bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Critical Current Density of Melt-Textured Y-Ba-Cu-O Superconductor Containing Fine Y2BaCuO5Inclusions
Authors: Kim Chan-Joong , Park Hai-Woong , Kim Ki-Baik , Lee Kyu-Won , Gye-Won Hong Gye-Won Hong
Published: October 2002

Melt-textured YBa2Cu3Oysuperconductor containing fine Y2BaCuO5inclusions (a few hundreds nanometers in size) was prepared by using of attrition-milled YBa2Cu3Oy/Y2BaCuO5powder with 1 wt% CeO2addition. It is found that the combination of the CeO2addition and the mechanical milling of the powder mixture is effective in reducing Y2BaCuO5size. The critical current density (Jc) of the sample containing fine Y2BaCuO5is higher than that of the sample containing coarse Y2BaCuO5.JcforH||c-axis of Y1.8Ba2.4Cu3.4Oywith coarse Y2BaCuO5was 1.1×104A/cm2and 0.56×104A/cm2, whileJcof Y1.8Ba2.4Cu3.4Oywith fine Y2BaCuO5was 2.0×104A/cm2and 1.16×104A/cm2at 1 T, 2 T and 77 K, respectively.
Room-Temperature Epitaxial Growth of CeO2 Thin Films on Si(111) Substrates for Fabrication of Sharp Oxide/Silicon Interface
Authors: Yoshimoto Mamoru , Shimozono Kazuki , Maeda Tatsuro , Ohnishi Tsuyoshi , Kumagai Masao , Chikyow Toyohiro , Ishiyama Osamu , Shinohara Makoto , Hideomi Koinuma Hideomi Koinuma
Published: October 2002

Room-temperature (20° C) epitaxy of high-melting point CeO2 thin films was achieved for the first time on Si(111) substrates. Cross-sectional high-resolution transmission electron microscopy, Rutherford backscattering spectrometry and ion scattering spectroscopy confirmed the formation of a sharp oxide/silicon heterointerface with no boundary amorphous layer and single crystallinity of the present CeO2 films. This was achieved by pulsed laser deposition in an ultrahigh vacuum under optimized oxygen partial pressures and by hydrogen termination of the Si surface.
Quantized Conductance Observed in Quantum Wires 2 to 10 µm Long
Authors: Honda Takashi , Tarucha Seigo , Saku Tadashi , Yasuhiro Tokura Yasuhiro Tokura
Published: October 2002

We observe quantized conductance in 2- to 10-µ m-long wires formed in a very-high-mobility modulation-doped heterostructure. These wires have a new gate configuration that facilitates strong lateral constriction despite the large separation between the surface and the electron channel. Random potential scattering in the wire causes a conductance dip near the threshold of the higher-lying subband. This scattering is strongly suppressed when only the ground subband is occupied. Wires longer than 20 µ m display a conductance step of 0.6 to 0.7 (2e2/h). This step is probably made more evident by the effect of thermal broadening as well as by a dip in the conductance near the threshold for the higher-lying subband.
Calculation of Absorption Spectra of YBa2Cu3O7-δ by Means of Xα Method
Authors: Maruyama Kazuo , Shinagawa Kiminari , Saito Toshiaki , Tachiro Tsushima Tachiro Tsushima
Published: October 2002

In order to clarify the absorption spectra of YBa2Cu3O7-δ (YBCO) in both the insulating state (δ=1) and superconducting state (δ=0), the electronic states are calculated by cluster approximation by means of the Xα method. The absorption peak observed in the mid-IR region in the superconducting state of YBCO is assigned to the transition from the O2 2p
z
orbital to the hybrid orbital of O1 2p
z
and Cu II 3d
z
2
in a hole-doped (CuO5)7- pyramid cluster, and the peak at 4.1 eV observed in the insulating state, to the transition from the O1 2p
z
orbital to the Cu I 4p
x
one in a (CuO2)3- chain cluster. The overall spectra are reproduced well using the transition energies and the oscillator strengths calculated by the Xα method.
Ultrafast Microwave Reflectometer for Density Profile Measurements on GAMMA 10
Authors: Tokuzawa Tokihiko , Mase Atsushi , Oyama Naoyuki , Ito Yasuhiko , Itakura Akiyosi , Teruo Tamano Teruo Tamano
Published: October 2002

A 12-18 GHz, broad-band reflectometer system has been applied to the central cell of the GAMMA 10 tandem mirror. A fast-sweep hyperabrupt varactor-tuned oscillator (HTO) is used as a source, which can be swept over the full frequency band in less than 5 µ s. The high-frequency fringes due to the change of cut-off layer can be distinguished from those due to the existence of density fluctuations, since the fluctuation level with frequency components larger than 20 MHz is much smaller than the average density (≤10-4) in GAMMA 10 plasmas. The reflectometer is applied to determine the density profiles under different operating conditions.
Hydrogen-Free Plasma-Enhanced Chemical Vapor Deposition of Silicon Dioxide Using Tetra-isocyanate-silane (Si(NCO) 4)
Authors: Irman Idris Irman Idris , Osamu Sugiura Osamu Sugiura
Published: October 2002

Deposition of silicon dioxide by plasma-enhanced chemical vapor deposition (PECVD) technique using tetra-isocyanate-silane (Si(NCO)4 : TICS) and oxygen for interlayer dielectric film application is proposed. Film properties strongly depend on the gas composition. The film which was deposited under an oxygen-rich condition was water-free after deposition. The film density, refractive index, resistivity, and dielectric constant were 2.3 g/cm3, 1.46, 5×1014 Ω·cm, and 3.6, respectively. The etch rate by buffered HF was 330 nm/min.
Application of Pulse High-Energy Electron Beams for Decomposition of Chlorofluorocarbon in Atmospheric-Pressure Air
Authors: Nakagawa Yoshiro , Adachi Singo , Kohchi Akito , Junichi Nagasawa Junichi Nagasawa
Published: October 2002

