bluuebunny/crossref_metadata_2025 huggingface dataset:
Proposal of Adaptive-Learning Neuron Circuits with Ferroelectric Analog-Memory Weights
Authors: Hiroshi Ishiwara Hiroshi Ishiwara
Published: February 2007

Novel adaptive-learning neuron circuits are proposed, in which a pulse frequency modulation (PFM) system is used and the interval of output pulses is continuously changed through the learning process. Key components of the circuits are adaptive-learning metal-insulator-semiconductor field-effect transistors (MISFETs) in which the gate insulator films are composed of a ferroelectric material and their polarity is gradually changed by applying input pulses to the gates. In the multiple-input neuron circuits, it is proposed that the adaptive-learning MISFETs be connected in parallel and the function corresponding to the excitatory and inhibitory synapses in a human brain be realized by applying positive and negative pulses to the gates of MISFETs. Finally, the layout of the synapse array between two neuron layers is discussed and the effectiveness of using a silicon-on-insulator (SOI) structure is demonstrated.
Novel Single-Step Rapid Thermal Oxynitridation Technology for Forming Highly Reliable Electrically Erasable Programmable Read-Only Memory Tunnel Oxide Films
Authors: Fukuda Hisashi , Makoto Yasuda Makoto Yasuda , Toshiyuki Iwabuchi Toshiyuki Iwabuchi
Published: February 2007

We have proposed a novel single-step rapid thermal oxynitridation (SS-RTON) technology to obtain highly reliable ultrathin electrically erasable programmable read-only memory (EEPROM) tunnel oxide films. The SS-RTON process can be achieved by rapid switching of the ambient gases (O2→N2O) at the midpoint of the oxidation period, while maintaining the oxidation temperature. The results indicate almost no increase in the oxide-trap-assisted leakage and/or in the electron trap density, resulting in the increase of the charge-to-breakdown value. This behavior of the SS-RTON film can be explained by the idea that the trap sites are reduced by forming strong Si-N bonds in bulk SiO2.
High-Performance Poly-Si Thin-Film Transistors with Excimer-Laser Annealed Silicon-Nitride Gate
Authors: Shimizu Kazuhiro , Nakamura Kyoutarou , Higashimoto Masayuki , Osamu Sugiura Osamu Sugiura , Masakiyo Matsumura Masakiyo Matsumura
Published: February 2007

We report, for the first time, that ArF excimer laser annealing can improve silicon-nitride film properties. It is shown that the 15-nm-thick top region of the laser preannealed film had a lower hydrogen content and a much lower etching rate than the as-deposited film. The laser preannealed film is very useful as the gate insulator of high-performance bottom-gate thin-film transistors fabricated with the laser-recrystallized poly-Si film. The field-effect mobility of electrons was as high as 200 cm2/V·s, while the mobility was as low as 40 cm2/V·s without preannealing the silicon-nitride film.
Two-Dimensional Contact-Type Image Sensor Using Amorphous Silicon Photo-Transistor
Authors: Yamaguchi Muneaki , Yoshiyuki Kaneko Yoshiyuki Kaneko , Ken Tsutsui Ken Tsutsui
Published: February 2007

We propose a novel two-dimensional contact-type image sensor using amorphous silicon photo-transistors (APTs) in order to form a compact image scanner. Each pixel of the sensor consists of an APT, a storage capacitor, and an amorphous silicon thin-film transistor (a-Si TFT). We have made a prototype 140×240-pixel sensor with a pixel size of 160 µm square. It is confirmed that the prototype APT sensor can detect an image under room light. Exposure for gray scale images is in the range of 10-1 to 7 lx·s. This TFT-switched, two-dimensional contact-type image sensor is promising for large-area applications because the process for APTs is fully compatible with that for conventional a-Si TFTs.
A Novel Fabrication Method for Polycrystalline Silicon Thin-Film Transistors with a Self-Aligned Lightly Doped Drain Structure
Authors: Kobayashi Kazuhiro , Murai Hiroyuki , Sakamoto Takao , Baert Kris , Tokioka Hidetada , Sugawara Takashi , Masutani Yuuichi , Hirofumi Namizaki Hirofumi Namizaki , Masahiro Nunoshita Masahiro Nunoshita
Published: February 2007

We have developed a novel and simple fabrication method for poly-Si thin-film transistors (TFTs) with a self-aligned lightly doped drain (LDD) structure. The feature of this method is the use of lateral etching of an n+ Si gate electrode to make an LDD region. The lateral etching is realized by plasma etching with SF6 gas. It is found that the etching length in the lateral direction, which is equal to the LDD length, is proportional to the overetching time. Hence, the LDD length is controlled precisely by the overetching time. By applying the fabrication method to make poly-Si TFTs, we have succeeded in decreasing the OFF current by more than one order of magnitude without decreasing the ON current, compared with a conventional poly-Si TFT. It is concluded that our method has a tolerance sufficient to fabricate the LDD structure with a high ON/OFF current ratio.
Poly-Silicon Thin-Film Transistors with Uniform Performance Fabricated by Excimer Laser Annealing
Authors: Asai Ichirou , Kato Noriji , Mario Fuse Mario Fuse , Toshihisa Hamano Toshihisa Hamano
Published: February 2007

