bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled plasmon–LO-phonon modes in GaInAs quantum wires
Authors: Mutluay N. , Tanatar B.
Published: July 2002

We study the collective excitation modes of coupled quasi-one-dimensional electron gas and longitudinal-optical phonons in GaInAs quantum wires within the random-phase approximation. In contrast to the higher-dimensional systems, the plasmon–phonon coupling is found to be strong at all linear carrier densities of interest. We calculate the oscillator strength of the numerically evaluated coupled modes and the Raman scattering intensity. The effect of phenomenological LO-phonon broadening on the collective excitation spectrum is also investigated.
Nanostructure of giant magnetoresistive oxide film Nd2/3Sr1/3MnO3 by scanning tunneling microscopy
Authors: Ramaswamy Geetha , Raychaudhuri A. K.
Published: July 2002

Scanning tunneling microscopy was used to study the surface nanostructure of the epitaxial film Nd2/3Sr1/3MnO3 that shows giant magnetoresistance. The surface morphology of the film consists of a number of overlapping platelets of about 30–35 Å diameter that grow at an angle of 35°–45° to the surface normal. The peak to peak height of the platelets are multiples of the c-axis lattice parameter of 7.85 Å showing that the growth of the platelets takes place by the layer by layer addition of one formula unit. The mean surface roughness is about 10 Å. In the range of a few microns the film exhibits no defects or dislocations. The film is unstable in ambient atmosphere and tends to get covered by an adsorbate layer. Tip-surface interactions cause the adsorbate to be dislodged exposing the surface nanostructure. The degradation of the film in real time when imaged in air was recorded. The adsorbates increase the surface roughness of the film.
Charging phenomena in low-voltage electron microscopy of laser-fractured fluoride surfaces
Authors: Johansen H. , Gogoll S. , Stenzel E. , Reichling M. , Matthias E.
Published: July 2002

Surfaces of fluoride crystals, fractured by a single excimer laser pulse and then covered by a thin conductive layer, are imaged by scanning electron microscopy in the low-voltage secondary electron mode. As a result of charging, at lower primary electron energies a contrast enhancement can be obtained for surface fragments that are no longer tightly attached to the crystal. This differs from high-energy (≳10 keV) imaging which only yields topographic contrasts and allows the analysis of the fractured structure by edge and shadowing effects. Even contrast inversion from positive to negative charging of an entire fragment can be achieved, depending on the primary electron energy. It is shown that this effect can be utilized to discriminate between fragments with a good mechanical contact to the bulk and partially detached ones by systematically studying the contrast as a function of electron energy and specimen inclination.
Magnetic susceptibility and energy levels in europium diglycollate and potassium europium fluoride
Authors: Bhattacharyya Sulava
Published: July 2002

Measurement of magnetic susceptibility was performed for trigonal europium diglycollate (EuDG) between 300 and 77 K. The magnetic properties for this compound and for tetragonal potassium europium fluoride (PEF) have been calculated using crystal field (CF) theory including intermediate coupling formalism. By fitting the experimental results with theoretical calculations, CF parameters of EuDG have been determined. These parameters are B02=52, B04=−904, B06=−240, B34=−585, B36=−223, and B66=−172, all in cm−1, which explain the observed energy levels in visible and IR region very well. Using the determined CF energy scheme of PEF several hyperfine properties for 151Eu have been estimated. The total width of estimated Mössbauer spectra was found to be 28.26 mm/s and the temperature independent isomer shift was found to be 1.8 mm/s.
A phenomenological theory of ion-beam synthesis of ternary compound in silicon
Authors: Barabanenkov M. Yu.
Published: July 2002

A model for the annealing stage of ion-beam synthesis of a buried layer of a ternary phase in silicon coimplanted with a relatively low dose of chemically active ions is presented. Physically, the system under investigation is a mixture of precipitates of two binary phases which are formed in the subsurface region of silicon as a result of chemical reaction between each implanted impurity and matrix atoms. During annealing, the precipitates of each binary phase function as alternative sinks for the solutes. Therefore, the ensemble of new phase inclusions is regarded as a superposition of precipitate pairs. Each pair involves the nuclei of both binary phases. The incorporation of an impurity atom into a binary phase inclusion is assumed to be controlled by the corresponding kinetic parameter. During annealing, binary phase inclusions play the role of seeds for ternary phase formation. Mathematically, the redistribution and chemical segregation of implanted species are described by a set of diffusion equations. The sink terms of the equations have been derived in the two-particle approximation which reflects the competitive growth of two phases. Generally, this set of equations is solved numerically; however, two assumptions allow the analytic solution: there are (i) chemical segregation of the reagent is a predominant mechanism of phase formation; (ii) the phases formed have a constant chemical composition. The model is successfully applied to the description of silicon oxynitride synthesis by silicon implantation with a substoichiometric dose of oxygen and nitrogen ions. The computer simulation showed that nitrogen atoms, collected on the oxide surface, change the interface mechanism of oxide growth into that of bulk diffusion, which eventually facilitates the ternary phase formation.
Calculation of hot electron distributions in silicon by means of an evolutionary algorithm
Authors: Jakumeit J. , Ravaioli U. , Hess K.
Published: July 2002

