bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of ion beam treatment and subsequent annealing on Au/GaAs contacts
Authors: Pécz B. , Radnóczi G. , Horváth Zs. J. , Barna P. B. , Jároli Erika , Gyulai J.
Published: July 2002

The effect of Xe++ and Ar+ ion beam treatment and subsequent annealing on the Au (55 nm)/n-GaAs system was studied using cross-sectional transmission electron microscopy. The maximum depth of observed defects caused by Xe++ ions (700 keV, 1×1014 ions/cm2) was about 400 nm from the interface in excellent agreement with the results of capacitance-voltage measurements. The formation of about 50-nm-thick polycrystalline region of GaAs was observed. The ion beam treatment resulted in the formation of defects (stacking faults, twins) down to a depth of 200 nm measured from the interface. Between 200 and 400 nm depth dislocation loops were formed. Amorphization has not been observed. The sharp Au/GaAs interface has been only slightly destroyed in the as-implanted sample. In contrast to pits in unirradiated samples, large flat grains of Au(Ga) solid solution grown into the highly damaged region of GaAs were found in the samples annealed at 450 °C after the ion beam treatment. The formation of a regrown GaAs covering layer was observed on the top of the reacted metallization. High dose implantation of Xe++ ions resulted in the formation of an amorphous GaAs layer with a thickness of about 750 nm. A phase transition caused by the ion beam was observed in this sample. During annealing at 400 °C the whole amorphous GaAs region recrystallized to single-crystal GaAs. Ion beam treatment with Ar+ ions (400 keV, 2×1014 ions/cm2) caused the formation of dislocation loops. In this case the growth of pits is similar to the case of simple annealing without bombardment.
Arsenic poisoning of magnetism in bcc cobalt
Authors: Singh David J.
Published: July 2002

Highly converged local spin-density approximation calculations are used to determine the effectiveness of As as a poisoning agent for the magnetism of bcc Co films grown on GaAs. To do this, supercell calculations of the magnetization were performed using an extension of the general potential linearized augmented plane-wave method for Co7As, Co15As, and Co31As. The effect of the nearest-neighbor relaxation around As impurities, calculated using total energy techniques, was included. It is found that substitutional As is moderately effective as a poisoning agent, each As atom contributes a moment of −3.8μB, and this may be important in explaining the discrepancy of 0.2–0.3μB between the calculated magnetization of bcc Co and the measured magnetization of bcc Co films on GaAs.
One-band ferromagnetism in the Hubbard–Hirsch model
Authors: Ivanov V. A. , Zhuravlev M. E.
Published: July 2002

Phase diagram of the Hubbard model with effective exchange interaction for temperatures above those of kinematical ordering is investigated. The concentration dependencies of Curie temperatures and magnetization are obtained.
On flow through porous material using a generalized Schwarz–Christoffel theory
Authors: Owen D. , Bhatt B. S.
Published: July 2002

In the present paper we extend the work of Richardson [J. Fluid Mech. 49, 327 (1971)], on the analysis of a model flow through a porous material, to include grooves of arbitrary shape using a generalized Schwarz–Christoffel formula. The analysis reveals that the findings of Taylor [J. Fluid Mech. 49, 319 (1971)] are still true.
High quality In0.15Ga0.85As/AlxGa1−xAs strained multi quantum wells grown by metalorganic vapor phase epitaxy
Authors: Buydens Luc , Demeester Piet , Yu ZongQiang , Van Daele Peter
Published: July 2002

We have investigated the growth of In0.15Ga0.85As/AlxGa1−xAs strained layer multi quantum wells with the metalorganic vapor phase epitaxy technique. X-ray rocking curves, photoluminescence, and photocurrent measurements clearly demonstrate the influence of the growth temperature on the quality of the deposited layers in this material system. The optimum temperature is found to be at about 650 °C. Photocurrent measurements on diode structures with these strained multi quantum wells as active layer show a clear shift of the exciton absorption peaks due to the quantum confined Stark effect. When the results are compared to the shifts seen for InGaAs/GaAs quantum wells, one observes an enhanced quantum exciton oscillator strength when high transverse electric fields are applied across the multi quantum wells. This property makes the InGaAs/AlGaAs material combination very suitable for use in vertical optical modulators.
Double-barrier resonant tunneling structures incorporating superlattice energy filters
Authors: Harness P. C. , Pritchard R. E. , Khamsehpour B. , Truscott W. S. , Singer K. E.
Published: July 2002

We have studied the electrical properties of GaAs/Al0.4Ga0.6As double-barrier resonant tunneling structures incorporating finite superlattices in the contact regions. The superlattices effectively act as energy filters defining the initial and final tunneling states. We have investigated an asymmetric device with one (emitter) superlattice and a symmetric device with two (emitter and collector) superlattices. These show significantly improved J(V) properties compared to other double-barrier structures and the superlattice tunnel diode.
Flux creep in the melt-processed Bi-based oxide superconductors including normal particles
Authors: Umemura Toshio , Egawa Kunihiko , Kinouchi Shin-ichi , Tanimura Junji , Nozaki Ayumi , Utsunomiya Shin
Published: July 2002