Uniform performance in poly-Si thin-film transistors (TFTs) has been successfully achieved by excimer laser annealing. Mobility and its uniformity over a substrate were 59±3 cm2/V·s for n-channel TFTs and 45±5 cm2/V·s for p-channel types. To achieve uniform performance, we combined step annealing that uses two energy levels, and small-pitch annealing that moves a beam forward by a small pitch. The proposed method can improve surface morphology and uniformity of grain size in poly-Si. A 400-stage CMOS shift register composed of these TFTs could operate at 5 V, and attained the speed of 1 MHz at 8 V.
Control of Si Solid Phase Nucleation by Surface Steps for High-Performance Thin-Film Transistors
Authors: Tanemasa Asano Tanemasa Asano , Kenji Makihira Kenji Makihira
Published: February 2007

The solid phase nucleation process of amorphous Si (a-Si) deposited by vacuum evaporation on thermally grown SiO2 layers on Si substrates having steps has been investigated. Steps were formed by either isotropic wet chemical etching of the SiO2 layer or anisotropic wet chemical etching of Si(100) followed by thermal oxidation. It has been found that solid phase nucleation is enhanced at the steps and that nucleation sites can be controlled by changing the step shape and a-Si thickness. Grain growth up to about 3 µm from the step edge has been observed. n-channel MOSFET's (metal-oxide-semiconductor field-effect-transistor's) which had steps at the source/drain edge were fabricated. They showed channel electron mobility of about 200 cm2/V·s, which is approximately one order higher than that obtained from MOSFET's fabricated in Si films formed by solid phase crystallization on flat SiO2/Si substrates.
Deep Level Characterization of Submillimeter-Wave GaAs Schottky Diodes Produced by a Novel In-Situ Electrochemical Process
Authors: Hashizume Tamotsu , Hasegawa Hideki , Sawada Takayuki , Grüb Andreas , Hartnagel Hans L.
Published: February 2007

Various preparation methods used for the fabrication of submillimeter-wave Pt/GaAs Schottky diodes are compared with respect to deep levels present in the diode surface region. In the samples prepared by the standard electron-beam evaporation process, three process-induced deep levels were detected with the concentrations in the range of 1013-1014 cm-3. On the other hand, these levels were very much reduced in the diodes produced by a new in-situ electrochemical technique. This appears to be related to the reported very low noise property of the latter diodes.
Impurity-Induced Breakdown in GaAs with Partially Ordered Si-Doping
Authors: Kostial Helmar , Ihn Thomas , Asche Marion , Hey Rudolf , Koch Klaus Ploog
Published: February 2007

The static and dynamic current-voltage behaviour including the temperature and magnetic field dependence are investigated in GaAs with dopants arranged in parallel monoatomic planes (δ-doping). The S-shaped I-V characterictics of such partially ordered structures are compared with homogeneously doped samples of the same effective concentration and compensation ratio. The dopant concentrations are below the metal-insulator transition, and the ground states and first excited states are still well seperated from the conduction band edge. The δ-doped samples show a lower critical breakdown field and a shorter branch with negative differential conductivity. The current densities remain higher in the post breakdown region, too, as long as impurity scattering is dominant. Significant differences with respect to oscillations and hysteresis loops are not found. Time resolved measurements allow to distinguish the times for initiation, filamentation and evolution at higher fields.
Minority-Carrier Lifetime in Heavily Doped GaAs:C
Authors: Strauss U. , Heberle A. P. , Zhou X. Q. , Rühle W. W. , Lauterbach T. , Bachem K. H. , Haegel N. M.
Published: February 2007

Electron lifetimes at 295 K and 5 K are measured by time-resolved photoluminescence in the picosecond and subpicosecond regime in GaAs:C epitaxial layers with hole concentrations from p
0=5×1017 to 4×1020 cm-3. The recombination is more efficient than the calculated one using the recombination coefficients of intrinsic GaAs. An enhanced, temperature independent Auger coefficient of (2±1)×10-29 cm6 s-1 is fitted to the measured lifetimes.
In-Situ Characterization of Compound Semiconductor Surfaces by Novel Photoluminescence Surface State Spectroscopy
Authors: Sawada Takayuki , Numata Kei-ich , Tohdoh Susumu , Saitoh Toshiya , Hasegawa Hideki
Published: February 2007

The recently proposed novel photoluminescence surface state spectroscopy (PLS3) technique is applied for in-situ, non-destructive and contactless characterization of variously processed surfaces of GaAs, InP and InGaAs. Chemically etched, anodized and passivated surfaces, as well as the original as-received surface, give rise to U-shaped surface state density distributions with characteristic charge neutrality energy levels, E
HO, which is consistent with the disorder induced gap state (DIGS) model. Annealing of as-received surfaces in hydrogen ambient leads to formation of discrete levels, possibly due to escape of As or P atoms. The effectiveness of a new UHV-based passivation scheme for InGaAs using an ultrathin MBE Si interface control layer (ICL) is also confirmed.
Oxidation of Sulfur-Treated GaAs Surfaces Studied by Photoluminescence and Photoelectron Spectroscopy
Authors: Oshima Masaharu , Scimeca Tom , Watanabe Yoshio , Oigawa Haruhiro , Nannichi Yasuo
Published: February 2007

The initial oxidation features of (NH4)2S
x
-treated GaAs have been investigated by photoelectron spectroscopy in order to correlate the photoluminescence (PL) degradation caused by oxidation with band bending and surface chemical bonding changes. Direct correlation between PL degradation and the Ga oxide formation resulting in drastic upward band bending is observed. It is also found that the S-passivated surface consisting of 1 to 2 ML Ga-S layer comparatively inhibits oxidation reaction, and that the underlying GaAs is oxidized leaving the surface Ga-S layer unoxidized. This indicates a possibility of reducing PL degradation by forming a thicker Ga-S passivation layer.
Electrical Characterization of Lateral P-N Junctions Grown on (111)A GaAs Nonplanar Substrates by Molecular Beam Epitaxy
Authors: Inai Makoto , Yamamoto Teiji , Fujii Mototada , Toshihiko Takebe Toshihiko Takebe , Kikuo Kobayashi Kikuo Kobayashi
Published: February 2007

