bluuebunny/crossref_metadata_2025 huggingface dataset:
Perturbation of the luminescent silicon emission by adsorbed dyes
Authors: Gorbounova Olga , Mejiritski Alexander , Torres-Filho Afranio
Published: July 2002

Fluorescent dyes have been used to impregnate partially oxidized porous silicon produced by stain etching. The properties of the structures produced have been studied by photoluminescence (PL) and IR spectroscopies before and after extensive solvent extraction of the dye. PL spectra from extracted wafers are different from nonextracted ones and show, most of the time, three peaks. One peak at 700 nm is assigned to luminescent silicon before the dye impregnation; a second emission peak resembles the dye luminescence from solution, and a third peak at 630–670 nm is attributed to silicon emission perturbed by the adsorbed dye. A model is proposed to account for this new peak, by including band splitting due to the adsorption of the dye molecules.
Structural modifications of aluminum-polyethylene terephthalate-aluminum systems as evidenced by thermally stimulated polarization currents
Authors: Thielen A. , Niezette J. , Feyder G. , Vanderschueren J.
Published: July 2002

The relaxation of thin aluminized polyethylene terephthalate (PET) films was investigated by means of the thermally stimulated polarization current method with the aim of evidencing structural modifications occurring during thermal treatment carried out under various conditions. The occurrence of a marked change in the charge exchange properties of the Al-PET interfaces upon annealing, previously advocated from thermally stimulated depolarization current measurements, has been confirmed. Molecular orientation and free-volume relaxation are shown to be determining factors governing the polarization processes in thin PET films.
Finite-time optimum refrigeration cycles
Authors: Ait-Ali Mohand A.
Published: July 2002

A class of conceptual optimum refrigeration cycles is considered with a fixed overall heat conductance and a specified refrigerant operating temperature range to bound the optimization problems. These cycles deal with maximum refrigeration power, maximum refrigeration load, and maximum heat rejection load for the case of a heat pump. The resulting one degree of freedom problems are solved with a variable arithmetic mean temperature difference in the heat exchangers. The maximum refrigeration power solution yields an analytical closed form optimality rule which constitutes a close lower bound solution to the maximum refrigeration load and maximum heat rejection load problems.
Study of molecular-beam epitactic growth of GaAs on (100) ScxE1−xAs/GaAs
Authors: Zhu Jane G. , Palmstro/m Chris J. , Carter C. Barry
Published: July 2002

The growth of GaAs on (100)ScxEr1−xAs/GaAs (x=0 and 0.3) by molecular-beam epitaxy has been studied using transmission electron microscopy. The initial stages of the three-dimensional growth of GaAs on lattice-matched Sc0.3Er0.7As have been investigated at different growth temperatures. Besides (100) epitactic GaAs, there are also areas of {111}- and {122}-oriented GaAs observed on ScxEr1−xAs. The latter has a simple twin relationship with the neighboring (100) GaAs. Areas of {111}-oriented GaAs have been observed only at growth temperatures above 400 °C and with moderate growth rates. The GaAs islands grown at 480 °C are faceted on {110} and {111} low-index planes. These GaAs islands are elongated along 〈011〉 directions. The anisotropy of the island shape is greater at higher growth temperatures. The growth of GaAs on ScxEr1−xAs as islands is considered to be due to chemical rather than strain effects. The morphology of GaAs layers grown on ScxEr1−xAs is shown to have a strong dependence on the growth conditions.
The influence of annealing on the interface properties of low-dose Si implanted n-layers in semi-insulating InP
Authors: Molnar B.
Published: July 2002

Differential Hall measurement and secondary ion mass spectrometry have been used to characterize the influences of room temperature Si implantation and annealing on the electrical properties of n-layers formed by direct implantation into liquid-encapsulated-Czochralski grown, Fe-doped InP substrates. The Si activation is affected by the background Fe level. The anneal-time influenced the electron mobility near the channel-substrate interface. Mobility degradation at the interface, present with customary anneal, could be avoided using long time anneal. The mobility changes have been correlated with the changes in the Fe distribution near the interface. The customary anneal-time introduced an Fe accumulation behind Rm, the maximum of the Si profile, followed by an Fe depletion. However, after long time anneals an Fe depletion was created between the Rm and Rm+2dRp of the Si profile and the Fe accumulation shifted behind Rm+2dRp.
Infrared intersubband transitions in double-quantum wells under the electric field
Authors: Soldatenko Yu. N. , Vasko F. T.
Published: July 2002

The possibility of observation of four peak absorption caused by transitions between the pairs of ground and the first excited tunnel-coupled states in double-quantum wells (DQWs) is studied. Comparison of ordinary and differential absorption spectra for different biases is carried out. It is shown that use of differential absorption spectra is very useful for investigation of IR transitions of electrons in DQWs (sensitivity of such measurements may turn out to be sufficient for IR investigation of even single DQWs in contrast to usual experiments that should be performed multi-DQWs structures).
Optical properties of (113) GaAs/AlAs superlattices grown by molecular beam epitaxy and atomic layer molecular beam epitaxy
Authors: Bacquet G. , Hassen F. , Lauret N. , Armelles G. , Dominguez P. S. , Gonzalez L.
Published: July 2002

