bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of absorption Fabry–Pérot modulators due to the influence of coupled cavities
Authors: Law Kwok-Keung
Published: July 2002

The influence of optical feedback from coupled cavities on the reflective responses of absorption-tunable Fabry–Pérot resonators has been examined and analyzed. The merits and improvements in performance of optical modulators utilizing the designs of coupled Fabry–Pérot resonators have been discussed. The variety of reflectivity responses available from coupled-cavity Fabry–Pérot structures provides enhanced flexibility in device designs which minimizes the sensitivity of single-cavity devices to variations in layer thicknesses and compositions, operating wavelength, and temperature.
Influence of the growth mode on the quality of metallic superlattices: The case of the (100) Felr system
Authors: Andrieu Stéphane , Snoeck Etienne , Arcade Philippe , Piecuch Michel
Published: July 2002

It is shown that it is possible to grow FeIr metallic superlattices where the growth of Fe on Ir as well as Ir on Fe is two dimensional. The two-dimensional growth is shown by the occurrence of reflection high-energy electron-diffraction (RHEED) oscillations during the growth of Fe on Ir (100) up to 4–7 planes, and during the Ir growth on the Fe surface for an unlimited thickness. Transmission electron microscopy thus shows that superlattices with flat interfaces on a large scale are obtained. The RHEED oscillations during Fe growth disappear after 4–7 deposited planes and the Fe growth becomes three dimensional. The quality of the superlattices is thus damaged by this three-dimensional growth.
Spectral narrowing of an optically pumped high-power D2O laser using the oscillator-amplifier system
Authors: Sasaki K. , Takada N. , Takahashi O. , Nagatsu M. , Tsukishima T. , Okada T. , Okajima S. , Tsunawaki Y. , Sudo S. , Sato K. N. , Kondo K. , Arimoto H. , Sato K.-I.
Published: July 2002

Spectrally narrow outputs of about 10 MHz (full width at half-maximum) are obtained from an optically pumped high-power (100 kW) D2O laser system by using the oscillator-amplifier configuration, in which a low-power single-mode output from a compact D2O laser with a short cavity length is amplified by a large D2O laser amplifier. In order to obtain spectrally narrow outputs from the amplifier, the following three conditions need to be satisfied: (1) the D2O gas pressure of the amplifier is adjusted in the range from 4 to 6 Torr; (2) the oscillation frequency of the compact laser is tuned in the range about 15–35 MHz lower than the Raman resonance frequency; and (3) the intensity of the compact laser beam injected into the amplifier is larger than about 50 W/cm2.
Pyroelectric properties of ferroelectric liquid crystal cells with chevron, bookshelf, and helical structures
Authors: O’Sullivan J. W. , Panarin Yu. P. , Vij J. K.
Published: July 2002

The pyroelectric properties of ferroelectric liquid crystal (FLC) cells possessing helical and surface stabilized structures have been investigated. Pyroelectric properties of a FLC cell depend on the applied voltage, the internal smectic layer structure, and the ratio of the cell thickness to the material pitch d/p0. For surface-stabilized FLC (SSFLC) cells, hysteresis of the pyroelectric signal was observed for both the chevron and the bookshelf structures and is explained by the intermediate domain states that arise from a distribution in the pretilt azimuthal angle. For the chevron structure a reverse hysteresis loop is observed which is explained by a stronger competitive effect of the ionic field compared to the surface anchoring forces. Cells containing helical structures are studied and for cells with a large d/p0 ratio a linear response of the signal to applied voltage is found. Possible implications of the results obtained for SSFLC cells for which the change in the spontaneous polarization in the decreasing voltage cycle occurs for a voltage lower than obtained during a voltage increasing cycle are discussed.
Measurement and analysis of lateral forces between magnets and high-T
c superconductors
Authors: Kuze Hiroaki , Onae Atsushi
Published: July 2002

In this paper we report measurements and theoretical interpretation of the lateral forces which act on YBa2Cu3Ox high-Tc superconductors in a magnetic field and on small magnets interacting with the high-Tc superconductors. The results of two types of experiments are described: In the first experiment, disk-shaped superconductor samples are moved along the symmetry plane of a pair of Helmholtz coils, the movement being perpendicular to the magnetic field of the coils. This measurement leads to the determination of the hysteresis curves of the superconductors. A Bean-type, critical-state model is considered in which the high-Tc superconductors are treated as an assembly of microscopic, spherical grains of uniform diameters. By taking the influence of the demagnetizing field and the Lorentz field into account, the magnetic response of the grains is derived. In the second experiment, a small magnet is laterally moved above the surface of a high-Tc superconductor, the axis of the magnet being kept perpendicular to the surface. It is shown that the observed lateral force is well reproduced using the grain model if an effective value of the bulk susceptibility is incorporated. The results are presented for both the sintered and melt-textured YBa2Cu3Ox, for the latter the effect of demagnetization being more important than for the former. Our treatment makes it possible to evaluate the lateral force using closed expressions without resorting to the numerical solution of the field equations.
Ferroelectric phase transition in thiourea:KBr composites studied with optical second-harmonic generation
Authors: Kroon Mark , Kroon Ron , Sprik Rudolf , Lagendijk Ad
Published: July 2002

