bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of GaInAs/InP Triple-Barrier Resonant Tunneling Diodes Grown by Organo-Metallic Vapor Phase Epitaxy for High-Temperature Estimation of Phase Coherent Length of Electrons
Authors: Riichiro Takemura Riichiro Takemura , Michihiko Suhara Michihiko Suhara , Takashi Oobo Takashi Oobo , Yasuyuki Miyamoto Yasuyuki Miyamoto , Kazuhito Furuya Kazuhito Furuya
Published: October 2002

To estimate the phase coherent length(L
C) of electrons in semiconductor, triple-barrier resonant tunneling diodes (TBRTDs) with GaInAs/InP heterostructures were fabricated by using organo-metallic vapor phase epitaxy (OMVPE). The current density-voltage (J-V) characteristics were measured at 4.2 K and 77 K. Moreover method of comparison between experimental and theoretical results is proposed. By comparing experimental result with theoretical result, the coherent lengths are estimated to be longer than 90 nm and 55 nm at 4.2 K and 77 K respectively.
Fully Strained Heavily Carbon-Doped GaAs Grown by Gas-Source Molecular Beam Epitaxy Using Carbontetrabromide and Its Application to InGaP/GaAs Heterojunction Bipolar Transistors
Authors: Ouchi Kiyoshi , Mishima Tomoyoshi , Mochizuki Kazuhiro , Tohru Oka Tohru Oka , Tomonori Tanoue Tomonori Tanoue
Published: October 2002

The lattice-matching conditions in extremely heavily C-doped GaAs (GaAs:C) layers were systematically investigated by using X-ray diffraction measurements from the (004) and (115) planes. The GaAs:C was grown by gas-source molecular beam epitaxy using carbontetrabromide ( CBr4) and was fully elastically strained up to a carrier concentration of 5×1020 cm-3. Even when the GaAs:C was annealed at 550° C, pseudomorphic lattice matching was maintained in spite of the decrease in the carrier concentration and the perpendicular lattice mismatch at the interface. Application of this GaAs:C to the base of InGaP/GaAs HBTs resulted in a current gain as high as 40 at a doping level of 1 ×1020 cm-3.
Spontaneous Formation of Nanostructures in InxGa 1-xAs Epilayers Grown by Molecular Beam Epitaxy on GaAs Non-(100)-oriented Substrates
Authors: Vaccaro Pablo O. , Kazuhisa Fujita Kazuhisa Fujita , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

In
x
Ga1-x
As was deposited by molecular beam epitaxy on GaAs substrates with various orientations. We found that an In0.5Ga0.5As epilayer grown on a (311)A-oriented substrate shows a corrugated nanostructure with a period of 35 nm along the (233) direction. The photoluminescence spectrum of a sample where the In0.5Ga0.5As nanostructure was covered with a GaAs cap layer shows a strong peak at 1.28 eV up to room temperature. We also deposited an amount of InAs equivalent to zero, one, two and three monolayers on GaAs (411)A, (211)A and (111)A just oriented and misoriented substrates. The surface morphology dependence on the amount of InAs deposited was observed by atomic force microscopy. A rich variety of InAs nanostructures was found to be formed on the surface.
Phototransistors Using Point Contact Structures
Authors: Nagamune Yasushi , Noda Takeshi , Ohno Yuzo , Arakawa Yasuhiko , Sakaki Hiroyuki , Watanabe Masanobu
Published: October 2002

We report on the photoresponse of point-contact structures under laser illumination conditions. The point contacts showed phototransistor action with high responsivity of more than 105 A/W and a high on-off rate, probably due to the efficient hole localization in the point contacts. We demonstrate an optical subtraction circuit using two point-contact phototransistors and an optical amplifier using a point contact phototransistor and a light-emitting diode.
Phonon Assisted Tunneling and Peak-to-Valley Ratio in a Magnetically Confined Quasi Zero Dimensional InGaAs/InAlAs Resonant Tunneling Diode
Authors: Wirner Christoph , Awano Yuji , Futatsugi Toshiro , Yokoyama Naoki , Nakagawa Tadashi , Bando Hiroshi , Muto Shunichi , Ohno Minoru , Miura Noboru
Published: October 2002

We studied phonon-assisted tunneling and the peak-to-valley ratio ( P/V ratio) of magnetically confined “dot-like” electron systems in an InGaAs/InAlAs triple barrier resonant tunneling diode. We observe phonon bottleneck, i.e., suppression of the nonresonant valley current and two mode narrow band GaAs- and AlAs-like longitudinal optical (LO)-phonon-assisted tunneling peaks. The P/V ratio increases remarkably with the magnetic confinement and has a maximum each time the energy separation of the confined states matches the GaAs-LO-phonon energy.
Emission Properties of YBa2Cu3O7-δ-Film Photoswitches as Terahertz Radiation Sources
Authors: Tani Masahiko , Tonouchi Masayoshi , Hangyo Masanori , Wang Zhen , Noriaki Onodera Noriaki Onodera , Kiyomi Sakai Kiyomi Sakai
Published: October 2002

Terahertz (THz) radiation is generated from biased YBa2Cu3O7-δ (YBCO)-film photoswitches by exciting them with femtosecond (fsec) laser pulses. The pump power, bias current and temperature dependence of the radiation amplitude is measured in order to characterize the emission properties of the high-critical-temperature (high-T
C) superconducting photoswitches. The radiation amplitude increases superlinearly with increasing pump power in the moderate pump power range and saturates at high pump power. The bias current dependence of the radiation amplitude shows superlinear increase for high bias current. The temperature dependence of the radiation amplitude increases with increasing temperature except near the critical temperature. The features observed in the measurements are explained by the thermal and transient changes of the complex refractive index, which affects the output coupling efficiency of the THz radiation from the high-T
C superconducting film to the free space.
Electrical Properties of Al/Al2O3/(Ba, Rb)BiO3/SrTiO3(Nb) Three Terminal Device
Authors: Toda Fumihiko , Yamada Tomoyuki , Katsufumi Hashimoto Katsufumi Hashimoto , Hitoshi Abe Hitoshi Abe
Published: October 2002