A new approach to simulate electronic transport at high energies in silicon is introduced, which is based on a mixture of evolutionary optimization algorithms and the Monte Carlo technique. The optimization technique of the evolutionary algorithm is used to find electron distributions which are in agreement with a given physical quantity, for example, a measured substrate current. In this way, the evolutionary algorithm can calculate backward the electron distributions from results of measurements. A mutation operator, which is based on the Monte Carlo technique, is used to direct the optimization of the evolutionary algorithm toward physically correct distributions. A comparison of the results of this new approach with electron distributions calculated by a full band Monte Carlo program demonstrates both the backward calculation ability of the evolutionary algorithm and the correctness of the physical model in the Monte Carlo-like mutation operator. It becomes obvious that the electron distribution in silicon is mainly determined by the scattering rates. By suppressing the optimization of the evolutionary algorithm the Monte Carlo-like mutation operator alone was found to provide a powerful new type of Monte Carlo technique. While these methods are not as precise as a full band Monte Carlo approach, they are shown to be numerically efficient and give also a good fit to reliability related hot electron effects.
Resonance enhancement of the photoemission from semiconductors with negative electron affinity
Authors: Gerchikov L. G. , Subashiev A. V.
Published: July 2002

The variation of photoemission from negative electron affinity semiconductor surface with the position of the surface Fermi level is theoretically studied. Resonance maxima both in photoyield and surface recombination rate (when the depth and the width of the quantum well in the band bending region (BBR) are close to the appearance of new quantum level) are predicted as a result of quantum character of the electron motion in the BBR. The resonance BBR transmission is expected to manifest itself in the temperature, doping, and thickness of the activation layer photoyield dependence. Experimental studies of the dependencies should help to monitor the evolution of the BBR during surface activation to the negative electron affinity state.
Chromium and nickel ion irradiation effects on the low- and high-temperature metal-semiconductor transitions in (V1−xCrx)2O3 ceramics
Authors: Kokabi H. R. , Studer F.
Published: July 2002

Chromium doped vanadium sesquioxide [(V1−xCrx)2O3] ceramic samples have been irradiated using medium energy chromium and nickel ions (52Cr:572 MeV, 64Ni:640 MeV) at various fluences (4×1011–1.1×1014 ions/cm2) and doping rates (x=0.3, 0.6, and 0.7). Irradiation has been carried out under vacuum and at room temperature. Irradiated samples have been characterized by electrical resistivity measurements as a function of temperature for the low- and the high-temperature transitions in the (V1−xCrx)2O3 system. Irradiation by chromium and nickel ions creates bilayered samples as the ions mean projected range were smaller than the sample thickness. The bilayer structure is characterized by two transitions at low temperature. Dealing with the high temperature positive temperature coefficient transition, the negative temperature coefficient behavior above this transition has been considerably attenuated due to the bilayered structure. In situ measurements on an irradiated sample have shown that after annealing the electrical characteristics for the low- and the high-temperature transitions tend to be close to those of an unirradiated sample. However, even an annealing at 380 °C does not eliminate all the irradiation effects.
Effect of inclusion of self-consistently determined electron temperature on the electron–plasmon interaction
Authors: Mansour Nabil S. , Diff Karim , Brennan Kevin F.
Published: July 2002

In this article, we present a comparison of three different formulations of the carrier–plasmon interaction in semiconductors that can be included within an ensemble Monte Carlo simulation. Two of the formulations, referred to here as the electron–field and electron–electron methods, can be considered as first-order quantum mechanical approaches in which the electron–plasmon interaction is treated as an additional scattering mechanism. The electron–field model formulation is corrected from previously published work following the approach of Popov, Solodkaya, and Bagaeva [Physica B 217, 118 (1996)]. The corrected electron–field model is compared to an improved, self-consistent electron–electron model and to the semiclassical method, by which the Poisson equation is solved self-consistently, for both steady-state bulk and transient transport. It is found that the corrected electron–field model, which is also formulated as self-consistent, and the new improved self-consistent electron–electron model predict nearly identical results in both steady and transient states. It is further found that the self-consistent quantum mechanical models compared to the semiclassical model do not yield precisely the same result, in agreement with previously published results. The addition of self-consistency to these models results in nearly equal plasmon occupation factors for both absorption and emission, leading to nearly equal absorption and emission rates at high carrier temperatures. Some caution must be exercised, however, in these results since a full temperature-dependent dielectric function has not been employed and it is possible that the quantum mechanical models may need some revision at high carrier temperatures. Nevertheless, the self-consistent quantum mechanical models predict the net average energy relaxation to be small, due to nearly equal absorption and emission rates, consistent with the semiclassical model.
Localized density of states in hydrogenated amorphous silicon/silicon nitride interfaces studied by transient voltage spectroscopy
Authors: Kawachi G. , Ishii M. , Konishi N.
Published: July 2002

