bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability of Source-to-Drain Non-Uniformly Doped Channel (NUDC) MOSFETs for Sub-Quarter-Micron Region
Authors: Shirahata Masayoshi , Okumura Yoshinori , Abe Yuji , Kuroi Takashi , Masahide Inuishi Masahide Inuishi , Hirokazu Miyoshi Hirokazu Miyoshi
Published: October 2002

We present an analysis of hot carrier degradation in source-to-drain nonuniformely doped channel (NUDC) metal oxide semiconductor field effect transistors (MOSFETs). Simulation has been performed in order to investigate the influence of the NUDC structure on the device characteristics. It is demonstrated that the hot carrier resistance of NUDC MOSFETs is almost the same as that of conventional MOSFETs when thin gate oxide is used. This is due to the drain electric field strength of NUDC MOSFETs, which becomes the same as that of conventional MOSFETs when the gate oxide is thin, since the drain electric field is not only affected by the channel impurity profile but also strongly influenced by the gate electrode.
Hydrogen Passivation on the Grain Boundary and Intragranular Defects in Various Polysilicon Thin-Film Transistors
Authors: Choi Kwon-Young , Yoo Juhn-Suk , Kim Min-Koo Han
Published: October 2002

We investigated the hydrogenation effects on two types of trap states in poly-Si thin-film transistors (TFT's), where the gate oxide thickness was varied from 1000 Å to 4000 Å and the active poly-Si layers were altered by different annealing methods. The decrease of threshold voltage, which is related to the density of deep states, has shown a similar tendency irrespective of device structures. However, the other device parameters, such as field-effect mobility and minimum leakage current, which are influenced by the tail states, are improved considerably in the poly-Si TFT's with a thick gate oxide or with postannealed active layers. It was verified by the comparison of trap state distributions that the tail states were decreased significantly in the above TFT's with the thick gate oxide and postannealed poly-Si layers.
Application of Electron Cyclotron Resonance Plasma Thermal Oxidation to Bottom Gate Polysilicon Thin-Film Transistors
Authors: Han Jung-In , Choong-Ki Kim Choong-Ki Kim , Chul-Hi Han Chul-Hi Han
Published: October 2002

Electron cyclotron resonance (ECR) plasma thermal oxidation, as a bottom gate polysilicon thin-film transistors (poly-Si TFT's) gate oxidation process and as a passivation process for the back-side channel, has been investigated. ECR plasma thermal oxidation provides a smoother interface on doped poly-Si films than low-pressure chemical vapor deposition (LPCVD), which results in better electrical characteristics in bottom gate poly-Si TFT's. Bottom gate TFT's with ECR plasma thermal gate oxide show an electron mobility of 4.33 cm2/Vs, which is three times the electron mobility obtained when using LPCVD oxide. ECR plasma thermal oxidation of the back-side channel passivates the back-side interface, which also leads to improvements of the TFT's characteristics.
Self-Aligned Offset-gated Poly-Si TFTs with Symmetric Source/Drain Characteristics
Authors: Park Cheol-Min , Min Byung-Hyuk , Jang Keun-Ho , Jae-Hong Jun Jae-Hong Jun , Min-Koo Han Min-Koo Han
Published: October 2002

We propose a new fabrication process for poly-Si thin film transistors in order to reduce leakage-current with a self-aligned offset-gated structure by employing a photo-resist reflow process. The new fabrication method makes the gate-oxide over the offset region with the assistance of sub-gate and reflowed photoresist. The new method does not require any additional offset mask step and the self-aligned implantation is applicable so that poly-Si TFT with the symmetrical offset length is easily fabricated. A symmetrical offset length from 0.7 µm to 2.3 µm is obtained successfully. The experimental results show that the maximum ON/OFF ratio is obtained with a considerable reduction in leakage-current when the offset length is 1.1 µm.
Transport Properties in Band-Tails of High Mobility Poly-Si TFTs
Authors: Serikawa Tadashi , Shirai Seiiti , Nakagawa Kazuo , Takaoka Sadao , Oto Kenichi , Murase Kazuo , Ishida Shuichi
Published: October 2002

Electrical properties of high-mobility polycrystalline silicon thin film transistors (poly-Si TFTs) are measured over the wide temperature range from 300 K to 1.5 K in order to clarify the role of band-tail states in the grain boundaries (GBs). Two distinct regimes of weak and strong localization of electrical transport have been identified below and above the carrier trap state density N
st≈1.0×1012 cm-2 in the GBs for high-mobility poly-Si TFTs. Poly-Si TFTs with a smaller carrier trap state density N
st (≈6×1011 cm-2) show metallic behavior where the mobility increases as temperature decreases. Poly-Si TFTs with larger N
st (≈1.5×1012 cm-2) show semiconducting behavior of mobility. At low temperatures, on the former poly-Si TFT the resistance changes due to the weak-localization effect and on the latter poly-Si TFT due to the variable-range hopping (VRH) in the regime of strong localization. In both regimes, negative magnetoresistances have been observed and interpreted by the quantum interference effect. All of these features are attributed to the band-tail states decaying exponentially from the band-edge, based on the observations of irregular GB structure in the poly-Si film from transmission electron microscope images and the roughness at the SiO2/poly-Si interface seen on atomic force microscope images.
Partially Bonded Silicon on Insulator Substrates for Intelligent Power ICs
Authors: Hiroaki Kikuchi Hiroaki Kikuchi , Kenichi Arai Kenichi Arai
Published: October 2002

A new isolated structure for intelligent power ICs was developed using a wafer direct-bonding technique. This structure has partially buried oxide films for dielectric isolation, and gaps are fabricated under them. In this bonding technique, bonding surfaces are crystalline silicon surfaces of the vertical output device region without buried oxide film. This bonding method leads to void-free bonding in the vertical output device region. Electrically perfect bonding was also obtained for the vertical output device in the new structure.
Comparison of Standard and Low-Dose Separation-by-Implanted-Oxygen Substrates for 0.15 µm SOI MOSFET Applications
Authors: Joachim Hans-Oliver , Yamaguchi Yasuo , Fujino Takeshi , Kato Takaaki , Yasuo Inoue Yasuo Inoue , Tadashi Hirao Tadashi Hirao
Published: October 2002