A three terminal device with the Al/Al2O3/(Ba, Rb)BiO3/Nb-doped SrTiO3 structure was fabricated using a superconducting base layer. The stable interface between (Ba, Rb)BiO3 and the artificial oxide barrier was obtained using in situ Al2O3 deposition. The output characteristics were measured as functions of input current. A current gain greater than 2 was obtained in the common emitter configuration.
X-Ray Diffraction Analysis of GaN and GaN/InGaN/GaN Double-Hetero Structures Grown on Sapphire Substrate by Metalorganic Chemical Vapor Deposition
Authors: Sato Hisao , Yoshiki Naoi Yoshiki Naoi , Shiro Sakai Shiro Sakai
Published: October 2002

The structural properties of the GaN layers and the GaN/InGaN/GaN double-hetero (DH) structures grown on sapphire (001) substrate using the metalorganic chemical vapor deposition (MOCVD) method were investigated using a high-resolution X-ray diffraction technique and transmission electron microscopy. Two experimental results were obtained. First, in the case of a single GaN layer, a transition of the film structure from grains, with relatively independent orientations at a thickness of 0.35 µ m, to a uniform film, with a mosaic structure at a thickness of 1.4 µ m, occurred. Second, in the case of a DH structure, we observed an increased mosaicity of both the InGaN and the capping-GaN layers as the InGaN film thickness increased from 20 nm to 110 nm. This increase in the degree of mosaicity also leads to dislocations.
Realization of Highly Resistive GaAs/Si Interface and Improvement of RF Performance for High Electron-Mobility Transistors Grown on Si Substrates
Authors: Miyagaki Shinji , Hara Naoki , Harada Naoki , Eshita Takashi , Kohki Hikosaka Kohki Hikosaka , Hitoshi Tanaka Hitoshi Tanaka
Published: October 2002

InGaP/InGaAs pseudomorphic high electron-mobility transistors (HEMTs) were fabricated on highly resistive GaAs-on-Si substrates. To improve the RF performance of HEMT/Si, the conductive layer at the GaAs/Si interface was suppressed by using H2-preheating instead of AsH3-preheating and by adding a low-temperature-grown AlGaAs layer near the interface. A high sheet resistance of 10–20 k Ω/sq. was obtained for the GaAs-on-Si substrate. By preventing the parasitic effects, the S-parameters of the HEMTs/Si were improved and a maximum frequency of oscillation (f
max
) of 85 GHz was achieved.
Effect of Composition on the Properties of Amorphous Silicon Carbide at a Certain Optical Gap
Authors: Shima Masaki , Terakawa Akira , Masao Isomura Masao Isomura , Shinya Tsuda Shinya Tsuda
Published: October 2002

The relationship between composition and optoelectric properties was investigated for a-SiC:H alloys with a constant optical gap (E
opt) and different compositions. The compositions, hydrogen content (C
H) and carbon content (C
C), and the optical gap of a-SiC:H were successfully controlled independently. E
opt of a-SiC:H can be expressed by a linear function of the compositions and a negative dependence of E
opt on C
C is observed for our samples. In the constant E
opt system, C
H increases with an increase in C
C in spite of a rise in the substrate temperature. In particular, the increase in the Si–H2 density is much more significant than that in the C–H bond density. This result suggests that the incorporated carbon atoms affect the bonding configuration between silicon and hydrogen. The film properties, such as photoconductivity and defect density, and solar cell performance become inferior both before and after light-soaking with an increase in C
C, namely the Si–H2 density. The Si–H2 bond is an important factor to consider when determining the stability of a-SiC:H as well as a-Si:H and a-SiGe:H.
Oxidation of Amorphous Silicon for Superior Thin Film Transistors
Authors: Miyasaka Mitsutoshi , Komatsu Tadakazu , Hiroyuki Ohshima Hiroyuki Ohshima
Published: October 2002

The effects of low-pressure chemical vapor deposition (LPCVD) conditions of silicon films on polycrystalline silicon (polysilicon) thin film transistors (TFTs) fabricated through a high temperature process are studied. An LPCVD amorphous film is not uniformly flat, but has its own structure consisting of many amorphous grains. The size of these amorphous grains changes in accordance with the deposition conditions, because the conditions change the film nucleation and growth rates. An amorphous film composed of large amorphous grains is converted into a polycrystalline film of large crystalline grains after crystallization in the solid phase during thermal oxidation. It is also found that an LPCVD amorphous film has two different phases, i.e., amorphous-I and amorphous-II. The amorphous-I is a well-known phase in which the amorphous grains grow in size as the deposition temperature falls. The amorphous-II is a newly found phase in which the amorphous grains decrease in size as the deposition temperature falls. The best amorphous film is obtained in the amorphous-I phase, being deposited under a condition of large mass transfer and slow surface reaction.
Novel Low-Temperature Double Passivation Layer in Hydrogenated Amorphous Silicon Thin Film Transistors
Authors: Wen-Shiang Liao Wen-Shiang Liao , Si-Chen Lee Si-Chen Lee
Published: October 2002