The Bi-based (2212) single grains including a large number of normal particles, (Ca,Sr)2Cu1O3, were synthesized by a melt process. To characterize the flux creep behavior in such a superconductor, magnetization measurements were performed at various temperatures and magnetic fields. The flux creep rate exhibited a maximum at 20 K in both magnetic fields parallel and normal to c axis. The magnetic field dependence of the pinning potential, U0, evaluated from the residual magnetization was not represented by the expression, B−α, in Y1Ba2Cu3O7 superconductors. The relation between U0 and the critical current density is discussed.
Synthesis and crystal growth of the high-T
c phase in Bi–Pb–Sr–Ca–Cu–O system with variation of excess concentrations of CaO and CuO
Authors: Wu Qianzhang , Fu Zhengmin , Zhang Aizhen , Huang Jiashan , Tang Disheng , Yao Pei , Chu Shaoyan , Yi Sunsheng , Rong Xishen , Zhang Anzhi , Cheng Xianan
Published: July 2002

Analyzing the results measured by x-ray powder diffraction, scanning electron microscope, energy dispersion x-ray analysis, and the standard four-probe techniques for eight groups of samples with different compositions of excess CaO and CuO, after quenching and annealing, shows that not only the much more stable 2223 phase in the Bi(Pb)–Sr–Ca–Cu–O system was obtained in a high fraction, but also its grain (plate shaped) size could be made larger than normally sintered. We attribute these effects to the annealing and/or the excess contents of CaO and CuO selected in this study.
Analytical solution of Mattis–Bardeen theory for surface impedance of superconductors
Authors: Zhou Shi-ping , Jabbar A. , Bao Jia-Shan , Wu Ke-qin , Jin Bian-jun
Published: July 2002

The exact solutions to the Mattis–Bardeen formula [Phys. Rev. 111, 412 (1958)] in the form of a double integral have been evaluated. The calculated values of surface impedance for aluminum (Al) and tin (Sn) superconductors are in excellent agreement with the typical experimental data of Biondi and Garfunkel [Phys. Rev. 116, 853 (1959)] and Sridhar [J. Appl. Phys. 65, 159 (1988)]. A microscopic theory to analyze the electromagnetic behavior of the YBa2Cu3O7−x superconductor has been suggested on the basis of its electronic structure. In considering the Cu-O chain role the nonlinear interaction between waves and these superconductors has been studied.
Influence of implant condition on the transient-enhanced diffusion of ion-implanted boron in silicon
Authors: Juang M. H. , Wan F. S. , Liu H. W. , Cheng K. L. , Cheng H. C.
Published: July 2002

Under high-dosage boron implant, the implant condition was found to be important for reducing the transient-enhanced diffusion of boron in Si and forming shallow p+n junction with good rectifying characteristics as well as high dopant concentration in the diffused region. The BF2+-implantation resulted in not only an excellent dopant activation but also a reduced anomalous diffusion due to the formation of amorphous layer and the scarce defects underneath the amorphous/crystalline (a/c) interface. The B+-implanted crystalline samples manifested a poor activation efficiency, and a largely anomalous diffusion at the high temperature with prolonged-time annealing ascribed to much damage induced by the high-dose implant. The B+-implanted pre-Si+-amorphized samples also displayed severely transient-enhanced diffusion in spite of the good dopant activation.
Anisotropic hardness and fracture toughness of highly aligned YBa2Cu3O7−δ
Authors: Goyal A. , Funkenbusch P. D. , Kroeger D. M. , Burns S. J.
Published: July 2002

The hardness and fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., Kc001<Kc100 or Kc010. Indentation crack length measurements on the (001) basal plane with the impression diagonals oriented parallel to the [100] and the [010] directions, indicate that the fracture toughness of these planes is K100/010air∼0.7 MPa m1/2. The hardness in this orientation was found to be 6.7 GPa. Measurements on a plane perpendicular to the basal plane resulted in a lower hardness of ∼3.8 GPa. This reduction in hardness is influenced by the extensive preferential cleavage of the (001) basal plane boundaries. The extremely low values of the fracture toughness suggest that considerable toughening would have to be achieved in melt-textured 123 for any practical bulk application. The presence of 211 phase and silver particles may serve to enhance the fracture toughness of aligned 123 by crack deflection and crack tip blunting respectively.
Electron subband filling and band renormalization in modulation spectroscopy of single modulation doped heterojunctions and δ-doped structures
Authors: Tang Y. S.
Published: July 2002

The physical processes in modulation spectroscopy of single modulation doped heterojunctions and δ-doped structures were discussed. Different spectral line shapes due to the modulation of electron subband filling and band renormalization induced Stark effect (or quantum confined Franz–Keldysh effect) [Miller et al., Phys. Rev. B 32, 1043 (1985)] were obtained based on self-consistent electronic structure and corresponding wave function calculations.
Photothermal beam deflection using the reverse mirage geometry: Theory and experiment
Authors: Manning Christopher J. , Palmer Richard A. , Chao James L. , Charbonnier François
Published: July 2002

This paper presents a mathematical model and supporting experimental data for the reverse mirage effect with absorption in the deflecting medium. The reverse mirage effect is defined as transverse photothermal beam deflection with the probe laser on the nonilluminated side of the interface. The model takes into account the Gaussian distribution of intensity in the probe beam, and is used to consider the phase of the photothermal beam deflection (PBD) response. The results of the mathematical treatment are shown to be in good accord with experiment. The theory shows, in agreement with Bićanić, that a plot of the natural log of the response magnitude versus probe distance is linear, and has a slope equal to the absorptivity. As an example of its application, this relationship is used to obtain absolute absorption coefficients in the mid-infrared for acetonitrile from step-scan Fourier transform ir PBD data. The theory is used to show that the largest absorptivity that can be measured by this method is approximately 650 cm−1. The phase is shown to exhibit monotonic behavior to a larger absorptivity, estimated to be greater than 3000 cm−1. The designs of the PBD accessory and sample cells are described in some detail, and a number of experimental considerations are discussed.
Time-resolved prebreakdown x-ray emission from polycrystalline alumina-bridged vacuum gaps for impulse stresses
Authors: Bommakanti R. G. , Sudarshan T. S.
Published: July 2002