The localized electronic density of states gL(E) at the hydrogenated amorphous silicon/silicon nitride (a-Si:H/Si3N4) interfaces is evaluated by transient voltage spectroscopy (TVS). The gL(E) at the a-Si:H/Si3N4 interface is found to have a broad peak and a deep minimum, respectively, around 0.9 and 0.47 eV below the conduction-band edge. The positive fixed charge at the interface makes the flatband voltage of the a-Si:H/Si3N4 system negative and, hence, there is a finite band bending at the interface even at the gate bias of 0 V. The gL(E) of different samples fabricated under various preparation conditions varies from sample to sample, whereas threshold voltages of a-Si:H thin-film transistors are almost independent of their preparation, suggesting the presence of an equilibrium mechanism between the positive fixed charge and the defect density. A modification of gL(E) at a-Si:H/Si3N4 interfaces by bias annealing is definitely observed using TVS. The overall results obtained by TVS seem to support the defect pool model.
Reply to ‘‘Comment on ‘Temperature dependence of the barrier height of metal-semiconductor contacts on 6H-SiC’ ’’
Authors: Smith S. R. , Evwaraye A. O. , Mitchel W. C.
Published: July 2002

We reply to the comment by Fröjdh and Petersson concerning the measurements of the barrier heights of Schottky diodes on 6H-SiC. We present the argument that the temperature range over which Fröjdh and Petersson present data does not allow accurate comparison with our results. The problem of interaction of deep levels in the capacitance-voltage measurements is refuted by deep-level transient spectroscopy data. We conclude that our data are accurate and our methods reliable.
Leakage current analysis for InyGa1−yPzAs1−z/AlxGa1−xAs double heterostructure lasers
Authors: Lan Sheng , Chan Yuen-Chuen , Xu Wan-Jing , Cui De-Long , Yang Cheng-Qing , Liu Hong-Du
Published: July 2002

A band offset diagram for the heterojunction InyGa1−yPzAs1−z/AlxGa1−xAs based on the transitivity rule and our measured band offset for In0.5Ga0.5P/GaAs is given. A carrier leakage analysis is developed and explains the experimental observations in 670 nm visible InyGa1−yPzAs1−z/AlxGa1−xAs double heterostructure (DH) lasers. The analysis based on the performance of this laser verifies that our band offset is more accurate than previous values. In contrast to GaAs/AlxGa1−xAs, InGaPAs/InP and InGaP/AlGaInP DH lasers, we found that the leakage of holes, rather than of electrons, is responsible for the high threshold current density of this type of laser.
90° phase-matched ultraviolet generation at 0.2660 μm in LiClO4⋅3H2O
Authors: Umemura N. , Kato K.
Published: July 2002

LiClO4⋅3H2O has been found to be 90° phase-matchable for ultraviolet generation at 0.2660 μm at a crystal temperature of 30.6 °C. A peak power as high as 28 MW with an average power of 2.2 W was obtained in a 1.5-cm-long crystal. Sellmeier’s equations and nonlinear constant of this crystal are reported.
Neutron-diffraction analysis of Nd2Fe17Nx: A reexamination
Authors: Hu Z. , Yelon W. B.
Published: July 2002

A sample of Nd2Fe17Nx previously studied has been remeasured with higher-resolution powder neutron diffraction. Rietveld analysis confirms the existence of two values of x. The higher x corresponds to nearly full occupation of the octahedral 9e site, while the lower value corresponds to partial occupancy of both the octahedral and tetrahedral 18g sites by nitrogen. The lattice changes for both compositions have been carefully examined.
Structural properties of cubic GaN epitaxial layers grown on β-SiC
Authors: Teles L. K. , Scolfaro L. M. R. , Enderlein R. , Leite J. R. , Josiek A. , Schikora D. , Lischka K.
Published: July 2002

Self-consistent tight-binding total energy calculations are performed to study the deposition of a few layers of cubic GaN on (100) β-SiC substrates. Cohesion energies, atomic displacements, dangling bond occupancies and surface reconstructions are calculated for a variety of epitaxial systems including monolayers of either Ga or N as well as single and double bilayers of GaN on either Si or C terminated substrates. The SiC substrates and Ga-N epitaxial layers are represented by 2×2 supercells of 9 Si and C monolayers plus the respective number of monolayers of Ga and N atoms. Depending on the system, surface atoms dimerize either symmetrically or asymmetrically resulting in either 2×1, c-2×2, or 2×2 surface reconstructions. At the substrate-epitaxial-layer interfaces, N binds stronger than Ga to either Si or C. Interface mixing is found to be energetically not advantageous for both C- and Si-terminated substrates, although for the latter the obtained small energy differences may suggest the possibility of mixing.
On-chip radiation detection from stacked Josephson flux-flow oscillators
Authors: Shitov S. V. , Ustinov A. V. , Iosad N. , Kohlstedt H.
Published: July 2002

Radiation measurements with double-junction stacked Josephson flux-flow oscillator on-chip coupled to a superconductor–insulator–superconductor detector are reported. Impedance matching between the oscillator and the detector has been achieved using a broad band coupling circuit. Radiation power in the detector up to 10 nW has been measured in the frequency range between 170 and 410 GHz. Coherent radiation from two stacked junctions has been observed both at the fundamental Josephson frequency and at its second harmonic. The distribution of the radiation power between the first two harmonics allows us to distinguish between mutually coupled in-phase and out-of-phase flux-flow modes in the junctions. Coherent operation of stacked Josephson junction oscillators in the millimeter and sub-millimeter wave band is demonstrated.
Effects of non-uniform charge injection on gain, threshold current, and linewidth enhancement factor for a 1.55 μm InP-based multiple quantum well laser
Authors: Jambunathan R. , Singh J.
Published: July 2002