We present results of an experimental study on the effect of the inclusion of ferroelectric thiourea particles in paraelectric amorphous KBr on the ferroelectric phase transition. The phase transition as a function of temperature has been observed with optical second-harmonic generation (SHG) of infrared light. The Curie temperature Tc shows a minimum as a function of the volume fraction x of thiourea in the composites at x=0.4. We describe the experimentally observed density dependence of the Curie temperature in a phenomenological mean-field model.
Point defect creation induced by solid state reaction between nickel and silicon
Authors: Masse J. E. , Knauth P. , Gas P. , Charaï A.
Published: July 2002

The injection of point defects into the silicon substrate consecutive to a solid state reaction between nickel and silicon was studied by transmission electron microscopy. By observation and determination of the density and size of interstitial type dislocation loops in the substrate at the different steps of the reaction, we could estimate that one interstitial is injected per 5000 nickel atoms.
Microstructural measurements of amorphous GeTe crystallization by hot-stage optical microscopy
Authors: Lu Q. M. , Libera M.
Published: July 2002

Time-resolved hot-stage transmission optical microscopy is used to characterize the nucleation and growth kinetics of amorphous GeTe thin-film crystallization. This technique provides experimental measurements of the fraction crystallized, the number of crystallites, and the crystallite size as a function of annealing time and temperature. The fraction-crystallized data are modelled using the Johnson–Mehl–Avrami formalism to give an Avrami exponent of 4, consistent with previous measurements via time-resolved reflection/transmission methods. Microstructural measurements provide sufficient data to deconvolute the individual contributions of nucleation and growth to this exponent. This work shows that crystallization of these films proceeds by nucleation at an increasing rate due to transient effects with isotropic two-dimensional growth in the film plane.
Anomalies of ohmic contacts on heteroepitaxial GaAs layers on Si after rapid thermal annealing
Authors: Wilke K. , Budnick B. , Ludwig M. H. , Heymann G.
Published: July 2002

This paper reports on resistance and capacity measurements of ohmic contacts which were deposited on heteroepitaxially grown, Si-doped GaAs layers on Si substrates. It is observed that the process of rapid thermal annealing (RTA) considerably affects the ohmic properties of subsequently deposited contacts. With rising annealing temperature, the electrical resistivity in the GaAs layer and thus, the contact resistance increased essentially. Although the chemical concentration profile of Si dopants is not changed by RTA, the number of electrically active carriers is lowered. Photoluminescence measurements confirm that Si donors on Ga sites perform a site exchange to As vacancies, thereby forming Si acceptors. The extent of this exchange process is considerably enhanced by the presence of a high dislocation density in the heteroepitaxial GaAs films.
Comparison of magnetic anisotropy and magnetization reversal in perpendicular recording media
Authors: Lairson B. M. , Liu W. , Payne A. P. , Baldwin C. , Hamilton H.
Published: July 2002

Comparisons of magnetic anisotropy and switching behavior of CoCr-based alloy and Co/Pd multilayer media were made using a vector vibrating sample magnetometer. Magnetic anisotropy energy was determined from angle-dependent measurements of the transverse magnetization, using a simple approximate expression for transverse moment versus applied field and rotation angle. Switching behavior was deduced from hysteresis and angle-dependent energy-loss measurements. The multilayers were found to switch by curling and domain wall motion, while the Co78Cr17Ta5 and Co70Cr15Ta5Pt10 media were found to switch by nearly coherent (Stoner–Wohlfarth) rotation. Plasma oxidation of the multilayers was found to slightly reduce the amount of coupling, but degraded readback amplitude to a contact recording transducer.
Dynamics of GaAs surfaces exposed to argon and hydrogen electron-cyclotron-resonance plasmas observed by real-time optical reflection spectroscopy
Authors: Weegels L. M. , Saitoh T. , Kanbe H.
Published: July 2002

The dynamics of the interaction of electron-cyclotron-resonance (ECR) plasmas with the surface of GaAs substrates are studied by real-time optical reflection spectroscopy. Analysis with a three-phase ambient/overlayer/substrate model yields information on the time-dependent composition of the near-surface region, such as the thickness, degree of amorphization, and oxide and void fraction in the overlayer. Using this technique, it is observed that the thickness of the damaged layer formed by the impact of energetic ions increases linearly with the ion energy during argon ECR sputter etching. Furthermore, the dynamics of a cleaning process with a hydrogen ECR plasma have been studied. At temperatures between 300 and 500 °C this cleaning can be characterized by a two-step process. During the first few seconds of exposure, the oxide layer is removed; in the second step, the GaAs is etched gently, which leads to a surface region with little damage to the crystal. At lower temperatures, cleaning is not successful and a thick damaged overlayer is formed.
Flicker noise in submicron metal oxide semiconductor field effect transistors with nitrided gate oxide
Authors: Triantis D. P. , Birbas A. N. , Zimmermann J. J.
Published: July 2002

Effects of the gate dielectric nitridation on the flicker (1/f) noise characteristics of submicron metal oxide semiconductor field effect transistors (MOSFETs) are reported. Low-frequency (1/f) noise measurements on nitrided and non-nitrided gate oxide MOSFETs of the same geometry have been carried out, showing different noise behavior with respect to the flicker noise amplitude and bias dependence. It is found that gate oxide nitridation not only increases the flicker noise amplitude, but also enhances the correlated mobility noise mechanism. The two orders of magnitude higher noise measured in nitrided structures is consistent with the approximately two orders of magnitude increase of the nitrided gate conductance reported in the literature.
Study of the alpha irradiation and thermal annealing of gold-doped n-type silicon
Authors: Ali Akbar , Iqbal M. Zafar , Baber N.
Published: July 2002