Hydrogenated amorphous silicon nitride ( a-SiN

x

:H) films fabricated by plasma-enhanced chemical vapor deposition (PECVD) at low temperatures (<150° C) tend to be oxidized within one month because of their porous structure which permits the percolation of H2O (moisture) molecules from air. The a-SiN

x

:H film deposited at a low temperature of 100° C oxidizes more quickly (within 1 day) due to its greater porosity. However, it is found that a very thin coating ( >6.4 nm) of PECVD a-Si:H can prevent the percolation of H2O molecules. Hence, for a-Si:H thin film transistor (TFT) with a 100° C-deposited 470-nm-thick a-SiN

x

:H passivation layer, the ON/OFF current ratio will be degraded by ∼2 orders of magnitude after 7 days of exposure to air. On the other hand, for the 100° C-deposited a-SiN

x

:H passivation layer with an additional 100° C-deposited 50-nm-thick a-Si:H coating, the measured ON/OFF current ratio does not show any sings of degradation for up to one week. Therefore, a novel low-temperature (<150° C) water-resistant a-Si:H coating on a a-SiN

x

:H passivation layer deposited at the same temperature, which can be consecutively processed using the same PECVD system without breaking the vacuum, is proposed.
Liquid Crystal Display Devices with Slit-Patterned Electrode Structures
Authors: Zhan He Zhan He , Zhihua Ling Zhihua Ling , Toshiaki Nose Toshiaki Nose , Susumu Sato Susumu Sato
Published: October 2002

We present a novel liquid crystal (LC) display device based on the molecular orientation effect referred to as the electrically induced hybrid twisted nematic (EHTN) LC molecular orientation in homogeneously aligned LC cells with slit-patterned electrode structures. With a simplified EHTN orientation model, we investigate the viewing-angle and contrast ratio characteristics of this display mode by a computer simulation using Berreman's 4×4 matrix calculus. A very high contrast ratio property is exhibited due to very low transmission levels in the “off" state. Moreover, the electrooptical characteristics of the EHTN LC display mode are studied by measuring the transmittances at various viewing angles. A wide viewing-angle and high contrast ratio property is demonstrated experimentally.
Distribution of Cathodoluminescence in Triple Quantum Well of ZnCdSe/ZnSe
Authors: Tadashi Mitsui Tadashi Mitsui , Naoki Yamamoto Naoki Yamamoto
Published: October 2002

The spatial distributions of cathodoluminescence (CL) in a triple quantum well (TQW) of ZnCdSe/ZnSe grown by metalorganic vapor phase epitaxy (MOVPE) method on GaAs(001) have been examined using a low-temperature CL measurement system combined with a transmission electron microscope (TEM). The CL intensity distribution appearing in the CL images of cross-sectional samples of the TQW can be attributed to the well thickness fluctuation in each QW layer and to competition among channels of recombination such as radiative recombination due to impurities and non-radiative recombination at defects. Moreover, plan-view CL images of the TQW samples show the distribution of the misfit dislocations at the interfaces of each QW layer individually, and reveal the thickness fluctuation in the individual QW layers.
Sintering and Dielectric Properties of Hydrothermally Synthesized Cubic and Tetragonal BaTiO3 Powders
Authors: Zhu Weidong , Akbar Sheikh A. , Asiaie Reza , Dutta Prabir K.
Published: October 2002

The sintering behavior of hydrothermally synthesized cubic and tetragonal BaTiO3 powders was studied as a function of temperature. In addition, the dielectric properties of the sintered samples were examined from room temperature to 200°C at a frequency of 1 kHz. The influence of powder characteristics and sintering temperature on the microstructure development and dielectric properties were investigated. It was found that tetragonal powders showed limited grain growth and higher final density upon sintering, whereas the cubic powder exhibited abnormal grain growth and lower density. This was attributed to more disperse and homogeneous particles in the tetragonal powders with fewer defects, as compared to the cubic powder. Correlations between the microstructure and the dielectric properties were developed. As expected, samples with finer grain size and higher density exhibited higher dielectric constant and lower loss.
Spectral Dependence of Time-Resolved Photoreflectance of Low-Temperature-Grown GaAs
Authors: Yu Jian-Shen , Ho Hsing-Cha , Horng Sheng-fu , Chi Cheng-Chung
Published: October 2002

Time-resolved photoreflectance (PR) traces taken from a low-temperature-grown(LT-)GaAs were observed to exhibit strong dependence on the laser wavelength as well as the growth condition and the annealing process to which it was subjected. The change in reflectance changes sign from negative to positive as the laser wavelength decreases across a certain crossover wavelength. Postgrowth annealing of LT-GaAs was found to result in blue shift in this crossover wavelength. The long tails of the PR traces can be explained using a simple model calculation which takes into account band filling, band-gap renormalization, and free-carrier absorption effects. The PR in the first few picoseconds was found to be dominated by hot-carrier effects. By decomposing the PR traces, an extra enhanced optical absorption besides the scattering of the carriers off their initial states was observed. Our results indicate that caution must be taken when measuring the lifetime of the photoinduced carriers by photoreflectance technique under similar experimental conditions.
Theory of Exciton Spontaneous Emission in Semiconductor Mesoscopic Quantum Disks Embedded in a Planar Microcavity
Authors: Mitsuru Sugawara Mitsuru Sugawara
Published: October 2002

We theoretically discuss the exciton spontaneous emission dynamics in mesoscopic quantum disks placed in an ideal planar microcavity. The disks approach macroscopic quantum wells as the disk diameter increases above the exciton resonant wavelength and approach microscopic quantum dots as the disk radius decreases below the exciton Bohr radius. We present formulae for exciton spontaneous emission, regardless of the disk radius and the exciton-photon coupling strength. By numerical calculations, we show continuous transition from the exponential decay in the weak-coupling regime to the oscillatory behavior due to the exciton-radiation field energy exchange in the strong-coupling regime. We clarify how the oscillatory behavior and emission spectra vary with the photon decay rate, the exciton dissipation time, exciton-cavity mode detuning, and the disk radius.
Temperature Dependence of Transmission Loss of Chalcogenide Glass Fibers
Authors: Ikuo Inagawa Ikuo Inagawa , Shouzo Morimoto Shouzo Morimoto , Toshiharu Yamashita Toshiharu Yamashita , Ichimin Shirotani Ichimin Shirotani
Published: October 2002