Electrical characteristics of lateral p-n junctions grown on (111)A GaAs nonplanar substrates by molecular beam epitaxy are investigated. According to current-voltage and capacitance-voltage measurements, it is clarified that uniformly Si-doped lateral p-n junctions have graded doping profiles at the intersection between the (111)A flat plane and (311)A side slope, and the lateral p-n interface becomes steeper with decreasing growth temperature. In the δ-doped lateral p-n junction, negative resistance is observed in the current-voltage characteristics. Assuming it is due to interband tunneling, we consider that the δ-doped lateral p-n junction has a steeper interface than the uniformly doped lateral p-n junctions. These junction characteristics are discussed in relation to the surface migration of Ga adatoms.
Interference Area of Universal Conductance Fluctuations in Narrow GaAs/AlGaAs Wires
Authors: Ochiai Yuichi , Onishi Taizoh , Kawabe Mitsuo , Ishibashi Kohji , Bird Jonathan Paul , Aoyagi Yoshinobu , Sugano Takuo
Published: February 2007

The low-temperature magnetoresistance of narrow GaAs/AlGaAs wires has been measured down to 80 mK at magnetic fields of up to 8.5 T. Analyzing the amplitude and correlation field of the universal conductance fluctuations in the low-temperature magnetoresistance, we study the magnetic field dependence of the conductance fluctuations in a mesoscopic narrow wire system. Conduction network paths in narrow wires have been resolved using Fourier analysis of the low-field magnetoresistance.
A Study on Electroabsorption Effects in Coupled Quantum Wells
Authors: Yuen-Chuen Chan Yuen-Chuen Chan , Kunio Tada Kunio Tada
Published: February 2007

Field-induced effects of optical absorption in coupled quantum wells, comprising two GaAs-AlAs quantum wells separated by a thin AlAs barrier, have been studied. The coupled system evolves into an uncoupled one, leading to large variations of the absorption coefficient at the absorption edge through the field-induced decoupling effect. The large linear shift of the quantum energy levels and an effective blue shift of the absorption edge with electric field lead to unique polarization and wavelength dependence of the electroabsorption effect.
Photoluminescence Study of Electron-Beam-Induced Damage in GaAs/AlGaAs Quantum-Well Structures
Authors: Tanaka Nobuyuki , Hidenori Kawanishi Hidenori Kawanishi , Tomonori Ishikawa Tomonori Ishikawa
Published: February 2007

We examined electron-beam-(EB) induced damage in GaAs/AlGaAs quantum-well (QW) structures as a function of EB energy and dose by Photoluminescence (PL) measurements. Upon 5 to 25 keV EB irradiation with doses less than 1×1018 cm-2, no effect on the photoluminescence properties was found. Even for a high electron dose of 1×1019 cm-2, only a slight reduction of the PL intensity was observed. The damage profile was found to exhibit an EB energy dependence. The most remarkable damage was induced at EB energies from 10 to 15 keV, extending to 120 nm from the surface. On the contrary, no damage was detected at a low energy of 5 keV and a high energy of 25 keV. This is because the low-energy electrons do not penetrate into the QW regions and the energy-loss rate of the high-energy electrons is too low to cause any damage.
Electroabsorption in an AlInAs/InP Type II Superlattice
Authors: Kobayashi Hideki , Yuichi Kawamura Yuichi Kawamura , Hidetoshi Iwamura Hidetoshi Iwamura
Published: February 2007

Electric-field-dependent optical absorption in an AlInAs/InP type II superlattice is observed at room temperature. The spectra of transmissivity and photoluminescence are also measured. The absorption coefficient changes with reverse-bias application at wavelengths of around 1.05 µm, where the linear absorption coefficient is small; however, photoluminescence peaks appear. These results reflect the characteristics of the type II superlattice in which optical transition is indirect in real space. The dependence of the optical properties on the thickness of the InP layer, which is the electron-confining layer, is also studied.
Numerical Study of Effect of Fabrication Damage on Carrier Dynamics in MQW Narrow Wires
Authors: Endoh Akira , Hiroshi Arimoto Hiroshi Arimoto , Shunichi Muto Shunichi Muto
Published: February 2007

To clarify the dependence of the exciton absorption recovery time on wire width in multiple quantum well (MQW) narrow wires, we performed numerical calculations using a simple model with damage effects. The drastic reduction in recovery time for heavily damaged wires is attributed to the formation of a “dead layer”, in which carriers vanish almost immediately, near the sidewalls. For lighter damage, the recovery time curve shifts downward with increasing damage as if surface recombination velocity had been increased. The carrier density profile for lighter damage indicates that the optical nonlinearity is not degraded for light damage although the recovery time is reduced.
A GaAs Junction-Gate FECFET(J-FECFET) for the Digital Integrated Circuits
Authors: Kim Chang-Tae , Yoon-Jong Lee Yoon-Jong Lee , Young-Se Kwon Young-Se Kwon
Published: February 2007

