface. The oxidation leads to the formation of Si-O-Zr and Si-O-Si bond structures in the films. Both films are stabilized by irradiation with a large irradiation energy. We interpret that both films are stabilized by the formation of Si-O-Zr bond structures, such as zircon, with saturation of oxygen concentrations at the surface.
Epitaxial Growth of Single-Crystal Ultrathin Films of Bismuth on Si(111)
Authors: Nagao Tadaaki , Doi Takumi , Sekiguchi Takeharu , Hasegawa Shuji
Published: October 2002

We have studied the epitaxial growth of bismuth overlayers on Si(111) surfaces by in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Lateral growth of texture two-dimensional (2D) nanocrystals takes place after the formation of an initial disordered wetting layer on the 7×7 DAS structure. After the coalescence of the texture 2D nanocrystals, alignment in their azimuthal orientation takes place. At slightly more than 15 monolayers, the growth front of the overlayer exhibits a perfectly long-range ordered Bi(0001)-1×1 surface. The films prepared on Si(111)-α-√3×√3-Bi or on Si(111)-β-√3×√3-Bi do not show as good quality as those on Si(111)-7×7. Thus, the initial disordered wetting layer formed on the 7×7 surface successfully accommodates the large 18% lattice mismatch between the Si(111) and Bi(0001) planes and allows the 2D nanocrystal to grow laterally.
Atomic Hydrogen Induced Step Bunching on High-Index GaAs Substrates for Fabrication of Novel Quantum Wire and Quantum Dot Arrays by Molecular Beam Epitaxy
Authors: Nötzel Richard , Ploog Klaus H.
Published: October 2002

We present our recent experiments on the effect of atomic hydrogen on the growth on planar and patterned high-index GaAs substrates by molecular beam epitaxy and its application to novel quantum wire and quantum dot arrays. The promotion of step bunching on GaAs (331)A substrates by atomic hydrogen to well-ordered multiatomic step arrays is utilized for the fabrication of modulation-doped conductive quantum wires with strong anisotropy of the electron conductivity. Atomic hydrogen induced step bunching on GaAs (311)A substrates combined with lithographic patterning of the substrate prior to growth produces uniform arrays of quantum dots.
Quantized Conductance in Pt Nanocontacts
Authors: Kenji Yuki Kenji Yuki , Shu Kurokawa Shu Kurokawa , Akira Sakai Akira Sakai
Published: October 2002

The conductance of Pt nanocontacts has been measured at room
temperature during the contact break of Pt relays. At low biases, the
conductance histogram exhibits a broad peak around 1G
0, (G
0 = 2e
2/h
is the conductance quantum) in agreement with previous experimental
results. Upon increasing the bias above 0.6 V, a well defined peak appears
at 1.7G
0 which decreases in height upon further increasing the bias.
Except for its position at a non-quantized value, the observed 1.7G
0
peak exhibits the same bias dependence as that of the quantized 1G
0 peak
of Au.
Electrical Properties of Nanometer-Sized Schottky Contacts on n-GaAs and n-InP Formed by in Situ Electrochemical Process
Authors: Sato Taketomo , Kasai Seiya , Okada Hiroshi , Hasegawa Hideki
Published: October 2002

The current transport characteristics of nanometer-sized Schottky contacts were investigated from theoretical and experimental viewpoints. A theoretical calculation of the three dimensional (3D) potential distributions showed that the potential shape underneath the nano-Schottky contacts was considerably modified by the surface Fermi level pinning on the air exposed free surfaces, producing a saddle point in the potential. The current–voltage (I–V) curves were strongly influenced by this saddle point potential and resulted in nonlinear log
I–V characteristics. Experimentally, the Pt nano-particles were selectively formed using the in situ electrochemical process on n-type GaAs and n-type InP substrates patterned using electron-beam (EB) lithography. Their I–V measurements were carried out using an atomic force microscopy (AFM) system equipped with a conductive probe. The log
I–V curves of the nano-Schottky contacts showed nonlinear characteristics with large n values of 1.96 for n-GaAs and 1.27 for n-InP and could be very well explained by the theoretical I–V curves considering the “environmental” Fermi level pinning.
Surface Structure of Si(110) “7×2”–Sn Observed by Scanning Tunneling Microscopy
Authors: An Toshu , Yoshimura Masamichi , Ueda Kazuyuki
Published: October 2002

