bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of critical current density and transition temperature of YBa2 Cu3 O7−x thin films by measurement of ac susceptibility
Authors: Li Yi-Qun , Noh Dongwook , Gallois Bernard , Tompa Gary S. , Norris Peter E. , Zawadzki Peter A.
Published: July 2002

A technique for the determination of the critical current of superconducting thin films by a current-dependent ac susceptibility measurement has been developed. This method has been used to characterize superconducting YBa2 Cu3 O7−x films grown in situ at 1073 K by metalorganic chemical vapor deposition. Two superconducting phases with transition temperatures of 91 and 84 K have been detected by the measurement of ac susceptibility as a function of temperature even though the variation of resistance with temperature indicated a sharp transition. The critical current densities of the two superconducting phases have been determined from the variations of ac susceptibility with current at constant temperature and found to be equal to 1.14×104 A/cm2 and 3.6×103 A/cm2 at 75 K. The advantages of the technique in comparison to current methods of measurement of critical current are discussed.
Identification of CoSi inclusions within buried CoSi2 layers formed by ion implantation
Authors: De Veirman A. , Van Landuyt J. , Reeson K. J. , Gwilliam R. , Jeynes C. , Sealy B. J.
Published: July 2002

High-dose Co ion implantation in Si at elevated temperatures is used to synthesize buried CoSi2 layers. It is shown that inclusions of CoSi occur in the CoSi2 layer, when the stoichiometry level is exceeded at the peak of the Co distribution. These CoSi precipitates are observed prior to annealing and after a 5 s rapid thermal annealing (RTA) at 800 °C. During furnace annealing at 1000 °C or for RTA at temperatures above 900 °C, the CoSi phase transforms into CoSi2. In this communication the results of a transmission electron microscopy study of the CoSi inclusions are correlated with the Co depth profile, as determined by Rutherford backscattering spectrometry.
Role of Eu2+ luminescent centers in the electro-optical characteristics of red-emitting CaS:Eu thin-film electroluminescent devices with memory
Authors: Ando M. , Ono Y. A.
Published: July 2002

In order to investigate the role of the Eu2+ luminescent centers in determining the electro-optical characteristics of red-emitting CaS:Eu thin-film electroluminescent (TFEL) devices with inherent memory, light irradiation effects on these characteristics were studied. Both the threshold voltage and the response time decreased by light irradiation at wavelengths of 400–600 nm. This wavelength region coincides with that of the direct-excitation spectrum of Eu2+. Furthermore, emission peak height at the trailing edge of the pulse drive voltage increased by light irradiation in the same wavelength region. Since this emission is assumed to be caused by recombination of diffusing electrons with holes located at the ionized Eu2+ luminescent centers, increase in the emission peak height at the trailing edge of the pulse drive voltage indicated an increase in the number of the ionized Eu2+ luminescent centers. From these arguments we conclude that ionized Eu2+ luminescent center is a possible source of positive space-charge, which is known to play a decisive role in the memory and response characteristics of TFEL devices.
Structure and temperature dependence of conductivity of Ag2.5Se-Se composite
Authors: Vitta Satish
Published: July 2002

Rapid solidification of Ag-53 at. % Se alloy resulted in the formation of a composite mixture of Ag2.5Se and Se. The microstructure consists of spherical Se grains of 2–20 μm size, randomly distributed in a matrix of Ag2.5 Se. The Se grains were found to be layered hexagonal while the Ag2.5 Se had an orthorhombic crystal structure. The unit cell size of this phase, however, was twice that reported for the equilibrium orthorhombic Ag2 Se compound. The conductivity σ variation with temperature in the range 80–320 K was found to be similar to that observed in degenerate semiconductors. The σ decreased from 295 Ω−1 cm−1 at room temperature to a saturation value of 70 Ω−1 cm−1 for temperatures <80 K. The results are discussed in terms of percolation conduction in the Ag2.5 Se phase.
Distributions of implanted Fe ions in quartz crystal and silicon
Authors: Wang Ke-Ming , Shi Bo-Rong , Guo Hai-Yan , Liu Ji-Tian , Zhao Qing-Tai , Liu Xiang-Dong , Wang Yun-Tao
Published: July 2002

The distributions of implanted Fe ions into both amorphized quartz crystal (SiO2) and silicon at energies of 100, 150, and 200 keV were studied by the Rutherford backscattering technique. The obtained projected ranges and range stragglings are compared with our calculated values based on an angular diffusion model and transport of ions in matter predictions. Good agreement is obtained between calculated and experimental values for projected range and range straggling in both cases within experimental error.
An observation of 650 °C deformation of Si surface under ultra high vacuum
Authors: Nakamura N. , Ohshima T. , Nakagawa K. , Miyao M.
Published: July 2002

Significant deformation of a grooved Si surface is discovered during low temperature processing (650–900 °C) in a ultra high vacuum. The lowest temperature at which deformation results is determined to be 650 °C for a (111)Si substrate. In addition, clear facets are formed after high temperature processing (850–900 °C). These new findings are tentatively considered to originate from the surface migration of Si atoms on atomically clean surfaces.
Cold barium cathode: glow-discharge characteristics in rare gases and application to gas-discharge displays
Authors: Mikoshiba Shigeo , Shinada Shin-ichi
Published: July 2002