We proposed and fabricated a new GaAs Junction-gate floated electron channel FET (J-FECFET) as a unit device for realizing the direct coupled FET logic circuit. By varying the active channel thickness with different mask stripe width in selective MOCVD, we show that the threshold voltages of the fabricated J-FECFET's can be controlled. The enhancement-mode J-FECFET demonstrates the maximum extrinsic transconductance of 350 mS/mm with the threshold voltage of -0.1 V. The depletion-mode J-FECFET's with the higher threshold voltages of -1.67 V and -4.0 V are obtained by reducing the mask stripe width. Negligible sidegate effect is observed in the fabricated J-FECFET.
High-Performance In0.49Ga0.51P/GaAs Tunneling Emitter Bipolar Transistors
Authors: Chung-Cheng Wu Chung-Cheng Wu , Shey-Shi Lu Shey-Shi Lu
Published: February 2007

Two techniques were used in the fabrication of InGaP/GaAs TEBTs and experimental results by the two fabrication techniques were compared. It is found that the TEBT fabricated by base diffused ohmic contact technique with base surface passivated by an InGaP layer shows a differential current gain as high as 306. To our knowledge, the current gain obtained was the highest value reported to date in InGaP/GaAs hetero-structure bipolar transistors with similar base doping (1×1019 cm-3) and thickness (100 nm).
Effects of Impurities in GaAs/AlAs Double-Barrier Structures on Resonant Transmission Coefficients
Authors: Fukuyama Hiroyuki , Takao Waho Takao Waho , Takashi Mizutani Takashi Mizutani
Published: February 2007

The resonant transmission coefficients for GaAs/AlAs double-barrier structures are estimated from the d2
I/dV
2-V characteristics of resonant tunneling diodes and the effects of impurities doped in these structures are investigated. The estimation method was proven to be reliable by comparing the I-V curve reproduced from the experimentally estimated coefficients with the measured curve. Double peaks were found in the transmission coefficient for samples doped with Si in the well. The two peaks observed are probably attributable to tunneling through the quasi-bound state created by impurities and to tunneling through the resonant state.
Panel-Type Semiconductor Optical Modulator Using Electron Depleting Absorption Control
Authors: Kuwamura Yuji , Minoru Yamada Minoru Yamada , Masahiko Suzumi Masahiko Suzumi
Published: February 2007

Operation of a newly proposed panel-type (or surface-illuminated-type) semiconductor optical modulator based on absorption control by electron depletion around the p-n junctions is demonstrated. Performance of a 61% on/off extinction ratio for 5.5 V variation of the applied voltage was obtained in a device having 39 p-n junctions.
Finite Element Light Emitter Simutator (FELES): A New 2D Software Design Tool For Laser Devices
Authors: Tan Genlin , Keith Lee Keith Lee , J. M. Xu J. M. Xu
Published: February 2007

Finite element light emitter simulator (FELES) is a new two dimensional finite element laser device simulator that self-consistently solves the electrical equations (Poisson's and the electron and hole continuity equations), the optical wave equation, the photon rate equation, and the thermal conduction equation simultaneously for devices of any arbitrary geometry and different material compositions. The simulation tool can be used for proof-of-concept and evaluation of device operation, and assists in the optimization and design of device structure.
Hydrogenated Amorphous Silicon Carbide Photoreceptor for Photoaddressed Spatial Light Modulator
Authors: Akiyama Koji , Takimoto Akio , Akifumi Ogiwara Akifumi Ogiwara , Hisahito Ogawa Hisahito Ogawa
Published: February 2007

A highly photosensitive hydrogenated amorphous silicon carbide (a-Si1-xCx:H) photoreceptor with a PIN diode configuration has been prepared by means of a plasma CVD method using SiH4and C2H2highly diluted with He. He-diluted plasma is effective in restraining the generation of CH2, CH3and Si-CH3configurations in the a-Si1-xCx:H film and markedly improves photoconductivity of the film. Using this photoreceptor, a photoaddressed spatial light modulator (PASLM) which operates in a transmission mode, has been fabricated with a ferroelectric liquid crystal. The PASLM exhibits a high resolution of 180 line pairs/mm, a response time of ∼50 µs and a contrast ratio of ∼30:1 under a write light (λ=565 nm) of 1.5 mW/cm2intensity.
Double-Mesa-Structure Vertical-to-Surface Transmission Electro-Photonic Device with a Vertical Cavity
Authors: Kurihara Kaori , Numai Takahiro , Ogura Ichiro , Kosaka Hideo , Mitsunori Sugimoto Mitsunori Sugimoto , Kenichi Kasahara Kenichi Kasahara
Published: February 2007

We report a high electronic-optical power conversion efficiency of 11.4% in the laser operation of a double-mesa-structure vertical-to-surface transmission electro-photonic device with a vertical cavity. This high conversion efficiency is due to both reduction in the device resistance and increase in light emission efficiency. To reduce electrical resistance, a double mesa structure with a highly doped region is proposed and the resistance reduction is analyzed. To increase light emission efficiency, efficient carrier confinement in the active region by a proton-implanted structure, threshold current reduction by photon recycling, and decreased light absorption by annealing after proton implantation are utilized. Electronic-optical conversion efficiency of over 10% is achieved in surface-emitting devices for the first time to the authors' knowledge.
Strained Single-Quantum-Well AlGaInP Laser Diodes with Asymmetric Waveguiding Structure
Authors: Kawanaka Satoshi , Tanaka Toshiaki , Yanagisawa Hironori , Shinichiro Yano Shinichiro Yano , Shigekazu Minagawa Shigekazu Minagawa
Published: February 2007