We have investigated the optical properties of GaAs/AlAs superlattices grown by molecular beam epitaxy (MBE) and atomic layer MBE (ALMBE) on {113}A-oriented GaAs substrates. The corrugation which appears in the samples obtained by MBE does not exhibit any periodicity. Phonon-associated replicas are only observed on the photoluminescence excitation spectra of ALMBE superlattices. It was found that the observed differences can be attributed to the growth techniques employed in the synthesis of the samples: MBE superlattices have rougher interfaces than the ALMBE ones, but a lower number of nonradiative recombination centers.
Electric-field induced converse piezoeffect in screw dislocated YBa2Cu3O7−δ thin films
Authors: Sergeenkov Sergei A.
Published: July 2002

A possibility of electric-field induced converse piezoeffect in screw dislocated thin YBa2Cu3O7−δ films is discussed. The magnitude of this effect, which is due to a strong polarization of heavily dislocated thin films in applied electric field, is found to depend concurrently on the film thickness and the number of dislocations in a sample.
Determination of depth profiles of E″ defects in irradiated vitreous silica by electron paramagnetic-resonance imaging
Authors: Sueki Minoru , Austin William R. , Zhang Lin , Kerwin David B. , Leisure Robert G. , Eaton Gareth R. , Eaton Sandra S.
Published: July 2002

Samples of vitreous silica with OH content <2 ppm (‘‘dry ’’) or 1200 ppm (‘‘wet ’’) were irradiated with x rays from Cr, Cu, and Mo tubes, and with γ rays from a 137Cs source (661 keV). Front surface doses ranged from 51 to 1800 Mrad. For each energy of the photons the number of E′ defects produced per megarad of radiation was higher for the ‘‘wet ’’ samples than for the ‘‘dry ’’ samples. The spatial distribution (depth profile) of the E′ defects was measured by spectral-spatial electron paramagnetic-resonance (EPR) imaging. Defects produced by the high-energy 137Cs γ rays were uniformly distributed through the 1.0 mm thickness of the samples. For the x rays, the EPR signal intensity decayed with distance into the sample, the decay being strongest for the lowest photon energies. The EPR profile was compared with the spatial distribution of the energy deposition (dose profile). The basic features of the EPR profile are determined by the dose profile, but in some cases there appears to be enhanced defect production near the surface of the sample.
Lattice instability analysis of a prototype intermetallic system under stress
Authors: Cleri Fabrizio , Wang Jinghan , Yip Sidney
Published: July 2002

The unstable structural responses of a model intermetallic lattice to hydrostatic and uniaxial loadings have been determined by elastic stability analysis and molecular-dynamics simulations. Two crystalline phases of Ni3Al, the naturally occurring L12 and a hypothetical D022, are analyzed to correlate the effects of structural symmetry with stress-induced lattice deformations. Under isotropic expansion, the former fcc lattice develops extensive cavitation and amorphization at critical isotropic tensile loading, whereas the latter, a tetragonal lattice, shows cleavage behavior. These qualitative differences do not appear in the elastic stability analysis. Both phases show similar responses to uniaxial tension. In all cases critical strains for lattice instability predicted on the basis of elastic stiffness coefficients are found to be in good agreement with direct simulations.
A simple numerical simulation model for space charge field formation in photorefractive materials
Authors: Turalski Wojciech , Miniewicz Andrzej
Published: July 2002

A simple numerical simulation model of space charge field formation in photorefractive materials is presented. The model considers microscopic statistical events occurring during writing of a phase grating by a light intensity pattern in weakly photoconducting materials. The model properly describes many characteristics of photorefraction phenomena found in the literature.
Reply to ‘‘Comment on ‘Equation of state of aluminum nitride and its shock response’ ’’ [J. Appl. Phys. 78, 5854 (1995)]
Authors: Dandekar Dattatraya P. , Abbate A. , Frankel J.
Published: July 2002

This reply reinforces the need for examining the internal consistency of longitudinal and lateral stress data under plane shock wave propagation. This was pointed out in an article by Dandekar, Abbate, and Frankel [J. Appl. Phys. 76, 4077 (1994)] to determine the shear strength of a solid. It also shows that shear strength of a crystalline solid under plane shock wave compression can be determined accurately from its reliable Hugoniot and applicable hydrodynamic compression of the solid.
Modification of the adhesion and contact resistance of the Ag/YBa2Cu3O7 interface with keV electron irradiation
Authors: Moss S. D. , O’Sullivan R. A. , Paterson P. J. K. , Snook I. K. , Russo A. J. , Katsaros A. , Savvides N.
Published: July 2002

The effect of 3.5 keV electron irradiation on adhesion and contact resistivity of the Ag/YBa2Cu3O7 interface has been studied using an evaporated silver layer on c-axis oriented superconducting YBa2Cu3O7 thin films. Electron doses ranged between 1016 and 1018 electrons/cm2. The Q-tip method of adhesion testing showed that even at the lowest electron dose adhesion is significantly improved. The contact resistivity of the interface was measured using a cross-junction four-point probe. Contact resistivity was unchanged at the lowest electron dose but increased as the electron dose increased. A theoretical model involving an electron irradiation damaged layer at the interface has been developed to explain measured contact resistivity changes.
Numerical simulation of limiting currents for transport of intense relativistic electron beams in conducting waveguides
Authors: Rose D. V. , Guillory J. U.
Published: July 2002

