bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Radiation-Induced Leakage Currents in Thin Oxides by Application of a Low Post-Irradiation Gate Bias
Authors: Chew-Hoe Ang Chew-Hoe Ang , Chung-Ho Ling Chung-Ho Ling , Zhi-Yuan Cheng Zhi-Yuan Cheng , Sun-Jung Kim Sun-Jung Kim , Byung-Jin Cho Byung-Jin Cho
Published: October 2002

We have observed that excess low-field leakage currents generated by 10 keV X-ray irradiation in thin gate oxides (4.5 nm) could be reduced by applying a low gate bias to the oxides after irradiation, regardless of the polarity of the applied gate bias. The reduction rate of radiation-induced leakage current (RILC) increased with the applied gate bias and began to saturate after 105 s. In addition, the reduction rate of RILC was significantly enhanced in a H2 ambient, suggesting a strong link between the reduction of RILC and trapped-hole annealing.
Control of the Conduction Type of Nondoped High Mobility β-FeSi2 Films Grown from Si/Fe Multilayers by Change of Si/Fe Ratios
Authors: Ken-ichiro Takakura Ken-ichiro Takakura , Takashi Suemasu Takashi Suemasu , Yoshihiro Ikura Yoshihiro Ikura , Fumio Hasegawa Fumio Hasegawa
Published: October 2002

Highly [100]-oriented nondoped β-FeSi2 continuous films were grown on Si (001) substrates from Si/Fe multilayers with different Si/Fe ratios (1.6–2.0). It was found that the conduction type of the grown layer changed from p-type to n-type when the deposited Si/Fe ratio was increased, suggesting that the conduction type of nondoped β-FeSi2 is governed by stoichiometry. Annealing of the samples at 900°C for up to 14 h decreased the carrier density and increased the mobility, but did not change the conduction type. A p-type sample gave the highest hole mobility ever reported; 13000 cm2/V·s at 50 K.
Widely Tunable Difference Frequency Generation in Periodically-Poled LiNbO3 Using an All-Solid-State Cr3+:LiSrAlF6 Laser
Authors: J. Vasa Husayin Parhat , Tatsuo Okada Tatsuo Okada , Mitsuo Maeda Mitsuo Maeda , Hirokazu Taniguchi Hirokazu Taniguchi
Published: October 2002

An all-solid-state tunable mid-infrared coherent source based on a quasi-phase-matched (QPM) difference frequency generation (DFG) is reported. The QPM-DFG was carried out by mixing a spectrally narrowed Cr3+:LiSrAlF6 laser with a diode laser (1020 nm) in a bulk periodically-poled LiNbO3 (PPLN) crystal with single grating period of 22.2 µm. Wide tuning range around 4.0 and 4.6 µm was obtained by tuning the laser and altering the PPLN temperature between 20 and 40°C. Even wider tuning range is expected by optimizing the PPLN grating period and expanding the tuning range of the Cr3+:LiSrAlF6 laser.
Ultrafast 168 GHz 1.5 ps 1 fJ Symmetric-Mach-Zehnder-Type All-Optical Semiconductor Switch
Authors: Ueno Yoshiyasu , Nakamura Shigeru , Tajima Kazuhito
Published: October 2002

We report on the ultrahigh-repetition all-optical switching of a semiconductor-optical-amplifier-based symmetric-Mach-Zehnder-type switch. Record high 168 GHz, 1.5-ps-wide, 10-dB-extinction switch windows were observed. This repetition rate is ten times higher than the semiconductor optical amplifier's cutoff frequency. The control optical pulse energy used was a record low 1 fJ (average power=170 µW). Clearly isolated 168 GHz components were also observed in the output pulses' optical spectrum, which was in contrast to the continuum-like spectrum of the input pulses.
Anomalous Phosphorus Cracker Temperature-Dependent Photoluminescence Spectra of InGaP Grown by Solid Source Molecular Beam Epitaxy
Authors: Cheng Yi-Cheng , Tai Kuochou , Chou Shu-Tsun
Published: October 2002

InGaP grown by solid source molecular beam epitaxy showed lower effective band-gap energy with increasing phosphorus cracker temperature. Anomalous photoluminescence (PL) spectra also indicated that a weaker ordering effect was initiated when the cracker temperature was higher. Since the variation of cracker temperature mainly changed the P2/P4 ratio, we believe that the more chemically reactive P2 incorporates more In into the epilayer. Therefore, InGaP grown under a more P2-rich condition has a higher In content which results in the lower band-gap energy instead of having an ordering effect.
Morphology Change of Artificial Crystal Originated Particles, and the Effect on Gate Oxide Integrity
Authors: Twan Bearda Twan Bearda , Paul W. Mertens Paul W. Mertens , Marc M. Heyns Marc M. Heyns , Rüdiger Schmolke Rüdiger Schmolke
Published: October 2002

The surface morphology and gate oxide integrity was examined on wafers containing Artificial Crystal Originated Particles. The wafers were subjected to heat treatments, epitaxial silicon deposition and polishing. All treatments except
polishing result in a significant defect smoothening, or even in complete defect annihilation. On these wafers, the defects no longer degrade the gate oxide integrity. Polishing only smoothes convex defect edges, leading to a reduction of the
leakage current with positive gate bias. The breakdown voltage remains nearly unaltered, implying that it is determined by the concave tip of the defect.
Highly Stable Single Polarization Operation of GaInAs/GaAs Vertical-Cavity Surface-Emitting Laser on GaAs (311)B Substrate under High-Speed Modulation
Authors: Arai Masakazu , Nishiyama Nobuhiko , Shinada Satoshi , Matsutani Akihiro , Koyama Fumio , Iga Kenichi
Published: October 2002