Deep level transient spectroscopy has been used to investigate the effects of alpha irradiation and thermal annealing on deep levels in gold-doped n-type silicon. Data on thermal annealing characteristics of the well-known gold acceptor up to temperatures as high as about 600 °C are reported. This level is found to be very stable, supporting the substitutional gold model for the acceptor center. Interaction of the gold-related defects with radiation-induced defects has been investigated using 5.48 MeV alpha particles for irradiation, combined with isochronal thermal annealing before and after irradiation. Irradiation produces the usual radiation-induced levels. A slight reduction in the gold-acceptor concentration is observed due to irradiation, contrary to an earlier reported study. A noticeable suppression of the thermal stability of this level is also observed after irradiation. The presence of gold leads to a significant enhancement of the anneal-out temperature of the well-known A-center defect. A deep level at Ec−0.34 eV, ascribed to the Fe–Au complex, is found to be enhanced by irradiation. No evidence is found to support the recently proposed gold-divacancy complex model of the gold acceptor—rather, the results strongly support the isolated substitutional impurity model for this center.
Selective compositional mixing in GaAs/AlGaAs superlattice induced by low dose Si focused ion beam implantation
Authors: Chen P. , Steckl A. J.
Published: July 2002

The Al-Ga interdiffusion induced by Si focused ion beam implantation and subsequent rapid thermal annealing (RTA) was investigated in an Al0.3Ga0.7As/GaAs superlattice structure with equal 3.5 nm barrier and well widths. Si++ was accelerated to either 50 or 100 kV and implanted parallel to sample normal at doses ranging from 1013 to 1015/cm2. The effect of rapid thermal anneal of 10 s at 950 °C was characterized by the secondary ion mass spectrometry technique. In the implanted region, the interdiffusion causing compositional mixing was significantly enhanced by the Si implantation. An ion dose as low as 1×1014/cm2 results in a two-order of magnitude increase in the interdiffusion coefficient, to a value of 4.5×10−14 cm2/s, producing a mixing effectiveness of ∼90%. In contrast, the RTA-only case produces an interdiffusion coefficient of 1.3×10−16 cm2/s and very little mixing. A strong depth dependence of the mixing process was observed at 100 keV implantation energy, with a ‘‘pinch-off’’ (more heavily mixed) region being formed at a certain depth. It is noticed that the depth where this enhancement occurred is not associated with either the maximum concentration of Si ions or of vacancies. Instead, it coincides with the positive maximum of the second derivative of the vacancy profile, which in turn represents a maximum in the vacancy injection generated by the presence of a transient vacancy concentration gradient. Based on these findings, a theoretical model was developed using vacancy injection as responsible for mixing.
Optimal simulated annealing schedules for self similar systems
Authors: Ergenzinger K. , Hoffmann K. H. , Salamon P.
Published: July 2002

The successful application of the stochastic optimization method known as simulated annealing can depend very much on the appropriate annealing schedule. While determining optimal schedules for arbitrary complex optimization problems is beyond the current scope, we here determine optimal schedules for a special class of systems with known properties. The state spaces of these special systems have the structure of self similar trees. Using methods of optimal control theory, we are able to predict the optimal schedule analytically for two distinct optimization criteria. These predictions are shown to be in good agreement with numerical results.
Two-dimensional electron gas mobility anomalies (and enhancement) in pseudomorphic AlGaAs/InGaAs/GaAs heterostructures
Authors: Litwin-Staszewska E. , Suski T. , Skierbiszewski C. , Kobbi F. , Robert J. L. , Mosser V.
Published: July 2002

Variation of two-dimensional electron gas mobility with carrier concentration ns has been examined for different modulation-doped heterostructures of AlGaAs/InGaAs/GaAs. It is demonstrated that, depending on the method, electrons are distributed among remote impurity sites and different values of mobility can be achieved for the same ns and in the same heterostructure. The origin of this finding is associated with the spatial correlations of remote impurity charges which form dipolelike objects consisting positively charged Si donors and negatively charged DX− states of the same donor. The effect of correlations causes enhancement of mobility of the order of tens of percent and can explain the appearance of the maximum on a mobility versus ns dependence.
Nuclear magnetic resonance study of proton exchanged LiNbO3
Authors: de Souza Ricardo E. , Engelsberg M. , Pacobahyba L. H. , do Nascimento George C.
Published: July 2002

Nuclear magnetic resonance (NMR) of 1H was employed to study the population of different sites in proton exchanged LiNbO3 using a variety of exchange conditions and proton donors. At least two different proton sites of vastly different mobilities were always found to be present. The ratio of their populations was measured in annealed and as-prepared samples and found to be strongly dependent upon the exchange conditions. A correlation between our NMR data and recent results obtained using other techniques is discussed in connection with various mechanisms that have been proposed for the changes in the refractive indexes.
Polarization dynamics of free carriers in CdSxSe1−x crystals
Authors: Daunois A. , Merle J.-C. , Bigot J.-Y.
Published: July 2002

