bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of Pulsed Laser Deposition Mechanism of WO3 Thin Films
Authors: Qiu Hong , Lu Yong-Feng
Published: October 2002

The growth dynamics of WO3 thin films by laser ablation of a WO3 monoclinic phase target was studied. Space and time-resolved optical spectra indicated the presence of neutral (WI), ionized (WII) and electronically excited molecule (WO) species in the plume. The reaction between W and O2 was manifested in the laser deposition. Raman spectra showed the films deposited over a target-substrate distance longer than 5 cm or (/and) under an ambient oxygen pressure lower than 200 mTorr deviated from the monoclinic phase of the target with shortened and bent bonds. This was due to the insufficient surface or (/and) gas oxidation. The oxygen pressure and the target-substrate distance were found to be important features in the stoichiometric and monoclinic phase formation. Both gas and surface reactions were responsible for the ultimate monoclinic phase formation in the pulse laser deposition. Parameters were optimised for the oxygen pressure and target-substrate distance.
Super-Resolution Near-Field Structure and Signal Enhancement by Surface Plasmons
Authors: Tominaga Junji , Kim Johoo , Fuji Hiroshi , Büchel Dorothea , Kikukawa Takashi , Men Liqiu , Fukuda Hisako , Sato Akira , Nakano Takashi , Tachibana Akihiro , Yamakawa Yuzo , Kumagai Masashi , Fukaya Toshio , Atoda Nobufumi
Published: October 2002

We describe surface plasmon enhancement by near-field interaction with Ag-scattering centers. By inserting mark trains between two Ag-scattering centers, the near-field signals were further enhanced in a super-resolution near-field structure. Observing the enhancement in more detail, it was found that surface plasmons are generated along the mark trains and are dispersed in a range of 1 µm along the marks and 40–50 nm normal to the multilayer stack.
Holographic Approach to Record and Retrieve Subwavelength-Size Objects Using Optical Near-Field
Authors: Kyoung-Youm Kim Kyoung-Youm Kim , Byoungho Lee Byoungho Lee
Published: October 2002

A holographic method for the storage and retrieval of subwavelength-size objects using optical near-field is proposed. Experimental results show that evanescent field components can be recorded and retrieved by our method and hence, an object whose size is smaller than the Rayleigh limit can be reconstructed. It may be an effective way of microhologram and suggests applications in biology and high-density optical memory systems.
Readout of Optical Disk Recorded by Pit Edge and Depth Modulation
Authors: Nakajima Junsaku , Terashima Shigeo , Ohta Kenji
Published: October 2002

We report a Read-only (ROM) disc which is recorded by pit edge and depth modulation (PEDM). The information recorded by pit edge modulation is read out through an RF signal channel, and that recorded by pit depth modulation is read out through a tangential push-pull signal channel by detecting signal polarity at the pit edge. Each signal is sliced with a single level and is combined with another signal so that a multi-value recording is realized without multiple level slicing. The information recorded and read out using tangential push-pull signal polarity can never be copied onto recordable discs. Thus, not only a larger recording density and a higher transfer rate but also secure information storage are achieved with no change of the current optical and mechanical systems.
Rewritable Multilevel Recording by Mark-Size Modulation on Growth-Dominant Phase-Change Material
Authors: Kiyono Kenjirou , Horie Michikazu , Ohno Takashi , Uematsu Takuya , Hashizume Takao , O'Neill Michael P. , Balasubramanian Kunjithapatham , Narayan Raghuram , Warland David , Zhou Ting
Published: October 2002

Rewritable multilevel recording based on reflectivity modulation, by means of two-level write intensity modulation and duty ratio control of writing and cooling pulses on conventional four-layer stack, was realized using an eutectic growth-dominant phase-change material. Tangential amorphous mark size modulation with the competitive process of amorphization and recrystallization during resolidification was observed.
Growth and Electronic Properties of Self-Organized Quantum Rings
Authors: Johannes Luyken Axel Lorke , M. Garcia Jorge , M. Petroff Pierre
Published: October 2002

A method is described which can be used to grow self-organized, nanoscopic InGaAs ring structures on GaAs substrate. Starting from self-organized InAs dots, the crucial step for the ring formation is a short annealing phase after the dots have been covered by a thin GaAs layer. Spectroscopic data are reviewed which show that the ring morphology can be preserved even after the InGaAs islands have been covered by additional cladding layers for the realization of electronically or optically active devices.
Growth of InGaAs Quantum Dots on the AlGaAs(311)B Surface
Authors: Akahane Kouichi , Kawamura Takahiro , Lan Sheng , Okada Yoshitaka , Kawabe Mitsuo
Published: October 2002

We have investigated the self-organization mechanism of InGaAs quantum dots (QDs) on GaAs(311)B substrates by changing the underlying materials beneath the QD layer. It was found that the QD growth on the (311)B surface is strongly affected by the underlying layer. The size uniformity and structure ordering of QDs were degraded if the QDs were grown on an AlGaAs layer. However, these properties of QDs were recovered by introducing a 40-nm-thick GaAs spacer layer on AlGaAs. The dependence of the QD properties on the spacer layer thickness suggested that there exists a long-range interaction between the InGaAs QDs and the underlying layer in the case of QD growth on the (311)B surface. This long-range interaction is considered to arise from the steep change in strain distribution at the interface of GaAs and AlGaAs and/or intermixing of the InGaAs layer with the underlying layer.
Self Size-Limiting Process of InAs Quantum Dots Grown by Molecular Beam Epitaxy
Authors: Toshiyuki Kaizu Toshiyuki Kaizu , Koichi Yamaguchi Koichi Yamaguchi
Published: October 2002

