bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure, magnetic properties, and magnetostriction of Sm0.5R0.5(Fe1−xCox)2 compounds (R=Nd,Pr)
Authors: Wang B. W. , Lee W. J. , Song J. S. , Min B. K. , Hao Y. M.
Published: July 2002

The structure, magnetic properties, and magnetostriction of Sm0.5R0.5(Fe1−xCox)2 compounds (R=Nd,Pr) have been investigated by using x-ray diffraction analysis, ac initial susceptibility, vibrating sample magnetometer, and standard strain techniques. It was found that the (Sm0.5Nd0.5)Fe2 compound with MgCu2-type cubic structure possesses low magnetocrystalline anisotropy and high ratio of magnetostriction to magnetocrystalline anisotropy. When Co is substituted for Fe, the Curie temperature of (Sm0.5Nd0.5)(Fe1−xCox)2 alloys exhibit a peak at x=0.25 and the saturation magnetization increases with increasing Co content when x<0.25 and decreases when x⩾0.5. The microstructure of (Sm0.5Pr0.5)(Fe1−xCox)2 alloys is nearly a single phase in the range of 0.75⩽x⩽1. The saturation magnetization and magnetostrictiom of the alloys exhibit a peak at x=0.25 and x=0.5, respectively.
Structures, electrical properties, and equation of state in Ca4Mn3O10 under high pressure
Authors: Yu R. C. , Meng G. W. , Chen L. C. , Bao Z. X. , Liu C. X. , Zhu J. L. , Li F. Y. , Liu Z. X. , Liu J. , Jin C. Q.
Published: July 2002

The structure changes and electrical properties in Ca4Mn3O10 under high pressure at room temperature have been studied using energy-dispersive x-ray diffraction with synchrotron radiation and resistance and capacitance measurements. A phase transition from an orthorhombic to a tetragonal phase occurred during increasing pressure to above 19.3 GPa. The equation of state of Ca4Mn3O10 was obtained from the V/V0–P relationship. The bulk modulus B0 and its first-order derivative B0′ of Ca4Mn3O10 were calculated based on the Birch–Murnaghan equation.
Computationally useful bridge diagram series. II. Diagrams in h-bonds
Authors: Perkyns John S. , Dyer Kippi M. , Pettitt B. Montgomery
Published: July 2002

Equations for calculating accurate 4-point and 5-point bridge diagrams in terms of h-bonds have been presented and solved for various phase points of the Lennard-Jones fluid. A method of finding a self-consistent solution for the bridge function and the radial distribution function is demonstrated. The significance of this result over bridge diagrams expressed as f-bonds, in terms of its applicability to charged and dipolar models is discussed. Two very simple phenomenological bridge diagram forms for the bridge function for this model are examined and found to give results almost as accurate and in some cases more accurate than previous forms in the literature. This work represents the first use of directly calculated 5-point bridge diagrams in terms of h-bonds, and the many extra orders of f-bond diagrams which they include, in an integral equation result.
Effects of substrate temperature on structural properties of undoped silicon thin films
Authors: Das Chandan , Dasgupta Arup , Saha S. C. , Ray Swati
Published: July 2002

Undoped silicon thin films were deposited by a radio frequency plasma enhanced chemical vapor deposition technique over a wide range of substrate temperatures (170–370 °C) using a mixture of silane and hydrogen gas. A low power density (35 mW cm−2) was chosen. The effects of substrate temperature on the structural properties of the films was studied. A distinct transition from amorphous to microcrystalline phase is observed with an increase in the substrate temperature (Ts). Raman spectroscopy shows the variation of amorphous and crystalline volume fractions in the silicon films. The amorphous matrix seems to be composed mainly of monohydrides in contrast to the usual dominance of polyhydrides. At the onset of crystallinity, the films have tiny crystallites and the grain size (δ) increases with Ts (at Ts∼370 °C, δ∼350 Å). The deposition rate increases with Ts and attains its maximum (28.2 Å min−1) at the amorphous to microcrystalline transition region. All the microcrystalline films with their differing crystallinities degrade less than their amorphous counterparts under light exposure. The film prepared at the edge of crystallinity shows considerable photosensitivity (photogain of ∼103).
Theoretical analysis of enhanced second-harmonic generation based on a self-formed antiguide structure
Authors: Sassa Takafumi , Umegaki Shinsuke
Published: July 2002