The dephasing dynamics of the continuum states has been investigated in bulk CdSxSe1−x mixed crystals with two- and three-beam four-wave mixing experiments using 10 fs pulses. Decay times, varying between 17 and 4 fs as a function of the density of electron-hole pairs (8×1016–1018 cm−3), indicate efficient Coulomb scattering with reduced screening as compared to bulk GaAs. Oscillations with 18 fs period which disappear within a few tens of femtoseconds are attributed to intervalence band quantum beats damped by intraband carrier thermalization.
Grating competition for charge carriers in photorefractive bismuth silicon oxide
Authors: Khoury Jehad , Cronin-Golomb Mark , Woods Charles
Published: July 2002

Charge carrier competition between the gratings produced in degenerate four-wave mixing in bismuth silicon oxide reduces steady-state diffraction efficiency, suppresses several processes of transient diffraction efficiency, and changes the concavity of reflection grating development.
Electric-field dependence of optical absorption properties in coupled quantum wells and their application to 1.3 μm optical modulator
Authors: Huang Yimin , Wang Junfu , Lien Chenhsin
Published: July 2002

A 1.3 μm modulator using light-hole–to-electron interband Stark shift in the lattice-matched AlInAs/GaInAs coupled quantum wells (CQWs) is investigated theoretically. The operation of this device is based on the lowest-energy absorption resonance corresponding to the first light-hole–to–electron transition (ELh1→Ee1). The resonant nature of this process results in a sharp absorption peak when the incident photon energy is equal to the energy-level separation. This device utilizes the significant enhancement of the Stark effect on the electronic states and the strong field-dependence transition dipole moments. Under an applied electric field, the energy spacing between ELh1 and Ee1 changes due to the Stark shift. The contrast ratio can be improved from 8:1 for the symmetric CQW to as high as 20:1 for the proposed asymmetric CQW structure. These contrast ratios are achieved by varying the applied electric field in the 0–70 kV/cm range. This large variation of optical absorption at 1.3 μm is obtained both by the enhanced Stark shift and by varying the overlap between the hole and electron envelope wave functions with an applied electric field and Stark effect for the proposed AlInAs/GaInAs CQW system.
Electronic and intersubband optical properties of p-type GaAs/AlGaAs superlattices for infrared photodetectors
Authors: Kim B. W. , Majerfeld A.
Published: July 2002

Existing theories of electronic properties and optical transitions in quantum-well structures are extended to p-type superlattices including the two heavy- and light-hole valence bands. These theories are then used to elucidate the normal incidence optical-absorption mechanisms including the Hartree and exchange-correlation many-body interactions on the basis of the one-particle local density approximation. The effects of doping density and doping configuration on the electronic structure and the intersubband optical properties of heavily doped p-type GaAs/AlGaAs superlattices are investigated for use in infrared photodetectors. It is shown that these many-body interactions cause significant changes to the subband energy structure and the optical-absorption coefficient, and that the doping level and doping configuration have an important effect on the properties of these superlattices. Peak absorption coefficients of 6000–10 000 cm−1 for normal light incidence at photon wavelengths of 8–10 μm are predicted for p-type GaAs/AlGaAs superlattices with well doping of 2×1019 cm−3. Because of the heavier effective mass of holes in the p-type structures, as compared to the n-type structures, a relatively slower degradation of the dark current with increasing doping density is expected. This, in addition to the higher absorption values that can be achieved with heavily doped p-type superlattices, renders them highly promising for normal incidence photodetectors.
ZnS:Sm grown by metalorganic chemical vapor deposition with Cl codoping
Authors: Kato Akira , Katayama Masayuki , Mizutani Atsushi , Ito Nobuei , Hattori Tadashi
Published: July 2002

Sm-doped ZnS thin films were grown by metalorganic chemical vapor deposition using diethyl- zinc, H2S, Sm(thd)3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione), Sm(hfa)3 (hfa=1,1,1,5,5,5- hexafluoro-2,4-pentanedione), SmCl3, and HCl. The following films were prepared: an undoped ZnS, a ZnS:Sm grown with Sm(thd)3 and without HCl, a ZnS:Sm,Cl grown with both Sm(thd)3 and HCl, a ZnS:Cl grown only with HCl, and a ZnS:SmCl3 grown with SmCl3. Very little Sm was incorporated when Sm(hfa)3 was used as the dopant source. In the ZnS:Sm, the Sm was not segregated at grain boundaries, at least at concentrations below 0.2 at. %. In the ZnS:Sm and the ZnS:Sm,Cl, the (200), (220), and (311) reflections of the cubic structure that the undoped ZnS and the ZnS:Cl exhibited were not detected, and preference for the (00⋅1) hexagonal orientation became stronger. The electroluminescence spectrum of the ZnS:Sm,Cl showed three satellite peaks appearing in each of the 7 nm ranges around the three dominant peaks seen in the ZnS:Sm. The total electroluminescence intensity of the ZnS:Sm,Cl increased as a result of the appearance of the satellite peaks. While the ZnS:Sm,Cl showed photoluminescence attributed to the self-activated centers, its intensity was less than 10−2 of that of the ZnS:Cl. A model is suggested that Sm-VZn (zinc vacancy)-Cl complex centers are formed by the Cl codoping and give rise to the satellite peaks.
Deposition of ultrathin silicon dioxide film from pyrolysis of tetraethoxysilane
Authors: Ong T. P. , Tobin Philip , Mele Thomas
Published: July 2002