Normal cathode fall Vn, reduced normal current density jn/p2 (p denotes pressure), and reduced position of negative glow dgp (dg is defined as a distance between the cathode surface and the brightest position in the negative glow) of a cold barium cathode in rare gases were measured. For He, Ne, Ar, Kr, and Xe, Vn=81, 82, 82, 73, and 71 V, jn/p2 =3.7, 3.0, 42, 41, and 37 μA cm−2 Torr−2, and dgp=0.75, 0.51, 0.21, 0.12, and 0.16 cm Torr, respectively. The operating voltage of the Ba cathode in 20 Torr Xe showed no change after 10 000-h dc operation, and there was no observable chemical interaction between the barium and Zn2SiO4:Mn phosphor. Barium cathodes were formed in an 8-in. diagonal gas-discharge panel for TV display by thermally dissociating Ba(N3)2: the operating voltage was 1/2, and the power consumption and required cathode area were 1/4 of the same parameters for a similar panel with a Ni cathode.
Ferromagnetic and speromagnetic behavior in a rapidly quenched Bi2O3-CuO-Fe2O3 system
Authors: Soeya Susumu , Nakamura Shin , Ichinose Noboru
Published: July 2002

Ternary oxides in the system Bi2O3-CuO-Fe2O3 were prepared by rapid quenching from the melt. In the x-ray amorphous region, ferromagnetic behavior was observed. The amorphous (Bi2O3)25(CuO)25(Fe2O3)50 specimen shows an irreversible thermomagnetization process below about 200 K, indicating the existence of magnetic frustration. Two kinds of 57 Fe Mössbauer absorption spectra indicate that at room temperature this specimen is composed of two magnetic phases: paramagnetic and ferromagnetic. Below about 200 K, the paramagnetic spins seem to gradually assume a speromagnetic order. On the other hand, the ferromagnetic phase may exist as less disordered clusters or microcrystals, and the cluster size is estimated to be about 100–300 Å. The magnetic frustration seems to be caused by the competition between exchange interactions at the interface of the ferromagnetic clusters and the speromagnetic matrix.
Temperature and energy dependence of ion-beam synthesis of epitaxial Si/CoSi2/Si heterostructures
Authors: Radermacher K. , Mantl S. , Kohlhof K. , Jäger W.
Published: July 2002

The formation of buried CoSi2 layers by high-dose Co+ implantation into Si depends sensitively on the implantation temperature. Continuous buried epitaxial layers are only obtained at implantation temperatures above ∼300  °C. At temperatures below ∼200 °C, the implanted Si amorphizes, and the Co profile appears shifted towards the surface by about 250 Å compared to implantations performed above 300 °C, such that no buried layers are formed. A larger sputtering yield of the amorphous than the crystalline Si and a larger mean projected range of the implanted Co+ ions in single-crystalline Si seem to be responsible for the observed shift. For sputtering yields of 100- and 200-keV Co+ ions, we obtained values of Y=2.0±0.1 at room temperature and Y=1.7±0.1 at 350 °C. Implantations with energies ≤50 keV in (100) Si and subsequent annealing yield CoSi2 precipitates or layers at the surface, but not buried layers. The growth of rhombohedral precipitates in (100)Si aggravates the formation of very thin buried silicides. The minimum thickness of buried epitaxial silicides in (100)Si produced by high-dose implantations seems to be ∼400 Å, which is significantly larger than the minimum thickness in (111)Si (∼200 Å). Rapid thermal annealing leads to lower specific electrical resistivity values (13 μΩ cm) than conventional furnace annealing. Rutherford backscattering, He+-ion channeling, transmission electron microscopy, and sheet resistivity measurements were employed to characterize the implanted samples.
Determination of critical layer thicknesses in IV-IV-alloy systems using reflection high energy electron diffraction intensity oscillations: Ge(100)/GexSn1−x
Authors: Gossmann H.-J.
Published: July 2002

The critical layer thickness, Θ2D, denoting the maximum thickness of a film that can be grown in a laminar fashion before further deposition leads to islands, is an important materials parameter for a heteroepitaxial system. Technologically interesting films are restricted to thicknesses below Θ2D. Of similar importance is the knowledge of the critical layer thickness Θc beyond which the strain in a film is relieved. The analysis of the damping of reflection high energy electron diffraction (RHEED) intensity oscillations provides a fast and convenient way to determine Θ2D. It is shown for the first time that strain and relaxation of the film can be obtained from an analysis of the periods of the oscillations. Since such measurements take place during growth, questions of metastability, such as the influence of deposition rates, temperature, and other growth parameters, can be easily addressed. The RHEED method is applied to the Ge(100)/GexSn1−x system which has been predicted to exhibit a direct band gap for compositions x≊0.4–0.8 [D. W. Jenkins and J. D. Dow, Phys. Rev. B 36, 7994 (1987)]. At room temperature all alloys with x<0.85 grow in the Stranski–Krastanow growth mode. In the range of compositions where a direct band gap is predicted Θ2D is less than 14×1015 cm−2 (≊30 Å); for pure Sn, Θ2D=2×1015 cm−2. In all cases the films are not pseudomorphic.
Design and surface chemistry of nonalloyed ohmic contacts to pseudomorphic InGaAs on n+GaAs
Authors: Wakita Arlene , Moll Nick , Fischer-Colbrie Alice , Stickle William
Published: July 2002

