bluuebunny/crossref_metadata_2025 huggingface dataset:
SOI-MOSFET/Diode Composite Photodetection Device
Authors: Yuko Uryu Yuko Uryu , Tanemasa Asano Tanemasa Asano
Published: October 2002

A new photodetection device, which is composed of a silicon-on-insulator metal-oxide-semiconductor field-effect-transistor (SOI MOSFET) and a pn junction diode, is proposed and the operation is experimentally studied. The photodiode is connected to the body of the SOI MOSFET. Carriers photo generated in the photodiode flow to the body and induce the bipolar action of the SOI MOSFET. As a result, the diode photocurrent is amplified by the SOI MOSFET. This operation is demonstrated by the fabrication of n-channel SOI MOSFET/pn+ photodiode and p-channel SOI MOSFET/n+p photodiode composite devices. Enhancement in current amplification by an electrically floating gate is demonstrated. A rather pronounced current amplification is observed for the n-channel/pn+ device. Shrinkage of gate length results in an increase in the current amplification factor. Current amplification up to about 100 is observed by shrinking the gate length to 0.8 µm.
Evaluation of SOI Substrates by Positron Annihilation
Authors: Akira Uedono Akira Uedono , Atsushi Ogura Atsushi Ogura , Shoichiro Tanigawa Shoichiro Tanigawa
Published: October 2002

The annihilation characteristics of positrons in Si-on-insulator (SOI) wafers were studied using a monoenergetic positron beam. From measurements of Doppler broadening spectra of the annihilation radiation as a function of incident positron energy, the line-shape parameter S of the buried oxide (BOX) layers fabricated by the separation-by-implanted-oxygen process was found to be smaller than that of a SiO2 film fabricated by conventional thermal oxidation. This was attributed to the suppression of the positronium formation in the BOX layer due to the trapping of positrons by defects; the charge state of the defects was estimated to be negative. Positrons implanted into the superficial Si layer annihilated from the trapped state by the defects. These defects were considered to be related to oxygen atoms, and the concentration of such oxygen-related defects was high at the region close to the SOI/BOX interface.
Charging Damage of Silicon-on-Insulator (SOI) Wafer Determined by Scanning Maxwell-Stress Microscopy
Authors: Takashi Matsukawa Takashi Matsukawa , Hideo Fujii Hideo Fujii , Masayoshi Nagao Masayoshi Nagao , Seigo Kanemaru Seigo Kanemaru , Hiroshi Yokoyama Hiroshi Yokoyama , Junji Itoh Junji Itoh
Published: October 2002

Charging damage of silicon-on-insulator (SOI) wafer induced by electron-beam (EB) lithography and reactive ion etching (RIE) has been investigated in terms of the surface potential change through the processes. Scanning Maxwell-stress microscopy (SMM) was utilized for measuring the SOI surface potential under a floating condition. Surface contamination due to resist residues was clearly observed in the SMM potential image. Negative charging of the SOI islands induced by EB lithography was observed particularly under an excessive EB exposure condition and conserved for several days. The cause of the negative charging is considered to be the trapping of electrons in the buried oxide of the SOI wafer.
Hydrogen-Robust Submicron IrOx/Pb(Zr, Ti)O3/Ir Capacitors for Embedded Ferroelectric Memory
Authors: Sakoda Tomoyuki , Moise Theodore S. , Summerfelt Scott R. , Colombo Luigi , Xing Guoqiang , Gilbert Stephen R. , Loke Alvin L. S. , Ma Shawming , Kavari Rahim , Wills Laura A. , Amano Jun
Published: October 2002

We have demonstrated that the scaling of IrO
x
(Pb(Zr, Ti)O3:PZT)/Ir capacitors can be extended into the submicron regime. The submicron IrO
x
/PZT/Ir capacitors were fabricated using a one-mask stack-etch process, integrated with an SiO2 interlayer dielectric, and contacted with Al metallization. The aggregate electrical properties of integrated PZT capacitor arrays are shown to be nearly independent of individual capacitor area in the range between 102 µm2 and 0.12 µm2. In particular, switched polarization values of more than 30 µC/cm2 were obtained for PZT capacitors with an individual capacitor area of 0.12 µm2. This result suggests that the lateral scaling can be achieved down to 0.1 µm2. Through the use of appropriate diffusion barriers, hydrogen-robust submicron PZT capacitors are obtained. No degradation in ferroelectric properties of submicron PZT capacitors was observed under the test conditions. These results suggest that PZT capacitors can be integrated into a standard complementary metal oxide semiconductor (CMOS) process flow with minimal degradation.
Analysis and Improvement of Retention Time of Memorized State of Metal-Ferroelectric-Insulator-Semiconductor Structure for Ferroelectric Gate FET Memory
Authors: Mitsue Takahashi Mitsue Takahashi , Hideki Sugiyama Hideki Sugiyama , Toshiyuki Nakaiso Toshiyuki Nakaiso , Kazushi Kodama Kazushi Kodama , Minoru Noda Minoru Noda , Masanori Okuyama Masanori Okuyama
Published: October 2002

Retention characteristics of metal-ferroelectric-insulator-semiconductor (MFIS) structures have been studied theoretically by considering effects of charge injections derived from the difference between leakage current densities in the ferroelectric and insulator layers. The calculated curves for time-dependent capacitance have shown good agreements with experimental results. The numerical results for the MFIS structure have indicated that excess current over a certain value through the ferroelectric and the insulator layers causes the retention time to rapidly degrade. An idea of inserting an insulator film between the metal and the ferroelectric layers in an MFIS has also been examined in order to cut down the currents through the ferroelectric layer. The calculations based on our model have found this metal-insulator-ferroelectric-insulator-semiconductor (M-I-FIS) structure to exhibit much longer retention time than the conventional MFIS.
Electrical Characteristics of Pt/SrBi2Ta2O9/Ta2O5/Si Using Ta2O5 as the Buffer Layer
Authors: Sang Choi Hoon , Tae Kim Yong , Seong-Il Kim Seong-Il Kim , In-Hoon Choi In-Hoon Choi
Published: October 2002