Time-resolved and time-coordinated observations of voltage and prebreakdown and breakdown x-ray emission associated with the surface flashover of ceramic-insulator-bridged vacuum gaps for pulsed excitations 0.15/20 μs are described. 99.9% pure polycrystalline alumina right circular cylinders (25.4 mm diam, 10 mm tall) were investigated. The alumina samples were of two types, i.e., machined on the cylindrical surface to (i) 0.8 μm surface finish and (ii) 0.25 μm surface finish. An inverse correlation between the frequency of occurrence of prebreakdown x-ray emission and the surface flashover strength is observed for all samples. The relationship between the onset time of the prebreakdown x-ray peak from voltage zero and the surface flashover strength, however, is seen to be in direct proportion, i.e., the longer the onset time of the x-ray peak from voltage zero, the higher is the flashover voltage. These novel experimental observations are analyzed to infer the origin of x radiation in the bridged vacuum gap and their dependence on the nature of the insulating surface. The results could not be explained satisfactorily by the conventional secondary emission avalanche theory. A thermally activated, field-assisted exoelectron emission model is believed to be in better qualitative agreement with the prebreakdown x-ray emission results reported here.
The effect of Young’s modulus on the surface-force-induced contact radius of spherical glass particles on polyurethane substrates
Authors: Rimai D. S. , DeMejo L. P. , Vreeland W. , Bowen Ray , Gaboury S. R. , Urban M. W.
Published: July 2002

The radius of contact, arising from surface force interactions, was determined using scanning electron microscopy for glass beads having nominal radii of 12 and 20 μm in contact with two polyurethane substrates, differing principally in Young’s modulus (3.83 and 41.7 MPa, respectively). It was found that the ratios of the contact radii scaled according to the model proposed by Johnson, Kendall, and Roberts [Proc. R. Soc. London Ser. A 324, 301 (1971)]. The works of adhesion calculated from these results were found to be approximately 0.12 J/m2.
Rapid thermal diffusion of boron implanted as boron difluoride in preamorphized silicon
Authors: Walker A. J.
Published: July 2002

The diffusion of boron, implanted into crystal and preamorphized silicon in the form of boron difluoride, has been studied using secondary-ion mass spectroscopy and cross-sectional transmission electron microscopy. A 90-keV silicon implant creates an amorphous layer extending from the silicon surface to a depth of 186 nm as measured by Rutherford backscattering spectroscopy. The as-implanted boron profiles are contained completely within the amorphous layer. Results indicate that boron diffusion in the amorphous layer is suppressed during rapid thermal annealing between 1000 and 1150 °C. Discussion of this is based on the effect of fluorine on the boron diffusion.
Long wavelength infrared photocurrent study of Si-SiGe heterostructures
Authors: Liu H. C. , Li Lujian , Baribeau J.-M. , Buchanan M. , Simmons J. G.
Published: July 2002

We report on an experimental long wavelength infrared photocurrent study of a series of a Si-SiGe double-heterostructure samples. The active region is a thin heavily p-type doped SiGe layer, and the photoexcited holes due to free-carrier absorption are collected over the potential barrier resulting from the Si-SiGe valence-band offset. Photocurrent spectra with different cutoff wavelengths are observed for samples with different SiGe compositions, arising from internal photoemission in the Si-SiGe heterojunction. Photocurrents at finite biases and at zero bias (i.e., photovoltaic operation) are studied. Optimizing device parameters may lead to detector structures for large focal plane arrays.
Laser surface treatment dominated by buoyancy flows
Authors: Schüssler A. , Steen P. H. , Ehrhard P.
Published: July 2002

An experimental setup is investigated wherein surface tension forces are suppressed during laser treatment and the melt pool convection is controlled by buoyancy forces. The structure of surfaces processed by this method differs from those of conventionally treated surfaces. A dimensionless measure of buoyancy-flow strength, namely the Grashof number, is employed to quantify the flow intensity that is linked to the breakdown of the covering particle coating. Using a two-dimensional numerical approach the flow and temperature fields are computed.
Mössbauer studies on tin-bismuth oxide CO selective gas sensor
Authors: Sharma Shambhu Sharan , Nomura Kiyoshi , Ujihira Yusuke
Published: July 2002

Tin-bismuth (Sn-Bi) oxide films prepared by spray-pyrolysis techniques were characterized by in situ conversion electron Mössbauer spectrometry in an atmosphere of CO and CH4. The isomer shift of Sn4+ in Sn-Bi oxide decreased at 250 °C and 400 °C in CO and CH4 atmospheres, respectively. An electrical resistance change was also observed at about 250 °C in CO atmosphere, which showed a selective behavior towards CO gas in comparison to CH4 and C2H5OH gases. These results show that CO gas interacted with bulk as well as with the surface of Sn-Bi oxide at low temperature. The increase in the sensitivity of CH4 and C2H5OH at temperatures around 400 °C at the expense of selectivity towards CO was interpreted in terms of surface as well as bulk interactions, and also the catalytic enhancement by reaction of decomposed products from CH4 and C2H5OH.
Increased peak current in AlAs/GaAs resonant tunneling structures with GaInAs emitter spacer
Authors: Choi Y. W. , Wie C. R.
Published: July 2002