We have demonstrated a dynamically stable polarization mode GaInAs/GaAs vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs (311)B substrate. The fabricated device exhibited a stable and single polarization under DC and high-speed modulation. Under DC operation, the orthogonal polarization suppression ratio (OPSR) was larger than 30 dB. We measured the time-resolved OPSR using square-wave modulation. It was found that the orthogonal mode was suppressed even for the first peak of the relaxation oscillation with OPSR>17 dB. In a 5 Gbps non-return-to-zero (NRZ) pseudo-random bit sequence (PRBS) modulation experiment, the OPSR was greater than 27 dB. These stable and single polarization characteristics were due not only to the anisotropic optical gain on a (311)B substrate, but also strained GaInAs/GaAs quantum wells and the thin oxide layer which was employed in this experiment.
Noise Suppression and Intensity Modulation in Gain-Saturated Semiconductor Optical Amplifiers and Its Application to Spectrum-Sliced Light Sources
Authors: Yamatoya Takeshi , Koyama Fumio , Iga Kenichi
Published: October 2002

We present a quantitative estimation of noise reduction in a gain-saturated semiconductor optical amplifier (SOA) for spectrum-sliced incoherent light sources. A noise reduction of 10 dB over a bandwidth of a few GHz was experimentally demonstrated. In addition, the intensity modulation of spectrum-sliced incoherent light using a GaInAsP/InP SOA modulator was carried out with a bit rate of 600 Mb/s. An error rate floor in bit error rate vs received optical power characteristics was removed with the help of this technique.
The Importance of the Collision of Impinging Atoms to Predeposited Atoms in Thin-Film Growth on a Cryogenic Substrate
Authors: Morikawa Hiroshi , Iwatsu Fumio
Published: October 2002

Field-ion microscope observation of Mo deposition on a W tip at cryogenic temperature revealed that each Mo atoms, once adsorbed on a tip, was sometimes displaced to a certain distance, due to the collision of impinging atoms. This collision occasionally brought about the rearrangement of atoms in a cluster. The rearrangement of atoms induced by the collision is considered to play a very important role, particularly in epitaxial growth on a cryogenic substrate.
Carbon-Nanotube Tip for Highly-Reproducible Imaging of Deoxyribonucleic Acid Helical Turns by Noncontact Atomic Force Microscopy
Authors: Takayuki Uchihashi Takayuki Uchihashi , Nami Choi Nami Choi , Masato Tanigawa Masato Tanigawa , Makoto Ashino Makoto Ashino , Yasuhiro Sugawara Yasuhiro Sugawara , Hidehiro Nishijima Hidehiro Nishijima , Seiji Akita Seiji Akita , Yoshikazu Nakayama Yoshikazu Nakayama , Hiroshi Tokumoto Hiroshi Tokumoto , Kousuke Yokoyama Kousuke Yokoyama , Seizo Morita Seizo Morita , Mitsuru Ishikawa Mitsuru Ishikawa
Published: October 2002

A carbon nanotube (CNT) was used as a tip for a noncontact-mode atomic force microscope (NC-AFM). A CNT tip was attached to an Au/Si tip by a well-controlled procedure in a scanning-electron-microscope (SEM) chamber. The NC-AFM with the CNT tip produced highly reproducible images of right-handed helical turns of linear deoxyribonucleic acid (DNA) with a spacing of 3.5 ±1.0 nm. The full-width at half-maximum (FWHM) of the cross section of DNA measured was 3.1 ±0.6 nm.
Viewing Angle Characteristics Using a Patterned Double-Twisted Vertical-Alignment Cell Mode
Authors: Seo Dae-Shik , Hwang Jeoung-Yeon
Published: October 2002

Viewing angle characteristics of a negative-type nematic liquid crystal (NLC) using a new patterned double-twisted (PDT) vertical-alignment (VA) cell mode without a negative compensation film on a homeotropic alignment layer were studied. Good voltage-transmittance curves were obtained. The viewing angle of a new PDT-VA cell without a negative compensation film was wider than that of a conventional VA cell. Fabrication processes using a new PDT-VA cell mode be carried out with only one-sided rubbing.
Field-Emission Characteristics of Hydrogenated Amorphous Carbon Films Prepared by Surface Wave Plasma
Authors: Nagatsu Masaaki , Sano Toru , Takada Noriharu , Guang Wang X. , Hirao Takashi , Sugai Hideo
Published: October 2002

Hydrogenated amorphous carbon films are prepared by a 40-cm-diameter planar surface wave plasma to apply them to field-emission display. The 2.45 GHz surface wave plasmas at 700 W give a film deposition rate of ∼15 nm/min in He gas mixed with a small amount of methane gas at a relatively low pressure of 100 to 200 mTorr. Preliminary experimental results show that the hydrogenated amorphous carbon films deposited on silicon substrates have good field-emission characteristics: a threshold electric field defined at 1 µA/cm2 was roughly 4 V/µm and an emission current of 0.1 mA/cm2 was achieved at an electric field of 7.5 V/µm.
Room Temperature Ferromagnetism in Novel Diluted Magnetic Semiconductor Cd1-xMnxGeP2
Authors: A. Medvedkin Gennadiy , Takayuki Ishibashi Takayuki Ishibashi , Takao Nishi Takao Nishi , Koji Hayata Koji Hayata , Yoichi Hasegawa Yoichi Hasegawa , Katsuaki Sato Katsuaki Sato
Published: October 2002

High concentration of Mn atoms has been incorporated in the surface region of II-IV-V2 type chalcopyrite semiconductor CdGeP2. Photoluminescence spectrum at 20 K shows a peak around 3.2 eV, suggesting that the incorporation of Mn introduces an energy gap much higher than that of the host semiconductor (E
g=1.83 eV). Prominent magnetic hysteresis loops with coercivity of 0.5 kOe has been observed at room temperature. Magnetic force microscope (MFM) measurements reveal a stripe-shaped domain pattern on the top surface. Magneto-optical Kerr ellipticity spectrum measured at room temperature show a prominent peak at 1.7 eV and a broad tail up to 3.5 eV. We tentatively attribute the ferromagnetism to the double exchange interaction between Mn2+ and Mn3+ states due to the structural feature of II-IV-V2 type chalcopyrite compounds.
High-Current Heavy-Ion Accelerator System and Its Application to Material Modification
Authors: Kishimoto Naoki , Takeda Yoshihiko , Lee Chi-Gyu , Umeda Naoki , Okubo Nariaki , Iwamoto Eiji
Published: October 2002