We have studied a Si(110) “7×2” ((1,6)×(2,2))–Sn surface by means of scanning tunneling microscopy (STM). High-resolution STM images have shown that Sn trimers and Si pentagons are arranged regularly in the “7×2” surface. The Si pentagons, which are the
elemental structures of clean Si(110) “16×2”, are rearranged in the presence of Sn trimers. The Si pentagons are pronouncedly imaged in the empty states, due to the charge transfer from Si pentagons to Sn trimers.
Electron Transport in Nanocrystalline Si Based Single Electron Transistors
Authors: Dutta Amit , Oda Shunri , Fu Ying , Willander Magnus
Published: October 2002

Electron transport has been studied by measurement and simulation of single electron transistors based on nanocrystalline silicon (nc-Si). Nanocrystalline silicon is formed in the gas phase of the SiH4 plasma cell by the coalescence of radicals. Digital chemical vapor deposition [CVD] technique using pulsed gas in the plasma is effective to obtain highly uniform Si quantum dots with an average size of 8 nm and dispersion of 1 nm. Single electron transistors have been successfully fabricated by deposition of nc-Si on top of heavily doped silicon nanoelectrodes with a gap of 15 nm which allows the study of electron transport through two or three nanocrystals. Coulomb blockade and Coulomb oscillations are observed in these devices at various temperatures, including room temperature. The observed Coulomb diamond structure is not as simple as in the case of metallic islands. With increasing gate voltage, the spacing between oscillation peaks decreases and the Coulomb diamonds reduce in size. These observations are explained on the basis of electron transport through a quantum dot with an energy gap between the highest occupied and the lowest unoccupied electron states. Modeling of such a system can reproduce measured electrical characteristics. The unequal spacing of gate oscillations and the reduced size of Coulomb diamonds are due to the interplay of Coulomb charging energy and the energy separation between the quantized energy levels.
Output Power Enhancement of a Chemical Oxygen-Iodine Laser by Predissociated Iodine Injection
Authors: Endo Masamori , Sugimoto Daichi , Okamoto Hideo , Nanri Kenzo , Uchiyama Taro , Takeda Shuzaburo , Fujioka Tomoo
Published: October 2002

Output power enhancement of a chemical oxygen-iodine laser (COIL) by an injection of predissociated iodine was studied. Iodine molecules were dissociated into atoms by the microwave discharge prior to injection. It was determined that predissociation caused a negative effect on the output power enhancement when this technique was applied to a conventional supersonic COIL. Model calculations revealed that the existence of atomic iodine at the plenum caused the dissipation of stored energy. It was demonstrated that decreasing the mixing point pressure was crucial to obtain output power enhancement by the predissociation technique. For this purpose, a low-pressure transonic mixing scheme with a grid nozzle array was developed. A 9% enhancement of output power was demonstrated.
Highly Selective GaAs/Al0.2Ga0.8As Wet Etch Process for the Gate Recess of Low-Voltage-Power Pseudomorphic High-Electron-Mobility Transistor
Authors: Chang Huang-Choung , Chang Edward Y. , Chung Chao-Cheng , Kuo C. T.
Published: October 2002