The temperature dependence of transmission loss for IR-transmitting chalcogenide glass fibers of sulfur (S)-based, selenium (Se)-based and tellurium (Te)-containing glasses were investigated above room temperature. The influence of temperature on transmission loss significantly depended upon the kind of chalcogen element in the glass. The losses of S-based and Se-based glass fibers were slightly sensitive to temperature. On the other hand, the loss of Te-containing glass fibers increased considerably with temperature. The higher the Te content was, the greater the temperature dependence of transmission loss became. The characteristic behavior of Te-containing glass fibers could be attributed mainly to the additional absorption of due to the increase in the number of thermally excited free carriers with Te content, analogous to Ge and GaAs semiconductors.
X-Ray Diffuse Scattering Study of Magnetite by the Valence-Difference Contrast Method
Authors: Toyoda Takeshi , Tanaka Satoshi Sasaki
Published: October 2002

We have observed the diffuse scattering distributions associated with the charge ordering of Fe2+ and Fe3+ above the Verwey transition temperature (T
V\cong123 K) in magnetite, Fe3O4, by synchrotron X-rays. At a specific wavelength of λ= 1.7421 or 1.7425 Å close to the Fe K absorption edge, the anomalous scattering effect makes it possible to distinguish Fe2+ ions from Fe3+ in the X-ray diffuse intensities. X-shaped diffuse patterns appeared at 130 and 150 K on the a
1
* - a
2
* plane around the 440-type reciprocal lattice point, which were not observed at 296 K. Even for the measurement at 130 K, the X-shaped pattern disappeared when the X-rays had a lower energy resolution. Cross-shaped diffuse patterns were also observed around the 400 and 800 reciprocal lattice points. The theoretical calculations suggest that these diffuse streaks are not due to thermal diffuse scattering. Our analysis of Huang scattering revealed that the observed diffuse patterns were plausibly caused by the local displacement with Fe2+ and Fe3+ pairing among the B sites.
Effect of Nb Doping on Fatigue in Lead Zirconate Titanate
Authors: Kaoru Miura Kaoru Miura , Masahiro Tanaka Masahiro Tanaka
Published: October 2002

We investigated the effect of Nb doping on fatigue in lead zirconate titanate (PZT), using the discrete variational Xα cluster method. From our calculation results, we conclude that Nb-doped PZT (PZTN) is less susceptible to fatigue than PZT because electrons released from oxygen vacancies occupy the Nb 4d states. This is consistent with our previous calculations; the effect of Nb doping on fatigue in PZT is the same as that of La doping on fatigue in PZT.
A Novel Gray-Scale Method for Ferroelectric Liquid Crystal Displays Utilizing Ultra-Fine Particles
Authors: Yasuda Akio , Takanashi Hidehiko , Keiichi Nito Keiichi Nito , Eriko Matsui Eriko Matsui
Published: October 2002

We have developed a novel gray-scale technique for ferroelectric liquid crystal (FLC) displays. This technique involves the addition of nanometer scale ultra-fine particles into the FLC mixture to produce micro domains, whose threshold voltages vary. Each domain has a different threshold for memory latching and is small enough to cover the full gray scale within one pixel element (less than 3 µm in diameter). Moreover, each domain maintains bistability, that is, this method doesn't inhibit passive-matrix driving. The voltage-transmittance ( V-T) curve of the cell depends on the particle-size distribution, such that if the particle-size distribution is sharp, the gradient of the V-T curve is small and vice versa. By X-ray diffraction analysis, wide tilt angle distribution of the smectic layers, which characterizes this nanometer scale particle-contained FLC, was found. The advantages of this technique are that an analog gray scale is possible and that the V-T curve can be controlled by selecting appropriate particles, which means no fundamental change in the fabrication process is required.
Preparation of Retardation Film for Supertwisted Nematic Liquid Crystal Display by Drawing and Poling
Authors: Kim Jong-Chul , Toshiyuki Watanabe Toshiyuki Watanabe , Seizo Miyata Seizo Miyata
Published: October 2002

Generally, it is very important to control the three-dimensional characteristics of the refractive index of retardation film in order to improve the viewing angle characteristic of a supertwisted nematic-liquid crystal display (STN-LCD). It is noted that the refractive index of film-thickness direction n

z
should be larger than that of the direction perpendicular to the drawing direction n

y
where that of the drawing direction is n

x
. Recently, we found that in-plane and out-of-plane birefringence of novel functionalized side-chain phenoxy polymer film can be controlled by drawing and poling. Thus, we have demonstrated that drawing and poling can produce the ideal retardation film for a STN-LCD with a relationship between refractive indices such as n

x
>n

z
>n

y
and n

z
=(n

x
+n

y
)/2. The color of the film satisfying the above conditions between two polarizing films did not change as a function of tilt angle and azimuth angle. In fact, the observed retardation R of this film is constant up to a 40° tilt angle against the front view of the retardation film without reference to the azimuth angle.
Neutral Particle and Plasma Density Distributions in a Processing Plasma Source
Authors: Sakamoto Hitoshi Nihei
Published: October 2002

Neutral particle and plasma density distributions in a plasma source are calculated by solving the diffusion equation. Although the boundary conditionn=0 at the wall is often used, it is not necessarily correct for practical plasma sources. We have used boundary conditions in consideration of the influxes into the wall; the densities at the wall are not zero. The distributions of neutral and plasma particles are expressed by the same formula. We can then compare those distributions by using the same formula. Some calculated examples are shown. The distributions at the target wall depend on the conditions at the side wall of the source and the initial distributions upstream of the source. By optimization of these conditions and the initial distributions, wide uniform distributions at the target wall can be obtained over a wide pressure range. The formulas are useful for the design of a plasma source.
Formation and Exchange Processes of Alkanethiol Self-Assembled Monolayer on Au(111) Studied by Thermal Desorption Spectroscopy and Scanning Tunneling Microscopy
Authors: Nishida Naoki , Hara Masahiko , Hiroyuki Sasabe Hiroyuki Sasabe , Wolfgang Knoll Wolfgang Knoll
Published: October 2002