The influence of buried oxide thickness on short-channel effects in silicon-on-insulator metal-oxide-semiconductor field-effect transistors (SOI MOSFET's) is investigated. It is shown by analytical modeling and numerical simulation that, although a thin buried oxide helps to reduce the charge-sharing component of source and drain electric fields through the oxide layer, substrate depletion underneath the thin buried oxide counteracts the oxide thinning. Although this effect is desired below the source and drain regions to maintain the SOI inherent low junction capacitances, it is detrimental to short-channel-effect suppression. The calculated results are experimentally confirmed on 0.1 µm SOI MOSFET's fabricated on both standard and low-dose separation-by-implanted-oxygen (SIMOX) substrates. A new structure for 0.15 µm SOI MOSFET applications on a thin buried oxide substrate is proposed in which substrate depletion below the channel-forming region can be suppressed locally using self-aligned deep ion implantation.
Property of Supercurrent Flowing through Superconducting Single-Electron Transistors with Weak Charging Effect
Authors: Hiroshi Okamoto Hiroshi Okamoto , Koichi Shimizu Koichi Shimizu , Yuichi Okuda Yuichi Okuda
Published: October 2002

The experimental characteristics of superconducting single-electron transistors consisting of Al/Al

x

O

y

/Al tunnel junctions at ∼60 mK are presented. The single-electron charging energy E
C of our devices is small in comparison with the superconducting gap energy of 170 µeV. It is revealed that the 2e gate-charge periodic supercurrent flows at a finite voltage. We also observe that the leakage of quasi particles into the island electrode occurs.
Phase Transition between c (4×2) and p (2×2) Structures of the Si(100) Surface at 6 K Caused by the Fluctuation of Phase Defects on Dimer Rows due to Dimer Flip-Flop Motion
Authors: Shigekawa Hidemi , Miyake Koji , Ishida Masahiko , Hata Kenji , Oigawa Haruhiro , Nannichi Yasuo , Ozawa Ryozo Yoshizaki , Nagamura Toshihiko
Published: October 2002

Dimers of the Si(100) surface previously observed at 120–140 K, which partially appeared to be symmetric, were frozen at 6 K, and an atomically resolved structural change between c(4×2) and p(2×2) arrangements of the Si(100) surface was observed for the first time by scanning tunneling microscopy. The observed change was due to the fluctuation of phase defects of a new type on dimer rows, which have a structure similar to that of the type-C defect. Dimer flip-flop motion at the phase boundary which induces the apparent phase transition, and creation and annihilation of the anti-phase domain were clearly observed.
Extremely Fast-Response, Highly Nonlinear Doped-Silica Single-Mode Fibers
Authors: Tamitake Itoh Tamitake Itoh , Ryuji Morita Ryuji Morita , Mikio Yamashita Mikio Yamashita
Published: October 2002

Temporal spectral dynamics of nonlinear propagation of ∼80 femtosecond optical pulses is investigated experimentally and analytically for the first time for two single-mode glass fibers of GeO2-doped fused silica and Er:GeO2-doped fused silica. Comparison between experimental and analytical results enables us to determine the nonlinear refractive indices and their response times to be 2.4 ×10-13 esu and 1.8 fs, respectively, for the former fiber and 4.0 ×10-13 esu and 2.1 fs, respectively, for the latter fiber. This suggests that these fibers are more efficient for compression of extremely short pulses than the conventional fused-silica fiber.
Orientation of Vanadyl Phthalocyanine Grown by Molecular Beam Epitaxy on KBr-KCl Mixed Crystals with Various Lattice Constants
Authors: Ken-ichi Hamamoto Ken-ichi Hamamoto , Satoru Nakao Satoru Nakao , Makoto Gomyou Makoto Gomyou , Hajime Hoshi Hajime Hoshi , Ken Ishikawa Ken Ishikawa , Hideo Takezoe Hideo Takezoe , Atsuo Fukuda Atsuo Fukuda
Published: October 2002

We have studied the effect of the lattice constants of substrates on the crystal orientation of films grown by molecular beam epitaxy. Vanadyl phthalocyanine films were epitaxially grown on KBr-KCl mixed crystals with continuously varying lattice constants. The unidirectional (3×3)R45° orientation and the bidirectional (√10×√10)R±27° orientation were predominant on the KBr-rich and KCl-rich substrates, respectively. We found that the orientation changes from the (3×3)R45° structure to the (√10×√10)R±27° structure at about the KCl fractions of 20 wt%.
Determination of Ion Confinement Time in RIKEN 18 GHz Electron Cyclotron Resonance Ion Source (ECRIS) under Pulsed Mode Operation
Authors: Nakagawa Takahide , Miyazawa Yoshitoshi , Hemmi Masatake , Chiba Toshiya , Inabe Naohito , Kase Masayuki , Kageyama Tadashi , Kamigaito Osamu , Akira Goto Akira Goto , Yasushige Yano Yasushige Yano
Published: October 2002

We have determined the ion confinement time in the RIKEN 18 GHz ECRIS under pulsed mode operation. The obtained ion confinement time increases as the charge state of the Ar ions increases. In order to explain this tendency the introduction of a depression in the potential of the plasma is necessary.
Cooling and Mass-Analysis of Molecules Using Laser-Cooled Atoms
Authors: Takashi Baba Takashi Baba , Izumi Waki Izumi Waki
Published: October 2002