A selective wet etch process for the gate recess of the GaAs power pseudomorphic high-electron-mobility transistors (pHEMT's) was developed. The power pHEMT's used in this study were epitaxially grown power Al0.2Ga0.8As/In0.2Ga0.8As pHEMT's with a 250 Å GaAs cap layer and a 300 Å Al0.2Ga0.8As electron-donating layer. The electron-donating layer was used as the etch-stop layer for the gate recess. A selectivity of 3400:1 was achieved for GaAs/Al0.2Ga0.8As layers using citric acid/tripotassium citrate/hydrogen peroxide etching solutions in this study. This is the highest selectivity for GaAs/Al
x
Ga1-x
As selective etching reported so far. The pHEMT's processed using this selective etching demonstrated good device power performance, and the wet recess process did not cause any contamination or damage to the device. The test data indicates that this selective etch process can be of practical use for forming the gate recess of the power pHEMT's with good device performance and excellent electrical uniformity.
Amorphous-to-Polycrystalline Silicon Transition in Hot Wire Cell Method
Authors: Mitsuru Ichikawa Mitsuru Ichikawa , Takeshi Tsushima Takeshi Tsushima , Akira Yamada Akira Yamada , Makoto Konagai Makoto Konagai
Published: October 2002

Hot Wire Cell method has been newly developed and successfully applied to grow polycrystalline silicon films at a low temperature with a relatively high growth rate. In the Hot Wire Cell method, reactant gases are decomposed as a result of reaction with a heated tungsten filament placed near a substrate and polycrystalline silicon films can be deposited at a growth rate of 0.9 nm/s without hydrogen dilution. The film crystallinity is changed from polycrystalline to amorphous by decreasing the total pressure. The model calculation of the Hot Wire Cell method is carried out and it is assumed that transition of crystallinity may be due to the shift in the preferential impinged radicals. X-ray analysis clearly showed that the films grown at the filament temperature of 1700°C have a very strong (220) preferential orientation. The films consist of large grains as well as small grains. These results suggest that the Hot Wire Cell method is a promising candidate to grow device-grade polycrystalline silicon films for photovoltaic application.
Resonant Detection and Frequency Multiplication in Barrier-Injection Heterostructure Transistors
Authors: Irina Khmyrova Irina Khmyrova , Victor Ryzhii Victor Ryzhii
Published: October 2002

A novel detector and harmonic multiplier – a barrier-injection heterostructure transistor (BIHT) – is proposed and evaluated. The structure of a BIHT is similar to that of a heterostructure field-effect transistor. The device utilizes thermionic injection of electrons to the BIHT channel in which the standing plasma waves are excited by an incoming signal. The combination of the strong nonlinearity of the dependence of the injected current on the channel potential with the high amplitude of the oscillation of the latter at resonant frequencies results in a significant enhancement of the responsivity and harmonic multiplication efficiency. The BIHT detectors and multipliers can be effective in the terahertz range of frequencies, surpassing the performance of Schottky-diode-based devices.
Comparison of Direct and Indirect Photometric Descriptions in Monte Carlo Lighting Simulation
Authors: Chen Li , Wang Xinsheng , Suzuki Masafumi , Yoshimura Noboru
Published: October 2002

According to the analytical aim and the dimension of the model, the photometric property of light source can be described either directly or indirectly in Monte Carlo lighting simulation. In this research, the simulations on the luminous intensity characteristics of louvered luminaire and the reflection characteristics of IC substrate are taken as models for the direct and indirect expressions of the luminous flux of light source. The advantage and differences of both methods are compared based on the respective simulation results. This study supplies a selection basis for the use of Monte Carlo techniques in lighting simulation.
Femtosecond Two-Photon Response Dynamics of Photomultiplier Tubes
Authors: Toshiaki Hattori Toshiaki Hattori , Yoshitsugu Kawashima Yoshitsugu Kawashima , Masahiro Daikoku Masahiro Daikoku , Hideyuki Inouye Hideyuki Inouye , Hiroki Nakatsuka Hiroki Nakatsuka
Published: October 2002

An intermediate state of two-photon photoemission processes in a photomultiplier tube was found and relaxation with a time constant of 270 fs was observed by time-correlated measurements using 15 fs, 800 nm optical pulses. Optical Bloch equation analysis of the signal intensity was carried out using a perturbation method.
Dielectric Investigation of BaTiO3 Thin-Film Capacitor
Authors: Yasuhiro Yoneda Yasuhiro Yoneda , Kiyoshi Sakaue Kiyoshi Sakaue , Hikaru Terauchi Hikaru Terauchi
Published: October 2002