The space-charge limiting current for an intense, magnetized, relativistic electron beam injected into a grounded metallic pipe is investigated with a 2(1/2)-dimensional particle-in-cell code. Comparisons between the simulation results, the well known Bogdankevich-Rukhadze limiting current, and more recent theoretical estimates of the limiting current are presented. Transmitted currents ≳15% above those predicted by the Bogdankevich–Rukhadze and other limiting current estimates are observed. However, good agreement between the simulation results and the analytic estimates of Uhm [Phys. Fluids B 5, 1919 (1993)] and Fessenden [Lawrence Livermore Lab. Rep. No. UCID-16527 (1974)] is found. For an injected current above the limiting value, a virtual cathode is formed which alters the transmitted current density profile of the beam. A theoretical estimate of the magnitude of the transmitted current under this condition is compared with simulation results. The predicted transmitted current is found to be valid only for injected currents slightly above the limiting current. In addition, the transition between vacuum and ion-focused-regime transport, with and without an applied axial magnetic field is simulated. For ion-focus-regime densities (np ∼ nb), the effect of the virtual cathode in limiting the beam transmission is greatly diminished as expected.
Observation and analysis of conductance oscillations in scanning tunneling microscopy of clean InP(110) surfaces
Authors: McAlpine N. S. , Haneman D.
Published: July 2002

We have observed oscillations in the differential conductance as a function of the width of the tunneling barrier formed between the tip of a scanning tunneling microscope and a clean cleaved InP(110) surface. The oscillations were analyzed in terms of a simple model for a field emitted tunneling current that experiences a finite reflectivity at the InP(110) surface due to the step in the potential at the sample side of the tunneling barrier. Oscillations were not found at high bias in accord with the energy dependence of the reflectivity, and quantitative agreement was found between the model-implied value of the surface work function and reported data.
An impurity-related bistable defect in thermally processed silicon
Authors: Nielsen K. Bonde , Holm B.
Published: July 2002

A process-induced metastable defect in n-type silicon is reported. The defect is found close to the wafer surface after combination of ambient gas-flow annealing at ≊900 °C depending on subsequent cleaning procedure. The defect gives rise to a band-gap level Ec−Et=0.25 eV observed by deep-level transient spectroscopy after reverse-bias cooling of the sample. Both annealing and generation of the defect proceed by 1st order processes. The activation enthalpies (ΔE) and pre-exponential factors (v) have been determined from Arrhenius analyses; the results are ΔE=0.63 eV and ν=1⋅1012 s−1 for annealing, and ΔE=0.65 eV and ν=6⋅1014 s−1 for generation.
Atomic layer epitaxy of GaAs from tertiarybutylarsine and triethylgallium
Authors: Aït-Lhouss M. , Castaño J. L. , García B. J. , Piqueras J.
Published: July 2002

GaAs growth by atomic layer epitaxy (ALE) from tertiarybutylarsine (TBA) and triethylgallium (TEG) in a chemical beam epitaxy (CBE) system is reported. A stable 4×8 surface reconstruction has been observed after Ga deposition at low substrate temperatures in the absence of TBA flux. The TEG reaction rate at the sample surface has been found to be lower under ALE conditions than under CBE growth conditions. No decay in the reflection high-energy electron diffraction intensity was observed after the ALE growth of 700 monolayers of GaAs at 550 °C. Grown samples exhibit p-type doping in the range of 1015 cm−3.
Monte Carlo simulation of multiphonon capture mechanism by deep neutral impurities in Si in the presence of an electric field
Authors: Palma A. , Jiménez-Tejada J. A. , Godoy A. , Melchor I. , Cartujo P.
Published: July 2002

The multiphonon emission capture mechanism by neutral centers, in the presence of an electric field below 1 MV/cm, has been numerically simulated by the Monte Carlo method. Based on common models for the initial and final states, a simple expression of the process probability has been calculated considering both nonpolar and polar electron–phonon coupling. The validity range of this expression is assumed for a carrier energy Ek<ET, where ET is the impurity level depth. In order to check the probability rate, this mechanism was included in the framework of a previous numerical procedure as one more mechanism for calculating the capture cross section as an electric-field function. This theoretical framework is given for both polar and nonpolar semiconductors. The Pt and Au acceptor levels in Si have been analyzed with the probability expression, particularized for the case of nonpolar coupling, by fitting the available experimental data of capture cross sections with the numerical results. In both cases, the values of the Huang–Rhys parameter have been confirmed with the experimental measurements and previous theoretical calculation without the applied field. According our calculations, the experimentally observed decrease of the cross sections at high fields is attributed to carrier heating. In the range of temperatures from 77 to 300 K, the dependence of the numerical capture cross sections appears as E−3/2 with a field between 5×104 V/cm and 1 MV/cm. The temperature dependence change of the numerical cross section at high electric field is also caused by electron heating.
Positron annihilation measurements of Pr-containing superconductor compounds
Authors: Jung K. , Byrne J. G. , de Andrade M. C. , Maple M. B.
Published: July 2002

Positron annihilation lifetime and Doppler broadening energy spectra have been measured in Pr-containing YBa2Cu3O7−δ as a function of temperature between 18 and 295 K. The defect-related positron lifetime component τ2 was independent of temperature for the PrBa2Cu3O7−δ compound and was very close to the value τ1 associated with bulk or defect-free material. These results indicate that the structure of this compound is nearly free of defects which trap positrons and that there is no electronic structure change during cooling. There was a slight temperature dependence below Tc for the Y0.5Pr0.5Ba2Cu3O7−δ compound. It was also found that a change in the positron Doppler line-shape parameter S occurred at the superconducting transition temperature for 0.5 Pr-containing compound but not for the 1.0 Pr-containing compound. These results show that the average electron momentum at the annihilation sites increases as temperature is lowered across the superconducting transition range for the 0.5 Pr-containing compound but not for the PrBa2Cu3O7−δ compound.
Magnetic anisotropy and interlayer exchange coupling in the sputtered Co/Ag multilayers
Authors: Feng J. W. , Kang S. S. , Pan F. M. , Jin G. J. , Lu M. , Hu A. , Jiang S. S. , Feng D.
Published: July 2002