The strained single-quantum-well AlGaInP laser diodes reported here can operate at high output powers and high temperatures through the use of asymmetric waveguiding structures (AWS). By examining the dependence of the laser characteristics on the strain, we first determined the appropriate amount of the strain to be introduced in the active layer. Introducing the AWS into the strained single-quantum-well lasers then reduced their internal optical loss from 14.6 to 8.8 cm-1 by shifting the beam profile peak. In addition, the associated reduction of the optical absorption in the waveguide decreased the threshold current by about 30% and increased the maximum output power by about 50%. As a result, a 60 mW stable CW operation at a wavelength of 690 nm is attained at temperatures as high as 90°C.
GaInAsP/InP Surface Emitting Lasers Grown by Chemical Beam Epitaxy and Wavelength Tuning Using an External Reflector
Authors: Yokouchi Noriyuki , Miyamoto Tomoyuki , Uchida Takashi , Inaba Yuichi , Fumio Koyama Fumio Koyama , Kenichi Iga Kenichi Iga
Published: February 2007

We have realized a 1.55-µm GaInAsP/InP vertical cavity surface-emitting laser grown by chemical beam epitaxy (CBE). The optical loss at the contact layer was lowered to reduce the threshold. The threshold at 77-K CW was 2.6 mA and lasing was possible up to -1°C with a threshold current of 147 mA (pulsed). By changing the cavity length employing an external reflector, continuous tuning of 40 Å was achieved for the first time. Our result indicates that a short cavity structure can provide continuous wavelength tuning due to its wide longitudinal mode spacing.
X-Ray Standing Wave Analysis of GaAs/Si Interface
Authors: Kawamura Tomoaki , Takenaka Hisataka , Uneta Makoto , Oshima Masaharu , Fukuda Yukio , Ohmachi Yoshiro , Izumi Koichi , Ishikawa Tetsuya , Kikuta Seishi , Zhang Xiao Wei
Published: February 2007

The X-ray standing wave technique is applied to analyze initial structure of ultrathin GaAs/Si(111) and GaAs/Si(100) epitaxial layers grown by molecular beam epitaxy and metal-organic molecular beam epitaxy. We used two GaAs/Si(111) samples prepared with As adsorption and without As adsorption before GaAs growth, and one GaAs/Si(100) sample prepared under the same conditions as final GaAs layers being a single domain. Roughness and continuity of GaAs/Si interfaces were characterized using high resolution transmission micrographs before X-ray standing wave analysis. The sample with the initial Si(111)1×1 surface passivated by As atoms shows the same fluorescence profiles of Ga and As reported previously. When Ga was deposited first on the initial surface, however, fluorescence profiles suggested that about half of the interfacial Ga atoms are exchanged with As atoms, leaving both Si-Ga-As and Si-As-Ga bondings at the interface. The GaKα fluorescence profile of the GaAs/Si(100) sample showed a behavior similar to that of GaAs/Si(111) without As passivation. This suggests that double domain formation of GaAs is dominant at the initial stage of GaAs growth, even the final layer structure is a single domain. From the theoretical calculation, the ratios of these two domains at the initial stage are estimated to be about 0.4 and 0.6.
Misorientation in GaAs on Si Grown by Migration-Enhanced Epitaxy
Authors: Kazuhiko Nozawa Kazuhiko Nozawa , Yoshiji Horikoshi Yoshiji Horikoshi
Published: February 2007

The misorientation of GaAs grown on Si(100) by migration-enhanced epitaxy is investigated using X-ray diffraction. In addition to the usual tilt misorientation of GaAs with respect to the Si substrate, almost all of the GaAs layers are found to exhibit a misorientation of rotation about the substrate surface normal. The misorientation depends systematically on the initial growth conditions such as the substrate off-orientation and the nucleation conditions of the first GaAs monolayer, which include growth initiations by Ga- or As-supply first and simultaneous supply of Ga and As4 with various V/III flux ratios. A model which describes the observed tilt is proposed, based on the relaxation of misfits perpendicular to the Si surface. Reducing unnecessary misorientation leads to better crystal quality even for thick (∼4 µm) samples including strained-layer superlattices, which can provide a very low dislocation density. The surface etch-pit densities are 6.2×104 cm-2 for the thick sample with a rotation angle β=2°, and 3.1×105 cm-2 for β=12°, even though they are grown under identical conditions except for the initial growth conditions.
Reduction Mechanism of Dislocation Density in GaAs Films on Si Substrates
Authors: Shimomura Hirofumi , Okada Yoshitaka , Matsumoto Hisashi , Kawabe Mitsuo , Kitami Yoshizo , Bando Yoshio
Published: February 2007

Significant reduction of dislocation densities in GaAs films grown on Si substrates have been demonstrated. High-quality GaAs films on Si with average etch-pit density on the order of 104 cm-2 have been obtained by combining the low-temperature growth technique and the atomic hydrogen irradiation. The reduction mechanism of dislocation density in GaAs on Si as well as possible growth kinetics have been discussed based on reflection high-energy electron diffraction (RHEED) and transmission electron microscope (TEM) observations. Most of the threading dislocations have annihilated in the low-temperature grown GaAs layers by forming closed loops. As a consequence of the dislocation density reduction, the electron mobilities of GaAs films on Si have been improved.
A Study of GaAs Digital ICs on Si Substrates
Authors: Onozawa Sachiko , Kimura Tamotsu , Inokuchi Kazuyuki , Sano Yoshiaki , Masahiro Akiyama Masahiro Akiyama
Published: February 2007