The exchange phenomena from hexanethiol ( CH3(CH2)5SH: HT) to octadecanethiol ( CH3(CH2)17SH: ODT) on a Au(111) surface have been studied by thermal desorption spectroscopy (TDS) and scanning tunneling microscopy (STM). The TDS study showed the existence of (CH3(CH2)5S)2 (C6–C6), CH3(CH2)5S–S(CH2)17CH3 (C6–C18), and (CH3(CH2)17S)2 (C18–C18) dimer species in the monolayer. Desorption peaks for each dimer species strongly depend on the immersion time in the ODT solution, which revealed the details of the exchange process in the HT monolayer. Namely, originally dimerized species of C6–C6 are gradually replaced by C6–C18 dimers, followed by the replacement of C18–C18 dimers. The STM study showed that the exchange occurred not randomly but at specific domains and in specific domain boundary regions. In addition, STM of annealed samples revealed that there exist at least two types of domains corresponding to those seen in the TDS peaks. Dimerization occurs in these regions. Our results show that the specific domains and domain boundaries act as important areas for exchange phenomena and monolayer formation.
Characteristics of a Stabilized Pulsed Plasma via Suppression of Side-Band Modes
Authors: Hahm Jin Hwan , Chi Kyeong Koo , Jung Chan Ouk , Young Bum Koh Young Bum Koh , Moon Yong Lee Moon Yong Lee
Published: October 2002

The instabilities caused by the reflected rf power in a pulsed-plasma operation employing modulated rf power was studied. By suppressing the side-band modes in the frequency domain, the pulsed plasma became more stable and produced less reflected power. The mode-suppressed pulsed plasma showed almost the same plasma characteristics as the conventional step-function-modulated pulsed plasma. The mode-suppressed plasma was applied to etch a polysilicon pattern. The etched polysilicon profile showed no charge-up defects, suggesting that the mode-suppressed plasma can be utilized for controlling the electron temperature in a more stable operation.
Highly Selective SiO 2 Etching Using CF 4/C 2H 4
Authors: Hiroyuki Sakaue Hiroyuki Sakaue , Akisiro Kojima Akisiro Kojima , Naomichi Osada Naomichi Osada , Shoso Shingubara Shoso Shingubara , Takayuki Takahagi Takayuki Takahagi
Published: October 2002

The relationship between the chemical structure of a polymer film and SiO2/Si selectivity was studied using X-ray photoelectron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR)-attenuated total reflection (ATR) measurements to achieve a highly selective SiO2 etching using mixed gases based on CF4. The analysis of the chemical structure of the deposited polymer film revealed that the formation of a polymer film with a low F/C ratio on the Si surface is necessary for a lower etch rate of Si, and the formation of a polymer film with a low concentration of C–H
x
species on the SiO2 surface is necessary to increase the etch rate of SiO2. Therefore, highly selective etching requires a deposited polymer film with a low concentration of fluorine and hydrogen atoms. The chemical structures of the deposited films depends on the exhaust rate. Based on these results, a highly selective SiO2 etching with a SiO2/Si selectivity of over 2000 was achieved at the low temperature of 20°C by controlling the exhaust rate using mixed gases of CF4 and C2H4.
Excellence of Gate Oxide Integrity in Metal-Oxide-Semiconductor Large-Scale-Integrated Circuits Based on P-/P-Thin-Film Epitaxial Silicon Wafers
Authors: Shimizu Hirofumi , Sugino Yuji , Suzuki Norio , Kiyota Shogo , Nagasawa Koichi , Fujita Masato , Takeda Kazuo , Isomae Seiichi
Published: October 2002

The substitution of Czochralski (CZ)-silicon (Si) wafers into p-(n-)/p-(n-) ( p-or n-layer on p-or n-Si substrate: resistivity of approximately 100 m Ω m) thin-film epitaxial Si wafers used as starting materials has been investigated with respect to application to metal-oxide-semiconductor (MOS) large-scale-integrated circuits (LSIs). The optimum epitaxial layer ( p-/p-structure) thickness for MOS-LSIs was determined to be approximately 1 µ m from the viewpoints of gate oxide integrity (GOI) improvement and cost effectiveness. With increasing epitaxial layer thickness from 0.1 to 0.3 µ m, the oxide defect density was greatly reduced and leveled off at approximately 1/30 that of a CZ-Si layer if the layer thickness is above 0.3 µ m. This is because microdefects in CZ-Si represented by crystal originated particles (COP) which cause weak spots in the gate oxide layer are covered by an excellent Si epitaxial layer on the CZ-Si surface. The p-/p-thin epitaxial structure results in very controlled resistivity for electrically active regions in the device, resulting in a lower cost of growth.
Effects of Growth Temperature on Er-Related Photoluminescence in Er-Doped InP and GaAs Grown by Organometallic Vapor Phase Epitaxy with Tertiarybutylphosphine and Tertiarybutylarsine
Authors: Fujiwara Yasufumi , Matsubara Naoteru , Tsuchiya Junji , Takashi Ito Takashi Ito , Yoshikazu Takeda Yoshikazu Takeda
Published: October 2002

The effects of growth temperature on Er-related photoluminescence (PL) have been investigated in Er-doped InP (InP:Er) and GaAs (GaAs:Er) grown by organometallic vapor phase epitaxy (OMVPE) using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBAs). In InP:Er, the PL spectra exhibit strong dependence on the growth temperature, and the intensity increases drastically in specimens prepared at temperatures lower than 550° C. Similar dependence of PL intensity on the growth temperature is observed in GaAs:Er. The activation energy obtained is about 3 eV in both materials. The activation energy is discussed based on atomic configurations of Er-related luminescence centers.
Magnetoresistance of Annealed CoNb/Cu Multilayers with Amorphous CoNb Magnetic Layers
Authors: Yan Shi-shen , Liu Yi-hua , Zhang Lin , Huang Ji , Wu Min , Zhang Ru-Zheng , Zhang Ya-ming , Mei Liang-mo
Published: October 2002