In laser structures where the active region consists of several quantum wells, non-uniform charge injection can occur. We examine the consequences of non-uniform charge injection on gain, threshold current, and linewidth enhancement factor. Non-uniform charge injection in a InP-based multiple quantum well laser was considered in order to analyze effects on gain, threshold current, and linewidth enhancement factor. We find that although the best values for gain, threshold current and linewidth enhancement factor occur under uniform charge injection conditions, these parameters do not suffer significant degradation under even highly non-uniform charge injection.
Structure and magnetic properties of SmMn2(Ge1−xSix)2
Authors: Wang Yin-gang , Yang Fuming , Tang N. , Hu Jifan , Zhou Kaiwen , Chen Changpin , Wang Qidong , de Boer F. R.
Published: July 2002

The structure and magnetic properties of SmMn2(Ge1−xSix)2 compounds (x=0–1.0) have been investigated. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Si for Ge leads to a linear decrease of the lattice constants and the unit-cell volume. In all compounds a transition from the ferromagnetic to the antiferromagnetic state is observed at a lower temperature T1, which first decreases, goes through a minimum at x=0.4–0.6, and then increases again with Si concentration. As temperature increases, for the compounds with x<0.3 both a antiferromagnetic–ferromagnetic transition and the ferromagnetic–paramagnetic transitions are observed as well at T2 and at the Curie temperature Tc, respectively. With increasing Si content the Tc decreases, whereas T2 increases from 140 K for x=0 to 215 K for x=0.2. For compounds with x≥0.3 the antiferromagnetic–paramagnetic transition was observed with increasing temperature and the Néel temperature increases with increasing Si content. The saturation magnetization at 1.5 K decreases first, goes through a minimum at x=0.6, and then increases again with increasing Si content. At room temperature, the saturation magnetization decreases monotonically from 3.27 μB/f.u. for x=0 to nearly zero for x=0.3.
Anisotropy of power losses in textured soft magnetic materials
Authors: Birsan M. , Szpunar J. A.
Published: July 2002

The purpose of this study is to develop a new method of correlating texture and power losses in soft magnetic materials. During the magnetization process, part of the loss could be attributed to the energy dissipation which takes place at the time of annihilation of domain walls. Domain walls appear and disappear when a ferromagnetic material is magnetized in a direction different from an easy magnetization direction. Starting from this model, we deduce analytical formulas which describe the anisotropy of the power loss in textured soft magnetic materials. The material’s texture is represented using the orientation distribution function. The validity of the model is tested by comparing the theoretical results with the experimental data obtained from a grain oriented 3% Si–Fe sample.
Optical and electrochemical properties of vanadium pentoxide gel thin films
Authors: Thi Be Bay Nguyen , Tien Pham Minh , Badilescu Simona , Djaoued Yahia , Bader Georges , Girouard Fernand E. , Truong Vo-van , Nguyen Le quang
Published: July 2002

Optical and electrochemical properties of vanadium pentoxide (V2O5) films prepared by sol-gel method from organic and inorganic precursors were studied. The organic gel was obtained by hydrolysis and polycondensation of vanadium isopropoxide dissolved in isopropanol. The inorganic gel was prepared from aqueous solution of sodium vanadate. Lithium insertion in LiyV2O5 films (0<y≤2.0) was investigated by cyclic voltammetry and electrochemical potential spectroscopy, showing good reversibility up to y∼2.0 and structure transitions from α phase to ε phase and δ phase in the range 0<y≤1.0. Highest values for chemical diffusion coefficient were about 3×10−10 cm2/s at y∼0.8, as determined from complex impedance measurements.
Voltage-tuneable Bragg reflector based on the quantum confined Stark effect
Authors: Govorov A. O. , Hansen W. , Kotthaus J. P.
Published: July 2002

We consider the Bragg effect in an in-plane reflector realized with a field-tuneable superlattice. The latter is induced via an interdigitated gate on a waveguide formed by a GaAs–AlAs quantum well system. In such a system the Bragg resonance arises from the laterally periodic modulation of the quantum confined Stark effect. The reflection coefficient is shown to be voltage tuneable, and the angular and frequency dependences are analyzed theoretically. We find that acceptable values of reflection can be achieved for frequencies close to the interband resonance. Furthermore, we point out that the in-plane Bragg reflector can be used to study exciton–polariton coupling in semiconductor waveguides.
The dc magnetization of YBa2Cu3O7−δ /Ag bulk composites
Authors: Ash C. L. , Harris D. C. , Hebboul S. E. , Garland J. C. , Almasan C. C.
Published: July 2002

We report dc magnetization measurements on YBa2Cu3O7−δ/Ag composite samples with different superconducting volume fractions p. All the samples with 0.35≤p≤1 display bulk behavior, with the Josephson coupling between the grains diminishing with increasing temperature. The p≥0.7 samples exclude flux from the entire volume and have higher values of the Josephson lower and upper critical fields Hc1J and Hc2J, respectively, indicating stronger coupling between the grains, and greater degree of pinning at the grain surface. The samples with 0.35≤p≤0.6 show partial flux exclusion and have significantly lower values of Hc1J and Hc2J, and lower degree of pinning at the surface of the grains. The p<0.35 samples do not exhibit bulk behavior at any temperature T<Tc indicating that there is no percolative pathway between the grains. The irreversibility lines H(T*) display the same p dependent clustering. The H(T*) for the samples with p≥0.7 are at higher fields for a given temperature, indicative of stronger pinning. The values of Hc1G at 10 K extracted from M(H) measurements lie between 200 and 400 Oe for all volume fractions, with no discernible p dependence.
Electrochromic control of thin film light scattering
Authors: Lindström T. , Kullman L. , Rönnow D. , Ribbing C.-G. , Granqvist C. G.
Published: July 2002