An antiguide structure having a core of lower refractive index confines lightwaves owing to Fresnel multiple reflection. Within a planar waveguide of a nonlinear-optical photoconductive polymer, the second-harmonic wave generated under the Cerenkov-radiation type phase matching can shape the antiguide structure to increase the second-harmonic power itself due to the optical confinement. Here, we theoretically analyze the enhancement.
New exchange-correlation density functionals: The role of the kinetic-energy density
Authors: Boese A. Daniel , Handy Nicholas C.
Published: July 2002

New density functionals, using the kinetic-energy density Tau are reported. The newly introduced variable enhances the performance of previous functionals, leading to highly accurate functionals with and without the use of exact exchange. All these functionals are compared to commonly used functionals for a large test set, looking also at reactions and hydrogen bonded systems. Furthermore, their physical plausibility is discussed.
Design of near-field optical probes with optimal field enhancement by finite difference time domain electromagnetic simulation
Authors: Krug John T. , Sánchez Erik J. , Xie X. Sunney
Published: July 2002

We report the three-dimensional electromagnetic simulation of gold nanoparticles with specific geometries as a means to the rational design of apertureless near-field scanning optical microscopy (NSOM) probes. Analytical solutions for field enhancement by spheroidal particles are used to provide physical insight for probe design. These solutions indicate that probes need to be not only sharp, but also finite in length in order to generate the highest field enhancement. Finite difference time domain (FDTD) simulations of gold particles illuminated by near infrared radiation are performed. Field enhancements for right trigonal pyramids are found to be size and wavelength dependent. Furthermore, the enhancements for these pyramidal particles are higher than for similar length conical particles, which in turn perform better than quasi-infinite conical probes. The particles we design with FDTD can be made using current nanofabrication techniques, and therefore hold great promise as apertureless NSOM probes. These right trigonal pyramids are particularly well suited for use in tip enhanced nonlinear optical microscopy or near-field Raman microscopy.
Periodic orbits in coupled Hénon maps: Lyapunov and multifractal analysis
Authors: Politi Antonio , Torcini Alessandro
Published: July 2002

A powerful algorithm is implemented in a 1-d lattice of Hénon maps to extract orbits which are periodic both in space and time. The method automatically yields a suitable symbolic encoding of the dynamics. The arrangement of periodic orbits allows us to elucidate the spatially chaotic structure of the invariant measure. A new family of specific Lyapunov exponents is defined, which estimate the growth rate of spatially inhomogeneous perturbations. The specific exponents are shown to be related to the comoving Lyapunov exponents. Finally, the ζ-function formalism is implemented to analyze the scaling structure of the invariant measure both in space and time.
Coupled maps with local and global interactions
Authors: Ouchi Noriyuki Bob , Kaneko Kunihiko
Published: July 2002

A coupled map lattice model with both local and global couplings is studied as a simple example of hierarchical pattern dynamics with different length scales of interactions. Several phases are classified according to domain structures, degree of chaotic dynamics, distribution function, and power spectra. In particular, a cascade process of formation and collapse of bubbles is found in some parameter regime. The state is characterized by spatiotemporal power-law correlation and few positive Lyapunov exponents. In a two-dimensional case, the state leads to a characteristic spatiotemporal pattern that may be regarded as a dynamic extension of a Turing pattern. The possible relevance to natural patterns is also discussed.
A nearly exact second-order finite-difference time-domain wave propagation algorithm on a coarse grid
Authors: Cole James B.
Published: July 2002

We introduce a new second-order finite-difference time-domain (FDTD) algorithm to solve the wave equation on a coarse grid with a solution error less than 10−4 that of the conventional one. Although the computational load per time step is greater, it is more than offset by a large reduction in the number of grid points needed, while maintaining high accuracy, as well as by a reduction in the number of iterations. In addition, boundaries can be more accurately characterized at the subgrid level. This algorithm is based on a second-order finite-difference Laplacian that is nearly isotropic with respect to the wave propagation direction. Although optimum performance is achieved at a fixed frequency, the accuracy is still much higher than that of a conventional FDTD algorithm over ‘‘moderate’’ bandwidths.
Sensitivity analysis of the MM5 weather model using automatic differentiation
Authors: Bischof Christian H. , Pusch Gordon D. , Knoesel Ralf
Published: July 2002