The in-plane uniaxial anisotropy and perpendicular anisotropy of sputtered Co/Ag(111) multilayers have been investigated by magnetic measurements and the in-plane ferromagnetic resonance (FMR) technique. The data-fitting analysis for the FMR experimental results about the angular dependence of the resonance field shows that the in-plane anisotropy cannot be fully described by only using the first-order term, and the second-order term must be included. Furthermore, the interface-induced anisotropy has been obtained by FMR. Both ferromagnetic and antiferromagnetic couplings have been revealed by hysteresis loop measurement. Specifically, a spin-flip phase transition has been observed in the sputtered Co/Ag(111) multilayers, which is attributed to the effects of the AF-coupling and in-plane uniaxial anisotropy.
Free electron laser dynamics, evolution of the bunching coefficients, and coherent harmonic generation
Authors: Dattoli G. , Giannessi L. , Ottaviani P. L. , Segreto A.
Published: July 2002

Free electron laser dynamics is characterized by the interplay between bunching and emission processes. The first mechanism can be quantitatively specified in terms of the so-called bunching coefficients, which determine the degree of the bunching at the fundamental and higher harmonics. We numerically solve the Liouville equation, which rules the longitudinal phase-space dynamics, and evaluate the bunching coefficients and associated harmonic generation. We develop a semianalytical method to study the harmonic generation and evolution in free electron laser oscillators.
Observation of systematic deviations of period in W/Si and W/C multilayers
Authors: Wu Liwen , Jiang Zuimin , Liu Wenhan , Zhang Shuyuan , Wu Ziqin
Published: July 2002

Cross-sectional transmission electron microscopy, selected area electron diffraction, and small-angle x-ray diffraction have been used to observe the systematic deviations of period in W/Si and W/C multilayers. The mean periods decreased gradually as the detected regions were located farther away from the substrate. To avoid destroying the multilayer, a method is suggested to measure the systematic deviation of period by using soft x rays with wavelengths below and above an absorption edge and hard x rays such as Cu Kα1.
A spectroscopic ellipsometry study of the interfacial stresses and their correlation with microvoids in very thin thermally grown SiO2 films
Authors: Logothetidis S. , Boultadakis S.
Published: July 2002

The intrinsic stress in the interfacial region of the SiO2/Si interface was estimated, with in situ spectroscopic ellipsometry (SE) during a dry etching process of thermally grown oxides, to be 3.8 kbar. Furthermore, the microvoids distribution, in very thin thermally grown SiO2 films studied with ex situ SE, was found to be correlated with the stress distribution in the direction of the oxide growth. The voids volume fraction exhibits an exponential decay behavior versus the oxidation time with a relaxation time similar to the strain relaxation time reported in the literature. The SE-calculated voids relaxation time, 60 min (12 min) for oxides grown at 900 °C (1000 °C), is also predicted from IR results obtained through the dependence of the Si–O stretching frequency on the oxidation time.
Antimony implantation into Si-B doping superlattices—damage and enhanced diffusion
Authors: Krüger D. , Jagdhold U. , Kurps R. , Zeindl H. P.
Published: July 2002

The influence of a heavy Sb ion implantation and subsequent annealing cycles in the temperature range of 800–1000 °C on B-delta doping superlattices in silicon layers grown by molecular beam epitaxy (MBE) was analyzed. Secondary ion mass spectroscopy (SIMS) measurements of these structures are used to investigate the generation and diffusion of point defects. The enhanced diffusion of B from the delta doping spikes in as grown and Sb implanted layers was theoretically described by solving the diffusion equation using the point defect model of TSUPREM−4 for different initial point defect distributions. To fit the experimental SIMS profiles the positively charged B-interstitial diffusion coefficient was changed from the default value of D=0.68 cm2/s to D=0.45 cm2/s. It was found that the given MBE growth process produces interstitials and vacancies with an almost constant average value of about 5×1016 cm−3. The Sb-implanted B modulation doped superlattice allows us to obtain a depth profile of the defect concentration. Assuming an overlapping of a constant value of 5×1016 cm−3 for interstitials and vacancies caused by the MBE growth with a distribution coming out of a damage calculation during Sb implantation, consisting of a flat high concentration region with an exponential decrease towards the level of the MBE layer, the main features of the B diffusion profile in the superlattice could be fitted. Thus, a simple initial point defect distribution model after implantation was able to explain the experimental situation.
Hydrogen-induced quantum confinement in amorphous silicon
Authors: O’Leary Stephen K. , Zukotynski Stefan , Perz John M.
Published: July 2002