Total and diffuse reflectance spectra were measured on Al surfaces covered with electrochromic W oxide films in colored and bleached states. Vector perturbation theory was used for analyzing the spectra. The diffuse reflectance appeared to originate from correlated (uncorrelated) interface roughness when the W oxide film was fully colored (bleached). Assuming partially correlated interfaces led to agreement between experimental and calculated spectra. The use of an electrochromic film appears a promising method to control the relative contributions of the interfaces to the resulting scattering.
Influence of tunneling on interlayer drag in double quantum wells
Authors: Raichev O. E.
Published: July 2002

The tunneling effect on the interlayer drag measurements in the independently contacted double quantum well system is studied theoretically. As a result of competition between the frictional drag and electron transfer between the layers, the transresistivity is significantly modified when the length of the system becomes comparable with the square root of the ratio of the drag transconductivity to the tunneling conductance.
The effects of ion sheath collisions on trench etch profiles
Authors: Chen Wenjing , Abraham-Shrauner Barbara
Published: July 2002

The effects of ion collisions in the plasma sheath on etch profiles of a long trench is modeled. The pattern transfer step is for trilayer lithography where the photoresist etches down to a silicon dioxide mask and the trench is etched in the substrate. The etch rate in the ion flux-limited regime varies as the ion energy flux which is calculated from the ion velocity distribution function. The form of the ion velocity distribution function consists of a sum of drifted Maxwellians. This sum fits experimental data for ion energy distribution functions with angular dependence for an argon plasma by a simulated annealing optimization procedure. Etch rate expressions for a drifted Maxwellian in a collisionless sheath are extended to the collisional sheath. The etch profiles are computed numerically by integration of characteristic equations for the profile points and by numerical computation of the profile at a given time.
An electrical resistivity study of Ce2Fe16.8 and the Ce2Fe17−xAlx and Ce2Fe17−xSix solid solutions
Authors: Vandormael D. , Grandjean F. , Bougrine H. , Ausloos M. , Middleton D. P. , Buschow K. H. J. , Long Gary J.
Published: July 2002

Electrical resistivity measurements have been carried out between 20 and 300 K on Ce2Fe16.8, on the Ce2Fe17−xAlx solid solutions, with x=0.4, 1, 2, 5, 6, 8, and 9, and on the Ce2Fe17−xSix solid solutions, with x=0.2, 0.4, 1, and 2, with the four probe method. The temperature dependence of the resistivity of Ce2Fe16.8 shows an inflection at 110 K, a feature which is also observed in the temperature dependence of the magnetization and is related to a magnetic phase transition from a helical structure, above 110 K, to a fan structure, below 110 K. The temperature dependence of the resistivity of Ce2Fe16.8 is characteristic over the investigated temperature range of weak antiferromagnetic behavior with incommensurate periodicity as has been observed in the earlier neutron diffraction study. The resistivity of Ce2Fe17−xAlx increases with temperature in agreement with a density of states at the Fermi level dominated by the d band. For a given temperature, the resistivity increases substantially and regularly with x for both series of solid solutions because of an increase in the number of conduction electron scattering potentials. This increase in resistivity also corresponds to a decrease in the number of conduction electrons due to their increasing transfer into the localized cerium 4f orbitals as the cerium valence state changes from a mixture of trivalent and tetravalent in Ce2Fe17 to predominantly trivalent in Ce2Fe17−xAlx and Ce2Fe17−xSix with increasing x.
Noise correlation measurements in bipolar transistors. II. Correlation between base and collector currents
Authors: Delseny C. , Pascal F. , Jarrix S. , Lecoy G.
Published: July 2002

Low-frequency noise measurements were performed on heterojunction bipolar transistors (HBTs) and presented in part I of this article. These measurements revealed a partial correlation between base and collector noise current sources. With the help of the current spectral densities determined in part I, the coherence function is calculated and studied versus bias in this second part. Important values of the coherence function are obtained at the highest bias. Then the spectral densities Sc and Snc associated to the correlated and uncorrelated parts of the collector current noise source are extracted and analysed. All spectra exhibit excess noise. A difference in shape is clearly observed because of an important generation-recombination component occurring around 1 kHz on the correlated part only. To compare the behavior of different transistors a normalized coupling coefficient is introduced. The correlation is seen to increase with the scaling-down of devices. The investigation of the coupling coefficient with collector current density leads to hypothesis concerning the origin of the generation-recombination (g-r) components. Some components are shown to originate in the intrinsic transistor, and others in the extrinsic one, depending on frequency and type of HBT. Mainly the noise correlation is due to leakage currents and/or recombinations in the base-collector junction.
Optimum sensitivity and two-dimensional modeling of microwave detected photoconductance decay carrier lifetime measurement
Authors: Ghannam Moustafa Y. , Mahmoud Samir F. , Nijs Johan F.
Published: July 2002