The dielectric properties of BaTiO3 thin film were investigated on a highly c-axis-oriented epitaxial thin crystal. It was confirmed by X-ray diffraction that the film thickness was 120 Å and that it was high-quality single-crystal film. The spread of crystal orientation of the BaTiO3 thin film was the same as that of SrTiO3 substrate. However, the dielectric properties of this thin film were different from those of the BaTiO3 bulk crystals and were explained by the space-charge effect. The space-charge polarization of this film strongly depends on temperature and this behavior was observed after the incubation time had passed. The experimental results are discussed in terms of the interaction between the polarities of domain and space charges.
Comparison of Light-Emission Efficiencies from Si–Metal-Oxide-Semiconductor Junctions and from Si in Scanning Tunneling Microscopy
Authors: Uehara Yoichi , Kuwahara Masashi , Ushioda Sukekatsu
Published: October 2002

We have investigated the mechanism of scanning tunneling microscope (STM) visible light emission from n-type Si(100). The current fluctuation theory that explained the light emission characteristics of the Si–metal-oxide-semiconductor (Si–MOS) tunnel junction is applied to the STM light emission from n-type Si(100). This theory reproduces the observed STM light emission spectra, and predicts that the light emission efficiency from the STM geometry is ∼1.5×104 times greater than that from the Si–MOS junctions. This prediction is consistent with our experimental result. Experimentally, the light emission intensity from the Si surface under the STM is comparable to that from the Si–MOS junction, although the tunneling current in the STM is 10-3 of the current in the Si–MOS junction. That is, the light emission efficiency from the STM is at least 103 times greater than that from the Si–MOS.
Highly Aligned α-Type Copper Phthalocyanine Formed on Rubbed Polyimide Alignment Layer
Authors: Manaka Takaaki , Taguchi Kohei , Ishikawa Ken , Takezoe Hideo
Published: October 2002

We have fabricated oriented copper-phthalocyanine (CuPc) films by vacuum deposition on rubbed polyimide (PI) alignment layers. It was found that the b-axis of α-type CuPc microcrystals changes its direction depending on the thickness of PI layers, namely, the b-axis is perpendicular to the rubbing direction on a thin rubbed PI layer but is almost perfectly aligned to the rubbing direction on a thick rubbed PI layer. The oriented structure on a thick PI layer was confirmed by a high dichroic ratio of about 4, which is expected in the optical absorption of α-type CuPc, and by highly oriented needle-shaped microcrystals observed by atomic force microscopy.
Influence of RF Power Supply on Electron-Cyclotron-Resonance Plasma with Mirror Confinement for SrTiO3 Thin Film Formation
Authors: Baba So , Miyake Shoji
Published: October 2002

In a low-pressure electron-cyclotron-resonance (ECR) plasma sputtering system with mirror confinement, variation of the plasma property by an RF power supply to the sputtering target has been studied. Without RF power supply, the electron temperature and the plasma density reached a maximum value around the center of the plasma column and around the ECR zone, respectively. These values became higher with increasing microwave power. With the introduction of RF power to the target material of SrTiO3 (STO), the ion flux and emission intensity of spectral lines in Ar gas were found to be negligibly varied. The ion and sputtered particle flux were found to be controlled by microwave power and RF power, respectively. A high film deposition rate was obtained, reaching a value of about 8.5 nm/min at a low gas pressure of 2.7×10-2 Pa.
Correlation between the Red Photoluminescence Band and the Oxygen-Deficient-Associated Defect Centers in γ-Irradiated Silica Glass
Authors: Sakurai Yuryo
Published: October 2002