Study of the growth of ultrathin (≤100 Å) silicon dioxide (SiO2) films by thermal pyrolysis of tetraethoxysilane (TEOS) has been conducted. The oxide growth follows a first-order or near first-order relationship with respect to partial pressure of TEOS. The reaction appears to proceed via heterogeneous decomposition with byproduct inhibition with no incubation period. An extremely slow growth process has been investigated for depositing the SiO2 film with monolayer thickness control, which is considered to be a critical requirement for forming ultra-large-scale integrated devices.
The effect of strain on hot-electron and hole longitudinal diffusion and noise in Si and Si0.9Ge0.1
Authors: Yeom K. , Hinckley J. M. , Singh J.
Published: July 2002

Monte Carlo methods are used to model the electron and hole high-field transport in both unstrained and compressively strained silicon and silicon-germanium alloy. The data are analyzed to determine in what way the thermal noise properties of the carriers are affected by compressive, in-plane strain. Results include the longitudinal diffusion coefficient, the longitudinal noise temperature, and the longitudinal noise spectral density, for electric fields in the range of 0–20 kV/cm. The results are qualitatively similar for silicon with 1% compressive biaxial strain and for Si0.9Ge0.1/Si(001). The effects of strain are found to be more pronounced for electrons than for holes and are primarily related to changes in the conductivity effective mass.
Electron momentum relaxation time and mobility in a free-standing quantum well
Authors: Bannov N. A. , Aristov V. A. , Mitin V. V.
Published: July 2002

Kinetic characteristics of the electron transport in a free-standing quantum well are studied theoretically. The quantization of acoustic phonons in a free-standing quantum well is taken into account and electron interactions with confined acoustic phonons through the deformation potential are treated rigorously. The kinetic equation for the electron distribution function is solved numerically for nondegenerate as well as degenerate electron gases and the electron momentum relaxation time and the electron mobility are obtained. At high lattice temperatures the electron momentum relaxation time is very similar to that obtained in the test particle approximation. Its dependence on the electron energy has steps which occur at the threshold energies for the dilatational phonons because an additional electron scattering by the corresponding acoustic phonon becomes important. The first mode makes the main contribution to the electron scattering, the contributions of the zeroth and the second modes are also important, the third and the higher modes practically unnoticeable for the studied electron concentrations and quantum well width. At lattice temperatures lower than the energy of the first dilatational acoustic mode the electron momentum relaxation time dependence on energy has additional peaks (in comparison with the test particle approximation) associated with electron scattering by several lowest acoustic phonon modes. These peaks occur near the Fermi energy in the degenerate case and in the energy range of the first dilatational modes in the nondegenerate case. They are especially pronounced for the degenerate electron gas. The temperature dependence of the electron mobility is similar to that described by the Bloch-Grüneisen formula, however we obtained a smaller negative exponent in the low temperature region.
Study of poling behavior of biaxially stretched poly(vinylidene fluoride) films using the constant-current corona triode
Authors: Giacometti José A. , Ribeiro P. A. , Raposo M. , Marat-Mendes J. N. , Carvalho Campos J. S. , DeReggi Aimé S.
Published: July 2002

This article reports systematic results of corona poling measurements obtained on biaxially stretched polyvinylidene fluoride films charged in dry air. Charging was performed using the constant current corona triode. The dependence of the poling process on the sample thickness, charging current, and successive charging processes was investigated. Phase transitions from α to δ and to β phases were observed when virgin samples were corona charged. The thermal pulse technique showed that the polarization profiles during charging can be made consistently almost uniform and that the ferroelectric reorientation can be associated with the rising plateau region displayed on potential buildup curves.
Sulfur and hydrogen passivation effects on thermal stability of RuO2 Schottky contact on n-type GaAs
Authors: Kim Eun Kyu , Son Maeng Ho , Park Young Ju , Lee Jeong-Gun , Min Suk-Ki
Published: July 2002

Effects of sulfur and hydrogen passivation on the thermal stability of RuO2 Schottky contacts on n-type GaAs have been studied by treatments with (NH4)2Sx solution and hydrogen plasma, respectively. The RuO2 thin films were deposited by dc magnetron sputtering using a Ru target and a mixture of argon and oxygen gases. The thermal stability of RuO2 Schottky contacts during thermal annealing in the temperature range from 200 to 550 °C for 10 min was investigated by current-voltage (I–V) measurements and Auger electron spectroscopy. For the sulfur treated sample, the ideality factor was constant at about 1.01 in the whole temperature range and the barrier height of 0.84 eV was maintained up to 350 °C. Hydrogenation treatment, however, was not so effective in preventing the thermal degradation compared to the sulfurization process. It is confirmed that the effective sulfur passivation to enhance the thermal stability of RuO2/GaAs is responsible for the suppression of an oxidation in the interface between GaAs and RuO2.
Base transit time of GaN/InGaN heterojunction bipolar transistors
Authors: Mohammad S. N. , Morkoç H.
Published: July 2002