Self-consistent simulation results are presented for the symmetric barrier AlAs/GaAs/AlAs resonant tunneling structures with a GaInAs emitter spacer well [Appl. Phys. Lett. 58, 1077 (1991)]. A simple model is used to handle the two-dimensional emitter accumulation electrons. These accumulation electrons below the emitter launching energy are treated as pseudo three-dimensional electrons, distributed continuously down to a certain minimum energy. With a proper choice of this bottom energy, a good agreement is achieved in the peak position between the simulation results and the experimental data. The best fit value of the bottom energy for the accumulated electrons was about 2/3ΔEc below the emitter conduction band edges for all diodes. Also, the simulation results could explain the systematic variation of the experimental peak current and voltage values as a function of the GaInAs spacer well depth. In order to provide a design guideline, the layer parameters were systematically varied and the simulation results on the peak current are presented. The peak current density is found to be most sensitive to the AlAs barrier thickness, especially to the emitter barrier thickness, and it is further increased by using an emitter spacer well. Based on our theoretical analyses, a 10-Å AlAs double barrier and 50-Å GaAs well with a 50-Å Ga0.9In0.1As emitter spacer well could produce a peak current density as high as 2200 kA/cm2.
Direct experimental evidence of a body-centered-cubic Co phase in radio-frequency-sputtered Co/Fe multilayers
Authors: Boher P. , Giron F. , Houdy Ph. , Baudelet F. , Fontaine A. , Ladouceur J. M. , Dartyge E. , Beauvillain P. , Chappert C. , Veillet P. , Le Dang K.
Published: July 2002

Radio-frequency-sputtered Co/Fe multilayers with layer thicknesses varying in the 8–100 Å range were studied by extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) techniques. While the Fe environment is body-centered-cubic (bcc) in all the samples, the Co environment depends drastically on the Co layer thickness. Under ≂20 Å, investigation at the Co K edge by XANES provides a bcc fingerprint in both polarization directions. The XANES profile becomes typical of a full hcp stacking only for Co layer thicknesses larger than 98 Å. This behavior is confirmed by EXAFS spectra at the Co K edge and NMR analysis. For Co layer thickness between 6 and 18 Å, eight first neighbors at 2.48 Å and six second neighbors at 2.83 Å are detected which match the bcc phase. Resonance peak at a very low frequency is also observed (198 MHz). The second shell radius appears at 2.78 Å only for larger Co layer thicknesses. This effect goes along with the NMR peak shift to higher frequency (220 MHz). All these results are consistent with a Co-bcc-like structure which changes into a hcp phase when the Co layer thickness increases.
Ultrasonic sensing of powder densification
Authors: Lu Yichi , Wadley Haydn N. G. , Parthasarathi Sanjai
Published: July 2002

An independent scattering theory has been applied to the interpretation of ultrasonic velocity measurements made on porous metal samples produced either by a cold or a high-temperature compaction process. The results suggest that the pores in both processes are not spherical, an aspect ration of 1:3 fitting best with the data for low (<4%) pore volume fractions. For the hot compacted powders, the pores are smooth due to active diffusional processes during processing. For these types of voids, the results can be extended to a pore fraction of 10%, at which point voids form an interconnected network that violates the model assumptions. The cold pressed samples are not as well predicted by the theory because of poor particle bonding.
Growth and structural properties of epitaxial GaxIn1−xP on InP
Authors: Bensaada A. , Chennouf A. , Cochrane R. W. , Leonelli R. , Cova P. , Masut R. A.
Published: July 2002

The growth of heteroepitaxial GaxIn1−xP on InP for 0<x<0.25 has been carried out by low-pressure metalorganic chemical vapor deposition and characterized by high-resolution x-ray diffraction and low-temperature photoluminescence measurements. The x-ray data indicate that the epilayers are under biaxial tensile strain and that, for samples with x<0.05, the lattice mismatch is accommodated almost completely by tetragonal distortions. From photoluminescence measurements, the energy band gap is found to vary monotonically with the Ga concentration; it also shifts linearly with the elastic strain in the layer. The calculated value of 0.99×104 meV per unit strain is in good agreement with that predicted from elasticity theory.
Orientation-dependent vibrating sample magnetometry of thin films of Y1Ba2Cu3O7−x
Authors: Mahajan Sukesh , Cappelletti R. L. , Rollins R. W.
Published: July 2002

We report vibrating sample magnetometry measurements of superconducting thin epitaxial films of Y1Ba2Cu3O7−x as a function of field orientation. The results are that the measured magnetic moment is always oriented perpendicular to the plane of the film and essentially depends only on the perpendicular component of the applied field. The moment exhibits saturation which is in accordance with a simple critical state model for trapping flux.
Quantitative determination of the recombining activities of 60° and screw dislocations in float zone and Czochralski-grown silicon
Authors: Mariani J. L. , Pichaud B. , Minari F. , Martinuzzi S.
Published: July 2002

We have characterized quantitatively the recombining activities of 60° and screw dislocations by their recombination velocities. This parameter was derived from the diffusion length determined by using the surface photovoltage method. Dislocations were introduced in initially perfect float zone and Czochralski-grown crystals, at different temperatures. The results show that 60° dislocations are much more active than screws, and that the activity increases markedly with oxygen content of the material and with the temperature at which dislocations were introduced.
E
1 electrolyte electroreflectance of GaAs modeled by Franz–Keldysh theory
Authors: Batchelor R. A. , Hamnett A.
Published: July 2002