It is experimentally shown that a pollutant (Freon) in at mospheric-pressure air can be decomposed by irradiation of pulse high-energy electron beams. Pulse electron beams having 100∼220 kV energy with about 500 ns pulse width and a current density of about 3 A/cm2 were injected into air contaminated with Freon-12 of 300∼4800 ppm. Freon-12 in the gas cell was reduced by about 5% per pulse. Freon might be decomposed to CO2, hydrides of Cl or F and intermediate large molecules through the chemical reaction between Freon, air and the mixed hydrogen or residual water vapor. The decomposition rate was almost constant even though the density of Freon was changed from 300 to 4800 ppm. The decomposition rate and the decomposed amount greatly increased upon increasing the beam energy (150 to 220 keV) and current (310 to 780 A). The efficiency of decomposition for beam power increased to 100 nmol/J upon increasing beam energy to 82 J per pulse.
High-Brightness InGaN Blue, Green and Yellow Light-Emitting Diodes with Quantum Well Structures
Authors: Nakamura Shuji , Senoh Masayuki , Iwasa Naruhito , Shin-ichi Nagahama Shin-ichi Nagahama
Published: October 2002

High-brightness blue, green and yellow light-emitting diodes (LEDs) with quantum well structures based on III-V nitrides were grown by metalorganic chemical vapor deposition on sapphire substrates. The typical green LEDs had a peak wavelength of 525 nm and full width at half-maximum (FWHM) of 45 nm. The output power, the external quantum efficiency and the luminous intensity of green LEDs at a forward current of 20 mA were 1 mW, 2.1% and 4 cd, respectively. The luminous intensity of green LEDs (4 cd) was about 40 times higher than that of conventional green GaP LEDs (0.1 cd). Typical yellow LEDs had a peak wavelength of 590 nm and FWHM of 90 nm. The output power of yellow LEDs was 0.5 mW at 20 mA. When the emission wavelength of III-V nitride LEDs with quantum well structures increased from the region of blue to yellow, the output power decreased dramatically.
Preparation of Sodium Ionic Conductor Based on Sol-Gel Method Using Aqueous Solution
Authors: Shimizu Youichi , Michishita Satoko , Takahiro Murata Takahiro Murata
Published: October 2002

A well-crystallized sodium super ionic conductor (NASICON: Na1+
x

Zr2Si

x

P3-
x

O12, 0≤x≤3) was synthesized by a sol-gel method from aqueous solutions of inorganic materials with an Na excess stoichiometric composition at a relatively low temperature of 850° C. A trace of monoclinic ZrO2 was observed, however, with increasing calcination temperatures up to 1000° C. It was found that the process of making sol from solutions was the most important step to reduce secondary phases such as ZrO2. NASICON thickfilms were also fabricated on a quartz substrate by a spin-coating method using a paste made from fine xerogel powder and isoamyl alcohol.
Ordered Quantum Dots: Atomic Force Microscopy Study of a New Self-Organizing Growth Mode on GaAs (311)B Substrates
Authors: Nötzel Richard , Temmyo Jiro , Tamamura Toshiaki , Fukui Takashi , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

We present an atomic force microscopy (AFM) study of a new growth mode found in the metalorganic vapor-phase epitaxy of strained InGaAs layers over AlGaAs buffer layers on GaAs (311)B substrates. With increasing InGaAs layer thickness, growth temperature and In composition, a morphological transition occurs from a uniformly modulated InGaAs layer to the formation of well-ordered rows of disk-shaped InGaAs dots buried beneath AlGaAs microcrystals due to lateral mass transport from the buffer layer. The growth mode is directly imaged at the onset of the transition where buried disks coexist with the initial modulated surface. From these distinct stages of the formation of the AlGaAs microcrystals, i.e., buried InGaAs disks, and their shape observed by AFM, the growth mode and ordering phenomena are discussed in detail.
Reduction of Mobile Pt Ion Density in SiO 2 and Si-SiO 2 Interface State Density in Pt-diffused Metal-Oxide-Semiconductor Structures
Authors: Deng Bei , Chang Shu Chang Shu , Hiroshi Kuwano Hiroshi Kuwano
Published: October 2002

Platinum diffusion into bipolar devices introduces mobile Pt ions into SiO2 films and causes the state density at the Si-SiO2 interface to increase. Mobile Pt ions make the devices unstable and the increase in the interface state density causes enhancement of leakage current. MOS, metal-phosphosilicate glass-oxide-semiconductor (MGOS) and metal-silicon nitride-oxide-semiconductor (MNOS) structures are fabricated on (111) and (100) substrates in order to investigate means of reducing these adverse effects induced by Pt diffusion. Mobile Pt ions, the interface state density and the flat-band voltage for these structures are measured. The experimental results show that the MGOS structure with the (100) oriented substrate is most beneficial in reducing the adverse effects of Pt-diffused devices.
Analyses of the Dispersion-Allocated Bright and Dark Solitons
Authors: Nakazawa Masataka , Hirokazu Kubota Hirokazu Kubota
Published: October 2002

This paper analyzes the dispersion-allocated soliton in which the concept of the average solitons can be extended to the reverse group velocity dispersion regions. An important dispersion requirement is given to maintain the soliton. It is shown that the soliton pulse width is modified when the initial amplitude is changed. This is due to the fact that the dispersion broadening causes the decrease in the amplitude, hence, the nonlinearity, but it can be controlled by using a larger initial amplitude.
Possible Current Oscillations in Field Emission from N-Type Silicon
Authors: Qing-An Huang Qing-An Huang
Published: October 2002

Band bending confines the electrons to a narrow surface potential well region during field emission from N-type silicon. This letter proposes a mechanism of electron tunneling both over the potential well and through the barrier, and estimates the emitted current. The current oscillation in field emission from N-type silicon is predicted for the first time.
Formation of Electrically Conducting Polypyrrole Fine Lines in Arachidic Acid Langmuir-Blodgett Films
Authors: Sha Seimei , Hirata Nobuaki , Ikezaki Kazuo , Kaihatu Minoru , Moriizumi Toyosaka
Published: October 2002