A theoretical analysis of the base transit time in npn GaN/InGaN heterojunction bipolar transistor has been performed. For the analysis the effect of band-gap narrowing, carrier degeneracy, and compositional grading of the base region has been considered. The analysis demonstrates that a nonuniform doping in the base region with a higher value at the emitter edge and a lower value at the collector edge together with a compositional grading is necessary for minimizing the base transit time.
Visible luminescence from branched silicon polymers
Authors: Kishida H. , Tachibana H. , Matsumoto M. , Tokura Y.
Published: July 2002

Luminescence spectra and their variation with temperature have been investigated for solid films of poly(methylphenylsilane) and its branched analogs. Introduction of branching points to the polymers enhances the broad luminescence band in the visible region while suppressing the sharp UV luminescence band due to the resonant recombination of the exciton. The intensity of the visible luminescence is observed to keep on increasing with decreasing temperature in contrast with the nearly temperature-independent intensity of the resonant luminescence. The behavior is interpreted in terms of phonon-assisted tunneling between luminescence centers and nonradiative ones.
Preparation and structural analysis of an Ag/NiO strained-layer superlattice
Authors: Kado Tetsuo
Published: July 2002

A new superlattice composed of Ag and NiO has been grown epitaxially on MgO(001) substrates by electron beam evaporation in ultrahigh vacuum. The samples were characterized by x-ray diffraction and cross-sectional high resolution transmission electron microscopy. Two component materials have different crystal structures; Ag has face-centered cubic structure and NiO has NaCl-type structure. Lattice mismatch between them is about 2%, and hence the superlattice should be classified as a so-called strained-layer superlattice. As a result of the structural analysis, it is estimated that Ag has face-centered tetragonal structure with the axial ratio c/a of 0.98–0.99 and that NiO has a tetragonally distorted NaCl-type structure with the ratio c/a of 1.04–1.05 in the superlattices, where direction of c-ax is parallel to the growth direction.
Angular-selective optical transmittance of highly transparent Al-oxide-based films made by oblique-angle sputtering
Authors: Le Bellac D. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Films with angular and spectral selectivity of the optical transmittance were produced by reactive magnetron sputtering with oblique incidence of the deposition species towards a substrate. These data could be reconciled with multiparameter fits to a model based on the Maxwell Garnett effective medium theory applied to a three-component structure with inclined columns, surrounded by voids, comprised of elongated Al particles in an Al2O3 matrix.
Effect of asymmetric barriers on performances of GaAs/AlGaAs quantum well detectors
Authors: Duboz J. Y. , Saminadayar L. , Gérard J. M.
Published: July 2002

Recently, the efficient tuning of the carrier capture efficiency of quantum well by introducing a barrier asymmetry was demonstrated [J. M. Gérard, Appl. Phys. Lett. 63, 240 (1993)]. The electron launching effect was proposed to improve the gain of multiquantum well detectors. In this article, we give experimental results on the dark current, noise, optical gain, responsivity, and detectivity of barrier asymmetric quantum well detectors. We confirm that the electron launching reduces the capture efficiency and thus improves the gain. In addition to this effect, the modification of the barrier potential profile induces a dark current reduction and a blue shift of the intersubband transition. All these effects are then taken into account for analyzing detector performances. As a result of the comparison between symmetric and asymmetric detectors, we do not see any net advantage of using asymmetric structures for improving detector performances.
Low-frequency noise measurements of AlxGa1−xAs/InyGa1−y As/GaAs high electron mobility transistors
Authors: Haddab Y. , Deveaud B. , Bühlmann H.-J. , Ilegems M.
Published: July 2002

Low-frequency noise measurements have been performed in the linear range of the I-V characteristics of pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As/GaAs high electron mobility transistors (HEMTs) grown by molecular beam epitaxy with different channel thicknesses. The results obtained show that the 1/f noise in such devices depends greatly on channel thickness. It is controlled by the penetration of the electron wavefunction into the barrier as well as by Coulombic effects for thin channels and by the increase in dislocation concentration for thick ones. Generation-recombination (G-R) noise is also present. It is mainly due to real-space transfer of electrons between the two-dimensional electron gas in the channel and the conduction band minimum in the AlxGa1−xAs barrier. Similar results were obtained for the G-R noise of Al0.22Ga0.78As/In0.20Ga0.8As/GaAs, Al0.3Ga0.7As/GaAs, and Al0.48In0.52As/In0.47Ga0.53As/InP HEMTs.
Comparison of P and Sb as n-dopants for Si molecular beam epitaxy
Authors: Nützel J. F. , Abstreiter G.
Published: July 2002

The incorporation properties segregation, activation, and desorption in Si molecular beam epitaxy of phosphorus (P) are investigated experimentally in comparison to antimony (Sb) over a temperature range from 300 to 900 °C with Secondary Ion Mass Spectroscopy and electrochemical Capacitance/Voltage measurements. P exhibits superior properties over the full temperature range.
Temperature dependence and effect of series resistance on the electrical characteristics of a polycrystalline diamond metal-insulator- semiconductor diode
Authors: Kang W. P. , Davidson J. L. , Gurbuz Y. , Kerns D. V.
Published: July 2002