Optimization of the measurement sensitivity using closed form analytical expressions derived from an electrical equivalent circuit is carried out for microwave detected photoconductance decay system used for nondestructive carrier lifetime measurement in silicon wafers. The effect of transverse inhomogeneity in the sample conductivity on the microwave power reflection is discussed using the equivalent circuit model. The effect of lateral inhomogeneity in the sample conductivity due to local illumination by a source with a laterally varying intensity is studied using an elaborate analytical two-dimensional model. Finally, the effect of transient lateral carrier diffusion in a sample subjected to a pulsed illumination on the extracted value of the lifetime is investigated.
Decomposition of 1,1-Dichloroethane and 1,1-Dichloroethene in an electron beam generated plasma reactor
Authors: Vitale S. A. , Hadidi K. , Cohn D. R. , Bromberg L.
Published: July 2002

An electron beam generated plasma reactor is used to decompose low concentrations (100–3000 ppm) of 1,1-dichloroethane and 1,1-dichloroethene in atmospheric pressure air streams. The energy requirements for 90% and 99% decomposition of each compound are reported as a function of inlet concentration. Dichloroethene decomposition is enhanced by a chlorine radical propagated chain reaction. The chain length of the dichloroethene reaction is estimated to increase with dichloroethene concentration from 10 at 100 ppm initial dichloroethene concentration to 30 at 3000 ppm. Both the dichloroethane and dichloroethene reactions seem to be inhibited by electron scavenging decomposition products. A simple analytic expression is proposed for fitting decomposition data where inhibition effects are important and simple first order kinetics are not observed.
Low resistance Pd/Zn/Pd ohmic contact to p-In0.82Ga0.18As0.39P0.61
Authors: Park Moon-Ho , Wang L. C. , Palmstro/m C. J.
Published: July 2002

We report on the investigation of a low resistance Pd/Zn/Pd contact to p-InGaAsP (λ=1.14 μm). The contact had a minimum contact resistivity of ∼3×10−7 Ω cm2 to the substrate doped to 2×1018 cm−3. The samples showed rather uniform surface and interfacial morphologies. X-ray studies showed the formation of a PdZn phase for samples annealed below 400 °C and this phase started to decompose at temperatures higher than 400 °C. Pd-III compounds (Pd2Ga5 and PdIn3) also started to form for annealing temperatures higher than 400 °C. The ohmic behavior can be understood in terms of the decomposition of the PdZn phase and the formation of Pd-III compounds for samples annealed at 400 °C or higher. The thermal stability of this contact at 400 °C was found to be stable, which is important for device applications.
Phase formation and stability of N+ implanted SiC thin films
Authors: Capelletti R. , Miotello A. , Ossi P. M.
Published: July 2002

Silicon carbide amorphous thin films have been bombarded with 100 keV N ions. Infrared-absorption spectroscopy has been used to study the effect of increasing ion doses, up to 5×1017 N+ cm−2, on the evolution of chemical bonding between Si, C, and N. The changes induced by thermal annealing at different temperatures, up to 973 K, on the stability of the bombardment induced SiCxNy phase are investigated, together with the effect of surface oxidation during the postannealing cooling of the films. The new phase is thermally stable within the temperature range investigated. At the highest implantation dose a threshold is reached above which N atoms are located as interstitial, or are weakly bonded in the host film. Annealing at high enough temperature induces migration toward the surface and subsequent loss of interstitial N.
Segregation and trapping of erbium at a moving crystal-amorphous Si interface
Authors: Polman A. , Custer J. S. , Zagwijn P. M. , Molenbroek A. M. , Alkemade P. F. A.
Published: July 2002

Segregation and trapping of Er during solid-phase crystallization of amorphous Si on crystalline Si is studied in a concentration range of 1016–5×1020 Er/cm3. Amorphous surface layers are prepared on Si(100) by 250 keV Er ion implantation, recrystallized at 600 °C, and then analyzed using high-resolution Rutherford backscattering spectrometry using 2 MeV He+ or 100 keV H+. The segregation coefficient k depends strongly on Er concentration. At Er interface areal densities below 6×1013 Er/cm2 nearly full segregation to the surface is observed, with k=0.01. At higher Er densities, segregation and trapping in the crystal are observed, with k=0.20. The results are consistent with a model in which it is assumed that defects in the a-Si near the interface act as traps for the Er.
Simple formulae for kinetic inductance of coupled superconducting microstrip lines
Authors: Kang Jinfeng , Han Ruqi , Xiong Guangcheng , Liu Xiaoyan , Wang Yangyuan
Published: July 2002

Simple formulae for the kinetic inductance of coupled superconducting microstrip lines in odd mode and even mode have been derived by using the conformal mapping technique. Based on the simple formulae, the geometrical effects of kinetic inductance in odd mode and even mode are analyzed and compared with those of magnetic inductance. The coupling effects of two proximity microstrip lines caused by the kinetic inductance are also studied. The kinetic inductance is dominant for smaller geometrical sizes but is less important than the magnetic inductance for larger geometrical sizes.
The piezoelectrically forced vibrations of AT-cut quartz strip resonators
Authors: Wang Ji , Momosaki Eishi
Published: July 2002