This paper presents the first sympathetic cooling of molecular ions using laser-cooled atomic ions. To this end, we developed a novel combination of sympathetic cooling and in situ mass spectroscopy that allows the use of laser-cooled atomic ions to detect sympathetically-cooled molecular ions non-destructively. We demonstrate this technique by cooling and mass-analysing ions of ultra-high-vacuum residual gas and externally introduced air in situ with less than 80 ions each, confined in a radio-frequency quadrupole (RFQ). This capability to detect and identify sympathetically-cooled molecules with potentially-high sensitivity in situ in an RFQ should be useful for molecular spectroscopy, chemical analysis and study of cold molecules and clusters.
Optical Properties and Blue and Green Electroluminescence in Soluble Disubstituted Acetylene Polymers
Authors: Kazuya Tada Kazuya Tada , Rahmat Hidayat Rahmat Hidayat , Masaharu Hirohata Masaharu Hirohata , Masahiro Teraguchi Masahiro Teraguchi , Toshio Masuda Toshio Masuda , Katsumi Yoshino Katsumi Yoshino
Published: October 2002

Intense photoluminescence (PL) was observed in soluble disubstituted polyacetylenes such as poly(1-phenyl-2- p-adamantylphenyl acetylene (PDPA-Ad) at 530 nm, poly(1-phenyl-2- p-triphenylsilylphenyl acetylene) (PDPA-TPSi) at 530 nm and poly(1-hexyl-2-phenyl acetylene) (PHxPA) at 455 nm, although they are considered to be derivatives of trans-polyacetylene. In monosubstituted acetylene polymers such as poly( o-trimethylsilylphenyl acetylene) (PTMSiPA), PL was negligible. Green and blue light emissions were observed from an electroluminescent (EL) device having soluble poly(diphenyl acetylene) (PDPA) derivatives (PDPA-Ad and PDPA-TPSi) and PHxPA as emission layers, respectively. EL emission is clearly observable under normal room illumination conditions. The electronic energy structures of the disubstituted PA derivatives are also discussed to interpret PL and EL characteristics.
Initial Stage of Microcrystalline Silicon Growth by Plasma-Enhanced Chemical Vapor Deposition
Authors: Arai Takeshi , Takuya Nakamura Takuya Nakamura , Hajime Shirai Hajime Shirai
Published: October 2002

We report the initial stage of growth of hydrogenated microcrystalline silicon (µ c-Si:H) film with less than 500 Å thick by conventional rf plasma-enhanced chemical vapor deposition (PECVD). Through studies of film deposited on thermally grown SiO2 with various types of morphology and film grown by a layer-by-layer (LbL) technique, it was found that the crystallinity strongly influenced on the induced surface roughness and it correlated with the SiH2/SiH intensity ratio. The thin film transistor (TFT) characteristics are determined not only by the film crystallinity but alsso by the morphology of SiO2 substrate, which suggest that the formation of the crystallite phase at the early stage of growth without increasing the interface roughness is essential for further improvement of the carrier transport properties.
Pulsed Field Magnetization of Melt-Processed Y–Ba–Cu–O Bulk Superconductor with No Weak Links
Authors: Itoh Yoshitaka , Yanagi Yousuke , Yoshikawa Masaaki , Oka Tetsuo , Yamada Yuh , Mizutani Uichiro
Published: October 2002

The applied field dependence of magnetic flux trapped by the pulsed field magnetization (PFM) method has been investigated for a small melt-processed Y–Ba–Cu–O bulk sample with a symmetric distribution of the trapped flux. It was revealed that the magnetic flux trapped in the sample decreases when the applied field exceeds a critical value, regardless of the existence of weak links, and that the reduction is marked in the center of the sample. Furthermore, the reduction was found to strongly depend not only on the PFM condition responsible for the heat generation but also on the cooling condition to dissipate the heat generated in the sample.
Formation of Stacking-Faults in Atomic Graphoepitaxial a-Axis YBa2Cu3Ox Thin Films on (100) SrLaGaO4 Substrates
Authors: Shintaro Miyazawa Shintaro Miyazawa , Masashi Mukaida Masashi Mukaida
Published: October 2002

The complicated crystalline microstructure of c-axis in-plane-aligned, a-axis oriented YBa2Cu3O

x

thin films on K2NiF4-type (100) SrLaGaO4 substrates is discussed in relation to surface irregularities inherent in the (100) SrLaGaO4 substrate. Transmission electron microscopy reveals that interlattice planes of YBa2Cu3O

x

shift by multiples of c/6 unit, resulting in anti-phase domain boundaries and stacking-faults. The formation of these defects can be correlated with the cobbled substrate surface and is modeled in terms of atomic steps on the cobbled surface based on our growth model named “atomic graphoepitaxy”.
Application of Position-Sensitive Proportional Counter to X-Ray Spectroscopy
Authors: Hasegawa Takeo , Fukumori Taichiro , Kunio Kaminishi Kunio Kaminishi , Tatsuro Matsuda Tatsuro Matsuda
Published: October 2002

A small position-sensitive counter with a single resistive anode wire was constructed for use in a double-crystal X-ray spectrometer system. Using this position detector we have measured Kα doublet X-rays in the positions of which are very close together and obtained the two corresponding rocking curves simultaneously, to determine the lattice constant differences in various crystals.
Microcrystalline Silicon Films Deposited by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition Using Helium Gas
Authors: Eon Lee Kyung , Hyoung Lee Wook , Sung-Chul Shin Sung-Chul Shin , Choochon Lee Choochon Lee
Published: October 2002

We have investigated the growth of microcrystalline silicon films by electron cyclotron resonance plasma chemical vapor deposition (ECR-PCVD) using He as the ECR gas at substrate temperatures in the range of 180 to 550°C with He to silane ratios (He/SiH4) of 1, 4, and 9. With ratios of 4 and 9, the volume fractions of microcrystalline silicon increase with temperature and exceed 90% at 550°C. To study the role of He plasma, we prepared silicon films using a layer-by-layer technique and found that long exposure to He plasma changes the structure of amorphous silicon to microcrystalline.
Fabrication of Gold Nanodot Array Using Anodic Porous Alumina as an Evaporation Mask
Authors: Hideki Masuda Hideki Masuda , Masahiro Satoh Masahiro Satoh
Published: October 2002