A new method is proposed for preparing electrically conducting fine lines in Langmuir-Blodgett films: during transference of arachidic acid L film containing pyrrole monomers to an indium-tin-oxide (ITO)-coated glass substrate, a voltage was applied between the ITO and the platinum counterelectrode dipped in the water subphase. From microscopic observations and conductivity measurements, it was confirmed that conducting filaments of polypyrrole were formed by this new method along the contact line between the substrate and the water surface by electrochemical polymerization of pyrrole monomers in an arachidic L film.
Downsizing Gold Wires to Submicron Range: A Self-Planarized Au Metallization Process by Selective Electroplating for Si LSI Applications
Authors: Lo Tai-chin , Chan Miu-ying
Published: October 2002

A self-planarized Au metallization process by electrolytic plating has been developed for metal interconnections in the submicron range. Gold wires with depth-to-width aspect ratio higher than 2 were fabricated in a buried structure within the dielectric spacer. By etching of Au and oxidizing the surface of TiW in the field, the gold wires can be selectively formed and planarized within the dielectrics. This process can provide desired properties of conductor structures for Si LSI applications. More important, the process is economically viable due to its simplicity and low cost in capital equipment purchase, maintenance and operation.
Magnetically Excited Plasma Oxynitridation of Si at Room Temperature
Authors: Yoshinaga Okamoto Yoshinaga Okamoto , Hideaki Nagasawa Hideaki Nagasawa , Daiske Kitayama Daiske Kitayama , Hiroyasu Kitajima Hiroyasu Kitajima , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

Good electrical quality Si oxynitride was successfully grown at room temperature using magnetically excited ( N2 + Ar) plasma. Si oxynitride, probably Si\SubtN\SubtO, was grown only when Ar was mixed with N2, while SiO\Subt was solely formed with N2 only. At the top surface of the grown film with mixed gas, SiO\Subt was always grown due to residual oxygen in N2 gas, so that the SiO\Subt/Si\Subt N2O structure was always obtained. Good capacitance-voltage characteristics were obtained although the growth rate was somewhat low. The ( N2 + Ar) plasma treatment after deposition of Si\SubsN\Subf powder on Si was also discussed.
InAsP/InGaP All-Ternary Strain-Compensated Multiple Quantum Wells and Their Application to Long-Wavelength Lasers
Authors: Kasukawa Akihiko , Yokouchi Noriyuki , Yamanaka Nobumitsu , Iwai Norihiro , Takeyoshi Matsuda Takeyoshi Matsuda
Published: October 2002

By introducing InGaP tensile-strained layers as barriers of InAsP compressively strained multiple quantum wells, InAsP/InGaP strain-compensated multiple quantum wells with high crystalline quality were successfully grown by metalorganic chemical vapor deposition. For the first time, a laser, emitting at 1.2 µ m, consisting of all-ternary quantum wells as an active layer was fabricated. The threshold current density of 1 kA/cm2 was obtained without the use of a separate confinement heterostructure layer for a cavity length of 1000 µ m.
Four-Pass Amplifier System Compensating Thermally Induced Birefringence Effect, Using a Novel Dumping Mechanism
Authors: Han K. G. , H. J. Kong H. J. Kong
Published: October 2002

We report on the four-pass amplifier which has operational reliability for dumping an amplified pulse and produces no hot spot which usually causes optically induced damage in the gain medium. By compensating for the polarization distortion caused by thermal birefringence, we could obtain the gain of 2.5×105 from the amplifier. Without compensating for the polarization distortion, we could not obtain the gain larger than 6×103 because of lasing and generation of a large number of pulses.
High Transparent Sheet Polarizer Made with Birefringent Materials
Authors: Wu Jin-Jei , Uchiyama Shoichi , Itoh Yoshitaka , Sonehara Tomio
Published: October 2002

We propose a kind of high transparent sheet polarizer, which is composed of highly birefringent multilayers. Passing through the polarizer, a normally incident unpolarized light can mostly be changed into a linear polarized light. The optical transmittance can be higher than 50 percent of incident light and better than a conventional polarizer. This optical element can be used in laser optics or liquid crystal display for saving the light source energy.
Low-Temperature Crystallization of Amorphous Si Films by Metal Adsorption and Diffusion
Authors: Sohn Dong Kyun , Lee Jeong No , Sang Won Kang Sang Won Kang , Byung Tae Ahn Byung Tae Ahn
Published: October 2002

We developed a new process for low-temperature crystallization of amorphous Si films, by adsorbing metal ions on the films. Amorphous Si films were deposited by low-pressure chemical vapor deposition, spin-coated by metal solutions and subsequently annealed in Ar atmosphere. The amorphous Si films coated with Cu and Au from 1000 ppm solutions almost completely crystallized at 530°C after 20 h. The fractal size of the Cu-adsorbed Si films was 30–50 µm at 530°C within 10 h. The application of Ag, Zn, Fe, Cr and Al solutions did not enhance crystallization of amorphous Si films. The enhancement of low-temperature crystallization by Cu and Au adsorption was deduced from the electronegativity, eutectic temperature and diffusion length. Secondary ion mass spectroscopy analysis indicated that the adsorbed Cu induced crystallization of amorphous Si films. The field-effect mobility of polycrystalline silicon thin-film transistors fabricated using the annealed Si films with Cu adsorption was 6–10 cm2/V·s before hydrogen passivation.
Cleaning of Silicon Surfaces by NF3-Added Hydrogen and Water-Vapor Plasma Downstream Treatment
Authors: Kikuchi Jun , Nagasaka Mitsuaki , Fujimura Shuzo , Horiike Hiroshi Yano
Published: October 2002