The origin of the red photoluminescence (PL) band at approximately 1.8 eV in the PL
spectra of oxygen-deficient-type silica glass was studied using electron spin resonance (ESR).
The ESR spectrum of oxygen-deficient-type silica revealed hyperfine (hf) interactions between
the unpaired electrons of radicals and neighboring 29Si atoms. Eight hf lines were recorded at
approximately 40.9, 9.5, 7.6, 4.26, 3.0, 2.5, 1.6, and 1.06 mT. The 40.9 mT line arises from
the primary 29Si hf structure of the E′ center (O3≡Si↑, ↑: unpaired electron). The other lines are
associated with oxygen-deficient-associated defect centers
[Si clusters or SiO
x
(x<2) structure]. We studied the relationship
between the intensity of the 1.8 eV PL band and the intensity of the
ESR signal which arises from the oxygen-deficient-associated defect
centers, in various silica glass synthesized by various methods in the
presence of different amounts of oxygen. We also studied the spatial
distributions of the 1.8 eV PL band intensity and the ESR signal
intensity in one silica glass sample. These results suggest that the
1.8 eV PL band in the PL spectrum of oxygen-deficient-type silica
glass is associated with the oxygen-deficient-associated defect
centers in silica glass.
Electronic-State Distributions of Ne* Formed by Energy Transfer from He(21S, 23S) to Ne at Thermal Energy
Authors: Tsuji Masaharu , Hisano Masahiro , Tanoue Takeshi , Nishimura Yukio
Published: October 2002

The excitation transfer from He(21S, 23S) to Ne at thermal energy has been studied by observing Ne* emissions from the excited Ne(2p5
n
l) states in a He flowing afterglow. The Ne(5s,5s
′,4d) states in the 20.56–20.70 eV region are produced through the He(21S)/Ne reaction, while the Ne(3p,3p
′,4s,4s
′,3d) states in the 18.38–20.05 eV region are formed through the He(23S)/Ne reaction. The initial formation rates and electronic-state distributions of each Ne* state are determined. The excitation-transfer mechanism is discussed on the basis of a reported theoretical prediction from the Landau-Zener curve-crossing model.
Measurement of Chromatic Dispersion of Optical Fibers Using Wavelength-Tunable Soliton Pulses
Authors: Norihiko Nishizawa Norihiko Nishizawa , Aritsune Muto Aritsune Muto , Toshio Goto Toshio Goto
Published: October 2002

The chromatic dispersion of optical fibers is measured using a compact wavelength-tunable soliton pulse generation system. In this system, an ultrashort optical pulse can be generated in a wide wavelength region and the wavelengths of the optical pulses can be changed simply by varying the fiber input power. Since the system is compact and changing the wavelength is very easy, measurement of the chromatic dispersion can be demonstrated easily using a simple setup. The magnitudes of the second- and third-order dispersions in the optical fibers are measured in the wide wavelength region from 1.32 to 1.93 µm. Since the pulse width of the soliton pulse is as narrow as 200 fs, the dispersion of the fiber can be measured in an optical fiber as short as 10 m.
Annealing Effect on Passivated Deep Levels in GaN Epilayers
Authors: Yuldashev Shavkat U. , Kang Tae Won , Jung Woon Hyung , Kwak My Young , Kim Nam Hwa , Ryu Young Sun , Kim Duek Young , Kim Tae Whan , Chung Kwan Soo
Published: October 2002

Transient extrinsic photoconductivity (PC) measurements on as-grown, hydrogenated, and hydrogenated and annealed GaN epitaxial layers grown on sapphire substrates using plasma-assisted molecular-beam epitaxy were performed to investigate the annealing effect on passivated deep levels in a GaN epilayer. A PC spectrum at room temperature showed that the deep-level state in an as-grown GaN epilayer was located 2.9 eV below the conduction-band minimum of the GaN epilayer. The photoionization cross section and the concentration of the deep levels for the as-grown GaN epilayers, determined from the dependence of the rise and decay times of the extrinsic PC response on the illumination intensity of the blue light-emitting diode with 2.9 eV, were 9.7×10-15 cm2 and 4.5×1014 cm-3, respectively. The concentration of the as-grown deep levels in the GaN epilayer was significantly reduced by the hydrogenation treatment, and this passivation effect was still effective after thermal annealing at a temperature up to 700°C. The activation energy of the deep levels and the dissociation energy of the complexes between the deep levels and hydrogen atoms were 0.55 eV and 3.0 eV, respectively. These results provide important information for improving the quality of devices utilizing GaN epilayers.
Chopping Frequency Dependence of Photoacoustic Spectrum in Porous Silicon
Authors: Toshio Kawahara Toshio Kawahara , Michiyo Mihara Michiyo Mihara , Jun Morimoto Jun Morimoto , Kenichi Tahira Kenichi Tahira , Akira Motohashi Akira Motohashi , Akira Kinoshita Akira Kinoshita , Toru Miyakawa Toru Miyakawa
Published: October 2002