Pseudomorphic layers of molecular-beam-epitaxy (MBE) grown InxGa1−xAs (xIn =.25 and 0.35) on heavily doped GaAs were studied for nonalloyed emitter and collector contacts to heterojunction bipolar transistors. Since the InGaAs layers in this study are coherent to the GaAs lattice, subsequent epitaxial layers can be grown after the ohmic contact with high quality. Contact resistances as low as 5×10−7 Ω cm2 have been obtained for a 60-Å layer of n+ InGaAs (x=0.35). These contact resistances are achieved through a combination of heavy silicon doping, which leads to a greater net donor concentration in InGaAs than in GaAs, and a low Schottky barrier height. The InGaAs layers, which are grown at a temperature of 380 °C, are heavily silicon doped to 2.4×1019 cm−3 by lowering the MBE growth rate. The chemical composition of the InGaAs surface was analyzed by X-ray photoelectron spectroscopy after selective etching in NH4OH:H2O2:H2O and after various surface treatments. The selectivity of the etch arises from the formation of In(OH)3, which has a low solubility in ammonium hydroxide solutions. The contact resistances after several surface treatments will be summarized.
A study of deep-level defects in metalorganic vapor-phase-epitaxy-grown ZnSe on GaAs by deep-level transient spectroscopy
Authors: Wang Y. H. , Li S. S.
Published: July 2002

Deep-level defects in Li+-implanted ZnSe epilayer grown by metalorganic vapor-phase epitaxy (MOVPE) on a GaAs substrate have been characterized by using the deep-level transient spectroscopy method under different post-implantation annealing conditions. Four electron traps with energy levels of Ec−0.3, 0.33, 0.55, and 1.02 eV and one hole trap with an energy level of Ev+0.23 eV were detected. Possible physical origins and formation mechanisms for these defects were discussed using the defect model proposed by Myles and Sankey [Phys. Rev. B 29, 6810 (1984)]. The results showed that interdiffusion between the ZnSe/GaAs heterointerface plays an important role on the formation of native defects in the MOVPE-grown ZnSe epitaxial films on the GaAs substrate.
Study of energy deposition in the electron-beam-pumped laser facility HAWK
Authors: Sweeney M. A. , Patterson E. L. , Samlin G. E.
Published: July 2002

The HAWK facility has been developed as a tool to investigate the kinetics of electron-beam-pumped lasers at a pressure of 1 atm for pump rates of 0.040–1 kW/cm3 and pump times of 0.05–1 ms. The highly collimated (1 cm FWHM within the lasing medium) relativistic electron beam propagates through fast valves that separate the accelerator vacuum from a 2-m-long vacuum isolation section, a 0.4-m-long gas-filled buffer section, and 0.7 m along a lambda-geometry laser cell. A 6.5 kG magnetic field confines the 1-MeV electron beam laterally and guides it around a 30° bend into the 3.3-cm-diam laser cell. A magnetic mirror at the far end of the laser cell reflects a large portion of the transmitted electron beam, thereby protecting the laser optics from the electron beam and making the axial deposition more uniform. In this paper we describe modeling of the electron beam energy deposition in HAWK using the three-dimensional Monte Carlo electron/photon transport code acceptm and compare our results with the measured energy deposition. These numerical simulations were begun during the design phase to define the operational range of the facility. There is good agreement between the calculated energy deposition in the laser cell and the deposition inferred from measurements with a segmented, totally stopping calorimeter at different axial locations in cases where hydrodynamic effects are unimportant. ln cases where these effects are important, however, the calculations can predict too large an amount of energy deposited in the laser gas. The numerical simulations are being used to infer the radial and axial deposition profiles of the electron beam energy as an aid in determining the electron-beam-pumped laser performance.
Environmental degradation of AlxGa1−xAs-GaAs quantum-well heterostructures
Authors: Dallesasse J. M. , El-Zein N. , Holonyak N. , Hsieh K. C. , Burnham R. D. , Dupuis R. D.
Published: July 2002

Data describing the deterioration of AlxGa1−xAs-GaAs heterostructures in long-term exposure (2–12 years) to normal room environmental conditions (∼20–25 °C, varying humidity) are presented. Optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron dispersion x-ray spectroscopy are used to examine AlxGa1−xAs-GaAs quantum-well heterostructure material that has hydrolyzed at cleaved edges, cracks, and fissures, and at pinholes in cap layers. The hydrolysis is found to be significant for thicker (>0.1 μm) AlxGa1−xAs layers of higher composition (x>0.85).
Contact spreading and the Au3In-to-Au9In4 transition in the Au-InP system
Authors: Weizer Victor G. , Fatemi Navid S.
Published: July 2002

An investigation is made of the third stage in the series of solid-state reactions that occur between InP and its most commonly used contact material, Au. This reaction, which results in the transformation of the contacting metallization from the pink-colored Au3In to the silver-colored Au9In4, is shown to be controlled by an In-Au exchange or kickout mechanism operating at the interface between the two phases. Contact spreading, a rapid lateral expansion of the contact metallization that can consume large quantities of InP during growth, is shown to be another manifestation of this final stage in the InP-Au reaction. A detailed description of the mechanisms, including an investigation of the kinetics of the processes involved, is presented.
Role of lead substitution in the production of 110-K superconducting single-phase Bi-Sr-Ca-Cu-O ceramics
Authors: Pierre L. , Schneck J. , Morin D. , Tolédano J. C. , Primot J. , Daguet C. , Savary H.
Published: July 2002