Native oxide was removed from silicon surfaces by NF3-added hydrogen and water-vapor plasma downstream treatment. It took 45 s to remove native oxide from a 6-inch silicon wafer. Fourier transform infrared attenuated total reflection (FT-IR ATR) measurement revealed that the surface roughness after the downstream treatment was the same as that after wet cleaning with 2% HF solution. A silicon epitaxial layer was grown on the surface cleaned by the downstream treatment. Although process temperature was as low as 100°C, the present downstream treatment induced the same effect as in situ hydrogen annealing.
Plasma Immersion Ion Implantation for Electronic Materials
Authors: Jones Erin C. , Barry P. Linder Barry P. Linder , Nathan W. Cheung Nathan W. Cheung
Published: October 2002

Plasma immersion ion implantation (PIII) is an emerging technology promising high dose-rate implantation and large-area processing compatibility. Innovations of this technique include: area-independent implantation time, concomitant deposition and implantation, and simple machine design and maintenance. This review summarizes the current understanding of PIII plasma dynamics, dosimetry, and electronic materials applications such as plasma doping for ultra-shallow junctions and high aspect ratio Si trenches, and subsurface synthesis of silicon-on-insulator materials.
Extremely Low ON-resistance Metal-to-Metal Antifuses with Al–Cu/10 nm-thick p-SiNx/Al–Cu Structure for Next Generation Very High Speed FPGAs (Field Programmable Gate Arrays)
Authors: Tamura Yoshimitsu , Kimura Yoshitaka , Chie Tsutsui Chie Tsutsui , Hiroshi Shinriki Hiroshi Shinriki
Published: October 2002

We present a novel metal-to-metal antifuse structure consisting of a plasma enhanced CVD (chemical vapor deposition) silicon nitride (p-SiN
x
) dielectric film sandwiched between two aluminum layers. The leakage current in the off-state is markedly reduced by using aluminum film as the upper electrode instead of Ti (titanium) or TiN (titanium nitride) film. A Al–Cu/10 nm-thick p-SiN
x
/Al–Cu structure antifuse provides sufficient long-term off-state reliability exceeding ten years at 3.6 V while keeping low breakdown voltage (10 V). An extremely low on-resistance of around 3 Ω and a narrow distribution are also realized. A new antifuse structure (Al–Cu/p-SiN
x
/Al–Cu(100 nm)/Ti/TiN/Al–Cu) highly compatible with the conventional via formation process in double metal interconnect wiring is proposed. This type of antifuse structure is very promising for next-generation very high-speed FPGAs.
Ultrauniform Chemical Mechanical Polishing (CMP) Using a “Hydro Chuck”, Featured by Wafer Mounting on a Quartz Glass Plate with Fully Flat, Water-Supported Surface
Authors: Hayashi Yoshihiro , Tsutomu Nakajima Tsutomu Nakajima , Takemitsu Kunio Takemitsu Kunio
Published: October 2002

For uniform device planarization by chemical mechanical polishing (CMP), the effect of a wafer-chuck structure on the polishing uniformity is examined. It is found that “ wafer mounting on a r igid plate (WOR)” structure is superior to “ wafer mounting on an elastic film (WOE)” structure for diminishing polishing fluctuation near the wafer perimeter. The WOR structure, however, generates abnormally polished spots in the wafer due to abrasive particle inclusion in the region between the rigid chucking plate and the wafer. A new WOR-type wafer chuck, called a “hydro chuck”, is developed: the chuck is made of a quartz glass plate with a fully flat water-supported surface. Water is continuously supplied on the quartz glass plate to form an aqueous hydro film, which suppresses slurry penetration between the rigid quartz glass plate and the wafer. Using the hydro chuck, an uniformity of ±200 Å in a 6′′ wafer is realized for CVD-SiO2 polishing.
Novel GaAs-Based Single-Electron Transistors with Schottky In-Plane Gates Operating up to 20 K
Authors: Jinushi Kei-ichiroh , Okada Hiroshi , Tamotsu Hashizume Tamotsu Hashizume , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

In an attempt to enhance the operation temperature of GaAs-based single-electron transistors (SETs), a novel Schottky in-plane gate (IPG) SET based on voltage-controlled depletion of two-dimensional electron gas (2DEG) was proposed, fabricated and characterized. For device fabrication, EB lithography and the in-situ electrochemical process were applied to a MBE-grown AlGaAs/GaAs 2DEG wafer, and narrow Pt IPGs with 200 nm length were realized on the side walls of 2DEG. The fabricated SETs clearly showed Coulomb oscillations with a Coulomb gap and Coulomb staircase at low temperatures. Coulomb oscillation was observed up to 20 K which is much higher than the operation temperature of split-gate devices having similar dimensions of several hundred nm. The small capacitance values as well as the observed strong bias dependences of device characteristics are explained in terms of the depletion characteristics of 2DEG with the Schottky IPG. The current leakage within the Coulomb gap is compatible with the cotunneling theory.
Lateral Tunneling Devices on GaAs (111)A and (311)A Patterned Substrates Grown by MBE Using Only Silicon Dopant
Authors: Hajime Ohnishi Hajime Ohnishi , Manabu Hirai Manabu Hirai , Kazuhisa Fujita Kazuhisa Fujita , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

A lateral interband tunneling transistor with gate-controlled negative differential resistance characteristics is demonstrated for the first time on a GaAs(111)A patterned substrate. Si-doped GaAs layers are grown on GaAs(111)A and GaAs(311)A patterned substrates by molecular beam epitaxy to fabricate lateral p-n junctions. Both samples show interband tunneling diode characteristics. Furthermore, a gate electrode is fabricated on the (111)A sample. The lateral tunneling transistor shows a modulated peak current density that ranges from 0.41 to 0.90 mA/cm2 by varying the gate voltage from -5.0 to 5.0 V at 77 K.
Crossover of Noise Power from Thermal to Shot Noise in Superconducting Mesoscopic Devices
Authors: Misaki Yukinori , Saito Atsushi , Hamasaki Katsuyoshi
Published: October 2002