The dependence of photoacoustic (PA) spectra on the chopping frequency in the range of 10 to 180 Hz was studied in porous silicon (PS) samples of varying thicknesses the PS layer. The enhancement of PA signals over those of bulk Si, reported in our previous work, is ascribed to the combined effects of interstitial gas “pressure” and intrinsic change of absorption. Although the enhancement seen in the long wavelengths, above 600 nm in the thick PS samples, is mainly caused by the “pressure" effect, the enhancement in the short wavelengths, below 600 nm, appears to be mainly due to the intrinsic effects related to the quantum confinement effect because it increases as the porosity increases and seems to remain at higher chopping frequencies (f=180 Hz). We could also estimate the thermal diffusivity of the PS samples from the crossover frequency of the change of slope in the log PA signal vs the log chopping frequency plot. The dependencies of the PA spectral edges on porosity and chopping frequency are shown and discussed in reference to the double layered structure model proposed in our previous work.
Influence of InxGa1-xAs (0≤x≤0.3) Cap Layer on Structural and Optical Properties of Self-assembled InAs/GaAs Quantum Dots
Authors: Wang Xiao Dong , Niu Zhichuan , Feng Songlin
Published: October 2002

Optical and structural properties of self-organized InAs/GaAs quantum dots (QDs) with In
x
Ga1-x
As or GaAs cover layers grown by molecular beam epitaxy (MBE) have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL) measurements. The TEM and AFM images show that the surface stress of the InAs QDs was suppressed by overgrowth of a In
x
Ga1-x
As covering layer on the top of the QDs and the uniformity of the QDs preserved. PL measurements reveal that red shifts of the PL emission due to the reduction of the surface strain of the InAs islands was observed and the temperature sensitivity of the PL emission energy was suppressed by overgrowth of In
x
Ga1-x
As layers compared to that by overgrowth of GaAs layers.
Electrical Properties of p- and n-GaSe Doped with As and Ge
Authors: Shigetomi Shigeru , Ikari Tetsuo , Nakashima Hiroshi
Published: October 2002

Hall effect measurements are carried out to study the carrier transport of GaSe doped with amphoteric impurities. The p-and n-type conductions were obtained for the As- and Ge-doped samples, respectively. The carrier transports in the As- and Ge-doped samples are associated with the deep acceptor level at 0.54 eV above the valence band and the deep donor level at 0.58 eV below the conduction band, respectively.
In-Situ Ellipsometric Observations of Thickness Change in the Layers of Ag/a-As2S3 Film System with Progression of Photodoping
Authors: Murakami Yoshihisa , Ogawa Tsutomu , Wakaki Moriaki , Kawabata Shuichi
Published: October 2002

The phenomenon of Ag-photodoping in an amorphous As2S3 film was
examined by an ellipsometric method. The observed ellipsometric parameters Ψ
and Δ were fitted using multilayer models. It was observed that the thickness
of each layer of the Ag, Ag-doped As2S3 and As2S3 system showed
a timed-dependency. From these behaviors, the main features of photodoping in a
double-layer, Ag/As2S3 were confirmed. The composition of Ag-doped
As2S3 layer was estimated to be Ag2.6As2S3 from the amounts
of consumed Ag and As2S3.