A high-current heavy-ion accelerator system has been developed to realize intense particle fluxes for material modification. The facility of a tandem accelerator attained 1 mA-class ion current both for negative low-energy ions and positive high-energy ions. The negative ion source of the key device is of the plasma-sputter type, equipped with multi-cusp magnets and Cs supply. The intense negative ions are either directly used for material irradiation at 60 keV or further accelerated up to 6 MeV after charge transformation. Application of negative ions, which alleviates surface charging, enables us to conduct low-energy high-current irradiation on insulating substrates. Since positive ions above the MeV range are irrelevant for Coulomb repulsion, the facility as a whole meets the needs of high-current irradiation onto insulators over a wide energy range. Application of high flux ions provides technological merits not only for efficient implantation but also for essentially different material kinetics, which may become an important tool of material modification. Other advantages of the system are co-irradiation by intense laser and in-situ detection of kinetic processes. For examples of material modifications, we present nanoparticle fabrication in insulators, and synergistic phenomena by co-irradiation due to ions and photons.
Spatial Inhomogeneity of Photoluminescence in an InGaN-Based Light-Emitting Diode Structure Probed by Near-Field optical Microscopy Under Illumination-Collection Mode
Authors: Akio Kaneta Akio Kaneta , Tomoaki Izumi Tomoaki Izumi , Koichi Okamoto Koichi Okamoto , Yoichi Kawakami Yoichi Kawakami , Shigeo Fujita Shigeo Fujita , Yoshihito Narita Yoshihito Narita , Tsutomu Inoue Tsutomu Inoue , Takashi Mukai Takashi Mukai
Published: October 2002

Spatial distribution of photoluminescence (PL) spectra has been assessed in an InGaN single quantum well (SQW)-based light-emitting diode structure by near-field optical microscopy under the illumination-collection mode. The obtained PL mapping image revealed a variation in both peak and intensity of PL spectra according to the probing location with a scale less than about 200 nm. The variation in PL intensity is from 0.8 to 1.8 in arbitrary units indicating that the internal quantum efficiency fluctuates from 10% to 50% within the active layer.
Novel Large-Area High-Resolution-Transmission-Electron-Microscopy Technique using Specimens Fabricated by a Focused Ion Beam Apparatus
Authors: Suematsu Hisayuki , Udo Koichi , Hisatsune Kunihiro , Yatsui Kiyoshi , Yamauchi Hisao
Published: October 2002

A novel large-area high-resolution-transmission-electron-microscopy (LA-HRTEM) specimen fabrication technique using a focused ion beam (FIB) apparatus was developed. Using this technique, the cation composition in a K–Al–Si–Sn–Ti–Zr–O specimen was analyzed by energy dispersive X-ray spectroscopy (EDS). The cation composition of regions located more than 200 nm away from the interface between a ZrO2 grain and SiO2 matrix was the same as that in ZrO2 and SiO2. This indicates that the accuracy of EDS analyses in the LA-HRTEM specimens was confirmed.
NOx Removal Using Ammonia Radicals Prepared by Intermittent Dielectric Barrier Discharge at Atmospheric Pressure
Authors: Nishida Mitsunori , Yukimura Ken , Kambara Shinji , Maruyama Toshiro
Published: October 2002

NO
x
removal was carried out at a temperature of 600°C using ammonia radicals, which were generated by flowing NH3 gas diluted with Ar gas through the dielectric barrier discharge with a one-cycle sinusoidal-wave power source. The discharge was intermittently formed between coaxial cylindrical electrodes with a space of 1.5 mm at an applied peak-to-peak voltage of 5–18 kV. The radicals were introduced in a reaction chamber and mixed with NO gas, which was diluted with N2. The dependence on the discharge power was measured by varying the repetition rate and applied voltage. The NO reductions at various flow rates and concentrations of NO gas could be expressed as a constant volumetric NO reduction rate. There was an optimum discharge power and an optimum mean residence time of NH3 gas for effective NO reduction.
Two-photon Absorption and Nonlinear Optical Properties of a New Organic Dye Trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene Sulfonate
Authors: Zhou Guangyong , Ren Yan , Wang Chun , Wang Dong , Zhao Xian , Shao Zongshu , Jiang Minhua
Published: October 2002

Trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HMASPS) is a newly synthesized dye that possesses a much greater two-photon-absorption (TPA) cross-section and much stronger upconversion fluorescence emission than common dyes (such as rhodamine) when excited with near infrared laser radiation. TPA induced upconverted lasing has been obtained in HMASPS solution in dim eth ylformamide (abbreviated as DMF) pumped by near infrared laser beam from 900 to 1150 nm. The central wavelength and bandwidth of the lasing are 626 nm and 26 nm. The upconversion efficiencies of 1cm-path HMASPS solution in DMF at 0.05 mol/l concentration at different wavelengths from 900 to 1150 nm were measured. The net upconversion efficiency from the absorbed pump energy to the upconverted lasing output was 14% at the pump energy level of 2.04 mJ when the pump laser beam was provided by Nd:YAG laser. The molecular TPA cross-section at 1064 nm was σ2=6.0×10-48 cm4·s/photon measured by using an open aperture Z-scan system. The linear absorption, single-photon induced fluorescence, two-photon induced fluorescence and two-photon induced upconverted lasing properties have also been studied in this paper.
Continuous-wave RbTiOAsO4 Optical Parametric Oscillator in Optical Frequency Interval Divider Scheme
Authors: Slyusarev Sergey , Ikegami Takeshi , Ohshima Shin-ichi
Published: October 2002