In the molecular beam epitaxy (MBE) growth of InAs quantum dots (QDs), we investigated the dot formation via the self size-limiting process. Accumulation of size-limited InAs QDs resulted in narrow inhomogeneous broadening of photoluminescence (PL) linewidth and low energy shift of PL peak position. Atomic force microscopy (AFM) and reflection high-energy electron-beam diffraction (RHEED) observations revealed the appearance of {136} facets on the side wall of size-limited InAs dots. It was proposed that the facet formation played an important role in the self size-limiting behavior.
Selective Growth of GaN/AlGaN Microstructures by Metalorganic Vapor Phase Epitaxy
Authors: Tomonobu Kato Tomonobu Kato , Yoshio Honda Yoshio Honda , Yasutoshi Kawaguchi Yasutoshi Kawaguchi , Masahito Yamaguchi Masahito Yamaguchi , Nobuhiko Sawaki Nobuhiko Sawaki
Published: October 2002

A GaN/AlGaN double heterostructure was fabricated on the (1101) facets of a GaN triangular structure prepared by selective area growth by metalorganic vapor phase epitaxy. The photoluminescence (PL) and cathode luminescence (CL) spectra were investigated to characterize the structure. It was found that the PL peak wavelength due to the GaN quantum well is dependent on the well thickness. However, the Al composition of the AlGaN layer is dependent on the position on the (1101) facet. The anomalous gradient of the composition is attributed to the difference in the diffusion coefficients of Al and Ga on the surface.
Selective Growth of Highly Packed Array of ZnCdS Quantum Dots with a Mask Prepared by Atomic Force Microscope Nanolithography
Authors: Avramescu Adrian , Ueta Akio , Uesugi Katsuhiro , Suemune Ikuo
Published: October 2002

Preparation of a highly ordered and packed array of ZnCdS quantum dots (QDs) by selective-area growth (SAG) is reported. For this purpose, we have developed a method to prepare nanoscale mask openings with an atomic force microscope (AFM) for SAG employing electron-beam-induced carbonaceous films. AFM anodization in a modulated-amplitude pulsed bias mode is applied, making it possible to obtain dotlike patterns with a resolution of ∼26 nm and an interdot distance of ∼100 nm in the masks ready for SAG. Nanoscale SAG of ZnCdS and ZnMgCdS alloys by metalorganic molecular-beam epitaxy is studied on (001) GaAs surfaces masked with the carbonaceous film. The array of ZnCdS/ZnMgCdS quantum dots each with a size of ∼26 nm as defined by the mask openings, and with a density of 1×1010 cm-2, is successfully grown with this method. The photoluminescence from the dot array, recorded at 30 K, is strong and shows a 6 meV blueshift as compared with that observed from the uniformly grown region.
Aharonov-Bohm Oscillation in Rings with Permalloy
Authors: Kotaro Tsubaki Kotaro Tsubaki
Published: October 2002

Aharonov-Bohm (A-B) rings with and without an inserted permalloy rod were fabricated from an AlGaAs/GaAs two dimensional electron gas (2DEG) wafer. The permalloy was a soft ferromagnetic alloy metal with a relative permeability µ of about 104, so that the effective susceptibility, including the demagnetizing effect, could be calculated from only the diameter and height of the permalloy rod. Magnetoresistance of the A-B rings with and without the permalloy rod was measured at T = 0.3 K using an external magnetic field. The magnetoresistance had oscillations of different periods in the two cases. The main oscillation periods of the rings with and without the permalloy rod were 7.5 Oe and 28 Oe, respectively, clearly indicating that the permalloy rod reduced the oscillation period. The reduction factor (26%) was consistent with the demagnetizing effect of the permalloy rod. If the permalloy rod is designed to be free of the demagnetizing effect, the reduction factor should reach the order of the reciprocal of relative permeability µ.
Nanoscale Structural Characteristics of Photodissolved Gold (111) Single Crystalline Surface
Authors: Murakoshi Kei , Kitamura Takahiko , Nakato Yoshihiro
Published: October 2002

The effect of photoillumination on electrochemical reactions of a gold electrode in KCl electrolyte solution was investigated. The electrode was dissolved by positive polarization in the electrolyte solution. Anodic current increased when the electrode was illuminated by 830-nm light. Scanning tunneling microscope images proved that dissolution of the gold electrode was accelerated by the photoillumination. The surface of the photodissolved electrode consisted of islands with a flat top and relatively narrow size distribution. In some cases, uniform structure consisted of small islands was formed by the illumination. The contribution of a highly localized photoexcitation mode at the surface was discussed to explain the characteristics of the photoformed surface nanostructure.
Electron Transport in an Array of Movable Metal Nanoparticles
Authors: Norihiko Nishiguchi Norihiko Nishiguchi
Published: October 2002

Electron transport via single electron tunneling in an array of ligand-stabilized metal nanoparticles is investigated numerically, considering that elastic ligands linking the nanoparticles allow nanoparticle vibrations. The resultant current–voltage characteristics show hysteresis and random telegraph signals of the current. We clarify that these transport properties are caused by hysteretic behavior of the kinetic states of nanoparticles and by intermittent transitions between the kinetic states.
Electron Phonon Interaction and Polaron Effects in Quantum Dots
Authors: Guldner Olivier Verzelen , Gérard Jean Michel , Robson Ferreira Robson Ferreira , Gérald Bastard Gérald Bastard
Published: October 2002