A highly ordered gold nanodot array was fabricated by vacuum evaporation using an anodic porous alumina membrane with through-holes of nanometer scale as a mask. This technique resulted in an orderly arrangement of Au dots with a diameter of approximately 40 nm over a large area on a Si substrate.
Temperature-Dependent Electrical Orientation of Poly(cyclohexylmethylsilane)
Authors: Keiichi Hirooka Keiichi Hirooka , Robert West Robert West , Yoshikazu Nakayama Yoshikazu Nakayama
Published: October 2002

Poly(cyclohexylmethylsilane)(PHMS) aligns perpendicular or parallel to the electric field depending upon the temperature for formation of films by casting on Al interdigital electrodes evaporated on glass substrates. The germ of this temperature dependence has been investigated by thermal analysis and Raman scattering measurements. The temperature of ∼14°C at which PHMS effectively aligns along the electric field is equal to the phase transition temperature of its side chains. The presence of interdigital electrodes induces the temperature-dependent ordering of PHMS even when no electric field is applied. This probably accounts for the direction of the electric field orientation of PHMS.
Possibility of Fractal Growth in Polymerization-Induced Epitaxy
Authors: Sano Masahito , Wada Momoyo , Asako Miyamoto Asako Miyamoto , Susumu Yoshimura Susumu Yoshimura
Published: October 2002

The possibility of fractal growth was investigated by analyzing atomic force microscopy images of a poly (tetrahydrofuran) epitaxial monolayer on graphite formed during polymerization of monomers. Usually, the film develops by uniform growth of elongated, flat islands filling the bare surface as polymerization continues. Occasionally, an irregular morphology was observed at a surface coverage of 0.75–0.80. Double logarithmic plots of the perimeter against the area of these irregularly shaped islands yield straight lines, from which the fractal dimension of the contour is estimated to be no greater than 1.80.
Depth-Sensitive X-Ray Scattering Topographic Observation of InAs Grown by Molecular Beam Epitaxy on GaAs
Authors: Suzuki Yoshifumi , Yoshinori Chikaura Yoshinori Chikaura , Hideki Kii Hideki Kii
Published: October 2002

Depth-sensitive X-ray scattering topography using a microbeam was carried out for a Be-doped InAs layer, which was epitaxially grown to a thickness of 1.0 µ m by MBE (molecular beam epitaxy) on a CrO-doped GaAs substrate with (001) surface orientation. Throughout the X-ray experiments, Co Kα radiation was used. The experimental results show that the depth sensitivity depends on the diffraction index, (004), (002) or (006). Although the FWHM of the X-ray diffraction rocking curve is large, the depth sensitivity for defects on the topographs has the same tendency as the penetration depth calculated by dynamical theory.
The High-Field Cured Polymer Networks in Nematic Liquid Crystals
Authors: Li Jianlin , Anderson James E. , Hoke Charles D. , Nose Toshiaki , Philip J. Bos Philip J. Bos
Published: October 2002

The polymer networks formed in nematic liquid crystals at high-field condition are studied. Assuming the networks are distributed uniformly, an polymer network contribution to the system free energy is added in the form of -½K
a(n·N)2, where K
a, n and N are polymer network coefficient, liquid crystal director and polymer network unit vector, respectively. Ignoring the polymer networks elasticity, the liquid crystal director configuration and elastic energy under the influence of an external electric field are calculated numerically. The obtained electro-distortional characteristics are found to depend on the value of K
a and N. The results are compared to the electro-optic threshold and hysteresis behaviors of a set of highly twisted nematic cells with different monomer concentrations. A good agreement between the monomer concentration and polymer network coefficient is presented.
High Frequency Properties of High Temperature Superconducting YBa2Cu3O7-δ Thin Films on LaAlO3 Substrates Utilizing Line and Ring Resonators
Authors: Jin Pyo Hong Jin Pyo Hong
Published: October 2002

Microwave properties of rf sputtered YBa2Cu3O7-δ thin films deposited on LaAlO3 substrates have been successfully characterized utilizing line and ring resonator techniques. Microstrip resonator structures with fundamental resonance at 7.015 GHz and third harmonic resonance at 20.21 GHz were developed and investigated for measuring rf surface losses. Temperature and input power dependence of the surface resistance of these high T
c superconducting films was performed and discussed. The resonant frequency shift with temperatures was observed. The best surface resistance of high T
c superconducting ring resonator was 0.314 m Ω at 20.21 GHz and was 20 times lower than that of the gold resonator with identical structures.
Negative Conductance Properties in Extremely Thin Silicon-on-Insulator (SOI) Insulated-Gate pn-Junction Devices (SOI Surface Tunnel Transistors)
Authors: Yasuhisa Omura Yasuhisa Omura
Published: October 2002

In this paper the occurrence of negative conductance at temperatures of less than 90 K in a silicon-on-insulator (SOI) surface tunnel transistor with a 10-nm-thick silicon layer fabricated on a separation by implanted oxygen (SIMOX) substrate is reported. Through comparison with the performance of an SOI surface tunnel transistor with a 90-nm-thick silicon layer, the advantages of the two-dimensional confinement effect are shown.
Green Electroluminescent Emission from Substituted Polyacetylenes
Authors: Sun Runguang , Masuda Toshio , Takayoshi Kobayashi Takayoshi Kobayashi
Published: October 2002

Electroluminescent (EL) cells fabricated utilizing monophenyl and diphenyl substituted polyacetylenes, i.e. poly(phenylacetylene) (PPA) and poly(diphenylacetylene) (PDPA) derivatives, as emitters are reported on. Green light emission from these polymers which are sandwiched between an ITO (indium-tin oxide) coated glass substrate and a Mg/Al cathode has been observed at a 6 V ITO forward bias. Among these polymers, poly[1-(p-n-butylphenyl)-2-phenylacetylene] (PDPA-nBu) shows the highest efficiency for green light emission. The EL efficiency was improved by doping an electron transporting material, 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD), in these polymers, and a fivefold increase in EL efficiency was achieved.
Very High-Density Recording on Exchange-Coupled Trilayer Magnetically Induced Super Resolution Media without Special Initializing Magnet
Authors: Matsumoto Koji , Tamanoi Ken , Tsutomu Tanaka Tsutomu Tanaka , Keiji Shono Keiji Shono
Published: October 2002