The speed characteristics and the sidegating effect of GaAs metal semiconductor field effect transistors (MESFETs) on Si substrates were studied. The propagation delay of a direct-coupled FET logic (DCFL) inverter with 0.3-µm-gate MESFETs was 19.9 ps/gate, which was about 15% larger than that for the inverter on undoped liquid-encapsulated Czochralski (LEC) semi-insulating GaAs substrates. As for the sidegating effect, devices on the GaAs on Si (GaAs/Si) substrates showed a smaller decrease in drain current than those on GaAs substrates as sidegate voltage increased.
Monolithically Integrated AlGaAs/InGaAs Laser Diode, p-n Photodetector and GaAs MESFET Grown on Si Substrate
Authors: Egawa Takashi , Takashi Jimbo Takashi Jimbo , Masayoshi Umeno Masayoshi Umeno
Published: February 2007

We have demonstrated the first successful fabrication of the monolithically integrated AlGaAs/InGaAs laser diode, p-n photodetector and GaAs metal semiconductor field-effect transistor (MESFET) grown on a SiO2 back-coated p-Si substrate using selective regrowth by metalorganic chemical vapor deposition (MOCVD). The reliability of the laser diode on the Si substrate can be improved by utilization of the strain-relieved AlGaAs/InGaAs laser diode with the InGaAs intermediate layer. During the GaAs layer growth, the p-n photodetector is formed near the surface of the p-Si substrate by the diffusion of As atoms. The use of SiO2 back-coated Si substrate is effective in suppressing unintentional Si autodoping and in obtaining a good pinch-off GaAs MESFET.
Extremely Low-Resistivity High-Electron-Concentration ZnSe Grown by Means of Selective Doping Method
Authors: Zhu Ziqiang , Kazuhisa Takebayashi Kazuhisa Takebayashi , Takafumi Yao Takafumi Yao
Published: February 2007

A novel controlled doping technique, the selective doping method, is presented for the first time in order to resolve the compensation problem in wide-band-gap II-VI compounds. With this method, high-quality n-type ZnSe layers with an electron concentration up to 3×1020 cm-3 and resistivity as low as 1×10-4 Ω·cm have been obtained. The paper describes in detail the growth and characteristics of n-type ZnSe layers heavily doped with chlorine by means of a selective doping method during molecular beam epitaxy. The selectively Cl-doped ZnSe samples with electron concentrations from 1018 to 1020 cm-3 have been characterized in terms of electrical and photoluminescence (PL) measurements. The electrical and PL results show that the selectively doped ZnSe layers are superior to uniformly doped ones, especially in the case of high Cl doping.
Adsorption and Dissociation Mechanism of Excited N2 on ZnSe Surface
Authors: Taketoshi Nakao Taketoshi Nakao , Takeshi Uenoyama Takeshi Uenoyama
Published: February 2007

Nitrogen molecular adsorption and dissociation on the ZnSe (100) surface has been examined by ab initio molecular orbital theory. Based on the electronic structure and energetics, the excited (3Σu
+) nitrogen molecule can be selectively adsorbed and dissociated on a Zn atom of the ZnSe surface. This result supports the contention recently presented that the p-type ZnSe layers grown by plasma discharge, which successfully realized blue-green lasers, is grown by the excited (3Σu
+) nitrogen molecular beam.
Light Emission from Quantum Well Structures Containing ZnS, ZnSe, and Related Alloys
Authors: Yu Z. , Ren J. , Lansari Y. , Sneed B. , Bowers K. A. , Boney C. , Eason D. B. , Vaudo R. P. , Gossett K. J. , J. W. Cook Jr. and J. F. Schetzina J. W. Cook Jr. and J. F. Schetzina
Published: February 2007

Properties of blue and blue-green laser diodes with ZnCdSe single- and multiple-quantum-well active regions are discussed. Blue, blue-green, and green light emitting diodes which employ ZnCdSe or ZnSTeSe as the active region of double heterostructure devices have also been prepared and tested. Properties of ZnS-ZnSSe and ZnS-ZnCdS quantum well structures are also reported. These structures emit intense photoluminescence in the ultraviolet spectral region.
Flux and Charge Quanta in Junctions and Macroscopic Quantum Effect
Authors: Masanori Sugahara Masanori Sugahara , Nobuyuki Yoshikawa Nobuyuki Yoshikawa
Published: February 2007

A study is made on the physical conditions of the appearance of the Josephson effect and the single-charge effect in the junctions of superconductor and normal metal. When the electrodes of a bridge junction are made of high-T
c oxide superconductor, and the bridge part is made of highly resistive material of a kind of oxide similar to the superconductor, a single charge-quantum device with working temperatures up to T
c can be realized with a relatively large device size.
Lower-Submicron Patterning Process for BiSrCaCuO High-Tc Superconducting Thin Films
Authors: Fujiwara Shuji , Yuasa Ryokan , Furukawa Hiroaki , Masao Nakao Masao Nakao , Shigeo Suzuki Shigeo Suzuki
Published: February 2007

Ion bombardment enhanced etching (IBEE) has been successfully applied to BiSrCaCuO high-T
c superconducting thin films using nonaqueous Br2 solution. It was found that the etch rate of the damaged region which was formed by the ion irradiation with a 200 keV Si++ focused ion beam was enhanced with the Br2 treatment. The critical dose of the IBEE process was about 1×1014 ions/cm2, which is roughly the same as the dose which destroys the superconductivity of the film. Bridge structures with a width of 0.2 µm were successfully fabricated with little degradation in T
c and J
c. The 0.2-µm bridge had a J
c value of more than 105 A/cm2 below 20 K.
Fabrication of High-Quality Perovskite Oxide Films by Lateral Epitaxy Verified with RHEED Oscillation
Authors: Ohkubo Hiroyuki , Kanda Naoki , Mamoru Yoshimoto Mamoru Yoshimoto , Hideomi Koinuma Hideomi Koinuma
Published: February 2007