Low-frequency noise properties of all-thin-film superconducting Nb-(constrictions)-NbN point contacts have been investigated. This type of contact can be regarded as a superconducting mesoscopic system, and its quasiparticle characteristic can be analyzed effectively Blonder, Tinkham and Klapwijk ( BTK) theory based on the Bogoliubov-de Gennes equation. We also discuss on white noise in Nb-(constrictions)-NbN point contacts, in the clean and ballistic limit. The temperature dependence of crossover voltages between thermal noise and shot noise in the ballistic system is in good agreement with calculated values.
Rectangular AlGaAs/AlAs Quantum Wires Using Spontaneous Vertical Quantum Wells
Authors: Pan Wugen , Yaguchi Hiroyuki , Onabe Kentaro , Ito Ryoichi , Usami Noritaka , Shiraki Yasuhiro
Published: October 2002

We propose a lateral confinement enhanced rectangular AlGaAs/AlAs quantum wire (QWR) structure grown in situ, which utilizes the Ga-rich AlGaAs spontaneous vertical quantum wells formed during the growth of the AlGaAs epilayer in the V-grooves. AlGaAs/AlAs QWR structures have been grown on V-grooved substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE), and been investigated by transmission electron microscopy, photoluminescence and cathodoluminescence measurements.
Preferentially (105)-Oriented SrBi2Ta2O9 Films Prepared by Laser Ablation Method
Authors: Yoshihiro Oishi Yoshihiro Oishi , Wenbiao Wu Wenbiao Wu , Keigo Fumoto Keigo Fumoto , Masanori Okuyama Masanori Okuyama , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

SrBi2Ta2O9 thin films are prepared on both Pt sheet and Si wafer by the laser ablation method using an ArF excimer laser below 500°C. Crystallographic properties of the film are characterized with substrate temperature (T
s) and O2 gas pressure as parameters. SrBi2Ta2O9 thin films are oriented preferentially to (105) on both Pt sheet and Si wafer. X-ray photoelectron spectra (XPS) depth profile reveals a homogeneous composition and XPS signals of Bi suggest oxygen deficiency of the film on the Si wafer. The films deposited on Pt and Si consist of spherical grains of about 250 and 200 nm diameter, respectively. A good capacitance-voltage (C–V) hysteresis curve is obtained in the metal oxide semiconductor (MOS) structure of the SrBi2Ta2O9 film on SiO2/Si at T
s of 500°C.
GaInNAs: A Novel Material for Long-Wavelength-Range Laser Diodes with Excellent High-Temperature Performance
Authors: Kondow Masahiko , Uomi Kazuhisa , Niwa Atsuko , Kitatani Takeshi , Watahiki Seiji , Yazawa Yoshiaki
Published: October 2002

We propose a novel material, GaInNAs, that can be formed on GaAs to drastically improve the temperature characteristics (T
0) in long-wavelength-range laser diodes. The feasibility of our proposal is demonstrated experimentally.
InAs–GaAs Quantum Pyramid Lasers: In Situ Growth, Radiative Lifetimes and Polarization Properties
Authors: Bimberg D. , Ledentsov N. N. , Grundmann M. , Kirstaedter N. , Schmidt O. G. , Mao M. H. , Ustinov V. M. , Egorov A. Yu. , Zhukov A. E. , Kopév P. S. , Alferov Zh. I. , Ruvimov S. S. , Gösele U. , Heydenreich J.
Published: October 2002

We have realized injection lasers based on InAs–GaAs and InGaAs–GaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 Å. The structures with relatively small dots (∼80 Å) exhibit properties predicted earlier for quantum dot (QD) lasers such as low threshold current densities (below 100 Acm-2) and ultrahigh characteristic temperatures (T
0=350–425 K). For operation temperatures above 100–130 K, T
0 decreases and the threshold current density increases (up to 0.95–3.3 kAcm-2 at room temperature) due to carrier evaporation from QPs. Larger InAs QPs (∼140 Å) providing better carrier localization exhibit saturation of the ground-state emission and enhanced nonradiative recombination rate at high excitation densities. The radiative lifetime shows a weak dependence on the dot size in the range 80–140 Å being close to ∼1.8–2 ns, respectively. A significant decrease in radiative lifetime is realized in vertically coupled quantum dots formed by a QP shape-transformation effect. The final arrangement corresponds to a three-dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. We achieved injection lasing in such an array for the first time.
Ultrafast Metal-Semiconductor-Metal Photoconductive Switches Fabricated Using an Atomic Force Microscope
Authors: Itatani Taro , Segawa Kazuhito , Matsumoto Kazuhiko , Ishii Masami , Nakagawa Tadashi , Kimihiro Ohta Kimihiro Ohta , Yoshinobu Sugiyama Yoshinobu Sugiyama
Published: October 2002

The oxidation using an atomic force microscope was applied in the fabrication of ultrafast metal-semiconductor-metal photoconductive switches. The photoconductive gap was formed by the oxidation of a 4 nm-thick-titanium layer. The photoconductive gap which was 100 nm wide and covered with the oxidized titanium which is not only a good insulator but also transparent to the excitation beam. A full width at half-maximum response of 380 fs was obtained at a bias voltage of 10 V.
P-Type Conducting ZnSe and ZnSSe by N2-Gas Doping During Molecular Beam Epitaxy
Authors: Hishida Yuji , Yoshie Tomoyuki , Yagi Katsumi , Keiichi Yodoshi Keiichi Yodoshi , Tatsuhiko Niina Tatsuhiko Niina
Published: October 2002

Highly conductive p-ZnSe and ZnSSe can be grown by N2-gas doping without any activation process during molecular beam epitaxial growth. Photoluminescence spectra indicated that the properties of N2-gas- and nitrogen-radical-doped ZnSe with nearly equal N
A–N
D are almost the same. Using the N2-gas doping method, the first laser oscillation from a ZnSe-based laser diode without nitrogen-radical doping was achieved. The LED driving voltage was 3.8 V at the operating current of 20 mA.
High-Frequency Characteristics of SrTiO3 Thin Films in the mm-Wave Band
Authors: Ikuta Kenji , Yohtaro Umeda Yohtaro Umeda , Yasunobu Ishii Yasunobu Ishii
Published: October 2002