We obtained a high carrier-to-noise ratio (CNR) of 47 dB and a low jitter of 8% for 0.33 µm mark length ( 0.66 µm mark pitch) on exchange-coupled trilayer magnetically induced super resolution (MSR) media. This media is composed of a readout layer, an intermediate layer, and a writing layer. The magneto-optical signal is read through an aperture at the focal point between a front mask and a rear mask. The double mask can be formed by applying a readout magnetic field smaller than 300 Oe.
Preparation of Crystallized Ba-Rich Ba1-XCaXWO4 Solid-Solution Films by an Electrochemical Method at Room Temperature and Their Luminescence
Authors: Woo-Seok Cho Woo-Seok Cho , Masahiro Yoshimura Masahiro Yoshimura
Published: October 2002

Well crystallized solid-solution Ba1-
X

Ca

X

WO4 films have been prepared on tungsten substrates in an electrolytic solution containing Ba2+ and Ca2+ ions by an electrochemical method at room temperature (25° C). CaWO4 film showed only blue emission at liquid nitrogen temperature (-196° C), strongly suggesting that it consisted of well crystallized defect-free crystals. However, the other films did not luminesce at this temperature.
Substrate Effects on the Epitaxial Growth of AlN Thin Films Using Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Desposition
Authors: Ju-Won Soh Ju-Won Soh , Jin-Hyeok Kim Jin-Hyeok Kim , Won-Jong Lee Won-Jong Lee
Published: October 2002

Highly c-axis oriented AlN films were fabricated on various substrates by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) at a substrate temperature of 500°C. The degree of c-axis orientation depends sensitively on the substrate: the standard deviations σ of AlN(0002) rocking curve peaks are 4.9°, 4.8°, 4.3°, 4.0° and 1.5° on SiO2, Si3N4, Si(100), Si(111) and α-Al2O3(0001) substrates, respectively. The amorphous interfacial silicon oxide layer on Si substrate has an important effect on the degree of c-axis orientation and in-plane alignment of the AlN film. The AlN films prepared by ECR PECVD have much lower surface roughness (R
RMS=1.1–1.9 nm) than the sputter-deposited films (R
RMS=3.0–9.0 nm), which offers lower propagation loss in SAW devices.
Rapid Thermal Diffusion of Indium in p-HgCdTe/CdTe
Authors: Park Seung-Man , Kim Jae Mook , Hee Chul Lee Hee Chul Lee , Choong-Ki Kim Choong-Ki Kim
Published: October 2002

In this study, the rapid thermal diffusion (RTD) of indium and its activation as a donor in p-Hg0.70Cd0.30Te/CdTe were investigated using atomic indium and electron concentration profiles obtained by secondary ion mass spectroscopy (SIMS) and differential Hall measurements, respectively. Photodiodes with a junction formed by the RTD of indium were also demonstrated. There are two diffusion components, a complementary error function fitted atomic diffusion component and an exponentially fitted fast diffusion component. The diffusion coefficients of atomic indium into p-Hg0.70Cd0.30Te by RTD can be fitted as D(T)( cm2/s)=1.45×10-2exp
(-0.772(eV)/kT) in the temperature range of 100–200°C. It is observed that diffused indium atoms are partially activated as donors and that the ratio of electron to diffused indium concentration is increased with increased diffusion depth from the surface. For photodiodes with an indium RTD junction, trap-assisted tunneling current is markedly suppressed. The origin of suppression of trap-assisted tunneling current can be explained by suppression of defect generation in the depletion region during junction formation by the RTD process.
Large Transmittance Changes Induced in Ga-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition
Authors: Tanaka Akio Suzuki , Takanori Aoki Takanori Aoki , Masahiro Okuda Masahiro Okuda
Published: October 2002

Thin films of ZnO:Ga (GZO) have been deposited on glass substrates at room temperature by a pulsed laser deposition technique using a Nd:YAG laser (λ=1064 nm). The 100-nm-thick GZO films grown in vacuum were dark brown and showed optical transmittance of less than 20% in the 300–3200 nm wavelength region. On the other hand, it was found that GZO films grown in vacuum and annealed at 400–420°C for 3–5 min showed an average transmittance of above 80% in the 400–3200 nm wavelength region. GZO films with large transmittance changes in the 400–600 nm wavelength region can be applied to high-density optical recording films.
Growth Mechanism of BaTiO3 Thin Film by Theoretical Calculation of Electronic Structure
Authors: Young-Seog Kang Young-Seog Kang , Isao Tanaka Isao Tanaka , Hirohiko Adachi Hirohiko Adachi , Soon Ja Park Soon Ja Park
Published: October 2002

The surface electronic structure of BaTiO3 and the adsorption of oxygen ion have been calculated using the DV-Xα cluster method. We use the concept of embedded clusters to model the BaTiO3 (001) surface, and O2- adsorption and Ba2+ coadsorption on the surface. We calculate the valence electronic states for the surface and those involved in adsorption. Using Mulliken's population analysis it is found that the adsorption of oxygen ion on the surface weakens the covalent bonds between Ti and O in the BaTiO3 substrate. In contrast, oxygen ion with coadsorbed Ba2+ ions results in stronger chemical bonding in the cluster than for the adsorption of only O2- ion. The present results indicate that epitaxial BaTiO3 thin films can be grown by simultaneous adsorption of groups of ions which have overall charge neutrality.
Electrical Characteristics of Ultra-Fine Trench Isolation Fabricated by a New Two-Step Filling Process
Authors: Shiozawa Katsuomi , Oishi Toshiyuki , Maeda Hiroshi , Murakami Taka-aki , Yasumura Kenji , Yuji Abe Yuji Abe , Yasunori Tokuda Yasunori Tokuda
Published: October 2002