We have systematically investigated the influence of the three parameters (temperature of sintering, lead content, and duration of the sintering) on the growth of the (2:2:2:3) phase in ceramics of nominal composition Bi2−xPbxSr2Ca2Cu3O10−x/2, and have determined the compositions and thermal conditions leading to ceramics with Tc≊110 K and containing more than 95% of this phase. We show that this result can be obtained by usual calcination near 880°C in air, without recurring to the introduction of excess in the constituants, providing that intermediate grinding are effected, in order to reactivate the formation of the (2:2:2:3) phase which otherwise saturates for long durations of sintering. The suitable nominal compositions (0.3≤x≤0.4) correspond to those that yield inside the grains a lead content in the vicinity of the limit of solubility for lead. From the results of the preceding investigations and of experiments effected on lead-substituted single crystals of the (2:2:1:2) phase, we have clarified the role played by lead, at the microscopic level, in the enhancement of the formation of the (2:2:2:3) phase. The inferred role is the establishment of strong bonding between the slabs which are the buildings blocks of the structure of the superconducting phases, these slabs being almost independent in the lead-free compounds. The origin of the stronger bonding is discussed.
The impact of the metallization technology on junction behavior
Authors: Polignano M. L. , Circelli N.
Published: July 2002

The influence of a titanium-titanium nitride (Ti/TiN) barrier metallization on the behavior of junctions has been investigated. Different geometries have been used in order to separate the various contributions to the electrical behavior of junctions. An increase of the reverse current of junctions is observed in the presence of Ti/TiN/Al:Si contacts. This fact does not produce an increase of junction defect density, since the reverse current of junctions remains within an acceptable range. The contribution to junction reverse current induced by Ti/TiN/Al:Si contacts has been characterized; it has been shown that it is related to contact perimeter, it is independent of many relevant process steps, and it is reduced by thermal treatments after metal deposition. By assuming that this contribution is due to a generation-recombination center induced by Ti/TiN contacts, the analysis of current-voltage characteristics versus temperature gives an activation energy for this contribution. However, at present the available data do not allow us to identify its cause.
Davydov splitting in arachidic acid-cyanine dye complex Langmuir–Blodgett films
Authors: Saito Kazuhiro , Ikegami Keiichi , Kuroda Shin-ichi , Saito Mitsuyoshi , Tabe Yuka , Sugi Michio
Published: July 2002

A water-soluble cyanine dye is adsorbed from the solution to form a salt with an arachidic acid monolayer at the air-water interface. Complex monolayers thus formed were deposited onto substrates by the vertical dipping method to form Langmuir–Blodgett (LB) films. The optical properties of these films were examined employing a linearly polarized incident light. The films showed a large in-plane anisotropy of light absorption in both visible (electronic transition) and infrared (vibrational transition) regions. The in-plane anisotropy of the LB film is explained as due to the alignment of dimers, each showing Davydov splitting, by flow orientation during dipping. The configuration of the dye molecules in the dimer was estimated using Davydov’s theory and the extended dipole model. The layered structure of the film was determined by the x-ray diffraction technique.
Graphite film prepared by pyrolysis of bacterial cellulose
Authors: Yoshino Katsumi , Matsuoka Ryuichi , Nogami Kou , Yamanaka Shigeru , Watanabe Kunihiko , Takahashi Mitsuo , Honma Masao
Published: July 2002

A new route of preparation of high quality of graphitized films has been demonstrated. Highly graphitized films with electrical conductivity as high as 6×103 S/cm have been prepared by pyrolysis of bacterial cellulose films at 2900 °C. These films can be well intercalated with acceptors and donors such as FeCl3 and K, resulting in the enhancement of conductivity. Temperature dependencies of thermoelectric power and electrical conductivity are similar to those of soft carbon.
Media noise in periodic multilayered magnetic films with perpendicular anisotropy
Authors: Sanders I. L. , Wilhoit D. R. , Lambert S. E. , Gorman G. L. , Yogi T. , Speriosu V. S.
Published: July 2002

Periodic, finely multilayered thin-film magnetic structures (≤200 Å) with high in-plane coercivity suitable for longitudinal recording investigations have been fabricated. CoPt20/Pd and CoPt12Cr17/Pd periodic multilayers can exhibit a perpendicular orientation, originating from surface anisotropy effects, with a magnitude depending on the thickness of the component layers. The perpendicular orientation influences the transition noise, but for the particular systems studied, the results suggest that for a given value of coercivity squareness, ≲0.8, the greatest improvements in media noise performance can be achieved through reduced exchange in films with a well-defined, in-plane orientation.
Langmuir diagnostics of an rf-magnetron discharge used for ion-assisted growth of PbTe epilayers
Authors: Cook J. G. , Das S. R. , Quance T. A.
Published: July 2002

The plasma potential and the electron density and electron temperature of an rf magnetron discharge used for the ion-assisted growth of PbTe epilayers on BaF2 are measured using Langmuir probe diagnostics. The effect of rf potentials at the probe on the measured plasma parameters is reduced by driving the probe to follow the plasma potential. The discharge parameters are determined as a function of substrate bias voltage and substrate rf power. The ion energy and flux necessary for the epitaxial growth of (111) PbTe on (111) BaF2 are determined.
Improvements in long-pulse, electron-beam-pumped XeF(C→A) laser performance
Authors: Litzenberger Leonard N. , Mandl A.
Published: July 2002