We present a general method for using automatic differentiation to facilitate model sensitivity analysis. Automatic differentiation techniques augment, in a completely mechanical fashion, an existing code such that it also simultaneously and efficiently computes derivatives. Our method allows the sensitivities of the code’s outputs to its parameters and inputs to be determined with minimal human effort by exploiting the relationship between differentiation and formal perturbation theory. Employing this methodology, we performed a sensitivity study of the MM5 code, a mesoscale weather model jointly developed by Penn State University and the National Center for Atmospheric Research, that is composed of roughly 40,000 lines of Fortran 77 code. Our results show that automatic differentiation-computed sensitivities exhibit superior accuracy compared to divided difference approximations computed from finite-amplitude perturbations. We also comment on a numerically induced precursor wave that would almost certainly have been undetectable if one used a divided difference method. © 1996 American Institute of Physics.
Theory of steady-state high-field hole transport in GaSb and AlxGa1−xSb: The impact ionization resonance
Authors: Brennan Kevin , Hess Karl , Chang Yia-Chung
Published: July 2002

Calculations of the steady-state impact ionization rate of holes in GaSb and AlGaSb are presented based on a Monte Carlo simulation with the unique inclusion of a complete band structure (derived using the K*P method) and quantum effects such as initial state collision broadening. It is determined, by comparisons to existing experimental data, that the holes in the split-off band play the most important role in impact ionization in both GaSb and GaAlSb. The experimental data are fit quite well at low applied electric fields where the recently discovered resonance in the hole impact ionization rate occurs. It is found that the resonance data can be explained, using the parametrized Keldysh formula, if the impact ionization threshold energy in both the heavy- and light-hole bands is ∼1.40 eV, roughly twice the band-gap energy, The threshold energy in the split-off bands is taken to be equal to the split-off energy for Δ>
Study of mercury cadmium telluride epilayers grown by metalorganic vapor-phase epitaxy
Authors: Raccah P. M. , Garland J. W. , Zhang Z. , Lee U. , Ugur S. , Mioc S. , Ghandi S. K. , Bhat I.
Published: July 2002

We report on the growth and characterization of HgCdTe epilayers grown by metalorganic vapor-phase epitaxy. The transport properties indicate that it is possible to grow epilayers with mobilities comparable to those of the best bulk-grown materials. Electrolyte electroreflectance studies have yielded depth profiles for the alloy composition, the strains, and the density of polarizable defects. These latter results indicate very clearly that the interface alloy/substrate is very sharp and does not extend over more than 2000 Å. Moreover, in the bulk of the epilayers the strains are low and comparable to those found in high-quality bulk single crystals.
Selective tungsten silicide formation by ion-beam mixing and rapid thermal annealing
Authors: Tsaur B-Y. , Chen C. K. , Anderson C. H. , Kwong D. L.
Published: July 2002

Smooth layers of tungsten silicide have been formed on silicon substrates by deposition of a tungsten film, As+ ion implantation through the film to produce ion-beam mixing, and rapid thermal annealing. This process has been used to form tungsten silicide selectively in patterned openings etched in the SiO2 film on oxidized Si wafers, without lateral silicide growth. Rapid thermal annealing results in the activation of the As implanted in the Si substrate, without significant redistribution, to form shallow n+-p junctions with good electrical properties.
Hydrostatic pressure measurements (≲12 kbar) on single- and multiple-stripe quantum-well heterostructure laser diodes
Authors: Epler J. E. , Kaliski R. W. , Holonyak N. , Peanasky M. J. , Herrmannsfeldt G. A. , Drickamer H. G. , Burnham R. D. , Thornton R. L.
Published: July 2002

Short wavelength Alx′Ga1−x′As-AlxGa1−xAs (x′∼0.85, x∼0.22) quantum-well heterostructure (QWH) laser diodes (well size Lz ≊400 Å) that operate continuously (cw) at 300 K are subjected to hydrostatic pressure (≲12 kbar). The emission spectrum and the light intensity versus current (L-I) curves are monitored to determine the pressure dependence of the direct (Γ) band gap and the threshold current. The band gap exhibits a linear pressure dependence with a noticeable change in slope at ∼4.5 kbar, similar to previously reported results for AlxGa1−xAs-GaAs QWH diodes. The threshold current increases monotonically with pressure, reflecting the increasing loss of carriers to the X and L bands. The short-wavelength cw limit of the system, i.e., a gain-guided laser with a 400-Å AlxGa1−xAs (x∼0.22) quantum well and no separate waveguide region, is determined to be ∼6980 Å.
Annealing effects on growth-induced optical birefringence in liquid-phase-epitaxial-grown Bi-substituted iron garnet films
Authors: Ando Koji , Takeda Norio , Koshizuka Naoki , Okuda Takashi
Published: July 2002