High-frequency dielectric characteristics of SrTiO3 (STO) thin films deposited by an electron cyclotron resonance (ECR) sputter on semiconductor substrates are presented. The measured dielectric constant of the STO thin films is from 20 to 125, depending upon deposition temperature and thin film thickness. This is kept constant at a frequency range up to 50 GHz. Dielectric loss expressed in terms of the Qf product is constant in the mm-wave band and is estimated to be comparable to that of bulk STO. STO thin films are found for the first time to be applicable to microwave monolithic integrated circuits (MMICs) operating in the mm-wave band.
Ferroelectric Nonvolatile Memory Technology and Its Applications
Authors: Sumi Tatsumi , Judai Yuji , Hirano Kanji , Ito Toyoji , Mikawa Takumi , Takeo Masato , Azuma Masamichi , Hayashi Shin-ichiro , Uemoto Yasuhiro , Arita Koji , Nasu Toru , Nagano Yoshihisa , Inoue Atsuo , Matsuda Akihiro , Fuji Eiji , Shimada Yasuhiro , Otsuki Tatsuo
Published: October 2002

Nonvolatile memory utilizing ferroelectric material is expected to be the ultimate memory due to its theoretical low power operation and fast access. We integrated a ferroelectric thin film using a standard complementary metal-oxide-semiconductor (CMOS) process and evaluated its basic characteristics and reliability including endurance and imprint effect. The film was prepared using a spin-on sol-gel method. A ferroelectric thin film formed using liquid source misted chemical deposition (LSMCD) was found to have almost the same characteristics as those of the film formed by the sol-gel method. No effects of the ferroelectric process on the CMOS transistors were observed. Design of ferroelectric memory cells and applications of the ferroelectric nonvolatile memory have been reviewed.
Imprint in Ferroelectric Capacitors
Authors: Warren William L. , Tuttle Bruce A. , Dimos Duane , Pike Gordon E. , Al-Shareef Husam N. , Ramesh Ramamoorthy , Evans Joseph T. , Jr Jr
Published: October 2002

We show that voltage offsets in the polarization-voltage characteristics of Pb(Zr, Ti)O3 capacitors can lead to imprint in ferroelectric memory devices. The thermal-induced voltage shifts (internal bias field) are in part attributed to the role of oxygen vacancy-related defect dipoles throughout the film. In support of this, it is found that donor doping at the Ti(Zr) sites reduces the thermally-induced voltage shifts. The stress-induced voltage shifts are found to be dependent on the Zr/Ti cation ratio. This compositional dependence is explained by considering the role of deep bulk Ti3+ centers and/or a compositional dependent oxygen vacancy density.
Formation Process of Highly Reliable Ultra-Thin Gate Oxide
Authors: Ohmi Kazuyuki , Iwamoto Toshiyuki , Yabune Tatuhiro , Miyake Toshiki , Ohmi Tadahiro
Published: October 2002

A new oxide formation process featuring thermal oxidation in a strongly reductive ambient, called hydrogen-radical-balanced steam oxidation (H*/H2O oxidation), followed by post-oxidation annealing has been developed. In this oxidation process, only the strong Si–O bond which is perfectly resistant even to the strongly reductive ambient survives and a high-integrity oxide film can be grown. From the results of the breakdown tests under constant current stress (Q
BD) and gate voltage shift (V
g shift) measurement under constant current stress, it has been revealed that the thin oxide film featuring high-integrity in breakdown and strong resistance to electrical stress is obtained by H*/H2O oxidation with post-oxidation annealing in Ar gas ambient. Furthermore, by adding O2 gas to the Ar annealing ambient, the same effect of the post-oxidation annealing in Ar gas ambient can be obtained in a very short time. This oxidation method is effective in forming thin oxide for use under a high electric field, such as a tunnel oxide for flush memories.
Oxide Formation on Si(100)-2×1 Surfaces Studied by Scanning Tunneling Microscopy/Scanning Tunneling Spectroscopy
Authors: Ikegami Hiroshi , Ohmori Kenji , Ikeda Hiroya , Iwano Hirotaka , Shigeaki Zaima Shigeaki Zaima , Yukio Yasuda Yukio Yasuda
Published: October 2002

The oxide formation on Si(100)-2×1 surfaces at room temperature has been studied by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The change in electronic structures due to oxidation has been discussed based on the spatially resolved STS spectra. It was found in the initial stage of oxidation that the local density-of-states (LDOS) of back bond states and dangling bond sites decreases dramatically at the oxidation-induced bright protrusions. The STS spectra of the 2×1 region with an oxygen exposure of 4.5 L suggest that oxygen atoms adsorb on the back bond sites. At the average SiO2 thickness of 0.4 nm, the surface states of Si(100)-2×1 vanish completely and the energy width of the gap near the Fermi level becomes very close to the band gap of bulk Si. In addition, the observed LDOS is spatially uniform in spite of the presence of bumps in the STM image. The STS spectra indicate the formation of the valence band and the conduction band of SiO2 at the oxide thickness of 0.4 nm.
Calculation and Analysis of the Intrinsic Carrier Concentration and the Einstein Relation for Heavily Doped Silicon from 77 K to 300 K
Authors: Zhixiong Xiao , Wei Tongli Wei Tongli , Zheng Jiang Zheng Jiang
Published: October 2002

On the basis of the Fermi integrals, the influence of the nondegenerate approximation, the degenerate approximation and nonparabolic energy bands on the calculation of the intrinsic carrier concentration and the Einstein relation has been analyzed for heavily doped silicon at low temperatures. The main results show that the degenerate approximation is appropriate up to the doping level of 1020 cm-3. At ultrahigh doping concentrations ( >1020 cm-3), it is necessary to adopt the nonparabolic energy band modilication.
Characterization of the Local Layer Structure of a Broad Wall in a Surface Stabilized Ferroelectric Liquid Crystal Using Synchrotron X-Ray Micro-Diffraction
Authors: Iida Atsuo , Noma Takashi , Miyata Hirokatsu
Published: October 2002