An ultra-fine trench isolation with superior electrical properties was formed using a new fabrication process. A void-free shape and sufficient thickness of the field oxide were realized by two-step filling using tetraethyl-ortho-silicate (TEOS) oxide as the lower layer and high-density CVD-SiO2 as the upper capping layer. The breakdown voltages were as high as 7.7 V, even for an isolation space as narrow as 0.13 µm. The subthreshold characteristics of the metal oxide semiconductor field effect transistor (MOSFET) isolated by the trench were kink-free. The threshold voltage of the parasitic MOSFET, furthermore, was more than 6 V, even without a channel stop implant to suppress punch-through.
Nitrogen Atomic-Layer-Doping on Ga-Terminated and Misoriented GaAs Surfaces by Metalorganic Vapor Phase Epitaxy Using Dimethylhydrazine
Authors: Saito Hisao , Toshiki Makimoto Toshiki Makimoto , Naoki Kobayashi Naoki Kobayashi
Published: October 2002

Nitrogen atomic-layer-doping on Ga-terminated and misoriented GaAs surfaces was performed by Metalorganic Vapor Phase Epitaxy (MOVPE) using dimethylhydrazine to investigate the role of the surface for nitrogen atom incorporation. Compared with the As-terminated surface, dimethylhydrazine molecules are preferentially decomposed on the Ga-terminated surface due to the catalytic effect, resulting in a higher doping efficiency. We also investigated the crystal orientation dependence of the nitrogen doping concentration. Nitrogen atoms are preferentially incorporated on the (n11)A surfaces (n≥3) than the (100) surface. For the (n11)A surface, the nitrogen doping efficiency increases with decreasing n value. This indicated the doping efficiency increases with the step density. In contrast, nitrogen atoms are incorporated less on the (n11)B surfaces (n≥3) than the (100) surface and their doping efficiency decreases with increasing step density. These results are ascribed to the difference of atomic bonding geometries for adsorption sites between (n11)A and (n11)B surfaces. The doping efficiency for A-type steps is twice as high as that for the (100) terraces while that for B-type steps is negligibly small.
Light Waveform in Time Domain and Relaxation Mechanism of ZnS:Cu,Br Dispersive Electroluminescent Devices
Authors: Yuri Nakatani Yuri Nakatani , Takeo Suzuki Takeo Suzuki
Published: October 2002

In a ZnS:Cu,Br dispersive electroluminescent device, we have observed a new behavior of a light waveform in the time domain, that is, the trailing edge emission splits into two peaks when the applied voltage falls at a certain rate. This suggests that the usual donor-acceptor (DA) pair relaxation process requires some modification according to the electric field. Based on experimental results, we propose a new relaxation process to explain the behavior of the light waveform. In the new relaxation process, the preferable combination of a DA pair under a high electric field changes spatially from that under a low electric field. The splitting phenomenon is peculiar to DA pair emissions such as ZnS:Cu,Br.
Imaging of Nucleic Acid Base Molecules on Pd(110) Surfaces by Scanning Tunneling Microscopy
Authors: Tanaka Hiroyuki , Yoshinobu Jun , Kawai Maki , Tomoji Kawai Tomoji Kawai
Published: October 2002

Scanning tunneling microscopy (STM) images have been obtained for the nucleic acid bases, adenine and thymine, deposited on Pd(110) single-crystal substrates in order to study the electronic structure and interaction between the DNA bases. The adenine and thymine molecular images are different, with distinct shapes and lateral dimensions that reflect the contours of the calculated molecular orbitals. Thus, adenine has triangular protrusions with lateral dimensions of ∼0.8 nm and thymine has round features of diameter ∼0.45 nm. Adenine tends to form dimers whereas thymine forms islands even at low eoverages.
Makyoh Topography: Curvature Measurements and Implications for the Image Formation
Authors: Szabó János , Ferenc Riesz Ferenc Riesz , Béla Szentpáli Béla Szentpáli
Published: October 2002

A new method is developed for the measurement of the radii of curvature R of mirror-like semiconductor wafers using the magic-mirror (Makyoh) method. A flat mirror is placed beneath the sample, thus a second, “contour” image of the sample is formed beside the sample image itself. From the size deviation of the two images that results from the curvature of the sample, R can be calculated. Experimental results obtained with mirrors with known curvature show good agreement with the calculations. Implications for the general image formation mechanism are discussed as well.
Characterization of Layered Polysilane
Authors: Nishimura Kohsuke , Nagao Yasuyuki , Yamanaka Shoji , Matsu-ura Hiroyuki
Published: October 2002

Layered polysilane synthesized according to a new recipe was characterized mainly by photoluminescence (PL) measurement. The PL spectrum of the as-prepared sample had a broad peak at 2.0 eV. The PL peak of a sample annealed at 300°C was also at 2.0 eV, and its PL intensity was several times greater than that of the as-prepared sample. The PL peak of a sample annealed at 400°C was red-shifted and its PL intensity was lower than those of the others. On the other hand, the PL emission from a sample rinsed in HF solution was blue-shifted and had a little lower intensity. The interpretations of the experimental results are discussed.
Electromagnetic Fault for Earthquake Lightning
Authors: Motoji Ikeya Motoji Ikeya , Shunji Takaki Shunji Takaki
Published: October 2002