We report on the magnetooptical evidence and theoretical modelling of polaron effects in semiconductor quantum dots. We show that polaron couplings lead to very large anticrossings in the far infrared magnetoabsorption transitions. A modelling of polaron levels by diagonalization of a Fröhlich Hamiltonian between uncoupled electron–Longitudinal Optical phonon states is in excellent agreement with experiments. A theoretical study of the polaron relaxation by means of the couplings to the phonon thermostat allows direct access to the polaron lifetimes.
Electrooptical Study of an In-Plane Switching Mode Using a Uniaxial Medium Model
Authors: Satake Tetsuya , Nishioka Takahiro , Saito Tadashi , Kurata Tetsuyuki
Published: October 2002

A new modeling method using a uniaxial medium model has been proposed to obtain a simple and quantitative expression for the transmittance of an in-plane switching (IPS) mode. In this model, the effective birefringence (Δ
n
eff) and the apparent optic axis rotation angle (φapp) are used instead of the original birefringence and the director profile, and Δ
n
eff changes when an electric field is applied to the IPS mode cell. The dependences of Δ
n
eff (measured as a retardation) and φapp on the applied voltage have been evaluated first by experiment. Δ
n
eff was reduced to 80% of the original value and φapp rotated 45° at the maximum transmittance (T
max). It has been confirmed that the transmittance can be reproduced satisfactorily by employing the model's expression using the observed Δ
n
eff and φapp values. Theoretical simulation has also been executed and the results supported the experimental results. The simulation has also shown that both the Δ
n
eff–Δ
n ratio and φapp at T
max are almost constant and do not depend on either the cell gap or liquid-crystal properties. T
max can be easily calculated using the uniaxial medium model.
Electronic Structure, Stark Effect and Optical Properties of Multistacked Dots
Authors: Giorgi Angela Vasanelli , Robson Ferreira Robson Ferreira , Roberto Cingolani Roberto Cingolani , Hiroyuki Sakaki Hiroyuki Sakaki , Gérald Bastard Gérald Bastard
Published: October 2002

We present the results of effective mass calculations for the electronic structure and optical properties of stacked quantum dots in the presence of a longitudinal electric field. Attention is focussed on strongly stacked dot structures, in which a vertical field acts on the electron in the same way as found in a quantum well. We have studied the dipole selection rules and oscillator strengths of stacked dots for intraband transitions (far-infrared absorption). In the case of interband transitions, we have studied the effect of a longitudinal electric field on the overlap between electron and hole wavefunctions. We have also calculated the absorption spectrum for structures of attached dots, taking into account Gaussian fluctuations in the vertical and lateral dimensions.
Reduction of Electron Decay Time Using Disordered Tunnel Barrier
Authors: Jae-Hyun Park Jae-Hyun Park , Shinji Senzaki Shinji Senzaki , Nobuya Mori Nobuya Mori , Chihiro Hamaguchi Chihiro Hamaguchi
Published: October 2002

The effects of ionized impurity in a tunnel barrier on electron tunneling are studied by performing time-resolved photoluminescence experiments using GaAs/AlGaAs asymmetric multiquantum wells (AMQWs) with a δ-doping layer. The photoluminescence decay time of two-dimensional electron gas in GaAs/AlGaAs AMQWs was measured and the results are compared with those of semiclassical Monte Carlo simulation.
Novel Current Blockade Effect in Arrays of Coherently Coupled Quantum Dots
Authors: R. Wegewijs Maarten , V. Nazarov Yuli , A. Gurvitz Shmuel
Published: October 2002

We study the transport properties of 3 coherently coupled quantum dots connected incoherently to leads. We predict a new current blockade effect to occur at high bias voltages exceeding the Coulomb blockade threshold. All relevant transport processes are incorporated using a density matrix approach. We calculate the resonant current analytically for the bias regime of interest.
A 1550 nm Single-Photon Detector Using a Thermoelectrically Cooled InGaAs Avalanche Photodiode
Authors: Yoshizawa Akio , Tsuchida Hidemi
Published: October 2002

We report a gated-mode single-photon detector sensitive to 1550 nm radiation using a thermoelectrically cooled InGaAs avalanche photodiode. At the operation temperature of 238 K, we have obtained a quantum efficiency of 24.3% with a dark-count probability per gate of 9.4×10-5.
Longitudinal Stark Effect in Parabolic Quantum Dots
Authors: Rinaldi Ross , DeGiorgi Milena , DeVittorio Massimo , Melcarne Angelo , Visconti Paolo , Cingolani Roberto , Lipsanen Harri , Sopanen Markku , Drufva T. , Tulkki Jukka
Published: October 2002

We present an experimental and theoretical investigation of the longitudinal quantum confined Stark effect in strain-induced parabolic InGaAs quantum dots. The electric field is applied in the plane perpendicular to the growth axis (quantum well plane), through a sub-micron gap opened in a metallic contact, which contains just a few dots. The changes in the microphotoluminescence (µ-PL) spectra were measured versus the bias, at low temperature. Due to the device geometry, the electric field profile in the gate is not constant resulting in an asymmetric Stark effect as a function of the applied field polarity. Calculations of the field profile in the conatct gap and of the distorsion of the parabolic-like potential as a function of the applied field have been made in order to correlate the observed changes in the electro-optical properties of the dots with the carrier spill over and wavefunction modifications under electric field.
Thermostabilization of Electrical Properties of InAs/GaAs Self-Assembled Quantum Dots Embedded in GaAs/AlAs Superlattices
Authors: J. Chiquito Adenilson , A. Pusep Yuri , C. Galzerani Sérgio Mergulhão , T. Moshegov Nicolai , L. Miller David.
Published: October 2002