We study how hydrogen-induced quantum confinement in hydrogenated amorphous silicon influences the distribution of tail states. To do this, the potential structure of this semiconductor is treated as being comprised of an ensemble of potential wells, these wells corresponding to unhydrogenated regions enveloped by hydrogenated regions. To evaluate the distribution of states, we determine the ground state associated with each well, and then average over the distribution of wells. We find that our calculated distribution of tail states exhibits an essentially exponential functional dependence, over several decades, and that this tail of states shifts toward the band edge as the hydrogen content is increased. This shift toward the band edge is suggested to be one of the factors responsible for the observed increase in energy gap with higher hydrogen content.
Three variable modeling of switching in ferroelectric liquid crystals
Authors: Elston S. J. , Ulrich D. C.
Published: July 2002

A model of switching in ferroelectric liquid crystals is developed which represents the devices using three variables. This is a useful approach because the switching process in ferroelectric liquid crystal devices takes place through the formation and evolution of domains. The three variables used then represent the background director orientation, the director orientation within evolving domains, and the net domain area which has evolved. Setting up a system in this way allows modeling of a wide range of switching conditions in devices. The modeling is compared successfully with experimental results.
Effect of rapid thermal annealing on the structural and electrical properties of a silicon-silicon oxide system
Authors: Choi W. K. , Chan Y. M. , Ah L. K. , Loh F. C. , Tan K. L. , Ramam A.
Published: July 2002

An investigation of the electrical and structural properties of rapid thermal annealed Czochralski silicon wafers has been carried out. The electrical properties examined here are the minority carrier lifetime, measured using the laser microwave photoconductance technique, and the donor concentration (Nd), determined by the four-point probe method. Thermal donors were intentionally introduced into the silicon and were found to be completely annihilated by the rapid thermal annealing (RTA) process. The minority carrier lifetime was found to increase significantly for wafers annealed at 900 and 1000 °C. It was concluded that due to the very short annealing time used in this work, a denuded zone was unlikely to form in silicon and be responsible for the increase in the lifetime. Infrared, x-ray photoelectron (XPS) and Auger electron spectroscopies were used for the structural analysis. Auger results showed that higher oxygen concentration could be found in a thicker layer of silicon in annealed wafers, as compared to the as-received, virgin sample. The XPS data showed that the SiO2:Si ratio increased from 0.28 for the virgin sample to 3.5 for wafers annealed at 1000 °C. It is suggested that the Auger and XPS data could be explained by considering oxygen outdiffused from the bulk of the silicon to the native oxide and the silicon next to the native oxide. We believe this is the first investigation of the effect of RTA on the behavior of oxygen and thermal donors, and its influence on the minority carrier lifetime of Czochralski silicon.
Molecular beam flux measurements and equilibria for As4, P4, As2, P2, and AsP
Authors: Wood C. E. C. , Johnson F. G.
Published: July 2002

The dynamic equilibrium between P2, As2, and AsP at 1000 °C has been studied by mass spectrometry of fluxes from a double effusion cell. From simple ion gauge measurements of heated and unheated fluxes we determined the ionization efficiency for the dimers P2 and As2 relative to the tetramers, P4 and As4. Simultaneous mass spectrometer and ion gauge measurements of the effusion fluxes allowed the relative ionization sensitivities for P2, As2, and AsP to be determined. From the mass spectrometry data it was possible to determine the equilibrium constant 1.9±0.4 and free energy −0.55 eV molecule−1 for the process As2+P2■2 AsP.
Thermally stimulated currents in CdTe polycrystalline films
Authors: Ramírez-Bon R. , Espinoza-Beltrán F. J. , Vigil O. , Zelaya-Angel O. , Sánchez-Sinencio F. , Mendoza-Alvarez J. G. , Stolik D.
Published: July 2002

Investigations of trapping centers have been carried out in CdTe polycrystalline films by using the thermally stimulated conductivity (TSC) technique. The measurements were performed in the temperature range from 80 to 300 K. The TSC spectra showed three peaks related to three trapping levels with energy activations of 0.18, 0.29, and 0.32 eV, respectively. The two first trapping levels correspond to known acceptor centers in bulk CdTe previously reported. It is suggested that the level at 0.32 eV is due to grain boundary defects characteristic of the polycrystalline films. The main parameters of these trapping centers have been determined by using known theoretical relations. The temperature dependence of the dark resistivity indicates that the impurity conduction does not make an important contribution to the TSC spectra of the films. From these measurements an activation energy of 0.49 eV for the conductivity of the films was found.
Theoretical comparison of GaInAs/GaAlInAs and GaInAs/GaInAsP quantum-well lasers
Authors: Issanchou O. , Barrau J. , Idiart-Alhor E. , Quillec M.
Published: July 2002

We give a detailed theoretical study of the optical gain for compressive and tensile-strained GaInAs/GaInAlAs quantum-well lasers, including valence-band mixing. We demonstrate that with strained quantum wells, lower thresholds and higher differential gains are expected. We also show that these characteristics are even better than those of the most usual GaInAs/GaInAsP system. The good experimental results already obtained tend to confirm the theoretical expectations.
Magnetization processes in samples with modulated anisotropy under the action of nonuniform magnetic fields
Authors: García A. , López E. , Aroca C. , Sánchez M. C. , Sánchez P.
Published: July 2002

In this paper we study the magnetic behavior of amorphous ferromagnetic ribbons having helical anisotropy with the helix axis perpendicular to the sample surface. It is shown that the magnetization processes under the action of a longitudinal magnetic field can be controlled by the nonuniform field produced by an alternating current, of the same frequency than the exciting field, flowing through the sample. Hysteresis loops with very different susceptibilities and coercive fields have been obtained by varying the amplitude of the current intensity and the phase differences between the exciting magnetic field and the current through the sample.
Optimization of a high-voltage trigatron switch
Authors: Mitchell I. H. , Choi P. , Bayley J. M. , Chittenden J. P. , Worley J. F.
Published: July 2002