Electrolyte electroreflectance spectra at the E1 transition were measured for 〈100〉 p-type GaAs electrodes of dopant density 2×1016, 7×1016, 2.7×1017, and 2×1018 cm−3. The spectra broadened with increasing reverse bias and increasing dopant density, which we believe to result directly from the increasing strength of the dc electric field, in contrast to the more usual assumption of low field conditions at the E1 transition. The intermediate field or Franz–Keldysh theory of Aspnes for a three dimensional M1 critical point has therefore been used to model the E1 and E1+Δ1 features as a function of dopant density and depletion layer voltage. For values of the collision broadening parameter, Γ, measured by other workers under low field conditions, it is shown that significant field induced broadening is expected and that spectra can be successfully modeled, provided the collision broadening is allowed to increase fairly rapidly with increasing energy.
Theoretical studies of tunneling effect on absorption spectrum of a quantum well with applied electric field
Authors: Li H. S. , Wang K. L.
Published: July 2002

The intersubband optical absorption and Stark effect of square and step quantum wells in the presence of applied electric field have been investigated theoretically. By considering the tunneling of photoexcited electrons under the influence of electric field in the quantum well, we obtain a shifted and broadened absorption spectrum from the tunneling of electrons. Such broadening leads to a decrease of absorption coefficient when the applied electric field is increased. For detector application of multiple quantum well devices, if efficient tunneling of the photoexcited electrons is desirable for high responsivity, the sharpness of the absorption peak needs to be compromised. Our results provide insight to this broadening and thus the optimization guideline for detector design.
Synthesis of a diamond and metal mixture by the chemical vapor deposition process
Authors: Kawarada M. , Kurihara K. , Sasaki K.
Published: July 2002

A mixture of diamond and metal film was synthesized by a hybrid process combining plasma-jet chemical vapor deposition and a plasma-spray process. Sprayed molybdenum and tungsten were changed to Mo2C and tungsten carbide, respectively, and the lattice constants of Ni, Fe, and Co were increased by carbon-plasma spraying. Adhesion of film to the substrate was improved using the hybrid process to form a layer 50 to 150 μm thick of mixed metal and diamond between the substrate and pure diamond film.
Cross-talk between neighboring pulse discharges in gas discharge displays
Authors: Suzuki Mutsumi , Mikoshiba Shigeo , Curzon Frank L.
Published: July 2002

Simultaneous pulsing of two, closely spaced discharge tubes inhibits the ignition of one of the discharges. Such cross-talk is prominent for discharge tubes having a floating cathode potential (i.e., with an impedance attached to the cathode), driven by short duration pulses, and having a long discharge path. The cross-talk originates from at least two mechanisms. First, a voltage jump at the cathode, induced by a capacitive coupling with another cathode, makes the anode-cathode potential smaller, and hence discharge ignition is inhibited. Second, wall charges induced by a discharge in a neighboring tube also inhibit ignition. The cross-talk can adversely affect the operation of gas discharge displays. It is demonstrated that cross-talk in the panel can be eliminated by adopting a dephasing drive technique.
Reflection high-energy electron diffraction and optical measurements on the molecular-beam epitaxial growth of one and two monolayers of InAs on GaAs
Authors: Dosanjh S. S. , Dawson P. , Fahy M. R. , Joyce B. A. , Murray R. , Toyoshima H. , Zhang X. M. , Stradling R. A.
Published: July 2002

We report here on the reflection high-energy electron diffraction, photoluminescence (PL), and photoluminescence excitation study of the direct growth by molecular-beam epitaxy of one and two monolayers (MLs) of InAs on GaAs. InAs can be grown pseudomorphically up to a thickness of 1 ML, deposition of 2 MLs results in three-dimensional nucleation. In the latter case our results suggest that the first ML is disrupted by the growth of the second. This finding is in contradiction of the Stranski–Krastanov growth mode. A 1-ML InAs quantum well (QW) with GaAs barriers produces intense luminescence at 1.465 eV, whereas for the intended 2-ML InAs QW sample, PL characteristic of InAs clusters with a most probable thickness of 3 MLs is observed.
Damage production and annealing in 28Si-implanted CoSi2/Si(111) heterostructures
Authors: Bai G. , Nicolet M.-A.
Published: July 2002

The damage in epitaxial CoSi2 films 500 nm thick grown on Si(111) produced by room-temperature implantation of 150 keV 28Si were investigated by 2-MeV 4He channeling spectrometry, double-crystal x-ray diffractometry, and electrical resistivity measurements. The damage in the films can be categorized into two types. In lightly (heavily) damaged CoSi2 the damage is in the form of point-like (extended) defects. The resistivity of lightly damaged CoSi2 films rises with the dose of implantation. Electrical defects correlate well with structural ones in lightly damaged films. The resistivity of heavily damaged films flattens off while the structural defects continue to rise with the dose, so that resistivity no longer correlates with structural defects. Upon thermal annealing, lightly damaged films can fully recover structurally and electrically, whereas heavily damaged films do so only electrically. A residual structural damage remains even after annealing at 800 °C for 60 min.
Steady-state conduction in high density polyethylene with field-dependent mobility
Authors: Kumar A. , Perlman M. M.
Published: July 2002