The electrical characteristics of the self-assembled quantum dots embbeded in GaAs wells of the GaAs/AlAs superlattices were studied by capacitance spectroscopy and were compared with results obtained for the dots embbeded in bulk GaAs. A much stronger electron localization was detected for the quantum dots embedded in the superlattice in comparison with those embedded in bulk GaAs. As a consequence, the electrical characteristics of the structures with quantum dots grown in superlattices were found to be significantly thermo-stabilized. It was shown that these structures present different strengths of the localization of electrons caused by the effective increase of the heights of the barriers when the dots were grown in the superlattices.
Electrical Properties of Nanometer-Sized Schottky Contacts for Gate Control of III–V Single Electron Devices and Quantum Devices
Authors: Sato Taketomo , Kasai Seiya , Hasegawa Hideki
Published: October 2002

The electrical properties of nanometer-sized Schottky contacts formed on n-GaAs and n-InP substrates by an in situ electrochemical process were studied both experimentally and theoretically to understand and improve their gate control behavior in single electron devices and quantum devices. From the current–voltage (I–V) measurements using a conductive atomic force microscope (AFM) system, the nano-Schottky contacts showed nonlinear log
I–V characteristics with large and voltage-dependent n values which cannot be explained by the 1D thermionic emission model. The behavior was explained by a novel 3D thermionic emission model including 3D potential distribution modified by an environmental Fermi-level pinning. The depletion characteristics were calculated on the basis of the new model including the environmental effects. The results showed small changes of the depletion layer width with a bias underneath the nano-Schottky contacts due to the environmental Fermi-level pinning. Control of Fermi-level pinning is thus crucial to obtain nano devices in the quantum regime that exhibit good behavior.
A Single-Electron Transistor Produced by Nanoscale Oxidation of InAs
Authors: Shigehiko Sasa Shigehiko Sasa , Satoshi Yodogawa Satoshi Yodogawa , Akio Ohya Akio Ohya , Masataka Inoue Masataka Inoue
Published: October 2002

Atomic force microscope (AFM) oxidation was applied for the direct oxidation of a thin InAs layer in order to fabricate a single-electron transistor (SET) from an InAs/AlGaSb heterostructure. By employing the oxidized InAs as an insulator to form an in-plane-gate structure, SET structures were fabricated. For the improvement of the electrical properties of the InAs oxide as an insulator, a thinner InAs channel layer (10 nm) was introduced. This layer enables the AFM oxidation process at relatively low tip voltages with reduced tip wear. An improved breakdown voltage of as high as 1 V with a negligible leakage current of less than 1 nA was obtained. By using the 10-nm-thick InAs channel layer, SETs with a one- or two-isolated island structure were fabricated. The device characteristics measured at 4.2 K show SET characteristics confirming the successful formation of the gate insulator. While the SET with one island showed reproducible Coulomb oscillations, the other showed unstable oscillatory behavior due to the sensitivity of the structure to background charges. The improved SET characteristics evidenced by the clear Coulomb diamond structure indicate that the introduction of the thinner InAs channel layer is critical.
GaAs-Based Single Electron Transistors and Logic Inverters Utilizing Schottky Wrap-Gate Controlled Quantum Wires and Dots
Authors: Kasai Seiya , Hasegawa Hideki
Published: October 2002

GaAs-based single electron transistors (SETs) and their logic inverters were successfully designed and fabricated using a Schottky wrap-gate (WPG) quantum wire and dot formation technology. Three-gate WPG SETs, which have two tunnel barrier gates and a center gate for a quantum dot-potential control, showed voltage gains larger than unity due to tight dot-potential control of the center WPG. The conductance peak position of the SET could be systematically controlled by changing the tunnel-barrier-control WPG voltages. A resistive-load single electron inverter utilizing a 3-gate WPG SET as a driver and a WPG quantum wire transistor as an active load was fabricated and it showed a proper inverter operation at 1.6 K and realized a logic transfer gain of larger than unity (1.3) for the first time in III-V semiconductor-based SET inverters. A III-V semiconductor-based complimentary inverter utilizing two 3-gate WPG SETs was also successfully fabricated for the first time and the inverter operation was also confirmed at 1.7 K.
Coulomb Blockade Related to an Anti-localization Effect in External Environment in an Array of Single Tunnel Junctions/Carbon Nanotubes
Authors: Haruyama Junji , Takesue Izumi , Hasegawa Tetsuro , Sato Yuki
Published: October 2002

We report on Coulomb blockade caused by a high-impedance external electromagnetic environment (EME) related to a localization effect in a single tunnel junctions/Carbon nanotubes system. Observed Coulomb blockade, supported by a linear temperature dependence of zero bias conductance, mathematically follows phase correlation theory, which explains the roles of EME and implies that tunneling of electrons is suppressed by transferring the energy to its EME with a total impedance Z
t(ω) higher than quantum resistance. Our high Z
t(ω), however, is strongly associated with anti-localization effect without any energy dissipation but actually contributes to Coulomb blockade, because its phase modulation by magnetic field modulates also Coulomb blockade. Is the energy transfer to such high impedance EME actually indispensable for Coulomb blockade?
Temperature Dependence of kBTC Noise in “Coulomb Blockade” Regime
Authors: Kenshi Tada Kenshi Tada , Yoshinobu Fujii Yoshinobu Fujii , Kenji Taniguchi Kenji Taniguchi
Published: October 2002