Optical birefringence in liquid-phase-epitaxial-grown (LPE) Bi-substituted iron garnet films was investigated with annealing. The optical birefringence was found to be composed of a stress-induced part and a growth-induced part. The growth-induced optical birefringence Δng was about 5×10−4 at λ=1.15 μm. Δng and the growth-induced magnetic anisotropy Kg disappeared after the annealing. Time constants for changes of Δng and Kg by the annealing were nearly the same and orders of a few hours at 1100–1150 °C. A deformation of the microscopic structure around bismuth ions seems to be responsible for both Δng and Kg. The large growth-induced optical birefringence in Bi-substituted iron garnet films plays an important role to achieve high efficiency TE-TM mode conversion in magneto-optical waveguides.
Optimum coupling junction and cavity lengths for coupled-cavity semiconductor lasers
Authors: Koch T. L. , Coldren L. A.
Published: July 2002

In this paper we investigate the dependence of the mode suppression in coupled-cavity semiconductor lasers on coupling junction parameters and cavity lengths. An effective mirror formalism is developed and combined with exact numerical analysis to explore the mode behavior across the entire relative cavity gain operating range of coupled-cavity resonators. A gap coupling model is also presented which permits one to deduce the optimum gap spacing for best mode suppression, as well as the dependence of this optimum gap spacing on relative cavity lengths. Finally, the exact numerical analysis is combined with spectral gain roll-off to explore the mode suppression of all modes of the system versus cavity lengths. Long-long and long-short geometries are shown to be desirable as well as some interesting new intermediate cavity length ratios. Calculations indicate that coupled-cavity 1.55-μm lasers with mode suppression in excess of 10 cm−1 to both near in and repeat modes are realizable.
Study of electronic levels in antimony and indium-doped gallium arsenide
Authors: Mitchel W. C. , Yu P. W.
Published: July 2002

We have studied heavily doped GaAs:Sb and GaAs:In by temperature-dependent Hall effect and photoluminescence spectroscopy. Both samples had good mobilities and the GaAs:In was semi-insulating. We have found a new deep level in GaAs:Sb at 0.47 eV below the conduction band. Both samples showed new weak luminescence bands near the intrinsic edge which are as yet unidentified.
Auger electron spectroscopy and electron loss spectroscopy comparative study of vacuum annealing effects on InP surface
Authors: Massies J. , Lemaire-Dezaly F.
Published: July 2002

Auger electron spectroscopy (AES) and electron loss spectroscopy (ELS) have been performed in order to investigate vacuum annealing effects on InP surface. Both techniques appeared suitable for detecting indium clustering induced by thermal surface decomposition through InM4.5N4.5N4.5 spectrum modifications (AES) and In plasmon excitation (ELS). The formation of In microinclusions at the surface is detected by the two techniques for annealing temperature of 460±30 °C. In addition, AES shows that phosphorus has a complex behavior near the surface involving diffusion from the bulk, surface segregation, and desorption. These competitive mechanisms are shown to result in phosphorus enrichment or depletion of the surface layer depending mainly on the annealing temperature.
Role of interface roughness and alloy disorder in photoluminescence in quantum-well structures
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

A formalism to study the effect of alloy disorder and interface roughness on the linewidths of excitonic emission spectra in quantum-well structures is developed. The study includes the cases where the alloy forms (a) the barrier region, (b) the well region, and (c) both the barrier and well regions of the quantum-well structures, and demonstrates the importance of alloy quality in all three cases. The relative importance of the effects of alloy disorder and interface roughness on the excitonic linewidths is discussed. As an illustration, the formalism is applied to AlGaAs/GaAs, InP/InGaAs, and InAlAs/InGaAs quantum-well structures and the results compared with the available experimental data.
Kinetics for changes in anisotropy, coercivity, and argon content of transition metal-rare earth films
Authors: Luborsky F. E.
Published: July 2002