A theory of steady-state conduction of injected space-charge-limited carriers (SCLCs) into high density polyethylene (HDPE) is presented. Injected carriers are deeply trapped at crystalline-amorphous boundaries before the steady state is reached. At elevated temperatures, they are thermally excited to the conduction band in the crystalline regions, and then hop with field-dependent mobility through defect states of the amorphous regions. A hopping site separation of 2.2 nm, corresponding to 9.4×1019/cm3, yields good agreement with experimental current-field characteristics for fields up to 0.5 MV/cm, in the temperature range 61–85.5 °C. The final current I versus field F and temperature T equation shows that the activation energy of the detrapping and transport processes are additive on a semilog plot of I/T vs 1/T. The total activation energy is 1.15 eV at 0.2 MV/cm, in agreement with others. The steady-state field distributions in the sample are calculated, and are independent of temperature in the above temperature and field ranges. The conditions under which our theory reduces to that of simple SCLC, field-independent mobility theory, and differences in conduction between linear low density polyethylene and HDPE are discussed.
Enhanced exciton absorption and saturation limit in strained InGaAs/InP quantum wells
Authors: Jiang Y. , Teich M. C. , Wang W. I.
Published: July 2002

A new approach for enhancing the exciton absorption and increasing the saturation limit in quantum wells (QWs), using tensile strain, is proposed. Because of the valence-band mixing in a strained QW, the in-plane hole mass can become very large or negative. This leads to a heavy electron-hole reduced mass (exciton mass), and therefore to a small exciton radius. Exciton absorption is substantially increased because of the increased electron-hole overlap probability in these small-radius excitons. The effects of saturation are also substantially reduced because of decreased charge-screening effects for small-radius excitons and because the rapid dispersal of the photon-generated excitons reduces the Pauli exclusion effect.
Intrinsic carrier concentration of narrow-gap mercury cadmium telluride based on the nonlinear temperature dependence of the band gap
Authors: Lowney J. R. , Seiler D. G. , Littler C. L. , Yoon I. T.
Published: July 2002

The intrinsic carrier concentrations of narrow-gap Hg1−xCdxTe alloys have been calculated as a function of temperature between 0 and 300 K for x values between 0.17 and 0.30. The new and more accurate relation for the temperature dependence of the energy gap, which is based on two-photon magnetoabsorption data, is used. This relation is further supported here by additional one-photon magnetoabsorption measurements for x=0.20 and 0.23, which were made with a CO2 laser. In this range of composition and temperature, the energy gap of mercury cadmium telluride is small, and very accurate values for the gap are needed to obtain reliable values for the intrinsic carrier density. Kane’s k⋅p theory is used to account for the conduction-band nonparabolicity. Large percentage differences occur between our new calculations and previously calculated values for ni at low temperatures. A nonlinear least-squares fit was made to the results of our calculations for ease of use. The implications of these results for Hg1−xCdxTe materials characterization and device operations are discussed.
Fluence limiting via photorefractive two-beam coupling
Authors: Wood Gary L. , Clark William W. , Salamo Gregory J. , Mott Andrew , Sharp Edward J.
Published: July 2002

The optimum performance of a photorefractive two-beam coupling fluence limiter is presented. A two-level, single-dopant-species model is used to determine the minimum transmitted fluence for different crystal dopant densities and incident fluences. The effects on limiter performance for different beam parameters such as the modulation ratio and crossing angle and for different crystal parameters such as the mobility, electro-optic coefficient, and dielectric constant are determined.
A mechanism for diborane induced selectivity loss in the chemical vapor deposition of silicon from SiH2Cl2
Authors: Lapiano-Smith D. A. , McFeely F. R.
Published: July 2002

The interaction between B2H6 and SiO2 was investigated by soft x-ray photoemission. Thermally activated, autocatalytic dissociative chemisorption of B2H6 on SiO2 to form elemental films was discovered at temperatures exceeding 550 °C. These surfaces are shown to be quite reactive towards SiH2Cl2. This process is thus a mechanism whereby the selectivity of chemical vapor deposition exhibited by SiH2Cl2 towards SiO2 can be rapidly degraded.
Antireflection properties of a graded-impedance stack of acoustical symmetric multilayers
Authors: Martin B. G.
Published: July 2002

A previous investigation [B. G. Martin, J. Appl. Phys. 66, 1931 (1989)] showed that acoustical symmetric multilayer (ASM) structures could be used as antireflection (AR) coatings. In the present investigation, we consider the AR properties of stacked ASMs, which offer a practical means for achieving graded impedance structures for virtually any gradient profile.
A novel technique for low-threshold and high-power InGaAs/GaAs strained-layer 0.98-μm buried heterostructure laser fabrication
Authors: Liou D. C. , Chiang W. H. , Lee C. P. , Chang K. H. , Liu D. G. , Wu J. S. , Tu Y. K.
Published: July 2002

A novel fabrication technique has been developed for InGaAs/GaAs strained-layer buried heterostructure lasers. Dielectric masks and Zn diffusion are not required in this technique. This novel fabrication process is much easier than the conventional approach and yields excellent laser results. A low threshold of 3 mA and high-power operation for lasing wavelength of 9800±20 Å have been achieved with graded index separate confinement heterostructure devices using this novel technique.
The circuit properties and complete fields of horizontal-wire antennas and arrays over earth or sea
Authors: King Ronold W. P.
Published: July 2002