Thermal noises in single-electron tunneling (SET) devices are categorized in detail into two noise components. Numerical simulation based on the `orthodox' single-electron theory revealed that the first noise component, due to electron tunneling across tunnel barriers, depends on the external bias point at low temperatures. The second noise component, caused by charge polarization on electrodes, shows no external bias dependence, which cannot be expressed by the `orthodox' theory. In the “Coulomb blockade” region, the second noise component was found to play a principal role in the thermal noise behavior of SET circuits.
Optical Up-Conversion Processes in InAs Quantum Dots
Authors: Paskov Plamen P. , Holtz Per-Olof , Monemar Bo , Garcia Jorge M. , Schoenfeld Winston V. , Petroff Pierre M.
Published: October 2002

Up-converted photoluminescence (UPL) in InAs/GaAs self-assembled quantum dots (QDs) is reported. With a resonant excitation of QDs we observe an efficient emission from the GaAs barrier. The excitation spectrum of the UPL shows that the signal disappears if the excitation energy is tuned below the absorption band of the QDs. The intensity of UPL exhibits an almost quadratic dependence on the excitation intensity. The observed effect is explained by a two-step two-photon absorption process involving quantum dot states as intermediate states.
Optical Study of Strain-Induced GaAs Quantum Dots
Authors: Nishibayashi Kazuhiro , Okuno Tsuyoshi , Mishina Tomobumi , Sugou Shigeo , Ren Hong-Wen , Masumoto Yasuaki
Published: October 2002

The excitation-intensity-dependent nonlinear luminescence as well as the luminescence of strain-induced GaAs quantum dots (SIQDs) was studied. The luminescence spectrum of SIQDs was composed of three well-resolved transitions and each transition had a different saturation excitation intensity. The increase and saturation of luminescence was more clearly seen in the nonlinear luminescence, where the saturation excitation intensities for each energy level were demonstrated to be proportional to the degeneracies of each level. The nonlinear luminescence spectra were simulated by rate equations, taking account of the relaxation rate, the recombination rate, and the state-filling effect caused by Pauli blocking. As a result of fitting, the relaxation rate was estimated to be about 30 ps.
Does a Randomly Organized Electrical Circuit Function as a Neuronal System?
Authors: Kiyoshi Kawamura Kiyoshi Kawamura , Yasuhiro Funabashi Yasuhiro Funabashi , Satoru Morita Satoru Morita , Kazumi Omata Kazumi Omata , Ken-ichi Oshio Ken-ichi Oshio , Yuko Osana Yuko Osana , Kotaro Oka Kotaro Oka
Published: October 2002

It is argued that a randomly fabricated electric circuit functions as an information processor. Indeed, the neuronal system of Caenorhabditis elegans (C. elegans) is a random network which processes various information for the survival of the worm. After properties of the connectivity of the neuronal system of the worm are reviewed to emphasize its randomness, it is confirmed that a network of resistors, which is topologically homologous to the neuronal network of C. elegans, can encode a decision table which is similar to the decision table of the native responses of the worm. Some structural properties, which are advantageous for the functioning of a random resistor network for an information processor, are discussed. In addition, it is suggested that a network of resistors with these propeties is a bundle of intertwisted
wires connected by some resistive particles.
A Double Quantum Dot as an Artificial Two-Level System
Authors: van der Wiel Wilfred G. , Fujisawa Toshimasa , Tarucha Seigo , Kouwenhoven Leo P.
Published: October 2002

We study an artificial two-level system formed by a double quantum dot. Microwave spectroscopy experiments are discussed, in which we show that the inter-dot coupling can be tuned from ionic-like to covalent-like. The current through the double dot system is dependent on the applied microwave power and, in case of strong inter-dot coupling, the separation between the bonding and anti-bonding state is power dependent as well. We measure the elastic and inelastic transitions between the two levels. The inelastic transition rates are well described by Bose-Einstein statistics. Acoustic phonons are the most effectively coupled bosons in the solid-state environment of the two-level system.
P-type Polycrystalline Si Films Prepared by Aluminum-Induced Crystallization and Doping Method
Authors: Matsumoto Yasuhiro , Yu Zhenrui
Published: October 2002

P-type polycrystalline silicon films were prepared by aluminum-induced crystallization and doping. The starting material was hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition on glass substrates. An aluminum layer with a different thickness was evaporated on the a-Si:H. Conventional thermal annealing was performed for crystallization. X-ray diffraction and secondary ion mass spectroscopy measurements were used to study the structural change and the Al profile in the films. Resistivity, Hall mobility, carrier concentration and spectral optical transmittance were measured to evaluate the electrical and optical properties of the films. Results showed that poly-Si films could be obtained by annealing a-Si:H films at 450 to 550°C for 5 to 60 min. In spite of a relatively high oxygen impurity content in the films, they are p-type, with low resistivity, high Hall mobility and carrier concentration of 0.06 (Ω·cm), 20 cm2/Vs and ∼1018 cm-3, respectively. This technique has great potential for solar cell mass production using low-cost glass substrates.
F Atom Adsorption on the Fluorinated Si(001) Surface
Authors: Ezaki Takahide , Ohno Takahisa
Published: October 2002

First-principles pseudopotential total-energy calculations have been performed to investigate the adsorption of a F atom on the F-terminated Si(001)-2×1 surface. We have determined several stable sites for the adsorbed F atom where energy differences and energy barriers between these adsorption sites are relatively small. It is shown that the incoming F atom can be adsorbed on the fully fluorinated Si(001) surface and break the substrate Si–Si bonds, which is contrary to the results of previous empirical potential simulation.
Anomalous Surface Amorphization of Si(001) Induced by 3–5 keV Ar+ Ion Bombardment
Authors: Kaoru Nakajima Kaoru Nakajima , Hisami Toyofuku Hisami Toyofuku , Kenji Kimura Kenji Kimura
Published: October 2002