Epitaxial growth of SrTiO3-x
and SrVO3-y
films by laser molecular beam epitaxy (laser MBE) has been controlled on an atomic scale. Reflection-high-energy-electron-diffraction (RHEED) intensity oscillation persisting for more than 50 periods was observed during the homoepitaxial growth of SrTiO3-x
film, indicating the lateral epitaxy in a unit cell layer-by-layer mode. The conductivity of SrTiO3-x
ultrathin films was sensitive to the oxygen pressure at the deposition to a far greater extent than was that of SrVO3-y
films.
The Virtual Scientist: connecting university scientists to the K–12 classroom through videoconferencing
Authors: McCombs Glenn B. , Ufnar Jennifer A. , Shepherd Virginia L.
Published: February 2007

The Vanderbilt University Center for Science Outreach (CSO) connects university scientists to the K–12 community to enhance and improve science education. The Virtual Scientist program utilizes interactive videoconference (IVC) to facilitate this connection, providing 40–50 sessions per academic year to a national audience. Scientists, defined as research faculty members, clinicians, postdoctoral fellows, graduate and medical students, and professional staff, participate through conventional volunteer recruitment and program announcements as well as outreach partnership efforts with other Vanderbilt centers. These experts present 30- to 45-min long, grade-appropriate content sessions from the CSO IVC studio or their own laboratory. Teachers register for sessions via an on-line application process. After the session, teachers, students, and experts are requested to complete an anonymous on-line evaluation that addresses both technical- and content-associated issues. Results from 2003 to the present indicated a favorable assessment for a promising program. Results showed that 69% of students ( n = 335) and 88% of teachers ( n = 111) felt that IVC improved access to scientists, whereas 97% of students ( n = 382) and teachers ( n = 126) and 100% of scientists ( n = 23) indicated that they would participate in future videoconferences. Students and teachers considered that the Virtual Scientist program was effective [76% ( n = 381) and 89% ( n = 127), respectively]. In addition, experts supported IVC as effective in teaching [87% ( n = 23)]. Because of the favorable responses from experts, teachers, and students, the CSO will continue to implement IVC as a tool to foster interactions of scientists with K–12 classrooms.
Construction of a lower body negative pressure chamber
Authors: Esch Ben T. A. , Scott Jessica M. , Warburton Darren E. R.
Published: February 2007

Lower body negative pressure (LBNP) is an established and important technique used to physiologically stress the human body, particularly the cardiovascular system. LBNP is most often used to simulate gravitational stress, but it has also been used to simulate hemorrhage, alter preload, and manipulate baroreceptors. During experimentation, the consequences of LBNP and the reflex increases in heart rate and blood pressure can be manipulated and observed in a well-controlled manner, thus making LBNP an important research tool. Numerous laboratories have developed LBNP devices for use in research settings, and a few devices are commercially available. However, it is often difficult for new users to find adequately described design plans. Furthermore, many available plans require sophisticated and expensive materials and/or technical support. Therefore, we have created an affordable design plan for a LBNP chamber. The purpose of this article was to share our design template with others. In particular, we hope that this information will be of use in academic and research settings. Our pressure chamber has been stress tested to 100 mmHg below atmospheric pressure and has been used successfully to test orthostatic tolerance and physiological responses to −50 mmHg.
Desert Survivors: the design and implementation of a television program to enhance local scientific literacy
Authors: Utz Jenifer C. , Rausch Candice M. , Fruth Laurie , Thomas Megan E. , van Breukelen Frank
Published: February 2007

Outreach efforts by faculty members are oftentimes limited in scope due to hectic schedules. We developed a program to enhance science literacy in elementary school children that allows experts to reach a tremendous audience while minimizing their time commitment. The foundation of the program is a television series entitled “Desert Survivors.” The episodes air on local cable access television and are available to teachers on DVD. Each episode features a guest expert who spotlights a particular organism and how that organism overcomes the myriad of hardships inherent to desert survival. Local classrooms are visited to solicit questions from students regarding the organism of interest. These videotaped questions are integrated into Desert Survivors television production and provide the guest expert with the basis to discuss the ecology, physiology, and evolutionary biology of the organism. The program is bolstered through the use of an interactive website. Assessment strategies are in place to ensure program efficacy. Herein, we describe the development of the program as a model for innovative outreach opportunities.
The strong-inference protocol: not just for grant proposals
Authors: Hiebert Sara M.
Published: February 2007

The strong-inference protocol puts into action the important concepts in Platt's often-assigned, classic paper on the strong-inference method ( 10 ). Yet, perhaps because students are frequently performing experiments with known outcomes, the protocols they write as undergraduates are usually little more than step-by-step instructions for performing the experiment. The strong-inference protocol, however, includes an explicit statement of possible experimental outcomes and the interpretation that would follow from each. This approach encourages thorough planning, enhances the efficiency of experimental designs, and increases the power of statistical analysis by explicitly stating a priori predictions as well as the statistical methods that will be used to test them. A sample protocol for an experiment investigating temperature-metabolism relations in chicken embryos is provided to illustrate the important components of the strong-inference protocol and to encourage instructors to incorporate this powerful research tool into undergraduate laboratory courses.
Are chicken embryos endotherms or ectotherms? A laboratory exercise integrating concepts in thermoregulation and metabolism
Authors: Hiebert Sara M. , Noveral Jocelyne
Published: February 2007