We propose the Pt/SrBi2Ta2O9/Ta2O5/Si structure for the application of nondestructive read-out memory. The Ta2O5 films were deposited on p-type Si (100) substrates by rf-magnetron sputtering and the SrBi2Ta2O9 films were deposited by metal organic deposition (MOD) method. Coercive field that decisively affects on the memory window becomes greater by inserting the Ta2O5 buffer layer between ferroelectric thin film and silicon substrate and thus the memory window also increases with an electric field to the SrBi2Ta2O9. The C–V characteristics of the Pt/SrBi2Ta2O9 (195 nm)/Ta2O5 (36 nm)/Si structure show memory window of 0.5–2.7 V at the applied voltage of 3–7 V. The leakage current density is 1.7×10-8 A/cm2, even at the high voltage of 10 V.
On the Capacitance Coupling Ratios of a Source-Side Injection Flash Memory Cell
Authors: Liu Chun-Mai , Brennan James , Chan Jr. , Guo Ping , Kordesch Albert V. , Su Kung-Yen
Published: October 2002

A new method for measuring the capacitance coupling ratios of non-volatile memory cells is reported. This method is applied to the source-side-injection (SSI) Flash cell. Conventional extraction methods are complicated by the presence of the select transistor. In this work the coupling ratios of a source-side injection Flash memory cell are extracted from source-follower voltage (V
sf) measurements of the Flash cell and a reference cell, in the read mode. Validity of these coupling ratios and a two-transistor memory cell representation under programming condition are confirmed via two-dimensional device simulations. These coupling ratios provide a solid base for a multilevel Flash cell circuit model.
Characteristics of Tunneling Nitride Grown by Electron Cyclotron Resonance Nitrogen-Plasma Nitridation and Its Application to Low-Voltage Electrical Erasable-Programmable Read-Only Memory
Authors: Min Kyeong-Sik , Chung Jin-Yong , Lee Kwyro
Published: October 2002

Characteristics of a tunneling-nitride insulator grown by low-temperature electron cyclotron resonance (ECR) nitrogen-plasma nitridation are presented. The ECR nitridation shows a very high growth rate at lower temperatures and the thickness is proportional to the growth time. For example, we obtain a thickness of 16 [nm] and a refractive index of 1.75 after the nitridation time of 80 [min] at 400°C. The barrier heights measured from the Fowler-Nordheim (F-N) tunneling current are 2.3 [eV] and 1.4 [eV] in the inversion and the accumulation modes, respectively. These lower heights allow us much faster programming and erasing times of an electrical erasable-programmable read-only memory (EEPROM) with the ECR nitride than those of the conventional EEPROM with the thermal oxide. A double-gate EEPROM with an ECR-nitride tunneling insulator was fabricated. Surprisingly, it does not show any threshold voltage (V
TH) degradation even after 100,000 cycles of programming and erasing.
Analysis of Gate Disturbance Degradation by Nitridation of Flash Tunnel Oxide
Authors: Arai Masatoshi , Hashidzume Takahiko , Nitta Toshinari , Odake Yoshinori , Matsuo Ichiro
Published: October 2002

In this work, an experimental analysis of gate disturbance degradation with negative bias stress caused by nitridation of flash tunnel oxide has been performed. Nitrided tunnel oxide successfully suppresses gate disturbance with positive bias stress, however, it enhances gate disturbance with negative bias stress. A similar gate polarity dependence has been observed in charge-to-breakdown and gate voltage shifts during Fowler-Nordheim stress. We propose the following dual-quality-layer model, which can explain all the polarity results. A poor-quality layer compared with base oxide is concurrently formed at the region where nitrogen atoms do not exist during nitridation. Subsequent to program/erase stress, more hole traps are created at the surface of tunnel oxide and modulate the energy band at the surface of tunnel oxide. Therefore, electrons can easily tunnel through the oxide with a negative bias stress because of the reduced barrier height at the surface of tunnel oxide.
Fabrication and Characterization of Pt/(Bi, La)4Ti3O12/Si3N4/Si Metal Ferroelectric Insulator Semiconductor Structure for FET-Type Ferroelectric Memory Applications
Authors: Kijima Takeshi , Fujisaki Yoshihisa , Ishiwara Hiroshi
Published: October 2002

For field effect transistor (FET)-type ferroelectric memories, c-axis oriented (Bi, La)4Ti3O12 films with small remanent polarization Pr of 4 µC/cm2 were investigated. Bi3.25La0.75Ti3O12 films were prepared by the sol-gel method on amorphous Si3N4 layers formed on Si substrates using atomic nitrogen radicals. It was found that the films formed using stoichiometric sol-gel solution did not crystallize even after annealing at 800°C in O2 ambient. Therefore, 2.5 to 7.5% excess-Bi solutions were used and such parameters as pre annealing and crystallization temperatures, film thickness and crystallization ambient were optimized. As a result, the well c-axis-oriented Bi3.25La0.75Ti3O12 films with good crystallinity and good surface morphology were obtained at temperatures higher than 600°C. It was also found in a Pt/100 nm-Bi3.25La0.75Ti3O12/3 nm-Si3N4/Si (metal/ferroelectric/insulator/semiconductor) structure that C–V characteristics showed a hysteresis loop with a memory window of about 1 V and both high and low capacitance values kept at zero bias voltage did not change for more than 3 h.
Physical Properties of Radiation Fields Produced by Multiple In-cloud Lightning Discharges
Authors: Lee Bok-Hee , Lee Seung-Chil , Ahn Chang-Hwan , Kawamura Tatsuo
Published: October 2002