The process of amorphization of Si(001) by 3–5 keV Ar+ ion bombardment is investigated using high-resolution Rutherford backscattering spectroscopy (RBS)/channeling with a depth resolution of ∼0.6 nm. Particular emphasis is placed on the effect of knocked-in oxygen atoms from a native oxide layer which usually exists at the surface in the industrial processes. No essential difference is observed in the amorphization process between the Si(001) wafers with and without a native oxide layer, showing no important role of the knocked-in oxygen in the amorphization process. The amorphization is found to proceed from the surface instead of from the projected range of the implanted ions or the peak depth of the ion-induced defects. The observed results can be explained in terms of preferential defect clustering at surfaces.
Distributions of Interface States and Bulk Traps in ZnO Varistors
Authors: Yasuhiro Ohbuchi Yasuhiro Ohbuchi , Toshio Kawahara Toshio Kawahara , Yoichi Okamoto Yoichi Okamoto , Jun Morimoto Jun Morimoto
Published: October 2002

The distributions for the activation energy E
T and the capture cross section σ of deep levels were studied by spectral analysis of deep level transient spectroscopy (SADLTS) in order to characterize precisely the bulk traps and the interface states in the Pr- and Bi-type ZnO varistors. Three bulk traps (B1′, B1 and B2) were observed by SADLTS. The origins of B2 and B1 appear to be the intrinsic defects of ZnO because these traps were not affected by various additives and E
T and σ of these traps in both types of ZnO showed almost identical distributions. The distribution of B1' in Bi-type ZnO varistors was different from that of B1′ in Pr-type ZnO varistors. This indicates that B1' is caused by the defects induced by either Bi or Pr ions, because the additives can change the forming process. Four interface states in Bi-type ZnO varistors (T0, T1a, T1b and T2) and two interface states in Pr-type ZnO varistors (T0 and T1) were clearly found. T2 was only detected for Bi-type ZnO varistors and had a slower time constant with broadening in the emission rate than the other interface states. The origin of T2 is considered to be the level relating to the spinel particle of Sb. T0, T1a and T1b are the discrete interface states. The distributions (ΔE
T and Δσ) yield data which is important in terms of understanding the characteristics of ZnO varistors.
Impurity Doping and Electrical Properties of GaAsP Heteroepitaxially Grown on GaP and Si by Metalorganic Molecular Beam Epitaxy
Authors: Nakamura Kazuhiro , Itoh Mitsunari , Yoshimoto Masahiro , Saraie Junji , Matsunami Hiroyuki
Published: October 2002

Impurity doping and electrical properties of GaAsP layers have been studied. Samples used in this study were GaAsP heteroepitaxially grown on GaP and Si substrates by metalorganic molecular beam epitaxy (MOMBE), using triethylgallium (TEGa), tertiarybutylarsine (TBAs) and phosphine (PH3) as source gases. Diethylzinc (DEZn) and tetraethyltin (TESn) were used as p- and n-type doping gases, respectively. Carrier concentrations of 5 ×1019 cm-3 for Zn-doped GaAsP and 2 ×1018 cm-3 for Sn-doped GaAsP were achieved. A GaAsP p-n diode was fabricated on a Si substrate, and its current–voltage characteristics were examined.
Dependence of Buffer Layer on the Distribution of InAs Quantum Dots
Authors: Kim Hyo Jin , Park Young Ju , Min Byung Don , Hyon Chan Kyeong , Park Se Ki , Kim Eun Kyu , Kim Tae Whan
Published: October 2002

We have investigated the dependence of the distributions of InAs quantum dots on the thickness of GaAs buffer layers grown on 2°-off (100) GaAs substrates by metalorganic chemical vapor deposition. When the thickness of the GaAs buffer layers was changed from 7 ML to 70 ML, the terrace widths were transformed from 25 nm to 75 nm due to the bunching effects of Ga adatoms. The magnitudes of the size and the density of InAs quantum dots on 2°-off GaAs (100) substrates, whose terrace widths, were changed by the thickness of the GaAs buffer layer, were successfully manipulated. Wire-shaped InAs quantum dots could also be fabricated by controlling the size and the density of the quantum dots.
Lateral Solid Phase Recrystallization from the Crystal Seed in Ge-Ion-Implanted Amorphous Silicon Films by Repetition Rapid Thermal Annealing
Authors: Seo Jin-Wook , Kokubo Yoshitaka , Aya Yoichiro , Nohda Tomoyuki , Hamada Hiroki , Kuwano Hiroshi
Published: October 2002

Lateral solid-phase recrystallization (LSPR) from the crystal seed selectively formed by excimer laser annealing in Ge-ion-implanted amorphous silicon (a-Si) is performed by rapid thermal annealing (RTA). The process is carried out as a basic research study to grow grains in the current direction along the channel from the drain to the source in poly-Si thin film transistors. In this letter, it is shown that repetition RTA, in which on/off of the setting temperature is periodically repeated with a certain heat pulse width, suppresses the random nucleation in a-Si films and enlarges LSPR grains compared with single RTA, when the heat pulse width is sufficiently shorter than the incubation time which is the time before the onset of nucleation.
Field Emitter Magnetic Sensor with Steered Focused Electron Beam
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji
Published: October 2002

A novel field emission magnetic sensor is proposed and its operation is theoretically analyzed. The sensor comprises a dual-gate wedge field emitter with a split gate having the double role of focusing and steering the electron beam. The electron beam deflection due to the Lorentz force is compensated by appropriate potentials applied to this electrode. The modeling results have been obtained using the Simion 3D 7.0 software package. The device has high sensitivity and its operation is not influenced by fluctuations in the emission current. Arrangements of mutually normal wedge emitters can be used for two-dimensional magnetic field sensing.
Ultraviolet Photoconduction of TiO2/Ge Bilayer Film
Authors: Matsuda Satoshi , Imamura Tsuyoshi , Sunada Junji , Tatsumoto Hideki
Published: October 2002