Temperature dependency and the series resistance effect on the electrical characteristics of a polycrystalline diamond-based (Au/Ti)/undoped-diamond/doped-diamond metal-insulator- semiconductor Schottky diode were investigated in a temperature range 25–300 °C. The current-voltage (I-V) characteristics of the device show rectifying behavior with the forward bias conduction limited by series resistance. Over the temperature range investigated, the I-V data confirmed that the conduction mechanism of the diode is controlled by thermionic field emission. Modifying the thermionic field emission equation to include the series resistance model allows the ideality factor and barrier height of the Schottky diode to be calculated. Temperature dependence of the ideality factor and apparent barrier height was determined. By extrapolating the forward saturation current data, the evaluated ideality factor was observed to decrease from 2.4 to 1.1 while the apparent barrier increased linearly from 0.68 to 1.02 eV in the temperature range from 25 to 300 °C. The Richardson plot, ln(I0/T2) vs 103/T, has linear characteristics and indicates a true barrier height of 0.31 eV. Analysis of the temperature-dependent series resistor measurements indicates a boron doping activation energy of 0.104 eV in the p diamond. The capacitance-voltage-frequency measurement confirmed that the measured capacitance varies with applied bias and frequency due to the presence of the Schottky barrier, impurity level, and high series resistance. Capacitance-frequency measurement at zero bias indicated that the degrading capacitance at high frequency is primarily due to the high series resistance of the bulk polycrystalline diamond.
Sidegating effect on Schottky contact in ion-implanted GaAs
Authors: Wu J. , Wang Z. G. , Fan T. W. , Lin L. Y. , Zhang M.
Published: July 2002

The sidegating effect on the Schottky barrier in ion-implanted GaAs was investigated with capacitance-voltage profiling at various negative substrate voltages. It was demonstrated that the negative substrate voltage modulates the Schottky depletion region width as well as the space charge region at the substrate-active channel interface.
CoSi2/Si1−xGex/Si(001) heterostructures formed through different reaction routes: Silicidation-induced strain relaxation, defect formation, and interlayer diffusion
Authors: Nur O. , Willander M. , Hultman L. , Radamson H. H. , Hansson G. V. , Sardela M. R. , Greene J. E.
Published: July 2002

The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si1−xGex layers were grown by molecular-beam epitaxy (MBE) and the silicides formed by different postdeposition reaction paths, were investigated using a combination of high-resolution cross-sectional transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. In two of the three sample configurations investigated, Co was deposited either (S1) directly on a strained Si1−xGex layer or (S2) on a sacrificial MBE Si overlayer on Si0.9Ge0.1. In the third sample configuration (S3) Si1−xGex was grown on a Si(001) substrate containing a buried ion-implanted CoSi2 layer. Only in sample configuration S2 was it possible to obtain a fully strained nearly defect-free CoSi2/Si0.9Ge0.1 structure. A high density of threading dislocations, corresponding to ≊60% relaxation at the Si0.9Ge0.1/Si interface, was observed in S1 while S3, in addition to the dislocations, exhibited a pronounced faceting at the CoSi2/Si interface.
Interfacial reaction in the sputter-deposited SiO2/Ti0.1W0.9 antifuse system
Authors: Baek Jong Tae , Park Hyung-Ho , Cho Kyung-Ik , Yoo Hyung Joun , Kang Sang Won , Ahn Byung Tae
Published: July 2002

The effects of annealing temperature on the interfacial reactions and the antifuse I-V characteristics of ultra thin SiO2 layer deposited on Ti0.1W0.9 substrate were investigated. The interfacial reactions were analyzed using x-ray photoelectron spectroscopy and Auger electron spectroscopy with the sample which is in situ annealed under ultra high vacuum or ex situ annealed in a nitrogen atmosphere. The surface of the Ti0.1W0.9 substrate was oxidized during sputter deposition of SiO2 layer. Ti, W oxides consist of Ti2O3 (Ti3O5), TiO2, WO2, and WO3. The WO3 and Ti2O3 decomposed into metallic W and Ti at 400 and 500 °C, respectively. The breakdown voltage of the antifuse decreased as the annealing temperature increased, due to the thinning of dielectric layer resulted from the decomposition of Ti, W oxides and the formation of metallic W and Ti. Annealing at 600 °C caused the reaction between metallic (Ti,W) and SiO2 layer and formed elemental silicon in the dielectric layer, where SiO2 layer completely lost its dielectric property. The breakdown of dielectric property might form a metallic channel in the SiO2 film, which mainly contains metallic W, Ti, and Si.
A steady-state heat conduction solution for optical disk recording using constant or periodically modulated laser irradiation
Authors: Shih O. W.
Published: July 2002

A fast method is presented for accurately calculating just the steady-state temperature in thin-film multilayers heated by continual laser irradiation. The key features are a simple coordinate transformation and a special lattice with which the steady-state portion of the heat conduction solution reported earlier [J. Appl. Phys. 75, 4382 (1994)] may be quickly and efficiently extracted. The earlier solution, expressed in terms of Fourier-transformed Green’s functions, was designed for temperature problems as typically found in optical disk recording situations. In particular, the laser irradiation was assumed to be modulated arbitrarily in time and finite in duration. As the pulse length increases, though, both execution time and memory requirements increase. Thus when long laser pulses are used to model continual laser irradiation, the numerical performance may degrade to unacceptable levels. For the case of periodically modulated laser irradiation (including constant laser irradiation as a special case) which is important for magneto-optical disk recording, the time and memory requirements can be reduced substantially by defining a new coordinate and lattice system in the space spanned by the time and scan directions. In frequency space, the new lattice filters out the frequencies which contribute to the transient part of the solution and retains only the frequencies which contribute to the steady-state part. The temperature formulas themselves remain unchanged; they are merely evaluated over a specially defined lattice which yields just the steady-state temperature more quickly. This paper describes the new coordinate and lattice systems, discusses some numerical issues, and compares the results of the steady-state theory to the results of the earlier original theory which includes the transients.
Unusual electric response of the dislocations and the impurity dipoles in KNbO3 single crystals
Authors: Ingle S. G. , Kakde R. N.
Published: July 2002