Work has been carried out to optimize the operation of a high-voltage trigatron switch. It is demonstrated here that the trigatron can operate in two different modes depending on the route of the initial breakdown. This initial breakdown can occur either to the adjacent electrode or to the opposite electrode. It is shown here that, for a given switch, the mode of operation depends only on the ratio of trigger voltage to working voltage. The optimization was based upon the suggestion that the optimum operation of a trigatron would occur when the trigger pin breaks down simultaneously to both the adjacent and the opposite electrodes. This occurs for the trigger to working voltage ratio, which results in equal mean electric fields across the main gap and the trigger gap. The experiments were carried out with working voltages, Vg, between −1 and −2 MV and with trigger voltage to working voltage ratios of between −2% and −8%. It is shown that the minimum delay and jitter figures are indeed obtained with the trigger voltage closest to this optimum value, Vt*. For the switch used here, this corresponded to a ratio of Vt*/Vg=−3.4%. A single switch was operated for two hundred shots with a working voltage of −2 MV and the optimum trigger voltage and gave an average delay of 44 ns with an overall jitter of 4.4 ns.
Intermixing produced by ion implantation: Case of II–VI semiconductor multilayers
Authors: Khalal K. , Chami A. C. , Ligeon E. , Fontenille J. , Hamoudi A. , Bérard G. , Cibert J.
Published: July 2002

II–VI semiconductor multilayers, containing a quantum well (ZnTe/CdTe/ZnTe or Cd0.6Hg0.4Te/HgTe/CdTe) have been implanted with Zn+ or Cd+ ions at different fluences and temperatures, and analyzed by Rutherford backscattering spectroscopy and channeling. Direct backscattering of channeled ions (He+) experiments show that the density of crystalline defects in the well increases with the fluence and the temperature of implantation, and confirms that layer intermixing takes place. A model has been used to link the accumulation of defects to vacancy trapping in the region where the vacancy free enthalpy is minimized; it happens that in the cases under study this trapping corresponds to a decrease of the elastic energy of the strained layer. Intermixing rules have also been analyzed.
Electrical conduction in ternary semiconductor Ga5Se20Te75 thin films
Authors: Das V. Damodara , Raju K. S. , Bhaskaran A.
Published: July 2002

Different thickness thin films of the ternary alloy Ga5Se20Te75 have been vacuum deposited on clean glass substrates held at room temperature at a very fast rate. The film resistance has been measured as a function of temperature during two cycles of heating and cooling. It has been found that the resistance-temperature (R-T) variation of the films during first heating and cooling is different, the R-T curve during heating lying above the R-T curve during cooling in the case of thinner films and below in the case of thicker films. There are two possible explanations for the difference in resistance variation during heating and cooling and between the thinner and thicker films. The first is due to the semiconducting nature of the material and the second is due to the removal of frozen-in defects and/or change in concentration depth profile. In addition to these, the phenomenon of self-annealing can also take place in thicker films. Log resistance vs reciprocal temperature plots are found to be linear, indicating activated conduction in the film material. It has also been found that resistance vs reciprocal thickness plot is near-linear as expected from the classical size effect theories. X-ray diffraction has established that the films are single phase. X-ray photoelectron spectroscopic (XPS) studies have revealed that the film surface is enriched with tellurium such as TeO2 [BE (3d5/2)=577 eV], in addition to the presence of selenium [BE (3d)=55.5 eV] and gallium in traces [BE (2p3/2)=1117 eV].
Reversible magnetization rotation in grain-oriented 3% Si–Fe
Authors: Birsan M. , Szpunar J. A.
Published: July 2002

In grain oriented 3% Si–Fe, the magnetization curve from saturation to remanence is mainly determined by the crystallographic texture. The saturation approach law describes the rotation of magnetization vector towards the magnetic field, which increases in strength in this region of the hysteresis curve. The orientation of the magnetization vector with respect to the easy magnetization direction can be experimentally determined measuring the torque produced by the magnetic field in a disk-shaped specimen. This torque is related directly to the spread of grain orientations and its measure allows us to evaluate different texture qualities.
Infrared studies of room temperature deposition of hydrogenated silicon oxide films in rf magnetron discharges
Authors: Bao Tien-I , Wu Ming-Shing , I Lin
Published: July 2002

The properties of a-SiOx:H thin films deposited at low temperature (∼ 50 °C) in a low energy magnetron rf plasma system with Ar/SiH4/O2 gas mixtures are investigated. In the low pressure regime (about 5 mTorr reactive gases), the surface reaction dominates in the film formation process. As the partial pressure ratio (ROS) of oxygen to silane increases, the Si-H related vibrational modes gradually disappear, and the film becomes stoichiometric SiO2 for ROS≥1. High quality oxide film can be deposited due to the low pressure environment and the plasma promoted surface process. In the high pressure regime (tens of mTorr) the deposited SiO2 films contain fine particles (tens of nanometer in size) and are porous (15% void) due to the gas phase homogeneous reaction and aggregation. The infrared absorbance spectra with normal and oblique incidence imply different origins of the half width and the shoulder intensity of the 1070 cm−1 Si-O(s) mode. In comparison with the low pressure dense films, the narrow half width of the high pressure film may be caused by the more ordered local structure which has a narrower distribution of bond angle and length, while the large shoulder intensity may be dominated by the larger (fine particle size) scale disorder.
Stable off-axis electron orbits in a longitudinal-wiggler free-electron laser
Authors: Carlsten Bruce E.
Published: July 2002