A continuous-wave optical parametric oscillator (OPO) of RbTiOAsO4 (RTA) is used as a light source for an optical frequency interval divider. Pumped by 1.5 W of the 532-nm second harmonic of the high power YAG laser, the OPO generates a power-stable signal-idler mode pair at 912 nm and 1292 nm with an output of 40 mW and spectral bandwidth of less than 5 KHz. The tuning characteristics are examined in detail. The result of the optical frequency interval division is presented.
Enhancement of Thermal Smoothing Effect on Laser Imprint with Soft X-Ray Radiation
Authors: Naofumi Ohnishi Naofumi Ohnishi , Hideo Nagatomo Hideo Nagatomo , Hideaki Takabe Hideaki Takabe , Hiroaki Nishimura Hiroaki Nishimura , Masaharu Nishikino Masaharu Nishikino , Hiroyuki Shiraga Hiroyuki Shiraga , Tatsuhiko Yamanaka Tatsuhiko Yamanaka
Published: October 2002

The initial imprint of mass perturbation due to spatial nonuniformity of laser intensity is one of the most important issues in laser fusion research. Several imprint mitigation schemes by the use of soft X-ray radiation have been proposed to enhance the thermal smoothing effect within the conduction region. One of the schemes uses external X-ray irradiation prior to laser incidence to produce preformed plasma. Another has a low-density foam layer and high-Z material to heat the foam radiatively and make it uniform in density.
Design of an Ultrahigh-Gain Ni-like Kr Soft-X-Ray Laser by Use of an Optical-Field-Induced Ionization-Initiated Transient Collisional Excitation Scheme
Authors: Maya Oki , Nagata Yutaka , Obara Minoru , Aoyagi Yoshinobu , Midorikawa Katsumi
Published: October 2002

We propose a Ni-like Kr soft X-ray laser operating on the 4d
1
S
0–4p
1
P
1 transition at 32.6 nm by a novel excitation scheme. In this scheme, Ni-like ions are prepared with almost 100% abundance by optical-field-induced ionization and the inverse bremsstrahlung heats the plasma efficiently. The numerical simulation predicts that an ultrahigh gain greater than 1000 cm-1 is achievable in low-density plasma (N
e=5.6×1019 cm-3) for a driving laser intensity of 1.75×1016 W/cm2. With longitudinal pumping, an output energy greater than 40 µJ and an energy efficiency of 7×10-5 are expected with 200 Torr Kr gas.
Two-Way Holographic Image Storage in Photosensitive Polymers
Authors: Aoshima Yasuo , Egami Chikara , Kawata Yoshimasa , Sugihara Okihiro , Tsuchimori Masaaki , Watanabe Osamu , Che Yanlong , Fujimura Hisashi , Okamoto Naomichi
Published: October 2002

We report two-way holographic image storage in azo polymers. Urethane-urea copolymers involve two photochemical reactions, photoanisotropic modification and surface modification. We can realize the recording of two holograms: (polarization volume hologram due to the anisotropy of azo side chain and surface relief hologram) that have different types of information. This is possible because the polarization volume hologram is rewritable while the surface relief hologram is thermally stable. Using the fact that the polarization volume hologram acts like a half wave plate, we can separately readout the different types of information.
High-Density Rewritable Optical Disk Using Groove Recording
Authors: Iwata Kazumi , Nakano Eiji , Hosoda Atsushi , Oishi Kenji , Ohshima Katsunori , Ito Fumihiko , Kondo Tetsuya , Ohgo Takashi , Nakagawa Eiji , Hayami Atsushi , Itonaga Makoto
Published: October 2002

For an optical disk system using an objective lens of numerical aperture (NA) 0.7 and a GaN laser, the performances of the groove-recording scheme were investigated. A disk having 17 GB capacity showed the initial jitter of 11.9% with an equalizer for digital versatile disks (DVD). With an adaptive equalizer and a Viterbi decoder, sufficiently low bit error rates and wide tilt margins were obtained.
Thermochromic Super-Resolution in Phase-Change Rewritable Disk with Double Mask Layer
Authors: Hatakeyama Masaru , Nomura Akihiko , Oishi Kenji , Tsujita Koji , Suzuki Yoshiaki , Ueno Ichiro
Published: October 2002

A new mask system for a thermochromically induced super-resolution (TSR) rewritable disk is proposed. In this system which consists of a high-sensitivity mask layer and a low-sensitivity mask layer, TSR effects are obtained in both read and write processes. At the high-density recording on a Ag–In–Sb–Te phase-change rewritable disk, cross-talk and cross-erase are improved.
Physical Characteristics and Format of Digital Versatile Disc Re-Recordable
Authors: Kato Masahiro , Yone Tatsuhiro , Yamaguchi Atsushi , Suzuki Shinji , Muramatsu Eiji , Taniguchi Shoji , Inoue Akiyoshi
Published: October 2002

The digital versatile disc re-recordable (DVD-RW) has been developed as a member of the digital versatile disc (DVD) family. The DVD-RW disc format is obtained by adding the re-writable feature to the DVD recordable (DVD-R) disc format. Therefore DVD-RW disc maintains playback compatibility with DVD-R and DVD read only memory (DVD-ROM). In order to realize this feature, the “groove wobble and land pre-pit method” has been adopted as a pre-formatting method for the DVD-RW disc. The land pre-pit (LPP) is one of the most important factors in DVD-RW discs because the characteristics of the DVD-RW disc are influenced by the LPP design. The characteristics of the DVD-RW disc can be improved by the optimization of the LPP design. Therefore, the LPP should be designed to obtain the best performance of the DVD-RW disc. We investigated optimization of the LPP design and determined the best conditions for a DVD-RW disc structure by optical simulation and experiments. This report focuses on the LPP design and shows the optimum conditions for the DVD-RW disc.
Characterization and Optimization of Atomic Hydrogen Cleaning of InP Surface for Selective Molecular Beam Epitaxial Growth of InGaAs Quantum Structure Arrays
Authors: Muranaka Tsutomu , Jiang Chao , Ito Akira , Hasegawa Hideki
Published: October 2002