A density of bound charges, q, which cancel piezoelectric polarization, appears at a fault zone upon the disappearance of piezoelectricity due to the release of seismic stress, σ. q is described as dq/ dt=-α dσ/ dt-q/ερ, where α, ε and ρ are the piezoelectric coefficient, the dielectric constant and the resistivity of the earth, respectively. A model of a fault with length 2a and displacement time τ gives q=[ασ0
ερτ(β/a)/(τ-ερ)]( e-t/τ- e-t/ερ) using the velocity of s-waves, β and the stress along the fault plane, σ0. The intensity of earthquake lightning (EQL) and its spatial distribution are calculated based on the excitation of molecules by electrons accelerated under an electric field using the assumed q, taking atmospheric polarization into account.
Oxygen Concentration in the Top Silicon Layer of Silicon-on-Insulator Materials Formed by Low-Dose Implantation of Oxygen
Authors: Saito Mina , Jablonski Jaroslaw , Katayama Tatsuhiko , Miyamura Yoshiji , Kazuyoshi Ikegaya Kazuyoshi Ikegaya , Masato Imai Masato Imai
Published: October 2002

Oxygen concentration in the top silicon layer of silicon-on-insulator materials formed by low-dose implantation of oxygen has been measured by means of secondary ion mass spectroscopy. A value of less than 1×1017 atoms/cm3 has been obtained. We propose that the oxygen concentration in the top silicon layer is controlled by oxygen out-diffusion during the wafer cooling process.
Control of Nematic Liquid Crystal Alignment Using Stripped Film Method
Authors: Yasushi Kawata Yasushi Kawata , Yasushi Mori Yasushi Mori
Published: October 2002

We investigate a new rubbing-free process for nematic liquid crystal (LC) alignment using the stripped film method. It was found that the direction of the nematic director, the pretilt angle and the tilt-up direction are determined by the peeling direction. The nematic director was aligned parallel to the peeling direction, and the pretilt angle increased in the direction opposite to the peeling direction. The value of the pretilt angle, 1.5°, was independent of the peeling speed. Device-quality alignment was realized on the surface of a stripped substrate.
Triangular-Facet Laser with Optical Waveguides Grown by Selective Area Metalorganic Chemical Vapor Deposition
Authors: Ando Seigo , Naoki Kobayashi Naoki Kobayashi , Hiroaki Ando Hiroaki Ando
Published: October 2002

A triangular prism-shaped GaAs/AlGaAs laser with rectangular optical waveguides at three corners is proposed and its preliminary lasing characteristics and waveguiding of lasing light are presented. This structure is grown by selective area metalorganic chemical vapor deposition (MOCVD) and consists of a (111)B growth plane and (110) sidewall facets. The advantage of the triangular facet is that the prism growth proceeds while maintaining the equilateral triangle shape even if there is a little fluctuation in the size or shape of the mask and if the layer thickness is increased up to about 1.5 µ m. Lasing at room temperature is observed by optical pumping of low energy (E
th<10 pJ). The lasing light can be successfully extracted from the point of the rectangular waveguides. The lasing mode is found to be a ring cavity mode of an inscribed equilateral triangle by the longitudinal mode spacing.
Stable Second-Order Optical Nonlinearity of Urethane-Urea Copolymers
Authors: Tsuchimori Masaaki , Watanabe Osamu , Shin-ichi Ogata Shin-ichi Ogata , Akane Okada Akane Okada
Published: October 2002

Second-order nonlinear optical properties of corona-poled urethane-urea copolymers have been studied by the second-harmonic generation (SHG) method. As compared with a polyurethane, the copolymers exhibited higher optimum poling temperature and better temporal stability of SHG coefficients (d
33). For one of the copolymers, d
33 at a fundamental wavelength of 1064 nm was 190 pm/V, and remained at 75% of the initial value after heat treatment at 100° C for 300 h.
In Situ Observation of the C49-to-C54 Phase Transformation in TiSi2 Thin Films by Transmission Electron Microscopy
Authors: Tanaka Hiroyuki , Sinclair Norio Hirashita
Published: October 2002

The C49-to-C54 phase transformation of TiSi2 has been studied by in situ transmission electron microscopy (TEM) in the high resolution mode using cross-sectional samples and by X-ray diffraction (XRD). XRD and TEM analyses suggest that the (131) plane of the C49 phase transforms to the (311) and/or (313) planes of the C54 phase. In Situ TEM observation shows that the interface of the transformation moves parallel to the Si substrate, while the direction of the transformation does not depend on the orientation of the C49 phase. The results indicate that the transformation occurs via the short-distance diffusion of atoms.
High Performance Fabry-Perot Modulator Using Interdiffused AlGaAs/GaAs Quantum Wells
Authors: E. Herbert Li E. Herbert Li , Wallace C. H. Choy Wallace C. H. Choy
Published: October 2002

Interdiffused AlGaAs/GaAs quantum well structures are being employed as an active cavity material in the Fabry-Perot reflection type modulators. An extremely large relative reflectance change (over 14000) is predicted, higher than any value that has been reported among the available literature today. This is due to an extremely low reflectance (∼10-5) at the resonance of the Fabry-Perot mode while simultaneously the change of reflectance is kept around the order of unity. The power consumption is reduced by 67% due to the highly sensitive electrons in the interdiffused wells. A wide operation wavelength range of over 100 nm is also observed.
Acoustic Emission (AE) Measurement Technique in Piezoelectric Ceramics
Authors: Hideaki Aburatani Hideaki Aburatani , Kenji Uchino Kenji Uchino
Published: October 2002

Special care must be taken in measuring the acoustic emission (AE) in piezoelectric ceramics, because a self vibration of the ceramics is caused by a power supply through a feedback system. Significantly different data from the results previously reported were obtained by eliminating the self vibration of the ceramics. The dynamic contribution of 180° and non-180° domain reorientation on the AE generation were discussed on the basis of AE data observed in lead zirconate-titanate (PZT) ceramics.
Effect of Aperture Closure in Intense Pulsed Light Ion Beam Measurement
Authors: Chishiro Etsuji , Katsumi Masugata Katsumi Masugata , Kiyoshi Yatsui Kiyoshi Yatsui
Published: October 2002