Off-axis electron orbits are investigated for a longitudinal-wiggler free-electron laser. Orbits are found that are very similar to orbits occurring for standard helical wigglers which produce transverse fields and these orbits can be classified as group-I, group-II, and reverse-group-II orbits. These orbits are shown to be stable in both first and second order from Liapounov’s first stability theorem. The stability is verified with numerical simulations.
Quantum interference in multichannel systems
Authors: Joe Yong S. , Khatun M. , Cosby Ronald M.
Published: July 2002

Quantum interference effects in four parallel channels are theoretically investigated. We attribute interference effects to the different electron paths, by calculating the difference between the conductance (electronic probability distribution) for the four channels and the sum of the conductances (probability distributions) obtained with only one channel open at a time. The large variations of the conductance difference and a periodic behavior of the difference of probability distribution indicate wave-function phase shifts and interference due to alternative electron paths through the parallel channels.
A comparison of electrochemical capacitance-voltage measurements with numerical simulations for pseudomorphic high electron mobility transistor structures
Authors: Jogai B. , Stutz C. E.
Published: July 2002

Electrochemical capacitance-voltage (EC-V) profiling is simulated numerically and the results compared with EC-V measurements for AlxGa1−xAs/InyGa1−yAs pseudomorphic high electron mobility transistor (p-HEMT) structures. The electrostatic potential is calculated at each etch step by solving the Poisson equation subject to surface pinning. The mobile charge is calculated within the Thomas-Fermi approximation. The calculated potential then forms the basis for the numerical EC-V, enabling the capacitance and apparent electron concentration to be computed. The reconstructed electron distribution has been compared with actual EC-V measurements on actual p–HEMT structures. The results affirm the ability of experimental EC-V to separate detailed features in the electron distribution, such as electrons localized in the δ layer and channel of p–HEMTs. Essentially, the reconstructed electron distribution is a warped version of the true distribution as determined from a self-consistent k⋅p calculation. In δ-doped p–HEMTs, for example, the separation between the charges in the δ layer and channel is less than the actual separation. This trend appears to agree with measured EC-V results. Subject to control over the etching uniformity, experimental EC-V should be capable of delineating detailed features in the electron distribution. Numerical EC-V has also been compared with standard capacitance-voltage (C-V) profiling. The reconstructed numerical C-V electron distribution agrees well with the numerical EC-V distribution.
Low frequency noise characterization of self-aligned InP/InGaAs heterojunction bipolar transistors
Authors: Ouacha A. , Willander M. , Plana R. , Graffeuil J. , Escotte L. , Willen B.
Published: July 2002

Low frequency noise characterization of self-aligned InP/InGaAs heterojunction bipolar transistors (HBTs) is reported. The choice of HBTs with various emitter dimensions permits the investigation of the effect of the emitter size on the low frequency noise performance of these devices. It is found that the shape of the input referred current noise spectra is changing with bias conditions. This allows for the possibility of considering that the origin of this noise could be changing from recombination noise at low bias to diffusion or minority carrier trapping 1/f noise at high bias.
Positron study of plasma-enhanced chemical vapor deposited silicon nitride films
Authors: Landheer D. , Aers G. C. , Sproule G. I. , Khatri R. , Simpson P. J. , Gujrathi S. C.
Published: July 2002

Positron annihilation spectroscopy has been combined with Auger electron depth profiling, elastic recoil detection, Fourier-transform infrared spectroscopy, and capacitance-voltage measurements to study silicon nitride films grown by plasma-enhanced chemical vapor deposition. For silicon-rich films the positron lineshape parameter is very close to that of undefected silicon, consistent with a strong hydrogen passivation effect. With increasing nitrogen content in the films, there is an increase in the number of unpassivated vacancy complexes available to trap positrons prior to annihilation. Detailed analysis gives a measure of the electric field induced in the silicon substrate by the presence of charge trapped in the silicon nitride near the interface. These results agree qualitatively with electrical measurements. Both the charge and the electric field are found to decrease with increasing nitrogen content. Incorporation of a small amount of oxygen in the films leads to a suppression of the feature in the positron spectrum associated with vacancy complexes in favor of a spectrum typical of oxygen related defects.
The hydridation and nitridation of GeSi oxide annealed in ammonia
Authors: Liu W. S. , Nicolet M.-A. , Park H.-H. , Koak B.-H. , Lee J.-W.
Published: July 2002

A 110-nm-thick Ge0.38Si0.62O2 film on Ge0.38Si0.62 was annealed in NH3 at 700 °C for 4 h and analyzed by Auger electron spectroscopy, backscattering spectrometry, x-ray photoelectron spectroscopy, and secondary-ion mass spectrometry. In the surface region of the oxide film, this annealing results in an incorporation of nitrogen bonded to germanium by the nitridation of GeO2. In the bottom region of the oxide film near the GeSi/oxide interface, elemental Ge appears. We attribute this process to the hydridation of GeO2 with hydrogen that comes from dissociated ammonia. Results obtained at 800 °C for a 380-nm-thick oxide film are similar. A model is proposed to explain the observed changes of the oxide after the ammonia annealing.
Raman effect in AlGaAs waveguides for subpicosecond pulses
Authors: Kao Y.-H. , Islam M. N. , Saylor J. M. , Slusher R. E. , Hobson W. S.
Published: July 2002