An oxide removal process for InP surface using atomic hydrogen cleaning was characterized and optimized for use in the selective molecular beam epitaxial (MBE) growth of InGaAs quantum structures. In-situ X-ray photoelectron spectroscopy (XPS), reflection high energy electron diffraction (RHEED), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used. Detailed XPS measurements clarified the effects of atomic hydrogen on the planar InP surfaces. The cleaning efficiently removed oxygen. However, the P/In atomic ratio on the surface depended sensitively on the cleaning procedure. Under the optimum low-temperature atomic hydrogen cleaning, the surface stoichiometry could be maintained and realized an atomically flat InGaAs/InP interface. This has led to the formation of uniform InGaAs ridge quantum wires (QWRs) with good optical properties.
Coulomb Charging Effects in an Open Quantum Dot Device at Zero Magnetic Field
Authors: Liang Chi-Te , Simmons Michelle Y. , Smith Charles G. , Kim Gil-Ho , Ritchie David A. , Pepper Michael
Published: October 2002

We report low-temperature conductance measurements of an open quantum dot device formed in a clean one-dimensional (1D) channel. At zero magnetic field, continuous and periodic oscillations superimposed upon 1D ballistic conductance steps are observed. We ascribe the observed conductance oscillations when the conductance through the dotGexceeds 2e2/h, to experimental evidence for Coulomb charging effects in an open dot. This is supported by the evolution of the oscillating features forG>2e2/has a function of both temperature and barrier transparency.
Charged Magnetoexcitons in Parabolic Quantum Dots II
Authors: Akiko Natori Akiko Natori , Shin Ohnuma Shin Ohnuma , Nguyen Hong Quang Nguyen Hong Quang
Published: October 2002

We study the interband absorption spectrum of a charged magnetoexciton in two-dimensional (2D) parabolic quantum dots containing N (0≤N≤12) electrons by using an unrestricted Hartree-Fock method. The calculated results show red shifts of interband transition energies, reduction of diagonal transition intensities and suppression of diamagnetic shift of transition energies, by the charging effect of a quantum dot. The mechanisms of these charging effects are clarified.
Effects of Dot Size and its Distribution on Electron Number Control in Metal-Oxide-Semiconductor-Field-Effect-Transistor Memories Based on Silicon Nanocrystal Floating Dots
Authors: Haining Wang Haining Wang , Nobuyoshi Takahashi Nobuyoshi Takahashi , Hideaki Majima Hideaki Majima , Takashi Inukai Takashi Inukai , Masumi Saitoh Masumi Saitoh , Toshiro Hiramoto Toshiro Hiramoto
Published: October 2002

Effects of dot size and dot size distribution on electron number control in silicon floating dot memories at room temperature are investigated by numerical calculation. When the dot size is sufficiently small and the size distribution is negligible, the number of electrons in the dot is precisely controlled by the Coulomb blockade and the electron number shows a staircase feature as a function of gate voltage. As the dot size increases and the size distribution increases, the staircase feature disappears due to the averaging effects. It is found that, to obtain a distinct staircase feature, the size distribution should be less than 7% for the 8-nm-diameter dot size and 12% for the 3-nm-diameter dot. These results provide good guidelines for setting device parameters for fabricating silicon floating dotmemories.
Design Considerations for Low-Power Single-Electron Transistor Logic Circuits
Authors: Moon-Young Jeong Moon-Young Jeong , Bong-Hoon Lee Bong-Hoon Lee , Yoon-Ha Jeong Yoon-Ha Jeong
Published: October 2002

We have investigated design considerations for low-power single-electron transistor (SET) logic circuits. Supply-voltage scaling is introduced as a method for reducing the power consumption of SET circuits. A detailed analysis of the effects of supply-voltage scaling is given on the basis of the behavior of a complementary capacitively coupled SET inverter circuit. It has been shown that the hysteresis caused by the supply-voltage-dependent threshold voltage of a SET quickly disappears as the temperature rises, and does not ruin the desired inverting operation at a practical operation temperature. Also shown is the considerable impact of the supply-voltage scaling on reducing the power expended by leakage and short-circuit. From the results of power-delay product and delay time, it has been shown that the supply-voltage scaling should be carried out within 20% of maximum supply-voltage to maintain overall circuit performance.
Single Photon Detection with a Quantum Dot Transistor
Authors: Shields Andrew J. , O'Sullivan Martin P. , Farrer Ian , Ritchie David A. , Leadbeater Mark L. , Patel Nalin K. , Hogg Richard A. , Norman Carl E. , Curson Neil J. , Pepper Michael
Published: October 2002

We propose and demonstrate a type of GaAs/AlGaAs modulation-doped field effect transistor (FET) which is sensitive to single photons. The FET contains a layer of InAs quantum dots formed using an in-situ, self-organising method, adjacent to the channel and separated from it by a thin AlGaAs barrier. Capture of a single photo-excited carrier by a quantum dot leads to a sizeable change in the source-drain current through the transistor, allowing the detection of a single photon. We show this is because the mobility of the electron channel is extremely sensitive to the charge trapped in the dots. This discovery may allow a new type of single photon detector to be developed which does not rely upon avalanche processes.
Resonant-Tunneling-Injection Photoluminescence of Single InAs Self-Assembled Quantum Dots Embedded in a Thin AlGaAs Barrier
Authors: Yutaka Ohno Yutaka Ohno , Shigeru Kishimoto Shigeru Kishimoto , Koichi Maezawa Koichi Maezawa , Takashi Mizutani Takashi Mizutani
Published: October 2002

We have investigated resonant-tunneling-injection photoluminescence (PL) of single InAs self-assembled quantum dots (QDs) which were embedded in the barrier layer of an n-GaAs/i-AlGaAs/n-GaAs tunneling diode. A triangular structure in the PL intensity-voltage characteristics of a single PL line was observed. This reflects the electron tunneling from a three-dimensional emitter to the zero-dimensional quantum level of the QD. In addition, three subpeaks and a broad bulge of the PL were superimposed on the triangular structure. The subpeaks were ascribed to the resonant tunneling of holes into valence quantum levels of the QD. The origin of the excess PL bulge which is obtained at off-resonance bias condition is also discussed.
Hysteresis Phenomena for the Series Circuit of Two Identical Negative Differential Resistance Devices
Authors: Gan Kwang-Jow
Published: October 2002