The one-dimensional vibration equations of crystal strips of AT-cut quartz with narrow width and finite length are given by Lee and Wang [J. Appl. Phys. 75, 7681 (1994)]. The mechanical vibrations of such strips have been studied by neglecting the coupling due to piezoelectric effect. In the present study, the one-dimensional equations are further expanded to include the piezoelectric effect. New sets of coupled equations which are much larger than the ones for the mechanical vibrations are obtained. By neglecting the components of high-order displacements and electric potentials, particular attention is given to the thickness-shear vibrations of the strips. Analytical solutions of the free vibrations, including components of thickness-shear, flexural, width-shear, width-stretch, width-flexural, and the zeroth- and first-order electric potentials, are obtained. The dispersion relations, frequency spectra, and mode shapes of the free vibrations are given as functions of the ratios of length to thickness and width to thickness. The forced vibrations are studied with these solutions, and forced response and capacitance ratios are obtained. Comparisons are made with known experimental results. A quartz strip resonator is studied with this seven modes model. The effect of the length of the electrodes, the width of the crystal, and the forcing frequency on the resonance frequency, vibration mode shapes, and capacitance ratios are obtained.
Observation of lasing from photopumped InGaN/GaN heterostructures in an edge emitting configuration
Authors: Shmagin I. K. , Muth J. F. , Kolbas R. M. , Krishnankutty S. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

Optically pumped lasing from InGaN/GaN single heterojunctions (SH) was observed in an edge emitting configuration at 77 K. The heterojunctions were grown by atmospheric pressure metalorganic chemical vapor deposition on c-plane sapphire substrates. The frequency tripled output of a mode-locked titanium:sapphire laser with a pulse width of 250 fs, operating at 280 nm, was used as the photoexcitation source. The nonlinear dependence of output emission intensity on input power density, the observations of a strongly polarized output emission, and distinct Fabry–Perot modes are discussed.
Anomalous capacitance–voltage profiles in quantum wells explained by a quantum mechanical model
Authors: Kundu Sudakshina , Biswas Dipankar , Datta Reshmi
Published: July 2002

We have developed a quantum mechanical model for understanding and explaining the capacitance–voltage (C–V) carrier profiles observed in quantum wells (QW). The external field imposed on the QW during C–V profiling changes the carrier distribution of the system. This model considers the effects of field and quantum confinement of the carriers in the well. The results obtained by iterative solutions of Schrodinger’s and Poisson’s equations give a better understanding of the experiments than the previous models where quantum confinement is ignored.
Magnetization curling in a disk with a uniaxial anisotropy
Authors: Ishii Y. , Nakazawa Y.
Published: July 2002

To investigate the behavior of the magnetization in a single-domain disk with a uniaxial magnetocrystalline anisotropy, the assumption is made that the magnetization changes its direction by the magnetization curling mode. In this mode, the deviation θ of the spin from the z axis at (r,φ,z) in the cylindrical coordinate is given by θ=a0+a1(r/R)+a2(r/R)2+a3(r/R)3, where R is the radius of the disk and a0–a3 are coefficients. An equilibrium spin configuration is obtained for a given applied field H by finding a set of values of a0–a3 that minimize the magnetic energy of the disk. Carrying out this procedure for various H, a hysteresis loop and the coercive force are obtained. It is found that the configuration in which the spins deviate from the z axis can be stable and, therefore, the hysteresis loop is not rectangular, even though an applied field is along the z axis. The deviation is larger for the spins near the lateral surface of the disk, and the spins near the center do not incline easily. Moreover, for a large magnetocrystalline anisotropy and a large diameter, the magnetization changes its direction upward and downward alternately with r. The nucleation field calculated with the present model agrees well with that of the curling mode in an oblate spheroid.
Fabrication and optical properties of ZnSe/ZnMgSSe multiple quantum wells grown by compound-source molecular beam epitaxy
Authors: Hayashi Shigeo , Manabe Yoshio , Tanahashi Ichiro , Tohda Takao
Published: July 2002

ZnSe/ZnMgSSe multiple quantum wells (MQWs) were fabricated by compound-source molecular beam epitaxy on GaAs epitaxial buffer layers. X-ray diffraction and photoluminescence revealed that the MQWs had excellent crystalline quality and optical properties. The roughness of the interface is less than an atomic layer. The exciton-longitudinal-optical phonon coupling constant is the same as that of ZnSe. Binding energy of a biexciton is such large value as 20 meV due to the quantum confinement effect.
Charge centroid and origin of generated and intrinsic bulk defects at 293 and 100 K in insulated gate field effect transistors
Authors: Kim H. S. , Williams C. K. , Reisman A.
Published: July 2002