Photoconductive TiO2/Ge bilayer films sensitive to Ultraviolet light are prepared by subsequent evaporations on quartz substrates at temperatures above 300°C for Ge and at room temperatue for TiO2. Two threshold photon energies characterize the photoconduction. One is the threshold of 2.5 eV when the photocurrent I
p begins to rise sharply irrespective of air ambience and the other is the threshold of 4.0 eV when I
p begins to decrease in vacuum. The origin of photoconduction is explained in terms of photoassisted dissociation reaction of unbound oxygen species which are induced at the interface in the non equilibrium junction of Ge and TiO2 layers. The effect of ethanol gas exposure to the sample on photoconduction is examined spectroscopically.
Electrical and Reliability Characteristics of an Ultrathin TaOxNy Gate Dielectric Prepared by O3 Annealing
Authors: Jung Hyungsuk , Sim Hyunjun , Im Kiju , Yang Dooyoung , Hwang Hyunsang
Published: October 2002

This letter describes a unique process for the preparation of high-quality tantalum oxynitride (TaO
x
N
y
) films via NH3 annealing of Ta2O5 followed by reoxidation in an O3 ambient for use in gate dielectric applications. Compared with tantalum oxide (Ta2O5), a significant improvement in dielectric constant was obtained by the ammonia treatment. Low-temperature reoxidation in an O3 ambient resulted in a significantly reduced leakage current. Compared with reoxidation in an O2 ambient, TaO
x
N
y
films prepared by reoxidation in an O3 ambient show less charge trapping under electrical stress.
Effect of Light Irradiation on Native Oxidation of Silicon Surface
Authors: Takenobu Yoshino Takenobu Yoshino , Shin Yokoyama Shin Yokoyama , Toshiaki Fujii Toshiaki Fujii
Published: October 2002

We found that shielding wafers from visible light is effective to prevent native oxidation of silicon. Hydrogen terminated p-Si(100) (8–12 Ω·cm) wafers were stored in wafer boxes under various brightness levels. The oxidation rate in a dark box (∼0 lx) is less than 0.01 nm/12 h, while that in a light box (∼1000 lx) is approximately 0.1 nm/12 h.
Determination of Anisotropic Diamagnetic Susceptibility of Polymeric Fibers Suspended in Liquid*
Authors: Yamato Masafumi , Aoki Hisashi , Kimura Tsunehisa , Yamamoto Isao , Ishikawa Fumihiro , Yamaguchi Masuhiro , Tobita Masayuki
Published: October 2002

Anisotropic diamagnetic susceptibilities of polymeric fibers in liquid suspensions determined by means of the method proposed recently by us were compared with those obtained by other methods including superconducting quantum interference device (SQUID) and magnetic torque meter. Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers and carbon fibers (CF) were used for the measurements. Both fibers exhibited positive diamagnetic anisotropy, i.e., χ
a
≡χ//-χ⊥>0, where the parallel direction is taken as the fiber axis. The values of anisotropic susceptibilities determined by these three different methods were in good agreement with each other, demonstrating the usefulness of the proposed method for the measurement of a single fiber.
Dielectric Constant Stability and Thermal Stability of Cu/Ta/SiOF/Si Multilayer Films
Authors: Lee Seoghyeong , Yang Sung-Hoon , Moon Hee-Soo , Park Jong-Wan
Published: October 2002

The effects of post plasma treatment on the dielectric properties and reliability of fluorine-doped silicon oxide (SiOF) films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) are studied. Also, the thermal stability of an electrodeposited Cu/sputtered Ta interconnect system with SiOF intermetal dielectrics was examined by annealing in a vacuum furnace. The stability of the dielectric constant of SiOF films was found to be improved by O2 post plasma treatment. Surface modification by the plasma treatment was effective for the prevention of water absorption and stabilization of the dielectric constant. The Cu/Ta/SiOF/Si system was thermally stable up to 500°C for 3 h. For the Cu/Ta/SiOF/Si multilayer structure, the plasma treatment seemed to play a significant role in suppressing the interdiffusion between SiOF and metal interconnects. By C–V measurement, the electrical stability of the Cu/Ta/SiOF/Si multilayer structure was found to be stable up to 500°C for 3 h.
Diffraction Measurement for Grating Formed in Optically Poled Polymeric Materials
Authors: Tsutsumi Naoto , Yamamoto Jun , Sakai Wataru
Published: October 2002

Recent development of all optical poling technique enables the creation of the photo-induced noncentrosymmetric polarization in the polymeric matrix. In this new method, third-order optical nonlinearity of coherent superposition between fundamental and second harmonic waves is significantly responsible for the creation of polar field which induces the noncentrosymmetric polarization (χ(2) polar structure) in the polymeric matrix. In this study, we employed a diffraction technique to investigate the gratings formed in optically poled polymeric materials. Increase of the diffraction intensity follows the increase (growth) of the second harmonic wave induced by the χ(2) polar structure. Diffraction efficiency increases with increasing film thickness up to 4.5 µm. The origin of the diffraction is ascribed to the higher-order of diffraction, i.e. the unsymmetrical grating formed at double spatial frequency between unpoled and poled fringes. These results gave direct evidence of existence of the periodic χ(2) polar structure in optically poled polymeric materials.
High-Reflectivity Semiconductor/Benzocyclobutene Bragg Reflector Mirrors for GaInAsP/InP Lasers
Authors: Madhan Raj Mothi , Jörg Wiedmann Jörg Wiedmann , Shunsuke Toyoshima Shunsuke Toyoshima , Yoshikazu Saka Yoshikazu Saka , Koji Ebihara Koji Ebihara , Shigehisa Arai Shigehisa Arai
Published: October 2002