Amorphous films of transition metal-rare earth alloys were prepared by rf bias sputtering ∼1000 Å thick, and were protected with ∼1000-Å SiO2, under conditions to provide an easy axis perpendicular to the film plane. Some of the kinetics of the changes in the parameters affecting the domain size were measured, namely the anisotropy, the coercivity Hc and the argon content. Both isothermal and isochronal exposures were used. The decrease in the perpendicular anisotropy K⊥ and Hc and the increase in the planar anisotropy all follow first-order kinetics, that is, the Johnson–Mehl–Avrami exponent n=1.0. The activation energy for the change in K⊥ was 1.0±0.2 eV. The changes in anisotropy were the rate limiting factor in the lifetime of the films. The Hc decreased with ΔE=0.6±0.2 eV while the Ar content decreased with ΔE=0.08±0.05 eV. Because of the large difference in activation energy for the change in Ar compared to the changes in K or Hc we conclude that the rate limiting step for the change in Ar is different than the rate limiting step for the changes in K and Hc. At least two mechanisms have been associated with the changes on annealing. One is the oxidation of the rare earth component even through the SiO2 overlayer; the other is the release of Ar which changes the local stress in the film or changes the degree of isolation of the columnar structure by the Ar.
Generation of positive charge in silicon dioxide during avalanche and tunnel electron injection
Authors: Fischetti Massimo V.
Published: July 2002

Avalanche and Fowler–Nordheim tunneling electron injections have been performed at constant current on a broad variety of differently processed Al-gate metal-oxide-semiconductor capacitors. It is found that the same type of positive charge (the ‘‘slow states’’) is generated during low-field and high-field electron injection. The maximum amount of positive charge which can be generated at a given electric field depends on processing and increases linearly with the average field in the oxide. However, the rate at which the positive charge is generated is controlled uniquely by the anode field, for a given polarity of the gate voltage. It follows that the role of the electron traps in the bulk SiO2—independent of their nature—is that of increasing both the rate and the total number of created defects by enhancing, respectively, the anode field, as a result of the distortion of the potential in SiO2, and the average field which must be increased to maintain a constant injected current. Processes described earlier for the generation of the interfacial defects such as interband impact-ionization and water-triggered mechanisms, do not account for the experimental results. In particular, the role of the water-related electron traps appears to be simply ‘‘electrostatic’’—as for other electron traps, such as arsenic—rather than ‘‘electrochemical,’’ as previously proposed. Instead, it is suggested that during the hot electron injection, a positive or neutral species emitted from the anodic region propagates to the Si-SiO2 interface creating the damage.
Ion implantation studies of polydiacetylene crystals
Authors: Elman B. S. , Thakur M. K. , Sandman D. J. , Newkirk M. A. , Kennedy E. F.
Published: July 2002

Effects of 150-keV arsenic ion implantation on polydiacetylene crystals are characterized with respect to modifications of structural, electrical, and optical properties of the parent materials. Structural modifications are studied by means of Rutherford backscattering spectrometry, Raman spectroscopy, and x-ray photoelectron spectroscopy. It is demonstrated that at low and intermediate fluences of implantation, structural changes are mainly associated with effects of the ion beam on the polymer side groups. dc resistivity measurements were performed in the 20 °K<T<290 °K temperature range and the results yield an exponential behavior of the resistivity ρ(T)=ρ0 exp(T0/T)m with the temperature-dependent exponential factor 1/2<m<1 where m → 1 at higher temperatures (T>190 °K) and m → 1/2 at lower temperatures (T<80 °K). Absorption spectra in the visible range from ion-implanted thin crystalline films are also presented and discussed.
A numerical analysis of Auger processes in p-type GaAs
Authors: Bardyszewski W. , Yevick D.
Published: July 2002

We calculate the contributions of pure collision and phonon-assisted Auger processes within the framework of the Kane model to the nonradiative lifetime of p-doped GaAs. Our approach employs refined expressions for the wavefunction overlap integrals. Further, in contrast to previous treatments, our theory correctly describes the temperature dependence of the optical phonon-assisted Auger processes. Our values for the Auger lifetimes are in good agreement with experimental results.
The role of hydrogen in the deposition, composition, and structure of semi-insulating polycrystalline silicon films
Authors: Verstegen B. , Habraken F. H. P. M. , van der Weg W. F. , Holsbrink J. , Snijder J.
Published: July 2002

Semi-insulating polycrystalline silicon films have been grown by a low-pressure chemical vapor deposition process between 565 and 623 °C. Rutherford backscattering spectrometry and nuclear reaction analysis were used to determine the layer composition and thickness. The O/Si concentration ratio in the films increases with increasing N2O/SiH4 input for N2O/SiH4<0.6. For N2O/SiH4>0.6, a saturation effect in the oxygen uptake was observed. Furthermore the O/Si ratio increases with increasing growth temperature. The hydrogen concentration increases more than linearly with the N2O/SiH4 input ratio for N2O/SiH4<0.5 up to an amount of 8.5 at. % at 600 °C. For N2O/SiH4>0.5 a saturation effect was observed in the hydrogen uptake. We suggest that the hydrogen is bound to silicon atoms, which are further coordinated with three oxygen atoms. Based on this model, the growth mode of the films at the temperatures considered is discussed.
Photoluminescence study of the growth of indium phosphide by metalorganic chemical vapor deposition
Authors: Zhu L. D. , Chan K. T. , Wagner D. K. , Ballantyne J. M.
Published: July 2002