CoNb/Cu multilayers with amorphous CoNb magnetic layers were prepared by rf-sputtering method and then annealed at various temperatures in a high vacuum. A maximum magnetoresistance ratio of 2.83% at room temperature was obtained under a relatively low saturation field of about 200 Oe for the optimum annealing temperature of 400° C. The structural, magnetic and transport properties were strongly influenced by the annealing temperature, and the transport properties were explained on the basis of granular multilayered structures. The magnetoresistance ratio also depends on the thickness of CoNb and Cu layers.
Development of a Beat Frequency Tunable Stabilized Axial Zeeman Laser
Authors: Shigeoka Toshitaka , Shingo Imanishi Shingo Imanishi , Satoshi Kawata Satoshi Kawata
Published: October 2002

A new axial Zeeman laser whose beat frequency varies from 0.7 MHz to 3.4 MHz was developed. The practical apparatus for realizing the beat-frequency tuning and the stabilization of the absolute frequency of the Zeeman laser is described. The capability of the Zeeman laser we have developed is verified by measurement of the transient response, long-term stability of the beat frequency, and relationship between the applied current for generating the magnetic field and the resultant beat frequency. The applications of this new Zeeman laser are discussed.
Deep Traps and Mechanism of Brightness Degradation in Mn-doped ZnS Thin-Film Electroluminescent Devices Grown by Metal-Organic Chemical Vapor Deposition
Authors: Wang Ching-Wu , Sheu Tong-Ji , Su Yan-Kuin , Yokoyama Meiso
Published: October 2002

Evidence from deep level transient spectroscopy (DLTS) and Fourier transform infrared spectroscopy (FTIR) measurements strongly supported the assertion that the degradation mechanism of ZnS:Mn AC thin-film electroluminescent (ACTFEL) devices is mainly due to the deep electron trap, E
t, which comes from the Mn activators reacting with water molecules. The photoluminescence measurements revealed that the Mn-related E
t trap behaves like a nonradiative center. Furthermore, the X-ray diffraction experiments indicate that the crystallinity of ZnS:Mn phosphor films were destroyed in some degree by the E
t trap. As a result, poor brightness characteristics including lower brightness and higher threshold voltage were obtained when samples become aged.
Switching Kinetics in Thick Film and Bulk Lead Lanthanum Zirconate Titanate Ceramics
Authors: Levstik Adrijan , Kosec Marija , Bobnar Vid , Cene Filipič Cene Filipič , Janez Holc Janez Holc
Published: October 2002

The fatigue effect and the time dependence of the current transient during polarization reversal in 8/65/35 lead lanthanum zirconate titanate (PLZT) ceramics were studied as a function of the electric field. The comparison to the Avrami expression has revealed that the nucleation process in a thick PLZT film is constant during polarization reversal and the dimensionality of the domain growth is D ∼0.5, indicating the existence of needlelike domains. Also, it was found that the dimensionality of the domain growth in bulk PLZT ceramics is D ∼1.5 and that the nucleation process is latent during polarization reversal.
Etching Effects on Ferroelectric Capacitors with Multilayered Electrodes
Authors: Chee Won Chung Chee Won Chung , Chang Jung Kim Chang Jung Kim
Published: October 2002

Dry etching of PbZr

X

Ti1-
X

O3 (PZT) thin film capacitors with RuO

X

/Pt multilayered electrodes was studied to examine the etching effects. PZT films were deposited on RuO

X

/Pt/Ti/SiO2/Si substrates by sol–gel process and Pt films were prepared by DC magnetron sputtering. PZT and Pt thin films were etched with Cl2/C2F6/Ar gas combination in an inductively coupled plasma (ICP) by varying the etching parameters such as coil RF power, dc-bias voltage to wafer susceptor, and gas pressure. Etching effects were investigated in terms of etch rate, etch selectivity, etch profiles, and electrical properties of etched capacitors. Quantitative analysis of the etching damage was obtained by calculating the shift of the coercive field and the switchable polarization in hysteresis loops. Finally, the etching damage mechanism was discussed and the optimization of etching processes for the fabrication of PZT capacitors was attempted to minimize the etching damage to ferroelectric capacitors.
X-Ray Scattering from Nonideal Czochralski Silicon Crystals for High Energy Synchrotron Radiation
Authors: Hitoshi Yamaoka Hitoshi Yamaoka , Shunji Goto Shunji Goto , Yoshiki Kohmura Yoshiki Kohmura , Tomoya Uruga Tomoya Uruga , Masahisa Ito Masahisa Ito
Published: October 2002

Nonideal Czochralski (CZ) silicon crystals were characterized systematically by double-crystal and triple-crystal diffractometry in the Bragg case for high energy synchrotron radiation. The crystals were either annealed at 780°C, 1000°C, and 1170°C, or lapped, with a mean abrasive particle sizes of 13 µm, 25 µm, and 42 µm. Triple-crystal diffractometry was performed at 60 keV of the BL14 vertical wiggler of the Photon Factory and double-crystal diffractometry by use of a Mo rotating-anode X-ray generator. Physical properties of the annealed and lapped crystals were studied quantitatively with respect to mosaic spread and lattice parameter fluctuation.
Effect of Multiple-Step Annealing on the Formation of Semiconducting β-FeSi2 and Metallic α-Fe2Si5 on Si (100) by Ion Beam Synthesis
Authors: Katsumata Hiroshi , Makita Yunosuke , Kobayashi Naoto , Shibata Hajime , Uekusa Masataka Hasegawa
Published: October 2002