The surface-wave and space-wave components of the electromagnetic field generated by a wave antenna of the Beverage or horizontal-wire type are determined and discussed. A knowledge of this complete field in the air over a conducting or dielectric half-space is essential for an over-the-horizon radar that makes use of both ionospheric reflection for detecting distant high-flying targets and the surface wave for detecting near and low-flying targets. Omnidirectional and directive arrays that include both wave antennas and a vertical monopole are described and analyzed.
Analysis of C films formed on single-crystal Cu by ion implantation and laser annealing
Authors: Withrow S. P. , White C. W. , Zuhr R. A. , McCamy J. W. , Pennycook S. J. , Hembree D. M.
Published: July 2002

Single-crystal Cu has been ion implanted with C to fluences of 1×1018/cm2 followed by laser annealing with nanosecond pulses from an excimer laser and subsequently etched in dilute nitric acid. Raman spectroscopy, Rutherford backscattering, and electron microscopy have been used to identify the distribution and morphology of the carbon at different stages of sample processing. Polycrystalline graphite and amorphous carbon films are typically produced over a wide range of processing conditions; well-ordered graphite can be formed as well. Small Cu crystallites are seen in areas where the etch lifted the C films off the substrate. However, extensive analysis by Raman spectroscopy and electron microscopy provides no evidence for the formation of the diamond phase of carbon.
Magnetism and magnetoresistance in epitaxial Fe/Cr(001) superlattices
Authors: Kamijo Atsushi , Igarashi Hitoshi
Published: July 2002

Epitaxial Fe/Cr(001) superlattices, having different topological interface roughnesses, were grown by the molecular beam epitaxy technique. The interface roughness was characterized by in situ reflection high-energy electron diffraction and ex situ scanning tunneling microscopy. The magnetic field (H) dependences for magnetization (M) and magnetoresistance (MR) have been discussed. Large topological interfacial roughness led to a substantial reduction in the MR ratio. In the case of superlattices with sufficiently small and similar topological interfacial roughnesses, the MR ratio decreased with lowering the superlattice growth temperature. M2 dependence for magnetoresistance, which was independent from the sample qualities, was found.
Simple energy balance considerations to compute laser-induced effects on carbon-implanted copper substrates
Authors: Singh Rajiv K. , Harkness S. , Qian F.
Published: July 2002

We have developed simple analytical methods to estimate the nonequilibrium thermal effects of pulsed nanosecond lasers on carbon-implanted copper substrates. This analytical method eliminates the use of detailed numerical solutions of the one-dimensional heat flow equation with nonlinear moving boundary conditions. The effect of laser variables, especially energy density and pulse duration, on the maximum melt depths, solidification velocities, and maximum surface temperatures have been determined. Comparison between the analytical and detailed computer solutions of heat flow equations have also been performed to determine the validity of these analytical solutions.
Oxidation state of Cu ions in H-charged YBa2Cu3O7−δ films
Authors: Balogh A. G. , Jaegermann W. , Briere M. A. , Stritzker B. , Zander W.
Published: July 2002

Photoemission experiments were performed on H-charged YBa2Cu3O7−δ films at room temperature. Samples produced by laser ablation were charged with H from the gas phase prior to the x-ray photoelectron spectroscopy measurements. X-ray photoelectron spectra clearly show the influence of H charging on the oxidation states of Cu ions. A linear correlation between H concentration and the intensity of the Cu 2p satellite line related to the mean line was found.
Critical current density of high-quality Bi2Sr2Ca2Cu3Ox thin films prepared by metalorganic chemical-vapor deposition
Authors: Yamasaki H. , Endo K. , Nakagawa Y. , Umeda M. , Kosaka S. , Misawa S. , Yoshida S. , Kajimura K.
Published: July 2002

Critical current densities Jc were measured in as-deposited, c-axis-oriented Bi2Sr2Ca2Cu3Ox thin films with Tc values as high as 97 K, which were prepared by metalorganic chemical-vapor deposition. These films showed high Jc (≳109 A/m2) at 77.3 K in high magnetic fields (≥1 T, H∥a-b plane). The best values are 3.3×109 A/m2 at 1 T and 9.1×108 A/m2 at 8 T, which are the highest Jc for Bi-oxide thin films among those reported so far. There were no signs of weak links in the Jc(H) behavior, and the surface morphology examined by scanning electron microscopy showed no apparent grain boundaries. The values of Jc decreased sharply when the applied field deviated from the a-b plane, and went to zero at the angles where the field component in the c direction is nearly equal to the irreversibility field Hc2* parallel to the c axis. The angular dependence of Jc of these films is most reasonably explained by the theory of intrinsic pinning.
Magnetic properties of R2Fe17CNx
Authors: Yang Ying-chang , Pan Qi , Zhang Xiao-dong , Ge Sen-lin
Published: July 2002

The crystallographic and magnetic properties of the series of R2Fe17CNx, where R=Y, Sm, Gd, Tb, Dy, and Er have been investigated in comparison with those of R2Fe17C and R2Fe17N3−δ. The results indicate that Sm2Fe17CNx, which possesses a higher Curie temperature, a larger saturation magnetization, and a stronger anisotropy field than Sm2Fe17C or Sm2Fe17Nx, seems to be a more favorable candidate for permanent magnet applications.
The quantum efficiency of HgCdTe photodiodes in relation to the direction of illumination and to their geometry
Authors: Rosenfeld D. , Bahir G.
Published: July 2002