The Raman effect in semiconductor waveguides below half-gap is studied both experimentally and numerically. We report the depolarized Raman gain spectra up to 300 cm−1 in Al0.24Ga0.76As at pump wavelengths of 0.515 and 1.55 μm from the measurement of the absolute Raman scattering cross sections using GaAs as a reference scatterer. In addition, the coupled propagation equations for the AlGaAs waveguides are modified to include the Raman effect. By solving the coupled propagation equations numerically, we verify that the energy transfer between two orthogonally polarized pulses demonstrated in previous pump-probe experiments [M. N. Islam et al., J. Appl. Phys. 71, 1927 (1992)] is caused by Raman effect. We also show numerically that the Raman effect induces spectral distortions on the pulses, and the energy transfer is inversely proportional to the pulse widths. The energy transfer results in a severe cross-talk problem for sub-picosecond pulses in AlGaAs waveguides. For example, the energy exchange is about 30% for 300 fs pulses under π phase shift conditions. Therefore, the Raman effect limits the performance of semiconductor waveguides in optical switching applications for sub-picosecond pulses.
Response to ‘‘Comment on ‘High temperature adsorption of nitrogen on a polycrystalline nickel surface’ ’’ [J. Appl. Phys. 78, 2141 (1995)]
Authors: Boughaba S. , Auvert G.
Published: July 2002

By discussing the three main comments on our paper, we demonstrate that our experimental conditions: low gas pressure and reaction area radius below the mean free path in the gas phase, are only compatible with a modification of the reaction surface without any diffusion limited process.
Surface impedance measurements of superconducting V3Si films by a microstrip resonator technique
Authors: Andreone A. , Cassinese A. , DiChiara A. , Salluzzo M. , Vaglio R. , Attanasio C. , Maritato L.
Published: July 2002

Using a ring microstrip resonator technique, the surface impedance of V3Si sputtered films has been measured as a function of temperature and dc and rf field amplitude. The results are analyzed in terms of the Bardeen–Cooper–Schrieffer theory and of a grain-boundary Josephson model, and discussed in the framework of the possible application of V3Si as a thin-film coating of superconducting rf cavities for particle accelerators.
Analysis of the electric relaxation in acrylate polymers with rigid side groups
Authors: Díaz-Calleja R. , Sanchis M. J. , Reis-Nunes R. C. , Pinto M. , Riande E.
Published: July 2002

The curves describing the temperature dependence of the dielectric loss for poly(4-acryloxyphenyl)–(4-chlorophenyl)–methanone exhibit a well developed subglass absorption followed in order of increasing temperature by an ostensible glass–rubber relaxation or α process. Free charge conductivity processes and blocking electrode phenomena become dominant in the α relaxation at frequencies below 10 Hz. An electric model is proposed to interpret the dielectric results covering the glassy state and the glass–rubber transition. The model is basically a parallel configuration involving a condenser (CΓα), a resistance (R), and a Havriliak–Negami-type impedance (ZHN*) coupled in series with an impedance (Ze*) representing the electrode phenomena. The circuit allows one to split the dipolar processes from both free charges and blocking electrode conductivity contributions to the real ε′ and loss ε″ parts of the complex dielectric permittivity at temperatures above the glass transition temperature of the polymer. At low frequencies the model predicts that ε′ and ε″ scale with frequency as ε′∼ω−(1+ᾱ) and ε″∼ω−ᾱ, the exponent ᾱ not being restricted to the conventional value of 0.5 commonly found in the literature.
X-ray reflectivity studies of the effect of surfactant on the growth of GeSi superlattices
Authors: Li Ming , Cui Q. , Cui S. F. , Zhang L. , Zhou J. M. , Mai Z. H. , Dong C. , Chen H. , Wu F.
Published: July 2002

X-ray reflectivity is applied to investigate the effect of a surfactant on the growth of Ge1−xSix/Si superlattices. It is demonstrated that the antimony layer deposited on the surface can effectively prevent the intermixing of silicon and germanium. The specular reflectivity curves show that the width of the interface is sufficiently reduced by the surfactant. The transverse scans show that the interface roughening exponent h for the sample with surfactant is larger than for the sample without surfactant, and the in-plane correlation length for the former is much larger than for the latter. This indicates that the surfactant makes less jagged and smoother interfaces and induces a different surface growth mode.
Electrical characteristics of epitaxial pn junction diodes fabricated on germanium-boron-doped silicon
Authors: Ang S. S.
Published: July 2002

The electrical characteristics of epitaxial pn junction diodes fabricated on boron-doped silicon epitaxial films counterdoped with germanium were investigated. Typical diode quality factors for these diodes ranged from 1.05 to 1.15 suggesting that carrier conduction is predominantly diffusion limited. A reduction in forward current activation energy was noted in these diodes with a concomitant decrease in bandgap energy. Current densities at large forward biases of the diodes fabricated on Ge/B-doped silicon were lower than those without germanium counterdoping. This is presumably attributable to a reduction in the effective doping concentration in the germanium/boron counterdoped layer as a result of bandgap narrowing, and an increase in carrier scattering due to the large atomic radius of the germanium atoms and increased imperfection density in the silicon crystal.