The hysteresis phenomena and current–voltage (I–V) characteristics of a series combination of two identical negative differential resistance (NDR) devices are analyzed. In this study, two different cases are discussed. The analysis shows that hysteresis phenomena in the combined I–V characteristics depend upon the electrical parameters of the series-connected NDR devices. The relationships between the hysteresis voltage and electrical parameters are studied. The effect of series resisitance on the combined I–V curve is investigated. Experimental results are demonstrated to support the analysis and discussion.
Hydrogen Promoted Copper Migration in the High Pressure Anneal Process
Authors: Fujikawa Takao , Yoshikawa Tetsuya , Ohnishi Takashi , Sato Toshiki
Published: October 2002

To meet the requirement of lower processing temperature in the high pressure anneal process (HiPA), Cu films deposited by physical vapor deposition (PVD) with addition of hydrogen were investigated. Experimental results on the hole filling performance under high pressure, the grain growth, the micro-hardness measurement and the film stress measurement revealed that the hydrogen addition markedly changes the properties of the Cu film. It is especially effective in softening the PVD-Cu film and/or in promoting the Cu atom diffusion which also promotes grain growth. As a result the processing temperature may be lowered down to around 400°C, which is the highest temperature allowable for the interconnection structures with organic low-k dielectric layers.
Electron Spin Resonance Measurement of Organic Radicals in Petroleum Source Rock Containing Transition Metal Ions
Authors: Uesugi Akihiko , Ikeya Motoji
Published: October 2002

The Electron Spin Resonance (ESR) spectrum with the width ΔH= 0.5±0.02 mT at g-factor of 2.0028±0.0005 of kerogen collected at the shallow part of a petroleum deposit has a broader peak than that collected in its deeper part (ΔH=0.4±0.02 mT). Two groups of samples were prepared. One was heated at several temperatures to liberate hydrocarbons and another was treated with pyridine, so that the generated hydrocarbons due to heating were removed. Narrowing of the linewidth was not caused by heating, but by treatment with pyridine. Molecular orbital calculation was performed to explain the septet-quartet ESR spectrum of organic radicals with g=2.0023±0.0005, A
1=0.625±0.003 mT (septet) and A
2=0.187±0.003 mT (quartet) in petroleum source rock and in heated carbonate: the presence of tert-butyl radical can be suitable to explain the septet-quartet spectrum.
Finite-Difference Time-Domain Analysis on Nonlinear Fabry-Perot Resonator in Optical Waveguide Geometry
Authors: Masamitsu Fujii Masamitsu Fujii , Toshihiro Okamoto Toshihiro Okamoto , Masanobu Haraguchi Masanobu Haraguchi , Masuo Fukui Masuo Fukui , Samir J. Al-Bader Samir J. Al-Bader
Published: October 2002

The finite-difference time-domain (FDTD) method is applied to investigate the characteristics of nonlinear Fabry-Perot (FP) resonators in optical waveguide geometries. Our treatment, which is the extension of Tran's method developed to analyse the characteristics of nonlinear photonic crystals, correctly reproduces analytical results on optical bistabilities of the FP resonator provided by Chen and Mills in 1987. It is found that the minimum power required for optical bistabilities is significantry decreased by adopting the optical waveguide geometry, compared with the case of Chen and Mills, i.e., a conventional nonlinear FP interferometer.
Investigations of Transient Ne-like Fe X-Ray Lasers Pumped by Femtosecond Laser System
Authors: Lin Jiunn-Yuan
Published: October 2002

Detailed simulations of a Ne-like Fe X-ray laser pumped by a femtosecond laser system are presented. In this study, we have investigated an efficient multiple pumping pulse configuration including two 150 ps prepulses and one 100 fs main pulse for transient X-ray lasers. The influences of pumping pulse delay, duration, and intensity are studied. Simulation results suggest that a high repetition rate and high gain tabletop X-ray laser at 255 Å can be achieved with a total pumping energy less of than 0.4 J.
Interaction of Light with Ordered Dielectric Spheres: Finite-Difference Time-Domain Analysis
Authors: Akihiko Shinya Akihiko Shinya , Masanobu Haraguchi Masanobu Haraguchi , Masuo Fukui Masuo Fukui
Published: October 2002

Using the finite-difference time-domain (FDTD) method, interaction between a gaussian wave and ordered dielectric spheres has been numerically calculated for the first time. Real-time images of the spatial distribution of the intensity of light coupling to the dielectric spheres have been presented for gaussian wave and plane-wave incidences. From the images for gaussian wave incidence, we have been able to clearly confirm a remarkable reduction in the light velocity for a flat photon band, i.e., a heavy photon band. It has been pointed out that the situation of the propagation of the gaussian wave is similar to that of the plane-wave. The transmittance T and reflectance R for the normal incidence of light to the ordered spheres have also been evaluated from the FDTD analyses. It has been found that T and R for the gaussian wave can be exactly estimated for the heavy photon band, differing from the plane-wave case.
Characterization of Highly Preferred Pb(Zr,Ti)O3 Thin Films on La0.5Sr0.5CoO3 and LaNi0.6Co0.4O3 Electrodes Prepared at Low Temperature
Authors: Il-Doo Kim Il-Doo Kim , Ho-Gi Kim Ho-Gi Kim
Published: October 2002