In this paper a theoretical study of the effect of the direction of the incident light on the quantum efficiency of homogeneous HgCdTe photodiodes suitable for sensing infrared radiation in the 8–12 μm atmospheric window is presented. The probability of an excess minority carrier to reach the junction is derived as a function of its distance from the edge of the depletion region. Accordingly, the quantum efficiency of photodiodes is presented for two geometries. In the first, the light is introduced directly to the area in which it is absorbed (opaque region), while in the second, the light passes through a transparent region before it reaches the opaque region. Finally, the performance of the two types of diodes is analyzed with the objective of finding the optimal width of the absorption area. The quantum efficiency depends strongly on the way in which the light is introduced. The structure in which the radiation is absorbed following its crossing the transparent region is associated with both higher quantum efficiency and homogeneity. In addition, for absorption region widths higher than a certain minimum the quantum efficiency in this case is insensitive to the width of the absorption region.
Defects in low-temperature electron-irradiated p-type silicon
Authors: Nubile P. , Bourgoin J. C. , Stievenard D. , Deresmes D. , Strobl G.
Published: July 2002

Defects in monocrystalline silicon have been studied in the past, in particular, defects induced by room-temperature electron and proton irradiations on both n- and p-type materials, and most of the corresponding defects have been tentatively identified. However, there are still several questions which remain to be answered such as the nature and behavior of the defects introduced in the range 4–300 K. In this work Czochralski-grown p-type material has been irradiated at three different temperatures (90, 200, and 300 K) and characterized by deep-level transient spectroscopy (DLTS) and lifetime measurements. The data show that the defects created after irradiations at 90 and 200 K are different from those reported in the literature for irradiations at 4, 77, and 300 K, showing that three annealing steps exist between 4 and 300 K. These defects are characterized and a tentative identification of them is made. Finally, an attempt to detect the defects responsible for the lifetime, i.e., the recombination centers, not observed by DLTS, using spin-dependent recombination is described.
Laser damage formation in KTiOPO4 and KTiOAsO4 crystals: Grey tracks
Authors: Loiacono G. M. , Loiacono D. N. , McGee T. , Babb M.
Published: July 2002

The grey track effect in KTiOPO4 and KTiOAsO4 is shown to be related to the presence of Ti+3. The susceptibility to grey track formation was maximum in crystals grown from tungsten-based solvents. The data shows that no clear correlations exist between grey track susceptibility and either ionic conductivity or crystal-growth temperature. The similarity of grey tracks with photorefractive damage in LiNbO3 suggests the effect can be eliminated by stabilization of Ti+3 using charge compensation.
Stress cancellation in silicon oxynitride/InP structures obtained by rapid thermal chemical vapor deposition
Authors: Lebland F. , Licoppe C. , Nissim Y. I.
Published: July 2002

Rapid thermal chemical vapor deposition was utilized to deposit silicon-based dielectrics on III-V materials at high temperature. Silicon oxynitride films can be deposited on InP at 750 °C with compositions varying between silicon dioxide and silicon nitride. Secondary ion mass spectroscopy and nuclear reaction analysis measurements show that the oxygen concentration in the layers varies continuously with the oxidant gas flow rate. The overall stoichiometry of the films can be controlled with this parameter. The composition of the layers has a direct incidence on the mechanical tension of the insulator/semiconductor structures. A highly sensitive optical setup has been developed to measure the tension on these samples in order to determine the stoichiometry of the silicon oxynitride (SiOxNy) film that leaves the structure unstressed. The stress-free film composition is shown to depend also strongly on the thickness of the layer. A study of the overall stress introduced in a structure during its fabrication is presented.
Micro-Raman study on GaAs layers directly grown on (100) Si by molecular beam epitaxy
Authors: Ito Akira , Ichimura Masaya , Usami Akira , Wada Takao , Kano Hirayuki
Published: July 2002

Micro-Raman spectroscopy is applied to evaluate change of the crystal quality in molecular beam epitaxial GaAs layers on Si after rapid thermal annealing (RTA). The forbidden transverse optical phonon is observed in the GaAs layers especially near the interface. In the as-grown state, the Raman frequency of the longitudinal optical phonon shifts toward higher frequency near the interface. This blue shift indicates the existence of the compressive stress due to the lattice mismatch between GaAs and Si. On the other hand, after the RTA, the Raman peak shifts toward lower frequency. This red shift indicates that the tensile stress exists near the interface because of the difference in thermal expansion. The stress change indicates the relaxation of the lattice mismatch stress near the interface by formation of dislocations during the RTA.
Crystallographic alignment analysis of Nd2Fe14B materials using standard x-ray powder diffraction spectra
Authors: Meisner G. P. , Brewer E. G.
Published: July 2002

The crystallographic alignment quality of anisotropic magnetic materials made from die-upset Nd2Fe14B (MQ-III) materials was determined using a phenomenological analysis of θ-2θ x-ray diffraction spectra. This analysis consisted of fitting a calculated diffraction spectrum for aligned Nd2Fe14B to an observed spectrum collected on a bulk MQ-III slab oriented with the c-axis alignment parallel to the direction normal to the surface of the slab. The calculated spectrum was then used as a standard for intensity shifts of diffraction peaks corresponding to crystallographic reorientation from random to c-axis alignment. Intensity shifts for other samples for Nd2Fe14B materials having various degrees of c-axis alignment were determined and compared to the standard shifts giving an alignment factor representing the nature and extent of the crystallographic alignment in the sample.