The local layer structure of the broad wall of a zig-zag defect in a thin-surface stabilized ferroelectric liquid crystal cell was characterized using a synchrotron X-ray microbeam of less than 5 µm spatial resolution. By using a rocking curve measurement at the broad wall, multiple or broad peaks were observed between a pair of peaks due to a chevron structure. These new peaks are clear evidence of a modified pseudo-bookshelf structure at the wall. For 1.5 µm thick cells, a bookshelf layer is relatively flat, but is accompanied by small areas of inclined layer connecting the bookshelf and the chevron structures. For 10 µm thick cells, the pseudo-bookshelf structure bends or undulates both perpendicular and parallel to the rubbing direction. No appreciable change in the layer spacing was observed in the modified pseudo-bookshelf structure. The temperature dependence of the broad wall layer structure was also measured.
Diffusivities and Activities of S Implanted into GaAs through an As-doped a-Si:H Film
Authors: Masanori Sakaguchi Masanori Sakaguchi , Katsuhiro Yokota Katsuhiro Yokota , Akira Shiomi Akira Shiomi , Haruya Mori Haruya Mori , Akiyoshi Chayahara Akiyoshi Chayahara , Yoshie Fujii Yoshie Fujii , Kiyohito Hirai Kiyohito Hirai , Hiromichi Takano Hiromichi Takano , Masao Kumagai Masao Kumagai
Published: October 2002

Sulfur (S) ions are implanted at 500 keV into GaAs through 120 nm a-Si:H films doped with arsenic atoms at a concentration of 2×1020 cm-3. The samples are annealed in Ar gas at temperatures of 700–1000°C for 15 min. The sheet carrier concentration increases with increasing implant dose and annealing temperature. The diffusivity of the S atoms decreases with increasing implant dose. Silicon (Si) atoms are also doped from the a-Si:H films into GaAs during annealing and S+ implantation. The distribution of the Si atoms becomes slightly shallower as the implant dose increases. The carrier concentrations, however, are left unchanged by Si doping.
Defect Formation during Hetero-Epitaxial Growth of Aluminum Nitride Thin Films on 6H-Silicon Carbide by Gas-Source Molecular Beam Epitaxy
Authors: Tanaka Satoru , Scott Kern R. , Bentley James , Robert F. Davis Robert F. Davis
Published: October 2002

Defect formation mechanisms in AlN thin films grown on 6H-SiC(0001) substrates have been investigated as a function of film thickness to 180 nm using conventional and high-resolution transmission electron microscopy (HRTEM). The presence of particular Si-terminated steps on the vicinal 6H-SiC surface caused the introduction of planar defects at the initial stage of growth. By contrast, micrographs of films deposited on the on-axis substrate showed a much lower density of defects. Atomistic structural models of the interface and deposited AlN are proposed based on the HRTEM images and the results of companion scanning tunneling microscopy (STM) studies of the vicinal 6H-SiC(0001) surface. The introduction of additional defects, which were primarily threading dislocations, was observed with increasing thickness of the AlN films.
Surface Tunnel Transistor: Gate-Controlled Lateral Interband Tunneling Device
Authors: Tetsuya Uemura Tetsuya Uemura , Toshio Baba Toshio Baba
Published: October 2002

We demonstrated a novel three-terminal tunnel device, the Surface Tunnel Transistor (STT), in which lateral interband tunneling current between source and drain is controlled by a gate voltage. The STT consists of a highly degenerate drain whose polarity is opposite that of the source, a channel with an insulated gate, and a source connected to the channel. The basic characteristics of the STTs were investigated by fabricating three types of STTs with mesa structures using a GaAs/AlGaAs system, as well as by a two-dimensional device simulation. An enhancement-type STT (E-STT) in which no electrons are accumulated on the channel surface at thermal equilibrium exhibited unsaturated transistor characteristics due to interband tunneling under source-drain reverse bias conditions. To increase the current density, a modulation doped STT (MD-STT) in which the channel was formed by modulation doping was also fabricated, and a tunneling current about 104 times larger than that of the E-STT was obtained. Moreover, the MD-STT showed negative differential resistance (NDR) characteristics under source-drain forward bias conditions. A channel doped STT (CD-STT) in which the channel region was directly doped with donors showed improved NDR characteristics with a peak current density of 3.7 µA/µm and a peak-to-valley current ratio (PVR) of 1.5 at room temperature. These values are larger than those of the MD-STT by a factor of 103 and 1.5, respectively. Furthermore, a PVR as high as 4.8 was obtained for the CD-STT by inserting a blocking layer between the drain and the overlapped channel layer to reduce the valley current.
Effects of Electron Beam Exposure Conditions on the Surface Modification of CaF2(111) for Heteroepitaxy of GaAs/CaF2 Structure
Authors: Hwang Sang-Man , Miyasato Keiichiro , Koji Kawasaki Koji Kawasaki , Kazuo Tsutsui Kazuo Tsutsui
Published: October 2002

Optimal conditions of electron beam exposure for the surface modification of CaF2(111) by simultaneous exposure of an electron beam and an As4 molecular beam were studied for the purpose of obtaining good electrical properties of heteroepitaxial GaAs films grown on modified CaF2. The amount of adsorbed As atoms on the CaF2 surface and the crystallinity of grown GaAs film evaluated from electron mobility and cross-sectional transmission electron microscopy were examined by changing the electron energy (V
E) and dose (D
E). It was found that with adsorption of 1 atomic monolayer of As on the modified CaF2 surface, the highest mobility of electrons and low defect density in the GaAs films were obtained when the value of V
E×D
E was a constant of about 300 mJ/cm2 in the range of 40 eV≤V
E≤300 eV. These results indicate that the degree of surface modification is governed by the total energy of incident electrons per unit area rather than V
E or D
E individually. In addition, a deviation from this relationship was observed at V
E of 20 eV and 3,000 eV. Possible models for this constant V
E×D
E rule are proposed, in which F vacancies or secondary electrons generated in the bulk CaF2 propagate to the surface of CaF2 to provide occupation sites of As atoms.
Fine Metallic Particles for Magnetic Domain Observations
Authors: Kitakami Osamu , Sakurai Tomoaki , Miyashita Yoichi , Takeno Yukio , Shimada Yutaka , Takano Hisashi , Awano Hiroyuki , Ando Keikichi , Sugita Yutaka
Published: October 2002