This paper describes some physical properties and statistical analyses of radiation fields associated with multiple in-cloud lightning discharges. A wide-band waveform recording system was employed to analyze the time-domain characteristics of the radiation fields. The radiation fields produced by in-cloud lightning discharges were significantly different from cloud-to-ground return stroke fields and showed pronounced bipolar pulse peak amplitudes comparable to those of cloud-to-ground return stroke fields. The time intervals between the subsequent strokes for both the positive and negative radiation fields decrease as the stroke order increases. The ratio of the peak of the subsequent strokes to the first stroke peak is distributed over a wide range. Little difference was observed compared with the results for both the positive and negative polarities. The time intervals between the superimposing narrow stepwise pulses in the initial half-cycle of the pronounced bipolar pulse were in the range of less than 12 µs and the mean values for the positive and negative polarities were 4.43 µs and 4.78 µs, respectively. The statistics on the parameters of the electric and magnetic field waveforms seem to provide a good quantitative estimate of the lightning protection device response to the electromagnetic pulse effects of in-cloud lightning discharges.
Computational Chemistry Study on Crystal Growth of InGaN/GaN
Authors: Inaba Yusaku , Onozu Takayuki , Takami Seiichi , Kubo Momoji , Miyamoto Akira , Imamura Akira
Published: October 2002

We carried out density functional theory (DFT) calculations and tight-binding quantum chemical molecular dynamics simulations to investigate the crystal growth of InGaN layers on a GaN(0001) surface under periodic boundary conditions. The periodic DFT calculations indicate that the formation of the uniform InGaN thin films is difficult, which leads to the segregation of In atoms in the InGaN thin films. The tight-binding quantum chemical molecular dynamics simulations suggest that the Ga polarity surface of the GaN(0001) is preferable for the construction of the smooth GaN thin films than the N polarity surface of the GaN(0001). Moreover, the formation of the smooth InN thin films was found to be difficult on the GaN(0001) surface.
GaN and InGaN Metal-Semiconductor-Metal Photodetectors with Different Schottky Contact Metals
Authors: Su Yan-Kuin , Chiou Yu-Zung , Juang Fuh-Shyang , Chang Shoou-Jin , Sheu Jinn-Kung
Published: October 2002

The characterizations of n-type doped GaN, p-type doped GaN and n-type doped In0.2Ga0.8N Schottky metal-semiconductor-metal (MSM) photodetectors were reported. The epilayers were grown on sapphire by metalorganic chemical vapor deposition (MOVCD). Schottky contacts were fabricated using Au, Ti, Ni and Pt metals. The dark and illuminated current–voltage characteristics of GaN and InGaN MSM photodetectors with different Schottky metals were studied. The n-GaN MSM photodetectors with Au Schottky contacts showed better responsivity than those with other metals and they were also better than Au/p-GaN and Ti/n-In0.2Ga0.8N MSMs. The effects of the pitch width between the interdigitate fingers and the thickness of Schottky metals on the characteristics of photocurrents were also studied.
Terahertz Electromagnetic Wave Generation from Quantum Nanostructure
Authors: Isao Morohashi Isao Morohashi , Kazuhiro Komori Kazuhiro Komori , Takehiko Hidaka Takehiko Hidaka , Takeyoshi Sugaya Takeyoshi Sugaya , Xue-Lun Wang Xue-Lun Wang , Mutsuo Ogura Mutsuo Ogura , Tadasi Nakagawa Tadasi Nakagawa , Chang-Sik Son Chang-Sik Son
Published: October 2002

We have investigated terahertz (THz) electromagnetic wave generation from semiconductor quantum nanostructures.The samples used in our experiment are a GaAs/AlGaAs symmetric triple-coupled quantum well and a GaAs/AlGaAs crescent-shaped quantum wire. The THz electromagnetic waves were generated by ultrashort optical pulse excitation and detected by a spatial electrooptic (EO) sampling method. Generation of a THz electromagnetic wave, which originats from quantum beats with three frequency components of 0.8, 1.0, and 1.8 THz, was observed in the symmetric triple-coupled quantum well. In a quantum wire, THz electromagnetic wave generation due to the instantaneous polarization accompanied by the creation of excitons by ultrashort optical pulse excitation was observed.
Current Status of Research and Development for Three-Dimensional Chip Stack Technology
Authors: Kenji Takahashi Kenji Takahashi , Hiroshi Terao Hiroshi Terao , Yoshihiro Tomita Yoshihiro Tomita , Yasuhiro Yamaji Yasuhiro Yamaji , Masataka Hoshino Masataka Hoshino , Tomotoshi Sato Tomotoshi Sato , Tadahiro Morifuji Tadahiro Morifuji , Masahiro Sunohara Masahiro Sunohara , Manabu Bonkohara Manabu Bonkohara
Published: October 2002

The national project of “Ultra High-Density Electronic System Integration” was initiated in 1999. This is the first project to focus on a niche area between electronic devices and systems. It aims to develop technologies for overcoming the problems in terms of performance of electronic systems. Three-dimensional (3D) LSI chip stacking, optoelectronics hybrid integration, and optimum circuit design are the technology categories. For the 3D stacking technology, a chip-based stacking technology is under extensive development that includes wafer preparation for chip stacking, wafer thinning, chip stacking, and inspection and testing. In this paper, the current development status of the 3D stacking technology, called V-STACK technology, is introduced.
Interconnect and Substrate Structure for Gigascale Integration
Authors: Morimoto Akihiro , Kotani Koji , Sugawa Shigetoshi , Ohmi Tadahiro
Published: October 2002