Polycrystalline semiconducting β- FeSi2 layers on Si (100) have been formed by ion beam synthesis. Results from two different annealing processes, either two-step (2SA) annealing up to 900° C or three-step annealing (3SA) up to 1100° C, are discussed. β- FeSi2 grown by 3SA has shown a typical direct band-gap energy (E
g
dir) of 0.88 eV and a high localized defect density (N
0) of 1.0×1018 cm-3, the latter being due to crystallographic mismatches or relevant defects at grain boundaries introduced during the transformation process from β to α. On the contrary, β- FeSi2 grown by 2 SA has shown a lower E
g
dir of 0.80 eV and a smaller N
0 of 1.7×1017 cm-3, the former arising from a deviation of the stoichiometric composition to the Si-rich side. Broad PL bands near 0.8 eV have been observed at 2 K from both 2SA and 3SA samples, and we assign these PL bands to optical radiative transitions intrinsic to β- FeSi2.
Measurement of the Expansion Velocity of the Electrode Sheaths in RF Glow Discharge and Its Physical Mechanism
Authors: Sugawara Kazumasa Sando
Published: October 2002

The time-resolved optical technique has been applied to RF glow discharge to measure the expansion velocity of the sheath of the RF glow in conjunction with the applied RF voltage. In the technique, the movement of the edge of the negative glow is assumed to indicate the expansion of the electrode sheath thickness. We have proposed a model of the sheath expansion which takes into account acceleration, by RF voltage, of electrons initially in the region from the sheath edge to the floating potential surface relative to the plasma. The values deduced using the model compare well with the experimental results.
Experimental Study of High-Power Millimeter Wave Transmission of Sapphire Window for Electron Cyclotron Range of Frequencies System
Authors: Kasugai Atsushi , Takahashi Koji , Sakamoto Keishi , Yamamoto Takumi , Tsuneoka Masaki , Kariya Tsuyoshi , Tsuyoshi Imai Tsuyoshi Imai
Published: October 2002

The possibility of use of a sapphire disk as an output window of a high-power and long-pulse gyrotron was investigated using an RF test facility with high-power gyrotrons. The dielectric loss tangents, tan
δ=1.8×10-4 (T/300)1.3±0.1 for 110 GHz and tan
δ=2.6×10-4 (T/300)1.3±0.1 for 170 GHz (T: absolute temperature in K), were obtained in the temperature range of 300 K to 600 K. The experimental results showed that RF reflection from the window became large due to the permittivity change with increasing temperature, which limits the applicable power for the sapphire window rather than the thermal runaway. Moreover, it was found that a 170 GHz, 1 MW, CW gyrotron is feasible using a two-port window system consisting of sapphire double disks more than 18 cm in diameter with a flat RF power profile.
Structure Analysis of A-Si 1-xCx:H with Dominant Tetrahedral Si–C Bonds Deposited by Hybrid-Plasma Chemical Vapor Deposition
Authors: Tadashi Fujii Tadashi Fujii , Masahiro Yoshimoto Masahiro Yoshimoto , Takashi Fuyuki Takashi Fuyuki , Hiroyuki Matsunami Hiroyuki Matsunami
Published: October 2002

Hydrogenated amorphous silicon-carbon (a-Si1-x
C
x
:H) was deposited by a new deposition method of hybrid-plasma chemical vapor deposition. In this method, pre-cracked CH4 by a microwave plasma is introduced into a chamber where SiH4 is decomposed by a radio-frequency plasma. A-Si1-x
C
x
:H films deposited by this method show high photoconductivity in the optical-bandgap range from 2.0 to 2.3 eV. The bonding structures in the films deposited by hybrid-plasma CVD were analyzed using Fourier transform infrared absorption and X-ray photoelectron spectroscopy. The films deposited with the microwave plasma contain 1.6–3 times larger tetrahedral Si–C bonds than graphitic C–C bonds, for the same carbon content. Decomposition of CH4 by the microwave plasma leads to a change of the main precursors for the vapor and/or surface reaction, and it is a promising process for obtaining a-Si1-x
C
x
:H with high-performance photoelectric properties resulting from the dominant tetrahedral bonds.
Ion Collection by a Hollow Probe in ECR Microwave Plasma under a Divergent Magnetic Field
Authors: Ohtsu Yasunori , Kouichi Kinoshita Kouichi Kinoshita , Hiroharu Fujita Hiroharu Fujita
Published: October 2002

Ion collection by a hollow probe has been studied in electron cyclotron resonance (ECR) microwave plasma under a divergent magnetic field where an ion beam was accelerated along the plasma axis. The ion current collected by the probe was found to consist of currents proportional to the geometric solid angle from the probe collector caused by the ion beam parallel to the probe axis. The effect of the ion beam energy and its injection angle to the probe has been also discussed.
Investigation of Pt/Ti Bottom Electrodes for Pb(Zr,Ti)O 3 Films
Authors: Sung-Tae Kim Sung-Tae Kim , Hyun-Ho Kim Hyun-Ho Kim , Moon-Yong Lee Moon-Yong Lee , Won-Jong Lee Won-Jong Lee
Published: October 2002

Pt films, as bottom electrodes for PZT capacitors, were deposited on Ti/SiO2/Si substrates using DC magnetron sputtering under various deposition conditions. The effects of post-annealing on surface morphology, element diffusion, microstructure and structural phase of the Pt films were investigated. The structure and electrical properties of PZT films deposited on Pt/Ti/SiO2/Si electrodes were also studied. As the deposition temperature of the Pt film increases and the deposition rate decreases, the film becomes dense so that Ti out-diffusion and film deformation are suppressed. The out-diffused Ti faciliates the formation of nucleation sites for perovskite PZT films. However, excess Ti out-diffusion not only decreases the total capacitance of the PZT films due to formation of an interfacial layer having a low dielectric constant but also degrades the leakage current characteristics of the PZT films due to deformation of the Pt electrode.
Computer Experiment on Soliton Excitation in Two-Dimensional Crystals
Authors: Tanaka Hideki , Ozawa Satoru , Hiki Yosio
Published: October 2002