A highly unusual electric response of the dislocations and the impurity dipoles in KNbO3 single crystals has been found. The etch pits representing these defects move in the structure carrying these defects with them. This shows that the defects have associated with them structural units that are orders of magnitude larger in physical size. Naturally these units are also associated with stress fields and electric effects on account of the ferroelectric nature of the crystal. The nature of the stress fields could be determined by studying the movement of the etch pits in response to the externally applied electric fields. It is found that the impurity dipoles in the observed pseudocubic (001) surface have stress fields similar to those of screw dislocations, and the dipoles in the front and side faces have stress fields similar to those of edge dislocations. The external dc field causes rotation of the dislocation loops and, hence, changes the domain structure. It may order or disorder the dislocations, the effect being reversible. Similar effects have been observed for impurity dipoles. Several consequences of the stress fields have been considered theoretically and observed experimentally. For example, the stress fields of impurity dipoles and dislocation loops lead to their mutual exclusion. Hence, at a given place in the crystal the domain structure is nucleated either by the dislocation loops or by the impurity dipoles. The conjoint domain nucleation, sometimes possible by an impurity dipole and a dislocation loop worked out on theoretical considerations, agrees with experimental observation. Large distance mutual interaction, bulk ordering, dependence of bulk ordering on the density of defects, and domain nucleation have all been explained on the basis of the structural units associated with the impurity dipoles and the dislocation loops.
Critical layer thickness in metal organic chemical vapor deposition grown InGaAs/GaAs strained quantum wells
Authors: Zhang Xiaobo , Briot Olivier , Gil Bernard , Aulombard Roger
Published: July 2002

A series of In0.14Ga0.86As/GaAs quantum well structures have been grown by metal organic chemical vapor deposition (MOCVD). The measured dependence of photoluminescence (PL) energies on well width is compared with calculation. By the energy shift, line width, and intensity change of PL spectroscopy, critical layer thickness has been identified. The critical layer thickness obtained for MOCVD-grown material was found in agreement with theoretical value, but is smaller than material grown by molecular beam epitaxy.
Synchrotron-radiation-induced photodoping using disilane molecular-beam epitaxy: Low-temperature high doping of B
Authors: Utsumi Yuichi , Akazawa Housei
Published: July 2002

Synchrotron-radiation (SR) -induced doping of B has been demonstrated using disilane molecular-beam epitaxy. By SR irradiation, B incorporation is enhanced by two to five times compared to growth without SR irradiation at 550 °C. Doped epitaxial film can be obtained using SR even at 80 °C where conventional gas-source molecular-beam epitaxy cannot, so far, achieve Si epitaxy. It was found that B concentration has linear dependence on the decaborane partial pressure. This suggests that the B incorporation is limited by the photolysis of decaborane and the photoinduced removal of hydrogen from adsorbed B hydrides. It was also observed that the electrical activation rate of B is enhanced by SR irradiation especially in the region where B concentration is close to the solid solubility.
Density fluctuations in hard-sphere systems
Authors: Fishman R. S. , Hill E. F. , Storsved T. K. , Bierwagen G. P.
Published: July 2002

In order to understand the effects of density fluctuations in composite systems, we have studied the effects of compression rate on the final density and density variations in a system of hard spheres. Systems of 900 and 1800 mono-sized spheres are placed in a box with periodic boundary conditions in the x and y directions and walls at z=0 and z=w(t). Using hard-sphere interactions between the particles, the cell is compressed at a constant rate κ∝−dw/dt under isothermal conditions until the pressure diverges and an overlap occurs between the particles or with the walls. The final particle volume is then subdivided into smaller cells, each containing about 15 particles with a local density p(x). Macroscopic fluctuations in the density are measured by the coarseness parameter Cp=σp/p̄, where σp is the standard deviation of the local densities and p̄ is the average density. Surprisingly, the coarseness reaches a maximum at intermediate compression rates and, within the range of compression rates studied, the most homogeneous particle packings are generated by fast compressions. For compression rates above 1, the distribution function of the local densities is a Gaussian with a mean close to the random dense packing value p(x)≊0.64. For compression rates below 1, local regions vary from randomly dense-packed [p(x)≊0.64] to close-packed [ p(x)≊0.74] with a correspondingly high coarseness. So for κ<1, the distribution function is bimodal with peaks near the random-dense packing and the close-packing values. At the highest compression rates, the pressure exhibits no anomalies and the radial distribution function shows no signs of crystallization. Consequently, the densities and coarseness are very reproducible. At slower compression rates with κ<1, large variations in the final densities and coarsenesses coincide with the formation of local crystallites in portions of the volume.