Intrinsic and generated bulk defects in the gate insulator of silicon insulated gate field effect transistors were examined using a continuous forward-bias pulsed injection technique to inject up to 1017 e/cm2 at 293 and 100 K, for insulator thicknesses ranging between 5.4 and 50.5 nm. The amount of trapping observed at 100 K was about 30 times greater than that at 293 K. The additional trapping at the reduced temperature was determined to come from two sources. One is trapping by existing shallow bulk defects, and the other is an increase in the density of generated bulk defects. The defect generation process is thought to be related to the neutral hole trap becoming unstable during injection, acting as an electron trap. This instability appears to be enhanced as the temperature is reduced to 100 K by a “freeze out’’ effect, or by higher energy carriers that result from a reduction in the thermal scattering. The defect generation rate follows a power law, much like a chemical rate equation, i.e., the rate of defect generation is dependent on the injection current density, much like a chemical reaction is dependent on pressure of the reactive species. The charge centroid of the generated defects, measured from the substrate/oxide interface, was determined at both temperatures and the centroid of the shallow electron traps was determined at 100 K. These were found to be in the range of 6–8 nm at 100 K and 10–16 nm at 293 K. Also, a defect free, or tunneling, region of 2–4 nm extent was determined to exist at each interface. This implies that when the oxide thickness decreases to about 4–8 nm, no threshold voltage shift should result from carrier injection at room, or low temperature, and in fact this behavior was observed in these devices (at least up to 1017 e/cm2 injected). It was found that the shallow traps can be rapidly depopulated by subjecting the devices to ordinary white light during normal device use, pointing to a possible method to improve device reliability at 100 K.
Improved magnetic information storage using return-point memory
Authors: Perković Olga , Sethna James P.
Published: July 2002

The traditional magnetic storage mechanisms (both analog and digital) apply an external field signal H(t) to a hysteretic magnetic material, and read the remanent magnetization M(t), which is (roughly) proportional to H(t). We propose a new analog method of recovering the signal from the magnetic material, making use of the shape of the hysteresis loop M(H). The field H, “stored’’ in a region with N domains or particles, can be recovered with fluctuations of order 1/N using the new method—much superior to the 1/N fluctuations in traditional analog storage.
Fluxon dynamics in discrete Josephson transmission lines with stacked junctions
Authors: Caputo P. , Darula M. , Ustinov A. V. , Kohlstedt H.
Published: July 2002

The experimental and numerical study of parallel one-dimensional arrays consisting of double-layer stacked small Josephson tunnel junctions is reported. In addition to several features already known for classic single-layer arrays, we find a new resonant state which corresponds to the locking of the fluxon oscillations to a frequency of small-amplitude oscillations of the superconducting phase in middle islands of small stacks. Numerical simulations of a simplified circuit agree well with experiments and confirm the suggested qualitative mechanism. In these experiments we find no indication for the so-called multiple-fluxon propagation in double-junction arrays.
Parametric amplification of radiation by the intrinsic Josephson effect
Authors: Preis Ch. , Sardar M. , Keller J.
Published: July 2002

The use of the intrinsic Josephson effect in layered high-Tc superconductors for parametric amplification of a signal in the presence of a strong pump radiation is investigated. Model calculations are performed both for thin films and massive material with a surface parallel to the c direction assuming normal incidence of the radiation with electric field parallel in c direction. In both cases a positive signal gain is obtained in a limited range of frequencies and pump power.
Critical temperature depth profiling and improvement of YBa2Cu3O7 weak links produced by ion modification
Authors: Tinchev S. S.
Published: July 2002

The in-depth distribution of the critical temperature in the YBa2Cu3O7 film, predicted by our recent modeling of ion modified high-Tc weak links is checked. Removing a surface layer of the film step by step using bromine-ethanol chemical etching, we observed a nonuniform in-depth critical temperature distribution and found that the film inside becomes granular after the modification. This region with reduced connectivity may be responsible for the Josephson properties observed. A new idea for improving these weak links is reported. If two modifications with different ion energy or different ions are used, it is possible to form the conducting channel inside the superconducting film with dimensions independent from variations in the film thickness. These junctions are expected to have lower long time drift. Additionally, the channel is created in the region of the film where the film properties are superior to those near the interface. This should strongly improve the yield of the working device on the chip.
Threshold behavior in backgating in GaAs metal–semiconductor field-effect transistors: Induced by limitation of channel–substrate junction to leakage current
Authors: Chen Y. H. , Wang Z. G. , Qian J. J. , Sun M. F.
Published: July 2002

An analytical model is proposed to understand backgating in GaAs metal–semiconductor field-effect transistors (MESFETs), in which the effect of channel–substrate (CS) junction is included. We have found that the limitation of CS junction to leakage current will cause backgate voltage to apply directly to CS junction and result in a threshold behavior in backgating effect. A new and valuable expression for the threshold voltage has been obtained. The corresponding threshold electric field is estimated to be in the range of 1000–4000 V/cm and for the first time is in good agreement with reported experimental data. More, the eliminated backgating effect in MESFETs that are fabricated on the GaAs epitaxial layer grown at low temperature is well explained by our theory.
Neutron transmutation doping as an experimental probe for CuZn in ZnSe
Authors: Wheeler E. D. , Boone Jack L. , Farmer J. W. , Chandrasekhar H. R.
Published: July 2002

Nuclear transmutation is employed in an investigation of copper doping in ZnSe. Copper atoms are introduced at zinc sites in ZnSe after crystal growth processes are complete. Since the copper dopants are introduced after growth, far from equilibrium, they are less able to form complexes with other dopants or lattice defects as they may do when present during crystal growth. Initial results are consistent with CuZn being involved in the copper red and copper green emissions in ZnSe but not in the I1d exitonic emission.