The effect of aperture closure on the irradiation of an intense pulsed light ion beam of ion current density (J
i) 1–8 kA/cm2 has been evaluated experimentally. By using biased ion collectors the aperture closure is observed for J
i>1 kA/cm2 and the closing speed increases with increasing J
i or decreasing aperture size. At J
i=8 kA/cm2, an aperture of diameter 0.3 mm is closed 40 ns after the rise of J
i. From the evaluation of the magnetic energy spectrometer, the effect is greater for heavy ions of C+, O+,··· than for protons.
Tight-Binding Analysis of the Optical Matrix Element in Wurtzite- and Zincblende-GaN Quantum Wells
Authors: Atsuko Niwa Atsuko Niwa , Tsukuru Ohtoshi Tsukuru Ohtoshi , Takao Kuroda Takao Kuroda
Published: October 2002

The polarization dependence of the optical matrix element in wurtzite- and zincblende-GaN quantum wells (QWs) is theoretically investigated, based on the s
p
3 tight-binding model which takes into account the spin-orbit interaction and crystal field splitting. The optical matrix element in wurtzite-GaN QWs has no dependence on the wave number due to its anisotropy along the c axis. We also show that the optical matrix element for the conduction-light hole transition in wurtzite-GaN QWs is about three times larger than that for bulk zincblende GaN. These results suggest that wurtzite GaN will be useful for light emitting devices due to its apparent high optical transition.
Photoluminescence Properties of GaN Grown under Ion Flux Reduced Condition by Plasma Enhanced Molecular Beam Epitaxy
Authors: Cho Sung Hwan , Tanaka Uitsu , Hata Kazutaka , Takahiro Maruyama Takahiro Maruyama , Katsuhiro Akimoto Katsuhiro Akimoto
Published: October 2002

Effects of nitrogen ion irradiation on photoluminescence (PL) properties at 77 K of undoped GaN grown by plasma enhanced molecular beam epitaxy were investigated. It was found that for epitaxial layers grown under ion irradiation conditions, the PL spectra were dominated by near band-edge emission at 357 nm (3.47 eV). However, deep-level emission at around 567 nm (2.2 eV) was also observed and the intensity of which was considerably strong. On the other hand, for GaN films grown with no ion irradiation, the intensity of the deep-level emission was two orders of magnitude less than that of the near band-edge emission. This result suggests that the nitrogen ions degrade the PL properties, i.e., create defect levels relating to emission at around 567 nm (2.2 eV).
RF Hollow Cathode Discharges with Tapered Shape
Authors: Taichi Fukuda Taichi Fukuda , Akio Matsuoka Akio Matsuoka , Yoshiomi Kondoh Yoshiomi Kondoh , Minoru Sugawara Minoru Sugawara
Published: October 2002

A hollow cathode with tapered shape (HCT) is developed in order to expand the range of operating pressures. Although the plasma density produced by the HCT becomes slightly lower than that by an ordinary hollow cathode, it is demonstrated experimentally that the range of operating pressures for stable RF hollow cathode discharge is expanded. It is shown that the position of the negative glow moves inside the HCT for different operating pressures to sustain the hollow cathode discharge.
Thermal Stability of Beryllium Atoms in Be δ-Doped GaAs Grown on GaAs(111)A by Molecular Beam Epitaxy
Authors: Hirai Manabu , Ohnishi Hajime , Kazuhisa Fujita Kazuhisa Fujita , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

We report on the thermal stability of Be in δ-doped GaAs layers grown on misoriented GaAs(111)A substrates. The diffusion coefficients of Be tend to become large as the substrates are misoriented from (110) to (001). These diffusion coefficients of Be are larger than those of Si used as a p-type dopant. The estimated activation energy of Be diffusion on GaAs(111)A is 1.42±0.12 eV and is smaller than that of Si-acceptor. This study indicates that the diffusion of Be is due to an interstitial diffusion mechanism; this is in contrast to that of Si-acceptor, which is due to a vacancy diffusion mechanism.
Metalorganic Chemical Vapor Deposition of YBa2Cu3Ox Thin Films Using Bis-Dipivaloylmethanato-Barium Bis-Tetraethylenepentamine Adducts as a Novel Barium Source
Authors: Hideaki Zama Hideaki Zama , Tadataka Morishita Tadataka Morishita
Published: October 2002

We have prepared YBa2Cu3O

x

thin films by metalorganic chemical vapor deposition using bis-dipivaloylmethanato-barium bis-tetraethylenepentamine adducts ( Ba(DPM)2-tetraen2) as a new Ba precursor. This precursor has much higher volatility than typical Ba sources such as Ba(DPM)2. A deposition rate of approximately 50 nm/h is achieved when the vaporizing temperature of Ba(DPM)2-tetraen2 is set at 140° C. This is seven times faster than that achieved using Ba(DPM)2 at a vaporizing temperature of 187° C. A 200-nm-thick film grown on a MgO(100) substrate has a minimum channeling yield of 6%. The compositional deviation of the films is ±4% for up to 100 h of use.
Growth and Some Properties of ErRh3B and ErRh4B4 Single Crystals
Authors: Okada Shigeru , Kudou Kunio , Shishido Toetsu , Fukuda Yuichi Sato
Published: October 2002

Single crystals of ErRh3B and ErRh4B4 have been grown from high-temperature copper metal solution using small pieces of erbium, rhodium powder and crystalline boron powder as starting materials. The as-grown ErRh3B and ErRh4B4 crystals have been used for chemical analysis. The Vickers microhardness and electrical resistivity of the crystals were measured, and oxidation at high temperature in air was studied. The Vickers microhardness value on (100) planes of ErRh3B crystals is in the range of 4.77–4.97 GPa. The microhardness value on (100) or (110) planes of ErRh4B4 crystals is in the range of 10.9–11.3 GPa. The electrical resistivity determined on ErRh3B and ErRh4B4 crystals are as follows: for ErRh3B: 25.6 µ Ω· cm; for ErRh4B4: 106.8 µ Ω· cm. The oxidation of ErRh3B and ErRh4B4 crystals begin at about 1030° C and 690° C, respectively.