Signal wave propagation properties for a high-speed gigascale integration (GSI) system LSI featuring an operation frequency of more than 10 GHz have been analyzed and discussed by solving the cylindrical
Maxwell's equations directly using a stacked coaxial structure. The results give us a good perspective and enable us to predict the ultrahigh-speed and miniaturized interconnect characteristics. The metal substrate structure is essential to suppress the substrate surface potential fluctuations and the substrate-induced signal attenuation and delay. The gas-isolated interconnect structure can effectively reduce the signal attenuation and delay. The combination of the gas-isolated interconnect and the metal substrate structure is the most promising solution for an interconnect and a substrate in GSI.
Dynamic Strain and Chip Damage during Ultrasonic Flip Chip Bonding
Authors: Masafumi Hizukuri Masafumi Hizukuri , Naoya Watanabe Naoya Watanabe , Tanemasa Asano Tanemasa Asano
Published: October 2002

The distribution of strain under a bump generated by ultrasonic flip chip bonding was dynamically measured using two-directional strain gauges. The strain gauges were designed to be sensitive in both the horizontal and vertical directions. Dynamic strains generated at the surfaces of the substrate and the chip were measured. The distribution of strain during Au bump formation was also measured and compared with that during flip chip bonding. Strain variations with time and position have been successfully measured during the bonding process composed of pre-press, ultrasonic and post-press steps. The strain field during ultrasonic application of flip chip bonding is found to be divided into two regions, while the strain field during Au bump formation is divided into four regions. Generation of chip damage such as crack and pad delamination, which was sometimes observed in ultrasonic flip chip bonding, is explained in term of the strain field in the bump area. It is shown that a high pressing load is effective to avoid damage of the chip surface.
A New Nucleation-Site-Control Excimer-Laser-Crystallization Method
Authors: Nakata Mitsuru , Inoue Kouki , Matsumura Masakiyo
Published: October 2002

A new nucleation-site-control method has been proposed for excimer-laser crystallization, where a cross-coupled phase shifter is placed on the sample surface. High thermal conductivity of molten Si flattens its temperature distribution shortly after laser-light irradiation, and, in turn, confines a low-temperature Si region to a very narrow area. Since nucleation can take place only in this narrow area of unmolten Si, not only is the number of nuclei limited to unity, but also the position of a nucleus can be determined. The usefulness of the proposed method is investigated theoretically and experimentally. A single grain as long as 5 µm in diameter was formed at the desired position.
Nonreciprocal Propagation Characteristics of 526 GHz Submillimeter-Wave in Transversely Magnetized Two-Layer Parallel-Plate Waveguide Containing p-InSb Slab
Authors: Yodokawa Shinichi , Kosaka Satoru , Obunai Tetsuo
Published: October 2002

The magnetic field dependence of 526 GHz submillimeter-wave propagation in two-layer waveguides containing p-type InSb slabs was studied in detail while varying the ambient temperature, and the results were compared with theoretical predictions. It was shown that, at the liquid nitrogen temperature, the submillimeter-wave propagation loss is very small, typically 0.3 dB/mm, and that fabrication of a submillimeter-wave image guide employing a p-InSb slab may be possible. At the dry ice temperature, slow surface wave resonance was clearly observed and a nonreciprocity of at least 15 dB was obtained with an insertion loss of 5 dB. These results indicate that the construction of nonreciprocal devices in submillimeter-wave monolithic integrated circuits may be possible. It is also suggested that this nonreciprocal wave propagation can be controlled by injecting plasma in the InSb slab.
Wavelength Dependence of InGaN Laser Diode Characteristics
Authors: Nagahama Shin-ichi , Yanamoto Tomoya , Sano Masahiko , Mukai Takashi
Published: October 2002

InGaN multi-quantum-well-structure laser diodes (LDs) with an emission wavelength of longer than 420 nm were grown on both an epitaxially laterally overgrown GaN (ELOG) substrate and an ELOG on a free-standing GaN substrate by a metaorganic chemical vapor deposition method. The wavelength dependence of InGaN LD characteristics was investigated. It was found that there was a strong relationship between the threshold current density and the emission wavelength of LDs. The LDs with the emission wavelength of 450 nm grown on the ELOG on a free-standing GaN substrate were demonstrated. The threshold current density and voltage of these LDs were 2.8 kA/cm2 and 4.5 V, respectively. The estimated lifetime was approximately 5000 h under 50°C continuous-wave operation at an output power of 5 mW.
Effect of Barrier Thickness on the Interface and Optical Properties of InGaN/GaN Multiple Quantum Wells
Authors: Kim Dong-Joon , Moon Yong-Tae , Song Keun-Man , Park Seong-Ju
Published: October 2002

We investigated the effect of barrier thickness on the interfacial and optical properties of the InGaN/GaN multiple quantum wells (MQWs) grown in a low-pressure metalorganic chemical vapor deposition system. The GaN barrier thickness in the InGaN/GaN MQWs was found to play a key role to determine the interfacial structural and optical characteristics of the MQWs. As the thickness of the GaN barrier layer was increased, the abruptness of the interface between InGaN and GaN layers deteriorated, probably due to the generation of defects induced by the strain accumulation in the MQWs. Accordingly, the intensity and the line-width of the photoluminescence taken from the MQWs were reduced and broadened, respectively with the increase of the GaN barrier thickness. The InGaN/GaN MQWs grown with an optimized barrier thickness showed an intense room-temperature photoluminescence at the wavelength of 479.5 nm with a very narrow full width at half maximum of 40.82 meV.
Native Defect Control of CdTe Thin Film Solar Cells by Close-Spaced Sublimation
Authors: Okamoto Tamotsu , Kitamoto Shinji , Yamada Akira , Konagai Makoto
Published: October 2002

The control of native defects in the CdTe thin film solar cells was investigated using a novel source for close-spaced sublimation (CSS) process which was prepared by vacuum evaporation with elemental Cd and Te (evaporated source). The evaporated sources were prepared on glass substrates at room temperature, and the Cd/Te ratio was controlled by varying the Cd and Te beam equivalent pressures. In the cells using the Te-rich source, the conversion efficiency was less than 0.2% because of the extremely low shunt resistance. On the other hand, a conversion efficiency above 15% was obtained by using the Cd-rich source. Capacitance–voltage (C–V) characteristics revealed that the acceptor concentration in the CdTe layer increased with increasing Cd/Te ratio of the evaporated source. Furthermore, photoluminescence spectra implied that the formation of the Cd vacancies in the CdTe layer was suppressed using the Cd-rich source.
Effects of Growth Temperature on Electrical Properties of InP-based Pseudomorphic Resonant Tunneling Diodes with Ultrathin Barriers Grown by Molecular Beam Epitaxy
Authors: Osaka Jiro , Matsuzaki Hideaki
Published: October 2002