The performance of the XeF(C→A) laser, pumped at a rate of 290 kW/cm3 with a 600-ns electron-beam pulse, has been improved through the optimization of the laser gas mixture and resonator output coupler reflectivity. An intrinsic efficiency of 1.1% and a specific output energy of 2 J/ℓ have been demonstrated. A uniformly pumped region of the gain medium was selected for diagnosis in these measurements. In a separate experiment with larger diameter mirrors, a total output energy of 4 J was recorded. These are the highest specific and total output energies reported thus far for a directly electrically excited XeF(C→A) laser. The laser pulse duration was 350 ns (FWHM), and the laser bandwidth was 160 Å. The small-signal net gain was measured during the electron-beam pulse at various wavelengths, and a peak gain of 0.4%/cm was observed. The sidelight fluorescence spectrum was also recorded.
On the validity of a thermal spike mixing model for low-Z metals
Authors: Bo/rgesen P. , Lilienfeld D. A. , Johnson H. H. , Alford T. L. , Wistrom R. E.
Published: July 2002

Low temperature ion beam mixing rates for Cu-Ti, Ni-Ti, and Fe-Ti layers have been found to be significantly lower than predicted by a popular semi-empirical thermal spike model. It has been proposed that the unavoidable hydrogen contamination of the as-deposited Ti films may have reduced the mixing rates, but the measurement of even lower mixing rates for Fe-V and Fe-Co bilayers shows the discrepancy to be more fundamental. Still, a systematic dependence on heat of mixing suggests that some sort of diffusional (thermal spike?) mechanism is involved.
X-ray conversion efficiency in Cu plasma produced by subnanosecond laser pulses
Authors: Soom B. , Weber R. , Balmer J. E.
Published: July 2002

The relative conversion efficiency of laser energy into x radiation in the range of about 0.8–5.5 keV was investigated as a function of irradiance for planar Cu targets. For two laser pulse durations at two wavelengths—100 ps / 670 ps at a wavelength of 1054 nm and 70 ps/470 ps at 527 nm—the requirements on the laser parameters for good conversion efficiency were established.
Simulation of high-frequency capacitance-voltage characteristics of amorphous/crystalline heterojunctions
Authors: Matsuura Hideharu M.
Published: July 2002

The model for simulating high-frequency capacitance-voltage characteristics of amorphous/crystalline heterojunctions has been developed, where the high frequency indicates a frequency higher than the reciprocal of the dielectric relaxation time of the amorphous semiconductor. The physical background of the space-charge density of the amorphous film and the built-in voltage of the heterojunction, which are experimentally obtained from the heterojunction-monitored capacitance method, is discussed using the calculated results.
Modified Kramers’ law for bremsstrahlung produced by complete beta particle absorption in thick targets and compounds
Authors: Shivaramu
Published: July 2002

External bremsstrahlung spectra produced by the complete absorption of beta particles from the decay of 32P in compounds, some of them used as nuclear radiation detectors including CdO, NaI, CsI, BiI3, HgI2, PbI2, and HgO, and in thick targets of Ni, Cu, Mo, Cd, Ta, and Pb, are measured using a NaI(T1) detector. The bremsstrahlung energy yields are calculated using the unfolded bremsstrahlung spectra. The effective atomic numbers of compounds for the bremsstrahlung process are interpolated from the energy yield data of elements and compounds. Although the experimental effective atomic numbers of compounds are consistently lower than the theoretical ones, the overall agreement between the experimental values and those derived from the Markwich and Van Greiken expression for the modified effective atomic number [A. A. Markowicz and R. E. Van Grieken, Anal. Chem. 56, 2049 (1984)] and from the expression for the mean atomic number, which has commonly been used for samples composed of more than one element, is good within experimental uncertainties. However, the experimentally derived effective atomic numbers are closer to the modified atomic numbers than to the mean atomic numbers. The linear relationship between the total energy yield and the atomic number Z does not strictly hold, and hence the equation of Kramers for total bremsstrahlung intensity is approximately valid. The exponent of the atomic number in the Kramers equation is found to be 1.08. The Kramers law is modified to give a better description of the experimental observations.
Ensemble Monte Carlo characterization of graded AlxGa1−xAs heterojunction barriers
Authors: Kamoua R. , East J. R. , Haddad G. I.
Published: July 2002

Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded AlxGa1−xAs heterojunction barriers using a self-consistent ensemble Monte Carlo method. In this paper, we consider barriers with two doping levels, 1×1015 cm−3 and 1×1017 cm−3, and two barrier heights, 100 and 265 meV. The 100-meV barrier resulted in small rectification at room temperature whereas the higher barrier exhibited considerable rectification. In both cases the structure with the lower doped barrier has resulted in a smaller current in both forward and reverse regions due to space-charge effects. The energy and momentum distribution functions deviate from a Maxwellian distribution inside the barrier region and in general show two peaks: one is comprised mainly of electrons near equilibrium and the second arises mainly from ballistic electrons. The higher doped structure resulted in a faster electron relaxation toward equilibrium as a function of position because the electric field decreases rapidly in the barrier region.
Some optical properties of infrared transmitting Bi-Ca-Sr-Cu-O glasses
Authors: Zheng Haixing , Lin Patrick , Xu Ren , Mackenzie J. D.
Published: July 2002

Glasses based on Bi2O3, CaO, SrO, and CuO were first prepared as precursors to polycrystalline superconducting ceramics based on these oxides. These glasses were found to be transparent in the infrared to 11 μm. The infrared cutoff is approximately 6.5 μm. The refractive indices are surprisingly high being about 2.9.
A model for the determination of the solid composition of ternary III-V and II-VI metalorganic chemical vapor deposition epilayers
Authors: Amir N. , Fekete D. , Nemirovsky Y.
Published: July 2002