La0.5Sr0.5CoO3 (LSCO) and LaNi0.6Co0.4O3 (LNCO) thin films were deposited on Pt/Ti/SiO2/Si substrates by DC reactive sputtering at 450°C and were annealed at temperatures ranging from 550°C to 750°C for 30 min in an O2 ambient to improve the crystallinity of the films and to reduce their resistivity. LSCO and LNCO thin films were successfully prepared at temperatures as low as 450°C. Pb(Zr0.48Ti0.52)O3 (PZT) thin films of 150 nm thickness were deposited on the LSCO and LNCO electrodes by DC reactive sputtering at a substrate temperature of 550°C. PZT films grown on LSCO and LNCO electrodes showed a (001) preferred orientation and had a uniform matrix of densely packed round grains. The leakage current density remained on the order of 10-7–10-9 A/cm2 at an applied voltage below 5 V. PZT thin films grown on LSCO/Pt showed a remanent polarization (2P
r) of about 46–52 µC/cm2, and a coercive voltage of about 1 V. PZT thin films grown on LNCO/Pt electrodes showed a lower coercive voltage (<0.6 V) and a smaller remanent polarization (2P
r) of about 28.8 µC/cm2 than those of PZT films grown on LSCO/Pt. LSCO/Pt and LNCO/Pt electrodes were essential for lowering the crystallization temperature as well as for obtaining good electrical properties of PZT capacitors.
Crystallization of SrBi2Ta2O9 Thin Films in N2 Ambient by Chemical Solution Deposition Method
Authors: Ogata Nobuhito , Nagata Masaya
Published: October 2002

Structural and electrical properties of SrBi2Ta2O9 (SBT) thin films crystallized upon annealing in an N2 ambient were investigated. These thin films were prepared on Pt/TiO2/SiO2/Si substrates by the chemical solution deposition (CSD) method. The films crystallized in N2 after calcination at a high O2 partial pressure in an N2/O2 mixed ambient showed good ferroelectric properties with remanent polarization 2P
r=13–14 µC/cm2, coercive field 2E
c=70–80 kV/cm, and leakage current density less than 1×10-7 A/cm2 at an applied voltage of 3 V. These ferroelectric properties are the same as those of the SBT crystallized in O2. However, the films crystallized in N2 after calcination at a low O2 partial pressure in an N2/O2 mixed ambient did not form SBT. TDS data showed that the carbon content of the film calcined in poor O2 was higher than that of the film calcined in rich O2. These results showed that the carbon residue within the film might disturb the formation of SBT.
Effect of Laser Wavelength for Surface Morphology of Aluminum Nitride Thin Films by Nitrogen Radical-Assisted Pulsed Laser Deposition
Authors: Ishihara Masatou , Yamamoto Kazuhiro , Kokai Fumio , Koga Yoshinori
Published: October 2002

AlN thin films were prepared on Si(100) substrates by the nitrogen radical-assisted pulsed laser deposition method at a low substrate temperature (200°C) as a function of the laser wavelength (1064, 532 and 266 nm). At the laser wavelength of 1064 nm, Al-rich AlN films were deposited and granular crystals with a diameter of 50 nm were observed on the film surface. The surface roughness (R
a) was 15 nm. At the laser wavelength of 266 nm, c-axis-oriented AlN thin films with smooth surfaces (R
a=5 nm) were obtained and the atomic ratio of N/Al was stoichiometric. The full width at half maximum (FWHM) value of the diffraction profile in the 2θ/θ scan mode was 0.55°. It was found that the use of an ultraviolet laser was more effective for preparing the c-axis-oriented AlN films with a stoichiometric concentration and smooth surfaces.
Enhancement of Etch Rate by the Addition of O2 and Ar in Chemical Dry Etching of Si Using a Discharge Flow of Ar/CF4 and CF4/O2 Gas Mixtures
Authors: Tsuji Masaharu , Okano Shinji , Tanaka Atsushi , Nishimura Yukio
Published: October 2002

The chemical dry etching of Si in a fast discharge flow was studied using a low-power (80 W) microwave discharge of Ar/CF4/O2 mixtures. The variation of etch rate was measured as a function of the O2 or Ar flow rate in order to determine the effects of the addition of O2 and Ar. The maximum etch rate was about 3600 Å/min at the Ar, CF4 and O2 flow rates of 2500, 100 and 10 sccm, respectively. This etch rate was larger than those obtained without the addition of O2 by a factor of 8 and without the addition of Ar by a factor of 23. Auger and XPS spectra of Si substrates and emission spectra of discharges were measured in order to examine the effects of the addition of O2 on the Si surface and discharge. The marked enhancement of the etch rate at low O2/CF4 flow ratios below 10% was explained by an increase in the F concentration and a decrease in the concentrations of carbons and CFn (n=1,2). The decrease in the etch rate at high O2/CF4 flow ratios above 10% was attributed to the formation of SiO2 on the substrate. The marked enhancement of the etch rate by the addition of Ar was explained by the generation of active Ar species which enhance [F] and [O] in the discharge flow.
Atomic Composition and Structural Properties of Blue Emitting BaAl2S4:Eu Electroluminescent Thin Films
Authors: Inoue Youji , Tanaka Isao , Tanaka Katsu , Izumi Yoshitaka , Okamoto Shinji , Kawanishi Mitsuhiro , Barada Daisuke , Miura Noboru , Matsumoto Hironaga , Nakano Ryotaro
Published: October 2002

We have investigated the compositional and structural properties of blue emitting BaAl2S4:Eu electroluminescent thin films fabricated by switching electron-beam evaporation using two targets. The use of X-ray photoelectron spectroscopy (XPS) revealed that the ratio of barium to sulfur in thin films is 1.0:2.0, which is identical to the stoichiometry of BaAl2S4. The X-ray diffraction (XRD) peaks from the thin film were assigned to those of a BaAl2S4 crystal. The photoluminescence (PL) spectrum shows emission from the 4f65d→4f7 transition of the activated Eu2+ ions in BaAl2S4 crystals. These results indicate that the crystalline phase in thin films is only BaAl2S4. The thin films also contain a large amount of oxygen impurities, which result in the formation of an Al2O3 layer and amorphous barium aluminate.
Local Non-Stationary Nature of Brain Waves from Demented Persons
Authors: Saji Ryoya , Konno Hidetoshi
Published: October 2002