Molecular dynamics computer simulation was used to show soliton excitation in two-dimensional mass-spring square-lattice model crystals. Central forces were considered between nearest neighbor atoms, and a lattice anharmonic potential up to the fourth order was taken into account. An input pulse displacement was applied to atomic rows in the crystal and the displacements of all atoms were computed. When the applied input was sufficiently large, the excitation produced exibited “multiple solitons”.
Simulation of Magnetostatic Wave Envelope Soliton Propagation in Yttrium Iron Garnet Films
Authors: Koike Takuro , Ito Tomoyasu , Tatsuya Hirao Tatsuya Hirao , Noritake Taguchi Noritake Taguchi
Published: October 2002

Although formation and propagation of magnetostatic soliton waves in YIG (yttrium iron garnet) films are attracting great attention, there has been no discussion about simulating soliton formation and propagation in YIG films from the viewpoint of circuit analysis and simulation. In this report, we propose a new algorithm to simulate the magnetostatic soliton wave output. We first describe the linear magnetostatic wave equivalent circuit model we have developed and then discuss the simulation algorithm, which combines the linear equivalent circuit model and the soliton wave solution of the nonlinear Schrödinger equation. The simulated results are in excellent agreement with reported experimental results. We also find that the proposed simulation is very effective to determine various physical parameters in the YIG film for given experimental conditions.
Single Process to Deposit Lead Zirconate Titanate (PZT) Thin Film by a Hydrothermal Method
Authors: Morita Takeshi , Kanda Takefumi , Yamagata Yutaka , Minoru Kurosawa Minoru Kurosawa , Toshiro Higuchi Toshiro Higuchi
Published: October 2002

The hydrothermal method to deposit lead zirconate titanate (PZT) thin film is a new method reported by Tsurumi et al.. in 1991. This method consists of two linked processes. We have found that the film deposited by the first process is not PZT but separated lead zirconate (PZ) and lead titanate (PT). In this paper, we report that a PZT thin film was successfully deposited by a single process. The chemical construction and composition of the film were analyzed. The Zr/(Zr+Ti) ratio of the PZT film was controlled by changing the ionic composition of the solution.
Characteristics of a Conical Piezocomposite Transducer with an Apodized Vibration Area
Authors: Takashi Mizuno Takashi Mizuno , Ken Yamada Ken Yamada , Kiyoshi Nakamura Kiyoshi Nakamura
Published: October 2002

A conical transducer with an apodized vibration area has been designed and fabricated using a piezocomposite material with 1–3 connectivity for creating limited-diffraction beams. The large electromechanical coupling coefficient k of the piezocomposite material increases the transducer sensitivity. It is shown that an almost uniform -6 dB beamwidth of 6–9 wavelengths is obtained in the axial range of z = 20 mm to 170 mm using a fabricated transducer 25 mm in diameter operating at 3.6 MHz. It is also demonstrated through preliminary experiments with B-mode imaging that high resolution is maintained over a large depth.
Propagation Characteristics of Leaky Surface Acoustic Wave on Proton-Exchanged 36° Y-X LiTaO 3
Authors: Shoji Kakio Shoji Kakio , Yasuhiko Nakagawa Yasuhiko Nakagawa
Published: October 2002

The propagation characteristics of leaky surface acoustic waves (LSAWs) on proton-exchanged 36°-rotated Y-cut LiTaO3 were investigated experimentally. The dependence of the insertion loss between transducer pairs on the proton-exchange depth and the number of finger pairs of the transducer were measured at a frequency of 210 MHz. The insertion loss of the LSAW for the free surface case was improved considerably by the proton exchange because bulk wave radiation from the transducer was suppressed. The change of the amplitude of the mechanical displacement perpendicular to the surface was also measured using a laser probe method.
Integration of Semiconductor Devices with Surface Acoustic Wave Using the Epitaxial Lift-Off Process
Authors: Suzuki Hiroji , Komine Kenji , Huang Qixin , Hohkawa Kohji
Published: October 2002

This paper presents results of a basic study of high-performance surface acoustic wave-semiconductor integrated circuits in which highly functional compound semiconductor devices and highly efficient surface acoustic wave (SAW) devices are monolithically integrated on the same substrate using epitaxial lift-off (ELO) technology. We improved the epitaxial lift-off process and made advances in wafer handling, etching and bonding. Using these improved processes, we have fabricated basic circuits for SAW-semiconductor cointegrated devices and succeeded measuring basic characteristics.
Experimental Characteristics of a Bolt-Clamped Short-Cylindrical Torsional Vibrator Using Shear Mode Piezoceramics Inserted in the Axial Direction
Authors: Manabu Aoyagi Manabu Aoyagi , Yoshikazu Murasawa Yoshikazu Murasawa , Toshiharu Ogasawara Toshiharu Ogasawara , Yoshiro Tomikawa Yoshiro Tomikawa
Published: October 2002

A torsional vibrator using shear mode piezoceramics inserted in the axial direction, developed 20 years ago for use in a mechanical filter exhibits good vibration performance. The authors applied this torsional vibrator to a high-power transducer shaped as a short cylinder with a large diameter. In this case, the torsional vibrator can easily be fabricated by bolt-clamping in the radial direction, and the small number of parts is beneficial to the fabrication. The vibrational characteristics of the torsional vibrator were determined previously using finite element analysis. In this paper, we report the results of a trial fabrication of such a torsional vibrator. As a result, it is clarified that this torsional vibrator exhibits superior vibration performance such that it could be applied to an ultrasonic high-power transducer, and that the torsional and bending vibrations on the disk are easy to couple to each other according to the dimensions of the vibrator.