A simple kinetic model for the metalorganic chemical vapor deposition growth of ternary III-V and II-VI epilayers denoted by AxC1−xB, is presented. The model yields the relationship between the solid composition x of the epilayer and the gas-phase concentrations of the constituents in various limiting cases. The solid composition x is given by x=(1+α−1×CGMC/CGMA)−1 =[1+α−1(1−Z−1)]−1 where α is a fitting parameter determined by the process parameters, CGMA and CGMC are the gas-phase concentrations of the metalorganic sources of A and C, respectively. The gas-phase composition Z is defined by Z=CGMA/(CGMA +CGMC). The predictions of the model are compared with measured data. The data points are calculated with one fitting parameter α, indicating the validity of the model.
Post-deposition sputter-etch induced optical anisotropy in evaporated gold films
Authors: Hodgkinson Ian J.
Published: July 2002

Gold films that are initially isotropic in the plane of the substrate following deposition at normal incidence are shown to become anisotropic as they are sputter etched with a beam of Ar+ ions. In situ monitoring of the optical transmittance at normal incidence for two polarizations during deposition and during etching shows that the effect increases with angle of incidence of the ion beam and depends strongly on the initial post-deposition morphology of the gold film. Films with an initial globular morphology subsequently exhibit the largest anisotropy, about 1%–2% in transmittance. Fully coalesced films show no anisotropy until they break up at very small thickness. Anisotropy versus mean transmittance deposition and etch paths are quite dissimilar and are indicative of different deposition/etch island morphologies.
Oxygen diffusion in carbon-doped silicon
Authors: Wijaranakula W.
Published: July 2002

Oxygen diffusion in carbon-doped silicon which received an extended isochronal anneal in the temperature range between 460 and 850 °C was studied. At temperatures below 690 °C, an enhanced oxygen diffusion was observed. This phenomenon has been previously suggested to be attributed to mobile stable carbon and oxygen complexes. In addition to these mobile species, it is proposed that the carbon and oxygen complexes could also act as an activated state in an enhanced diffusion process.
Effective longitudinal dielectric constant of a rectangular lattice of parallel conducting prolate spheroids
Authors: Lam John
Published: July 2002

The effective longitudinal dielectric constant is calculated for an infinite, three-dimensional, rectangular lattice of identical, parallel, conducting prolate spheroids. The problem is formulated by means of a matrix equation. The matrix elements are explicitly worked out. The matrix equation embodies all the multipole interactions among the spheroids exactly, and is solved analytically by iteration. An exact solution is obtained formally as an infinite series. It is shown that the interaction effects can be quantified completely by a shift in value of the depolarization factor of the spheroids. In the spherical limit, the results reduce properly to those previously derived directly for a lattice of spheres. In the opposite, acicular limit, the interaction-shifted depolarization factor is obtained in closed form, and numerical results are presented. The calculation of the effective longitudinal magnetic permeability of a lattice of magnetic prolate spheroids is similar. The magnetic permeability is obtainable from the dielectric constant by simple variable substitutions.
Crystalline anisotropy and loss effects on magnetostatic waves in layered yttrium iron garnet films
Authors: Buris N. E.
Published: July 2002

We report the effects of cubic and uniaxial anisotropy on the propagation of magnetostatic waves. When yttrium iron garnet films grown by the method of liquid-phase epitaxy on a [111] plane are biased in plane, the magnetization is aligned with the bias field only at six special orientations. In addition to frequency band shifts, the cubic anisotropy results in magnetostatic surface wave modes which have tilted plane phase fronts. Furthermore, the dB/μs loss of magnetostatic surface waves in multiple-layer films is not constant but varies with frequency.
Alloying of Ni/In/Ni/n-GaAs ohmic contacts induced by Ga-Ni-As ternary eutectic reactions
Authors: Jan C.-H. , Swenson D. , Chang Y. A.
Published: July 2002

The alloying behavior of Ni and Ni/In/Ni thin-film contacts to GaAs was studied using scanning electron microscopy and scanning Auger microscopy. A liquid was observed to form in both contacts upon annealing at 820 °C for three min. The cause of this behavior was postulated to be the presence of a ternary eutectic reaction in the gallium-nickel-arsenic system. Differential thermal analysis confirmed the existence in this system of the reaction L→NiGa+NiAs+GaAs at 810 °C. It was speculated that the liquid phase observed in the Ni/In/Ni contacts was due to the rapid segregation of indium metal to the contact surface and the subsequent melting of the nearly ternary interfacial region. These results demonstrated the inadequacy of rationalizing reactions between metals and compound semiconductors in terms of constituent binary phase equilibria.
3D-resolved determination of minority-carrier lifetime in planar silicon solar cells by photocurrent decay
Authors: Verhoef L. A. , Stroom J. C. , Bisschop F. J. , Liefting J. R. , Sinke W. C.
Published: July 2002