In the present paper, we show the local non-stationary nature of brain waves from demented persons by reconstructing various stochastic processes of averaged local quantities, e.g., fractal dimension, mean, variance, skewness and kurtosis. The characteristic random dynamic features of their local quantities are discussed in the two-dimensional (2D) phase space. The availability of their local non-stationary nature for diagnosing senile dementia is also discussed.
Quantitative Understanding of Electron Mobility Limited by Coulomb Scattering in Metal Oxide Semiconductor Field Effect Transistors with N2O and NO Oxynitrides
Authors: Takamitsu Ishihara Takamitsu Ishihara , Shin-ichi Takagi Shin-ichi Takagi , Masaki Kondo Masaki Kondo
Published: October 2002

A new model for electron mobility limited by Coulomb scattering, µc, for metal oxide semicunductor field effect transistors (MOSFETs) with N2O and NO oxynitrides has been proposed. It is shown that this model accurately represents the experimental mobility behavior, such as the difference of µc between pure oxides and oxynitrides and the dependence on the inversion layer electron density, using physically appropriate parameters of Coulomb scattering centers. The effects of the location of fixed charges and the multi-subband occupation are examined to investigate the physical meaning of this new model.
Influences of Residual Chlorine in CVD-TiN Gate Electrode on the Gate Oxide Reliability in Multiple-Thickness Oxide Technology
Authors: Moriwaki Masaru , Yamada Takayuki
Published: October 2002

Influences of the chemical vapor deposition (CVD)-TiN gate process on gate oxide integrity have been studied. The gate leakage characteristic and reliability of the gate oxide were drastically degraded by 1000°C annealing for thick oxide as compared to for thin oxide. By X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS) analyses, the oxide degradation is confirmed to be due to the formation of a weak spot induced by out-diffusion of residual Cl from the TiN gate electrode into the gate oxide. Out-diffused Cl reacts with defects in the oxide during the high-temperature anneal and forms trap sites. The weak spot which acts as a leakage path appears to be the local spot which has a larger amount of Cl-related trap sites. Controlling of impurities in the CVD metal gate is a key for realizing future multiple-thickness gate oxide technology.
Frequency Dispersion in Drain Conductance of InAlAs/InGaAs Hight-Electron Mobility Transisters (HEMTs) and Its Relationship with Impact Ionization
Authors: Kosugi Toshihiko , Umeda Yohtaro , Suemitsu Tetsuya , Enoki Takatomo , Yamane Yasuro
Published: October 2002

We investigated the frequency dispersion in drain conductance of 0.1-µm-gate InAlAs/InGaAs high-electron mobility transisters under various bias conditions in a frequency range from 9 kHz to 500 MHz using a network analyzer. The substrate current was monitored from the backside of the wafer as a measure of the impact ionization rate. The relationship between the frequency dispersion and the impact ionization is explained quite well by the model we employed here. According to the model, the extrinsic transconductance of the device is the main factor governing the frequency dispersion of the drain conductance.
Optical Binary-Phase-Shift-Keying Modulation of 10 GHz Using an Integrated Hybrid Device
Authors: Shin Myunghun , Lim Jiyoun , Kim Jeha , Kim Jeong-Soo , Pyun Kwang-Eui , Hong Songcheol
Published: October 2002

An integrated optical/RF hybrid device was designed and fabricated for binary-phase-shift-keying (BPSK) subcarrier modulation. The device is composed of two identical high-speed multiple quantum well electroabsorption modulators branched with two multimode interference couplers. Using the device, we demonstrated that a RF subcarrier of 10 GHz is directly modulated in a BPSK scheme with an independently applied RF carrier and digital signal.
All-Optical Two-Dimensional Serial-to-Parallel Pulse Converter Using an Organic Film with Femtosecond Optical Response
Authors: Tatsuura Satoshi , Wada Osamu , Furuki Makoto , Tian Minquan , Sato Yasuhiro , Iwasa Izumi , Pu Lyong Sun
Published: October 2002

In this study, we introduce a new concept of all-optical two-dimensional serial-to-parallel pulse converters. Femtosecond optical pulses can be understood as thin plates of light traveling in space. When a femtosecond signal-pulse train and a single gate pulse were fed onto a material with a finite incident angle, each signal-pulse plate met the gate-pulse plate at different locations in the material due to the time-of-flight effect. Meeting points can be made two-dimensional by adding a partial time delay to the gate pulse. By placing a nonlinear optical material at an appropriate position, two-dimensional serial-to-parallel conversion of a signal-pulse train can be achieved with a single gate pulse. We demonstrated the detection of parallel outputs from a 1-Tb/s optical-pulse train through the use of a BaB2O4 crystal. We also succeeded in demonstrating 1-Tb/s serial-to-parallel operation through the use of a novel organic nonlinear optical material, squarylium-dye J-aggregate film, which exhibits ultrafast recovery of bleached absorption.
Novel Process for High-Density Buried Nanopyramid Array Fabrication by Means of Dopant Ion Implantation and Wet Etching
Authors: Meishoku Koh Meishoku Koh , Tomomi Goto Tomomi Goto , Atsushi Sugita Atsushi Sugita , Takashi Tanii Takashi Tanii , Tomoyuki Iida Tomoyuki Iida , Takahiro Shinada Takahiro Shinada , Takashi Matsukawa Takashi Matsukawa , Iwao Ohdomari Iwao Ohdomari
Published: October 2002

A simple and high-throughput process to fabricate a high-density buried nanopyramid array (BNPA) on a Si surface has been developed by means of dopant ion implantation and wet etching. In this process, the combination of two interesting etching phenomena was utilized to form the BNPA. One is the enhanced etching of ion-exposed SiO2 in HF. The other is the newly found retarded etching of ion-exposed Si in hydrazine (N2H4). A p-type Si(100) substrate with 27-nm-thick SiO2 was exposed to 50-keV phosphorus ions with a dotted pattern. Then, the ion-exposed SiO2 was selectively etched away by dipping in HF. Finally, the BNPA was formed under the patterned SiO2 layer by dipping in hydrazine. By using this simple process, the BNPA with 250 nm pitch was successfully fabricated. The electrical property of the fabricated nanopyramid was also investigated using scanning Maxwell-stress microscopy (SMM).