Fine domain structures of a ferromagnetic specimen can be visualized by deposition of ultrafine ferromagnetic particles onto its surface. We have applied various ferromagnetic particles, such as Co, Fe, Co–Fe alloy and Permalloy, to observation of high-density recording states of thin-film recording media. These studies have revealed that single-domain particles mainly contribute to the domain pattern contrast, while very small superparamagnetic particles are so insensitive to the leakage field from the recording media that they deteriorate the image quality of the domain patterns. Therefore, suppressing the formation of the superparamagnetic particles is effective in improving the resolution and the image quality of the observed domain patterns. In order to suppress the formation of superparamagnetic particles, we have attempted to synthesize hcp-Co particles with large uniaxial anisotropy by alloying Co with some elements which increase the fcc ⇔hcp transformation temperature, but all the Co and Co-alloy particles exhibit a pure high-temperature fcc phase.
Ce3+, Fe3+-Induced Optical Absorption in Ce, Fe:YAG Prepared by Coprecipitation
Authors: Manabu Gomi Manabu Gomi , Tomohiko Kanie Tomohiko Kanie
Published: October 2002

To investigate optical transitions induced by Ce3+ and Fe3+ in garnet, Ce, Fe-substituted Y3Al5O12 (Ce, Fe:YAG) ceramics have been successfully prepared by urea coprecipitation and subsequent heat treatment at temperatures as low as 820–880° C. Absorption spectra of Y2.9Ce0.1Al5-
x

Fe

x

O12 (x=0–1.0), estimated by diffuse reflection measurements, showed that, as x increases, the absorption peak at h ν=2.7 eV due to the 4f–5d transition in Ce3+ remains unchanged, while a new broad absorption peak occurs at around 1.4 eV. These results indicate that the transition at 1.4 eV observed in Ce-substituted iron garnet, which strongly enhances the magneto-optical effect, is not the 4f–5d transition in Ce3+ shifted by the influence of the next nearest neighbor ions.
Charge-Carrier Transport in Liquid-Crystal Based Organic Photoconductors*1
Authors: Adam Dieter , Werner Römhildt Werner Römhildt , Dietrich Haarer Dietrich Haarer
Published: October 2002

In this work we have used a one-dimensional model which incorporates energetic disorder to analyse the anomalous temperature dependence of the charge-carrier mobility in the liquid crystalline discotic twin HPAT2 and the broadening of the photocurrent decays. In order to render the main ideas as transparent as possible we have aimed at the simplest possible description which still includes the basic features. The model allows a closed-form expression for the Laplace transformed photocurrent. The temperature dependence of charge-carrier mobility can simply be calculated analytically if assuming a boxlike trap distribution. Assuming a temperature dependent trap parameter we could model the anomalous temperature dependence of charge-carrier mobilities. This temperature dependent peculiarity of the trap distribution is inferred from the temperature dependent molecular dynamics in the D
h
phase, as concluded from X-ray measurements and NMR experiments. A `parallel connection' of different types of columns with different characteristic trap distributions could reproduce the broadened decay of photocurrent transients. The parallel connection was concluded from a homeotropic polydomain texture as seen in the polarizing microscope.
Characterisation of Deformed and As-cast Microstructure of Copper-Aluminium-Iron Alloys-II: Influence of Increased Fe Solute (α+β-Phase)
Authors: Pal Hiranmay , Swapan Kumar Pradhan Swapan Kumar Pradhan , Madhusudan De Madhusudan De
Published: October 2002

Five compositions of aluminium iron bronze in the (α+β)-phase region containing 2.5 to 5 at.% Fe and 5 to 15 at.% Al have been prepared for microstructural characterization by X-ray diffraction line-profile analysis, optical and scanning electron microscopy, microhardness and magnetic susceptibility studies. The solute dependence of the defect parameters as revealed from X-ray study reflect the microstructural evolution in the deformed state especially near the α/(α+β) boundary. The influence of increased presence of Fe results in the lowering of stacking fault energy of pure Cu. Optical and scanning electron microscopy reveal the grain sizes and grain boundary structure, containing dispersed Fe-rich precipitates, Fe3Al. Microhardness studies of the alloys depict the cumulative influence of Al and Fe3Al precipitates in increasing the hardness (from 79.0 to 139.5 Kg/mm2). These Fe-rich precipitates are primarily responsible for increased ferromagnetic behaviour of the materials.
Amorphous Layer Formation on Nickel Alloy Surface by Intense Pulsed Ion Beam Irradiation
Authors: Mitsuyasu Yatsuzuka Mitsuyasu Yatsuzuka , Yoshiyuki Hashimoto Yoshiyuki Hashimoto , Tohru Yamasaki Tohru Yamasaki , Hitoshi Uchida Hitoshi Uchida
Published: October 2002

The formation of an amorphous layer due to irradiation of intense pulsed ion beams (PIBs) has been studied experimentally. A mixed carbon and fluorine PIB with energy of 180 keV, ion beam current density of 180 A/cm2 and pulse duration of 30 ns is irradiated on a Ni65Cr15P16B4 alloy, resulting in the formation of an amorphous layer on the substrate surface to a depth of 0.66 µ m which is consistent with the thermal diffusion length. Repeated irradiations of PIB lead to the formation of an amorphous phase at depths exceeding 0.66 µ m from the surface. PIB irradiation leads to rapid heating of the substrate surface to its boiling point (2732° C), and the cooling rate from the melting point to the glass transition point is estimated to be 2.2×109° C/s which is larger than the critical cooling rate for amorphous layer formation of nickel alloys.