In modern production schemes for Si solar cells, defect passivation and impurity gettering are often used to improve material quality and thereby cell efficiency. These processes generally alter the spatial uniformity of minority-carrier transport parameters over the wafer and may result in minority-carrier lifetime and diffusion length variations both lateral and in depth. In polycrystalline Si these spatial dependences are already present due to the nature of the material. We present an extension of the photocurrent decay method to determine the diffusion length in a three-dimensionally resolved fashion. From a single photocurrent decay curve the back-surface recombination velocity, the average minority-carrier diffusion length, and an asymmetry factor which qualitatively describes the depth dependence of the diffusion length are determined. This is done using the three observables: quantum efficiency, fundamental decay time, and intercept of the extrapolated decay curve with the time-zero axis. Lateral resolution is obtained by focusing the light beam to a small spot on the cell and measuring the current decay curve as a function of position on the cell. It is shown that light-pulse durations longer than the minority-carrier lifetime and wavelengths longer than 950 nm are required. These conditions are met by using modulated wavelength-tunable light from a Ti:sapphire laser. Measurements on monocrystalline cells show that the decay time is independent of wavelength and light-pulse duration, as predicted by theory. Furthermore, the intercept with the time-zero axis was shown to increase with increasing pulse duration and wavelength. Measurements on a set of polycrystalline Si cells were performed showing that gettering treatments during cell production result in depth-dependent lifetimes.
Photoquenching phenomenon enhanced by proton irradiation in semi-insulating GaAs
Authors: Kuriyama K. , Takahashi H. , Kawahara H. , Hayashi N. , Watanabe H. , Sakamoto I. , Kohno I.
Published: July 2002

In undoped semi-insulating GaAs, we have found that the quenching phenomena of photoconductance and infrared absorption are enhanced by proton irradiation above 1013 /cm2, accompanied by an increase in near-band-edge infrared absorption. These phenomena disappear with the annihilation of the proton-induced near-band absorption by annealing at 350 °C. It is suggested that the enhanced photoquenching phenomena arise from the increase in the quenchable component due to the transition from the ionized midgap electron trap (EL2+) to the neutral EL20.
Transient spectroscopy of deep levels in thin semiconductor films
Authors: Ng K. , Chao I.-W. , Hunt C. E. , Churchill J. N.
Published: July 2002

Characterization of deep levels in thin-film semiconductors by capacitive pulse transient spectroscopy has been analyzed and verified by measurement. Numerical calculations show that highly resistive thin films create a degradation of signal and possible sign inversion of the signal. Experiments on silicon on insulator and molecular beam epitaxy GaAs Schottky barrier capacitors verify the calculated signal deviation.
Charge-to-mass separation in a current coaxial lens
Authors: Brown I. G. , Kelly J. C.
Published: July 2002

We present results demonstrating the charge state separation of an ion beam in a purely cylindrical geometry using the azimuthal magnetic field of a straight conductor. This geometry, called a current coaxial lens, has advantages for the analysis of intense ion beams where it is important to minimize space charge blow-up of the beam due to loss of space charge neutralization. A metal vapor vacuum arc ion source was used to produce an annular, low energy, aluminum ion beam of total beam current several tens of milliamperes and with charge state components Q=1+, 2+, and 3+ at energies of 20, 40, and 60 keV, respectively. Separation of the three different charge state fractions of the beam was measured. The method has been shown to be effective for the case when the beam pulse is long compared to all ion transit times involved and the beam current is high in terms of the need for space charge neutralization.
Site-selection spectroscopy, energy transfer, and laser emission in Nd3+-doped Ba2MgGe2O7
Authors: Ferry Michael J. , Kliewer Michael L. , Reeves Roger J. , Powell Richard C. , Allik Toomas H.
Published: July 2002

A detailed spectroscopic and pump wavelength dependent laser study has been performed on Nd3+ ions in Ba2MgGe2O7. Site-selection spectroscopy experiments reveal fifteen distinct crystal field sites for the Nd3+ ions. At room temperature, excitation of ions in any one of these sites is followed by efficient, thermally activated energy transfer to ions in a site having a laser emission transition at 1054 nm. Laser-pumped laser experiments were performed to determine the pumping threshold and slope efficiency of laser action in this material for different monochromatic pump wavelengths. The measured slope efficiencies were found to be pump wavelength dependent and ranged from 6% to 22%. Excited-state absorption of pump photons was shown to be responsible for this variation in the slope efficiency.
One-dimensional hetero-junction structure in polysilane
Authors: Isaka Hiroaki , Matsumoto Nobuo
Published: July 2002

A new model is presented for an electronic structure of polysilane which contains plural phases. This structure corresponds to the heterojunction structure between one-dimensional semiconductors with different band gaps (one-dimensional heterojunction model, 1-D HJ model). Measurements of UV absorption, excitation, and emission spectra show that photoexcited energy transfers between phases and recombines radiatively in smaller band-gap regions. The 1D HJ model explains this mechanism and also explains the origin of the large differences in mobilities between electrons and holes in polysilanes.
Characterization of rf-sputtered SnOx thin films by electron microscopy, Hall-effect measurement, and Mössbauer spectrometry
Authors: Stjerna Bertil , Granqvist Claes G. , Seidel Agneta , Häggström Lennart
Published: July 2002

SnOx films, made by reactive rf magnetron sputtering onto unheated glass, were studied by electron microscopy, Hall-effect measurements, and Mössbauer spectrometry. Transmission electron microscopy showed that the films were polycrystalline with a grain size of ∼15 nm. Hall-effect measurements gave a sharp resistivity minimum (down to 2.8×10−3 Ω cm) and electron concentration maximum (up to 1.2×1020 cm−3 ) at a specific O2/Ar gas-flow ratio during sputtering. Mössbauer spectrometry indicated that the most conducting films only consisted of the SnO2 phase, and that a SnO phase appeared at low O2/Ar ratio where it lowered the conductivity.
Effect of variations in water content on sub-T
g aging of glass
Authors: Jewell John M. , Shelby James E.
Published: July 2002