The impact of growth temperature on the epitaxial layer structure and the negative differential resistance characteristics of pseudomorphic In0.53Ga0.47As/AlAs/InAs resonant tunneling diodes (RTDs) with the high peak current density of 5–10×104 A/cm2 grown by molecular beam epitaxy was studied. For RTDs with a nominally symmetrical structure and with an InAs sub-well layer thinner than an estimated critical thickness, strong asymmetry in current–voltage characteristics was observed at growth temperatures below the critical growth temperature of 410°C, while a slight reverse asymmetry was observed at higher temperatures. Examinations of the RTD structures by transmission electron microscopy and atomic force microscopy indicated that three-dimensional growth of InAs at lower temperatures degrades the top-AlAs barrier structure. These asymmetric characteristics are explained in terms of the barrier structure asymmetry caused by temperature-dependent growth kinetics by using a simplified current density calculation model.
1.55 µm Wavelength Strain-Compensated InxGa1-xAs/InyAl1-yAs Electroabsorption Modulators with High Extinction Ratio and Low Polarization-Dependent Loss
Authors: Kim Tae Whan , Lee Dea Uk , Choo Dong Chul , Kim Jae Ho , Jung Min , Kim Moon Deock , Jeong Hyeon Don , Yoo Keon-Ho , Kim Jin Young , Lim Han-Jo
Published: October 2002

Photocurrent (PC) measurements were carried out to investigate the excitonic transitions in In
x
Ga1-x
As/In
y
Al1-y
As multiple quantum wells with and without an applied electric field. Transmission electron microscopy showed that high-quality 11-period strain-compensated In0.64Ga0.36As/In0.47Al0.53As electroabsorption modulator structures with high-quality heterointerfaces were grown by molecular beam epitaxy. The results for the PC data at 300 K for several applied electric fields showed that many excitonic transitions shifted to longer wavelengths as the applied electric field increased. The calculated value of the interband transitions from the first electronic state to the first heavy-hole state were in qualitative agreement with those obtained from the PC measurements. The maximum extinction ratio at a wanelength of 1.55 µm under an applied voltage of -1.5 V was 14.3 dB, the polarization-dependent loss at an extinction ratio of 14.3 dB was less than 0.5 dB, and the coupling losses were below 1.5 dB per facet at 1.55 µm. These results indicate that the electroabsorption modulators fabricated utilizing srain-compensated In0.64Ga0.36As/In0.47Al0.53As multiple quantum wells hold promise for high-efficiency devices in the 1.55-µm spectral range.
Gain Switching Enhancement in Asymmetric Coupled Quantum Wells
Authors: J. Yoon Sean , Insook Lee Insook Lee
Published: October 2002

Optical gain switching is theoretically investigated in various InGaAs/InP coupled quantum well structures. Our calculations are based on the k ·p method with 6 ×6 Luttinger-Kohn Hamiltonian and on the density matrix formalism with intraband relaxation. Our results show that the gain of asymmetric coupled quantum wells (CQWs) is substantially reduced under electric field, compared with that of symmetric CQWs or single quantum well (SQW) structures. This is mainly attributed to the increase of the differences in the dominant transition energies due to the enhanced Stark effect. The asymmetric structures were obtained by varying the width or the depth of the two wells constituting the CQWs. Using these asymmetric CQWs, gain switching at lower voltage can be achieved.
Numerical Study of Beam Extraction Phenomena in an Ion Thruster
Authors: Yasushi Okawa Yasushi Okawa , Haruki Takegahara Haruki Takegahara
Published: October 2002

Ion beam extraction phenomenon is one of the most important processes in an ion propulsion system because ion beam current and beam accelerating voltage dominate thrust. In order to evaluate the beam extraction capability, which is determined by the interrelation between discharge plasma properties and beam accelerating conditions, there is a need to understand the problems of ion sheath formation. This study has been performed to develop a numerical simulation code which is capable of investigating the ion beam extraction phenomena in the ion thruster. In the calculation, both ions and electrons were treated as particles in a particle-in-cell routine to determine the ion sheath self-consistently. The calculation results of electric potential contours and extracted currents were compared with the experimental ones and they were found to be in good agreement. In addition, it was confirmed that the ion beam extraction capability can be simulated in a wide range of beam accelerating voltage.
Band-Gap Bowing Parameter of the InxGa1-xN Derived From Theoretical Simulation
Authors: Yen-Kuang Kuo Yen-Kuang Kuo , Wen-Wei Lin Wen-Wei Lin , Jiann Lin Jiann Lin
Published: October 2002

The band-gap energy and band-gap bowing parameter of the wurtzite InGaN alloys are investigated numerically with the CASTEP simulation program. The simulation results suggest that the unstrained band-gap bowing parameter for the wurtzite InGaN alloys is b=1.21±0.03 eV. The simulation results also show that the width of the In
x
Ga1-x
N top valence band at the Γ point decreases when the indium composition increases and has a value of 7.331 eV for the GaN (x=0) and 6.972 eV for the In0.375Ga0.625N (x=0.375).
Electrical and Optical Properties of CdS Films Grown by Photochemical Deposition From Aqueous Solutions
Authors: Kumaresan Ramanujam , Ichimura Masaya , Takahashi Ken , Takeuchi Kazuki , Goto Fumitaka , Arai Eisuke
Published: October 2002