Fabrication techniques of high-reflectivity deeply etched semiconductor/benzocyclobutene (BCB) Bragg reflectors by multiple sequential steps of CH4/H2 reactive ion etching (RIE) and O2 plasma ashing are presented. 1.55-µm-wavelength GaInAsP/InP lasers with such reflectors exhibited low threshold current and high differential quantum efficiency with high uniformity. Threshold current as low as 7.2 mA and differential quantum efficiency as high as 50% from the front cleaved facet were obtained for a laser with a 160-µm-long active region and 15 distributed Bragg reflectors (DBRs) on the rear side. The reflectivity of the 15 DBRs was estimated to be as high as 95% from the threshold current dependence on the active region length. Finally, a preliminary aging test under room temperature CW conditions showed stable operation for more than 5000 h.
Enhanced Fatigue and Data Retention Characteristics of Pb(Zr, Ti)O3 Thin Films by the Selectively Nucleated Lateral Crystallization Method
Authors: Lee Jang-Sik , Joo Seung-Ki
Published: October 2002

Fatigue and data retention characteristics of Pb(Zr, Ti)O3 (PZT) thin films by the selectively nucleated lateral crystallization (SNLC) method were investigated. By placing the top Pt electrode inside the grain and directly on the grain boundary, we measured and compared the electrical properties of PZT thin films based on the grain boundary. When there was no grain boundary underneath the top electrode, no loss in switched polarization up to 2×1011 cycles and no data loss after 30000 s of memory retention at room temperature with the Pt/PZT/Pt structure were observed. However, serious degradation of the fatigue and data retention characteristics of PZT thin films occurred when there was a grain boundary in the area studied. In this study, we show that when there is no grain boundary in the area measured, no degradation such as fatigue and retention occurs, thus the main source of degradation is the grain boundary in PZT thin films.
Ferroelectric Properties of (PbxLa1-x)(ZryTi1-y)O3 Thin Films Prepared by Modified Pulsed Laser Deposition Process
Authors: Cheng Hsiu-Fung , Ling Yung-Chien , Lin I-Nan
Published: October 2002

A two-step pulsed laser deposition (PLD) process, including PLD at a substrate temperature lower than 150°C and rapid thermal annealing (RTA) at around 550°C (30 s), has been successfully applied for growing (Pb
x
La1-x
)(Zr
y
Ti1-y
)O3, (PLZT, x=0.97, y=0.664) thin films. Fatigue-free, large remanent polarization, P
r=19 µC/cm2, (with coercive field E
c=78 kV/cm and low leakage current density J
l ≤1 ×10-5 A/cm2 at 400 kV/cm) characteristics can be achieved when a SrRuO3 layer is used as a buffer layer. Interdiffusion between layers remains pronounced when an amorphous SrRuO3 layer is used as a buffer layer, which markedly degrades the electrical properties of PLZT films. Only the crystalline SrRuO3 layer can effectively suppress the interdiffusion of species and improve the ferroelectric behavior of the PLZT films. Such a modified PLD process possesses an overwhelming advantage over the in situ PLD process in terms of its simplicity and compatibility with device fabrication processes.
Effects of Processing Routes on Structures and Dielectric Properties of Lead Iron Niobate-Lead Magnesium Niobate Binary System
Authors: Yu Youhua , Feng Chude , Li Chengen , Yang Yi , Yan Haixue
Published: October 2002

The binary system of lead magnesium niobate [Pb(Mg1/3Nb2/3)O3, PMN] and lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] has been chosen to investigate the influence of different preparation routes on the microstructures and properties by means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersion spectrometer (EDS) and dielectric measurements. It is found that for the binary system (1-x)PFN–xPMN, the change in Curie temperature is approximately linear with respect to PMN content in the range of x=0 to 0.5. With the increase in x, the Curie points shift to lower temperatures. Both calcining and sintering conditions have a non-negligible influence on the microstructure and the dielectric properties. The dielectric and other properties of samples prepared by single-step and two-step precalcination routes are compared and the possible mechanisms are discussed. Samples mixed-sintered at an appropriate temperature exhibit a different dielectric behavior, which is also discussed in detail in this paper.
Silicon-Based PbTiO3/Pb(Zr, Ti)O3/PbTiO3 Sandwich Structure
Authors: Ren Tian-Ling , Zhang Lin-Tao , Liu Li-Tian , Li Zhi-Jian
Published: October 2002

A silicon-based PbTiO3/Pb(Zr0.53Ti0.47)O3/PbTiO3 (PT/PZT/PT) sandwich structure prepared by sol–gel method is proposed. The two PT layers in the structure are used as seeding layers to improve the crystallization of the PZT ferroelectric thin films. X-ray diffraction analysis (XRD) and Energy-dispersive X-ray spectroscopy (EDX) results show that the sandwiched PZT films are well crystallized at lower temperature. Compared with the ferroelectric structure with only one PT seeding layer, the electrical and ferroelectric properties of the PZT films in the sandwich structure are further improved. The maximum dielectric constant of about 900 is obtained at the coercive field 20 kV/cm, and the remnant polarization is 19 µC/cm2. The leakage current density is less than 5×10-9 A/cm2 as the applied voltage is below 200 kV/cm. The retained polarization does not reduce clearly after 8×109 read/write cycles.