Sodium trisilicate glasses were heat treated for times up to 1000 h at 400 °C. The rate of structural relaxation that occurs under these conditions is controlled by the initial water content as well as by the changes in water content that occur during the heat treatment. The relaxation of the enthalpy is predicted by the Tool–Narayanaswamy model, providing that the initial differences in water content and the changes which occur during the aging process are included in the model via the activation energy for structural relaxation.
Si incorporation in laser-melted AlxGa1−xAs-GaAs quantum well heterostructures from a dielectric source
Authors: Kish F. A. , Hsieh K. C. , Major J. S. , Sugg A. R. , Plano W. E. , Baker J. E. , Holonyak N.
Published: July 2002

Data are presented describing the incorporation of Si in locally laser-melted AlxGa1−xAs-GaAs quantum well heterostructures from a thin-film dielectric source. The composition of the melted material, the effects of the Si source (SiO2 or Si3N4) on impurity incorporation, and the doping behavior are examined via secondary-ion mass spectroscopy, electron dispersion x-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The data indicate that upon melting, a (Si)y(AlxGa1−xAs)1−y alloy is formed from which impurity-induced layer disordering may be effected. After annealing the melt region is found to contain crystalline segregates, which are attributed to rapid thermal quenching of the melt. Applications of these results to the fabrication of buried-heterostructure lasers by laser-assisted disordering are discussed.
Two-phase structure of plasma-polymerized thiophene-passivated GaAs Schottky-like metal-insulator-semiconductor diodes
Authors: Horváth Zs. J.
Published: July 2002

Recently GaAs metal-semiconductor Schottky and plasma-polymerized thiophene-passivated metal-insulator-semiconductor (MIS) diodes were studied. The capacitance-voltage (C-V) results were evaluated by a simple mechanical application of the Schottky capacitance theory to the MIS devices. In this communication it is shown that there is a large discrepancy between the experimental C-V characteristics obtained for the MIS diodes and the theoretical ones following from the depletion layer capacitance theory. The only reasonable explanation of this discrepancy is a two-phase structure of the MIS devices, where one phase has a low- and the other has a high-voltage intercept of the C−2-V plot.
Formation and properties of In-doped high-conductivity CdSe evaporated film
Authors: Hayashi Toshiya , Saeki Ryo , Suzuki Tatsuro , Fukaya Mitsuru , Ema Yoshinori
Published: July 2002

High dark-conductivity CdSe films have been prepared by coevaporation of CdSe and In, and the physical properties of the films were investigated. The dark conductivity of the films at 25 °C ranged from 0.68 to 3800 S cm−1. The conductivity type was n-type and In was found to act as the donor in CdSe films.The film structure was of hexagonal zinc sulfide type with a preferential orientation of the (002) planes parallel to the substrate. Analyzing the film structure in detail by x-ray analysis, it was found that the In atoms were doped substitutionally into the CdSe during the low-concentration doping stage and then doped interstitially during the high doping stage.
Mechanisms controlling temperature dependent mechanical and electrical behavior of SiH4 reduced chemically vapor deposited W
Authors: Joshi R. V. , Prasad V. , Krusin-Elbaum L. , Yu M. , Norcott M.
Published: July 2002

The effects of deposition temperature on growth, composition, structure, adhesion properties, stress, and resistivity of chemically vapor deposited W deposited purely by SiH4 reduction of WF6 are discussed. At lower deposition temperatures, due to incomplete Si reduction reaction, a small amount of Si is incorporated in the film. This elemental Si in W is responsible for the observed high stresses and high resistivities over a wide temperature range. With the increase in the deposition temperature, the conversion of incorporated Si as well as the initial Si reduction are taking place, stimulating increased grain growth and thereby relieving stress and reducing resistivity. The optimum values for stress and resistivity are achieved around 500 °C, as Si content is at its minimum. At higher temperatures the reaction between residual Si and W, is the prime cause of resistivity increase.
Internal energy distributions in a shielded plasma device
Authors: Trkula Mitchell , Nogar N. S. , Keaton G. L. , Anderson J. E.
Published: July 2002

A shielded plasma device has been used extensively in plasma synthesis and plasma processing. In order to optimize these processes, optical diagnostics were used to study the device operated at 545 kHz and pressures between 2.5 and 580 Torr. Plasma-induced emission for Ar, N2, and N+2 suggested that a local thermodynamic equilibrium point of view was inappropriate. Spatially resolved laser-induced fluorescence and laser absorption measurements were performed on the metastable argon state 3P2 and the radiative state 3P1. The metastable profiles were described in terms of a kinetic model dominated by electron-atom kinetics. The model was used to determine the electron temperature Te as a function of axial position and total gas pressure. These temperatures were found to lie in the range of 5000 K at 580 Torr to 11 000 K at 25 Torr.
Study on Zn-, Cd-, or Hg-addition into TlBaCuO
Authors: Xin Y. , Sheng Z. Z.
Published: July 2002

Nominal ZnTlBaCuO4.5, CdTlBaCuO4.5, and HgTlBaCuO4.5 samples have been prepared under different conditions and have been studied by resistance and ac-susceptibility measurements compared to nominal TlBaCuO3.5 samples. In general, the ZnTlBaCuO4.5 samples required less strict heating conditions to reach zero resistance near liquid nitrogen temperature; the CdTlBaCuO4.5 samples had lower Tc; the HgTlBaCuO4.5 samples showed slightly improved Tc at certain conditions. In contrast to La2−xSrxCuO4, Zn-addition did not significantly depress Tc of TlBaCuO. This observation is worthy to be investigated further. Hardness of the ZnTlBaCuO4.5 and CdTlBaCuO4.5 samples was greatly increased, which could have importance in the practical applications of these materials.