Recently, we have established a novel deposition technique for semiconductor thin films, namely photochemical deposition (PCD), in which the compound formation is activated by ultraviolet illumination. In the present work, the electrical properties of the PCD-CdS films grown under different conditions are analyzed and presented. Their resistivity is high at room temperature and decreases with increasing temperature with an activation energy of about 0.9 eV.
Stress Evaluation in a Bulk High-Temperature Superconductor during Field-Cooling Magnetization
Authors: Takashima Hideyoshi , Tsuchimoto Masanori , Onishi Toshitada
Published: October 2002

Stresses in a bulk high-temperature superconductor are numerically evaluated during the magnetization process by field cooling. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. The stress distributions are obtained through numerical analysis with the finite-difference method. Two numerical codes are combined in the iterative calculation. Peak values of the maximum hoop, radial and shear stresses are obtained under different conditions during the magnetization.
Femtosecond Noncollinear Optical Parametric Amplification in the Mid-Infrared Range with 1.25 µm Pumping
Authors: Rotermund F. , Petrov V.
Published: October 2002

We study noncollinear three-wave interaction in a traveling wave optical parametric amplifier operating in the mid-infrared spectral range between 6 and 8 µm using HgGa2S4 and AgGaS2 as nonlinear optical crystals. Calculations reveal that matching of the group velocities in both crystals is possible in a wider spectral (or angular) region for type-I interaction. High-power femtosecond pulses at 1.25 µm from a Cr:forsterite regenerative amplifier are used for pumping the optical parametric amplifier at a repetition rate of 1 kHz. Experimentally we verify the advantages of noncollinear interaction by increasing the conversion efficiency approximately sixfold in the saturation regime as compared to the collinear case. The maximum idler energy measured near 6 µm exceeds 4 µJ and typical pulse durations are about 300 fs.
Red-Light-Emitting Organic Electroluminescent Devices with Bisanil Dye as Emitter
Authors: Yu Junsheng , Chen Zhijian , Sone Masato , Miyata Seizo , Li Minrun , Watanabe Toshiyuki
Published: October 2002

Double-layer organic thin film electroluminescent (EL) devices having red emission have been constructed using bisanil dyes. The basic structure of the EL device consisted of a hole-transport layer and a luminescent layer between the indium-tin-oxide (ITO) glass and magnesium electrodes. The hole-transport layer was a N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)-doped poly(N-vinylcarbazole) (PVK) film. The luminescent layer consisted of a host material, 8-hydroxyquinoline aluminum (Alq3), and bisanil dye as the dopant. The full width at half maximum (FWHM) of the PL and EL spectra of two bisanil dyes is as narrow as 50 nm. Among the two materials studied by us, the N,N′-bis[4-(N,N-dimethylamino)-benzylidene]diaminomaleonitrile (BAM) showed a better EL performance. A bright pure red light with a peak at 620 nm and a maximum luminance of 6230 cd/m2 was observed.
Efficient Electroluminescence from a Rubrene Sub-Monolayer Inserted between Electron- and Hole-Transport Layers
Authors: Matsumura Michio , Furukawa Takumi
Published: October 2002

Efficient electroluminescence (EL) was obtained from rubrene by inserting its sub-monolayer between the Al-hydroxyquinoline (ALQ) and diamine layers. The highest EL current efficiency of 5.8 cd A-1 was attained by inserting a 0.05-nm-thick rubrene layer between the ALQ and diamine layers; in addition, the current-voltage curve was shifted to a lower voltage. These properties are favorable for the construction of efficient EL devices. The enhanced EL efficiency and the shift of the current-voltage curves are attributed to efficient trapping of holes by rubrene molecules at the interface.
The Effect of the Crystalline Phase on the Sintering and Microwave Dielectric Properties of CuO-doped (Bi0.95Sm0.05)NbO4 Ceramics
Authors: Chen Ying-Chung , Tzou Wen-Cheng , Yang Cheng-Fu , Cheng Ping-Shou
Published: October 2002

The crystalline phase and the microwave dielectric properties of the 0.5 wt%-CuO-added (Bi0.95Sm0.05)NbO4 ceramics are developed. The intensity of the low temperature form of the (Bi,Sm)NbO4 (α-form) first increases, reaches a saturation value at 1000°C, and then decreases with the increase of the sintering temperature. The α-form (Bi,Sm)NbO4 disappears at 1040°C, the high temperature form of the (Bi,Sm)NbO4 (β-form) starts to appear at 980°C and then the intensity of the β-form (Bi,Sm)NbO4 increase with the increase of the sintering temperature. The dielectric constants (ε
r) show no apparent change but the quality values (Q×f) first increase, reach a maximum at 1020°C, and then decrease with the increase of the sintering temperature. As the sintering temperature increases from 1020°C to 1040°C, the temperature coefficients (τf) critically change from -15.1 ppm/°C to -203.5 ppm/°C.
Measurements of Electron Temperature and Density of a Micro-Discharge Plasma Using Laser Thomson Scattering
Authors: Noguchi Yasuyuki , Matsuoka Akira , Bowden Mark D. , Uchino Kiichiro , Muraoka Katsunori
Published: October 2002

Laser Thomson scattering was successfully applied to measure electron temperature (Te) and electron density (ne) in a micro-discharge plasma. This is the first time that this method has been used to obtain otherwise inaccessible plasma information from the near vicinity (0.3 mm) of a material surface. The key of the success was the suppression of strong stray laser light by using a triple-grating spectrometer. Values of electron temperature and density wereTe=(0.4–1.6) eV andne=(6–10)×1018m-3, depending on the time from the beginning of the pulsed discharge. The technique developed here is readily applicable to plasma display panel (PDP) discharges.
Leakage Current Characteristics of (Ba,Sr)TiO3 Thin Films Deposited on Ru Electrodes Prepared by Metal Organic Chemical Vapor Deposition
Authors: Kil Deok-Sin , Park Jong-Bum , Yoon Dong-Soo , Song Chang-Rock , Cho Ho Jin , Kim Younsoo , Yu Yong-Sik , Roh Jae-Sung , Yoon Hee-Koo
Published: October 2002