This investigative laboratory exercise uses the different relations between ambient temperature and metabolic rate in endotherms and ectotherms as a core concept to answer the following question: What thermoregulatory mode is employed by chicken embryos? Emphasis is placed on the physiological concepts that can be taught with this exercise, including methods for measuring rates of oxygen consumption, the relation between oxygen consumption and metabolic rate, the influence of temperature on metabolic rate, and the differences between endotherms and ectotherms both in the overall magnitude of metabolic rate and in the shape of the relation between metabolic rate and ambient temperature. Included in this article are respirometer designs suitable for teachers working with a wide variety of budgets and available equipment, specific laboratory protocols for collecting data, sample data, thought questions with sample answers, and suggestions for classroom implementation as a 1-, 2- or 3-wk laboratory exercise that can be taught at a variety of undergraduate levels.
TK3 eBook software to author, distribute, and use electronic course content for medical education
Authors: Morton David A. , Foreman K. Bo , Goede Patricia A. , Bezzant John L. , Albertine Kurt H.
Published: February 2007

The methods for authoring and distributing course content are undergoing substantial changes due to advancement in computer technology. Paper has been the traditional method to author and distribute course content. Paper enables students to personalize content through highlighting and note taking but does not enable the incorporation of multimedia elements. Computers enable multimedia content but lack the capability of the user to personalize the content. Therefore, we investigated TK3 eBooks as a potential solution to incorporate the benefits of both paper and computer technology. The objective of our study was to assess the utility of TK3 eBooks in the context of authoring and distributing dermatology course content for use by second-year medical students at the University of Utah School of Medicine during the spring of 2004. We incorporated all dermatology course content into TK3 eBook format. TK3 eBooks enable students to personalize information through tools such as “notebook,” “hiliter,” “stickies,” mark pages, and keyword search. Students were given the course content in both paper and eBook formats. At the conclusion of the dermatology course, students completed a questionnaire designed to evaluate the effectiveness of the eBooks compared with paper. Students perceived eBooks as an effective way to distribute course content and as a study tool. However, students preferred paper over eBooks to take notes during lecture. In conclusion, the present study demonstrated that eBooks provide a convenient method for authoring, distributing, and using course content but that students preferred paper to take notes during lecture.
A novel approach to physiology education for biomedical engineering students
Authors: DiCecco J. , Wu J. , Kuwasawa K. , Sun Y.
Published: February 2007

It is challenging for biomedical engineering programs to incorporate an indepth study of the systemic interdependence of cells, tissues, and organs into the rigorous mathematical curriculum that is the cornerstone of engineering education. To be sure, many biomedical engineering programs require their students to enroll in anatomy and physiology courses. Often, however, these courses tend to provide bulk information with only a modicum of live tissue experimentation. In the Electrical, Computer, and Biomedical Engineering Department of the University of Rhode Island, this issue is addressed to some extent by implementing an experiential physiology laboratory that addresses research in electrophysiology and biomechanics. The two-semester project-based course exposes the students to laboratory skills in dissection, instrumentation, and physiological measurements. In a novel approach to laboratory intensive learning, the course meets on six Sundays throughout the semester for an 8-h laboratory period. At the end of the course, students are required to prepare a two-page conference paper and submit the results to the Northeast Bioengineering Conference (NEBC) for consideration. Students then travel to the conference location to present their work. Since the inception of the course in the fall of 2003, we have collectively submitted 22 papers to the NEBC. This article will discuss the nature of the experimentation, the types of experiments performed, the goals of the course, and the metrics used to determine the success of the students and the research.
A laboratory exercise to illustrate increased salivary cortisol in response to three stressful conditions using competitive ELISA
Authors: Haussmann Mark F. , Vleck Carol M. , Farrar Eugenia S.
Published: February 2007

Perceived stress activates the hypothalamus-pituitary-adrenal axis, resulting in the release of glucocorticoids into the systemic circulation. Glucocorticoids cause the elevation of blood glucose, providing the necessary energy for the organism to cope with stress. Here, we outline a laboratory exercise that uses a competitive ELISA kit to illustrate the response of salivary cortisol concentrations to three stressful conditions. Twelve undergraduate students in the General and Comparative Endocrinology course at Iowa State University were subjected to presentation stress, fasting stress, and competition stress to determine their effect on salivary cortisol concentrations. Students had elevated salivary cortisol in response to each of these stresses compared with basal conditions. These results reiterate the importance of glucocorticoids as mediators of the stress response. This study also incorporates the use of the ELISA technique, a modern laboratory tool used to determine the amount of endogenous antigens in plasma or saliva. This laboratory exercise can easily be adapted to fit into already existing physiology and endocrinology curriculums.
The efficacy of interactive lecturing for students with diverse science backgrounds
Authors: Ernst Hardy , Colthorpe Kay
Published: February 2007

Learning is an active process, and, as such, interactive lectures are considered as the educational best practice. This study investigated the efficacy of interactive lecturing in a module of eight respiratory physiology lectures in a second-year Physiology course with two distinct subcohorts: students with strong science backgrounds and those without. The comparison of student performance in the summative examinations of respiratory physiology allowed us to evaluate the efficacy of interactive lecturing for each subcohort. Formal teaching evaluations were used to gauge the students' perception of interactive lectures. To further validate our findings, we repeated the study in the following year. The introduction of interactive lecturing significantly improved learning outcomes, with this improvement being maintained for the period of this study. Furthermore, students with limited prior knowledge, who had typically performed very poorly in this module, achieved a similar learning outcome to those students with a good science background. From these summative results and the students' perceptions, we concluded that students that are alert, motivated and interested in the subject, and engaged in learning activities and that are being encouraged to think and receive constant feedback on their progress will become confident in their learning abilities and have improved learning outcomes.