Leakage current characteristics of (Ba,Sr)TiO3 (BST) thin films deposited by metal-organic chemical vapor deposition (MOCVD) on Ru bottom electrodes were investigated. CVD-BST thin film on an Ru electrode showed much higher leakage current density than that on the Pt electrode. In the case of the CVD-BST thin film deposited on the PVD-BST(30 Å)/Ru or N2O-plasma-treated Ru electrode, the leakage current density showed a very small value of about 2×10-8 A/cm2 at ±1 V and the dielectric loss was about 0.006. It was found that oxygen atoms adsorbed on the surface of the Ru bottom electrode during the deposition of PVD-BST or N2O plasma treatment played a key role in restoring the barrier height at the bottom interface.
Spatial Profile Measurements of Charged Particles in Capacitively-Coupled RF (13.56 MHz) Oxygen Discharges
Authors: Kouji Kaga Kouji Kaga , Takashi Kimura Takashi Kimura , Kazuyuki Ohe Kazuyuki Ohe
Published: October 2002

The spatial profiles of negatively charged particles were measured in a capacitively-coupled RF oxygen discharge over the pressure range from 0.1 Torr to 0.5 Torr using a Langmuir probe. The measured profile of negative ions was approximated as a parabolic function, while that of the electrons was uniform for the entire discharge except in the sheath. The measured profiles of negative ions and electronegativity were compared with the simplified theoretical model.
Effect of CuO-based Oxide Additives on Bi2O3–ZnO–Nb2O5 Microwave Ceramics
Authors: Chen San-Yuan , Lin Yih-Jaw
Published: October 2002

Different kinds of CuO–MO
x
mixtures were used to investigate their role in the microstructure evolution, sintering densification and microwave properties of Bi2(Zn1/3Nb2/3)2O7 (BZN) ceramics. Without the addition of CuO–MO
x
mixtures, pure BZN ceramics have to be sintered above 900°C. However, a comparable bulk density to that of pure BZN ceramics sintered at 950°C can be achieved for 2 wt% 0.29BaCO3–0.71CuO-added at 850°C and 0.15CuO–0.85MoO3-added BZN ceramics at 800°C, which was attributed to the liquid-phase sintering. A higher dielectric constant along with a smaller Q factor was obtained in 0.29BaCO3–0.71CuO-added BZN ceramics because of the formation of the BaBi2Nb2O9 phase. On the other hand, a larger Q factor of ∼1500 can be obtained at about 850°C for 1 wt% 0.15CuO–0.85MoO3-added BZN ceramics. However, as the 0.2CuO–0.8GeO2 mixture was used, a partial transformation of pseudo-tetragonal Bi2(Zn1/3Nb2/3)2O7 to cubic (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 phase was induced possibly because both Zn2+ and Ge4+ have similar ion radius and electronegativity. With increasing 0.2CuO–0.8GeO2 content, a decrease in microwave properties was also obtained due to an inhibition of sintering densification since a eutectic liquid phase was not formed.
Estimation of Crystallinity and Crystallite Size of Cellulose in Benzylated Fibres of Oil Palm Empty Fruit Bunches by X-Ray Diffraction
Authors: Deraman Mohamad , Zakaria Sarani , Murshidi Julie Andrianny
Published: October 2002

Benzylated fibre (BzF) was produced from fibres of oil palm empty fruit bunches (EFBs) using benzyl chloride in an etherification reaction for 2 h at two reaction temperatures, 100°C and 110°C. Estimates based on X-ray diffraction data show decreases of approximately 15 and 17%, respectively, in the crystallinity of cellulose, and 36 and 54% in the size of crystallites cellulose in the BzF(100°C) and BzF(110°C) samples. This indicates a greater effect on crystallite size than on crystallinity because the conversion of some crystalline cellulose in the crystallite domain into an amorphous state is accompanied by the breakage of the crystallite domain into smaller sizes. Furthermore, the results also indicate that the increase of reaction temperature from 100°C to 110°C results in a larger change in crystallite size than in crystallinity.
Cell Gap Measurement Method for Single-Polarizer Reflective Liquid Crystal Cells
Authors: Lee Gi-Dong , Yoon Tae-Hoon , Kim Jae Chang
Published: October 2002

A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid crystal (TN LC) cell by using a spectrometer is proposed. By rotating a LC cell, we can measure the cell gap of a LC cell as well as the wavelength dependence of retardation Δn
d.
Characteristics of Indium-Tin-Oxide/Silver/Indium-Tin-Oxide Sandwich Films and Their Application to Simple-Matrix Liquid-Crystal Displays
Authors: Sawada Masato , Higuchi Masatoshi , Kondo Susumu , Saka Hiroyasu
Published: October 2002

We developed low-resistivity transparent conductive films having the structure of indium-tin-oxide/silver/indium-tin-oxide (ITO/Ag/ITO). The thin silver film was sandwiched by ITO films. Our goal was to study the characteristics of the sandwich films and the display characteristics of simple-matrix liquid-crystal displays (LCDs) fabricated using the sandwich film. The electrical and optical characteristics of the sandwich films depended greatly on the thickness of the ITO and silver layers. Low resistivity and high transmittance were obtained when the film structure had a thickness of ITO/Ag/ITO: 40 nm/15 nm/40 nm. The simple-matrix LCD fabricated using a sandwich of ITO/Ag/ITO exhibited 27%–48% reduction in the level of crosstalk compared to the conventionally available simple-matrix LCDs fabricated using a single-layer ITO film; thus, the display performance was improved.
Anomalous Difference between Replacements of D–H and H–D in Oxide Ceramics by Exposure to Air Containing H2O and D2O Vapors
Authors: Iizuka Emi , Horikawa Tomoaki , Tsuchiya Bun , Soda Kazuo , Morita Kenji , Iwahara Hiroyasu
Published: October 2002

We have investigated the exchange of deuterium (or protium) implanted into an oxide ceramic, SrCe0.95Yb0.05O3-δ, for protium (or deuterium) due to exposure to H2O (or D2O) vapor at room temperature by means of the elastic recoil detection (ERD) technique. It is found that D is completely exchanged for H by exposure to H2O vapor, while H is hardly exchanged for D by exposure to D2O vapor, namely there exists a great isotope difference between the exchange of D for H and that of H for D. This result suggests a new model of replacement reactions; dissociative absorption of H at the surface, diffusion of H and release of D due to H–D mix-molecular bulk recombination and the subsequent trapping of H in the vacant trapping sites. In order to clarify the reaction leading to the great isotope difference, the experiments on the retention of H and D by simultaneous H+, D+ implantation and the release of 5 keV D2
+ implants by 0.5 keV H2
+ irradiation and that of 5 keV H2
+ implants by 0.5 keV D2
+ irradiation have been done. The retention experiment shows that the D/H ratio of the saturation implantation concentration is 1.3. Competition among H–H, H–D and D–D bulk recombination prefers to enrich D more than H, which is opposite to the isotope difference observed. The release experiment shows that the slow and continuous decay of 5 keV D2
+ implants is induced by long-term 0.5 keV H2
+ irradiation, while that of 5 keV H2
+ implants is hardly induced by long-term 0.5 keV D2
+ irradiation. The latter result suggests that the isotope difference in the hydrogen diffusion is one of the origins of the major isotope difference.
Chemical Properties of a Perfluoropolyether Lubricant with Functional Groups of Pentafluorobenzyl on Hard Disk Media
Authors: Hara Hiroki , Nishiguchi Ikuzo , Sugi Seiki , Yamamoto Yoshimasa , Tsuboi Shigeru , Itoh Kotaro
Published: October 2002

A perfluoropolyether lubricant (LUB-B) with pentafluorobenzyl functional groups at both ends of the main chain was synthesized by the authors, and the chemical characteristics of its film of 2.0±0.2 nm thickness on hard disk media were investigated by time-of-flight secondary ion mass spectrometry and compared with those of a synthesized lubricant (LUB-A) with benzyl groups and the commercial AM3001 lubricant with (3,4-dioxomethylenephenyl)methyl groups. AM3001 lost 94% of its functional groups from the main chain on the disk surface after a 672-h exposure even in a regular clean room at 23°C and 55%RH. LUB-A lost 35% of its functional groups after a 768-h exposure. LUB-B hardly lost any of its functional groups even after a 768-h exposure, and showed the highest chemical stability. It was suggested that hydrolysis at the ether linkage between the main chain and the functional group eliminated the functional groups from the main chain. The decomposition rate seemed to depend on the chemical stability of the benzyl cation.
Dehydrogenation of Nitrogen-Containing Carbon Films by High-Energy He2+ Irradiation
Authors: Yoshiaki Ohkawara Yoshiaki Ohkawara , Shigeo Ohshio Shigeo Ohshio , Tsuneo Suzuki Tsuneo Suzuki , Haruhiko Ito Haruhiko Ito , Kiyoshi Yatsui Kiyoshi Yatsui , Hidetoshi Saitoh Hidetoshi Saitoh
Published: October 2002

It is well known that amorphous carbon and related films consist of nano-sized carbon clusters. With the incorporation of hydrogen into these films, the hydrogen termination limits the cluster size and decreases the bond strength among clusters. In this study, dehydrogenation from amorphous hydrogenated carbon nitride films was accomplished using 3.75 MeV-He2+ irradiation. The hydrogen atoms forming methyl and ethylene groups were mainly removed from the film during the irradiation procedure. With the progress of dehydrogenation from methyl and ethylene groups, the degree of order of the atomic configuration became large, resulting in an increase of the cluster size. The mechanical properties of amorphous films were improved due to cluster growth.
Characteristics of Indium Tin Oxide Films Deposited by DC and RF Magnetron Sputtering
Authors: Deng Wenli , Ohgi Taizo , Nejo Hitoshi , Fujita Daisuke
Published: October 2002

Conductive and transparent indium tin oxide (ITO) films with a thickness of 100 nm were deposited onto glasses and Si(100) wafers by direct current (DC) and radio frequency (RF) magnetron sputtering. The formation and the annealing effect of films were studied by the measurements of resistivity, optical-transmission, X-ray diffraction and scanning tunneling microscopy (STM). Experimental studies indicated those films deposited by DC sputtering in a 1% O2 in an O2/Ar gas mixture, without annealing, have the lowest resistivity and the highest transmission. In addition, the films deposited by RF sputtering in a 3% O2 in an O2/Ar gas mixture, with annealing in air at 300°C for 2 h, have better resistivity and transmission.
Electron-beam Initiated Transfer of Ge from Ge Islands on SiO2 Surfaces to the Tip of a Scanning Tunneling Microscope
Authors: A. Shklyaev Alexander , Masakazu Ichikawa Masakazu Ichikawa
Published: October 2002

Extraction of Ge from Ge islands on SiO2 surfaces using the scanning tunneling microscope (STM) was found to be initiated by an electron beam of about 1 nA from the scanning electron microscope (SEM). As a result, 10-nm-wide lines of bare SiO2 in the layer of Ge islands were created. The Ge extraction from the sample was accompanied by needle growth on the tip apex, which was observed with the SEM. As a function of the negative tip bias voltage, the extraction was stable at about -4 V, and the efficiency of extraction increased as the tunneling current increased. The results suggest that the electron beam initiates fluctuations of the tunneling current and chemically-assisted field-evaporation is triggered. The observed effect shows possibilities for fabricating nanostructures on dielectric surfaces using the STM.