The growth of unintentionally doped indium phosphide by low pressure metalorganic chemical vapor deposition (LPMOCVD) using triethlylindium and phosphine has been investigated by low temperature photoluminescence (PL). Pregrowth annealing was found to result in improved crystalline quality of the seed surface. The predominant acceptor impurity on the annealed substrate surface and in the initial epitaxial region (1200 Å) was shown to be carbon. The major acceptor impurity in thicker epilayers further away from the substrate interface was determined to be Zn. Silicon was also identified from the PL spectra, though its concentration might be much smaller than that of zinc. No deep level impurities were observed in this material. Most important of all, the highly resolved exciton PL spectrum demonstrated that excellent quality InP comparable to the best material grown by vapor phase epitaxy could be grown by LPMOCVD without the need for phosphine cracking.
Trapping characteristics of Te-related centers in GaAs1−xPx
Authors: Calleja E. , Muñoz E. , Jimenez B. , Gomez A. , Garcia F. , Kellert F.
Published: July 2002

Transient capacitance and photocapacitance techniques have been used to study the characteristics of two electron traps related to Te in GaAs1−xPx: Te. Levels En1 and En2 have thermal activation energies of 0.17 and 0.27 eV, respectively, and their thermal electron emission and capture rates deviate markedly from Schockley–Read–Hall theory for near band gap crossover compositions. Such centers are found for 0.3<x≤1, are linked to the X conduction band minima, and their photoionization thresholds are 0.5 and 1 eV, respectively. Trap concentrations have been studied as a function of Te doping level, Zn diffusion temperature, and N content (x>0.4) in GaAsP LEDs. It is suggested that both defects belong to the DX type, and they have been described by a large lattice relaxation model. Franck–Condon energies of 0.3 and 0.95 eV have been determined, respectively. The properties of present Te-related defects are quite similar to donor related centers in AlxGa1−xAs, including the nonexponential capacitance transients found in near x∼0.4 compositions. It is important to mention that both centers have very large hole capture coefficients (σp>10−14 cm2) and behave as efficient recombination centers.
Magnetic microcrystals and surface layers in as-quenched and hydrogenized Fe90Zr10 glass
Authors: Wronski Z. S. , Zhou X. Z. , Morrish A. H. , Stewart A. M.
Published: July 2002

Conversion-electron Mössbauer spectroscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction were used for surface studies of the as-quenched and hydrogenized metallic glass Fe90Zr10. Surface layers of as-quenched ribbon, paramagnetic at room temperature, were found to be overlaid by a ferromagnetic thin film. The overlayer is composed of α-Fe microcrystals and a crystalline compound (Fe3Zr). Magnetic α-Fe microcrystals are about 500 Å in diameter and are oriented with the (200) plane parallel to the Fe90Zr10 ribbon plane. Mössbauer spectra show that the magnetic moments of the precipitated small particles lie in the ribbon plane. A hydrogen-induced magnetic phase transformation, previously reported for bulk Fe90Zr10, was observed in the amorphous surface layers. At the same time, the magnetic crystalline overlayer disappears on the ribbon shiny surface.
Ar ion beam and CCl4 reactive ion etching: A comparison of etching damage and of damage passivation by hydrogen
Authors: Mu X. C. , Fonash S. J. , Yang B. Y. , Vedam K. , Rohatgi A. , Rieger J.
Published: July 2002

Damage produced in single-crystal silicon by two distinctly different dry etching techniques, Ar ion beam etching and CCl4 reactive ion etching is characterized and compared using spectroscopic ellipsometry, reflected high- energy electron diffraction, and current-voltage (I-V) characteristics of Au contacts to the etched Si. Secondary ion mass spectroscopy is also used to further characterize the CCl4 exposed samples. The effectiveness of low-energy hydrogen ion implants in passivating this dry etching induced damage is explored. The restoration of I-V characteristics caused by H+ implants is correlated with the evolution of the spectroscopic ellipsometry, reflected high- energy electron diffraction, and secondary ion mass spectroscopy data.
Effect of UV preionization on optical breakdown induced by a pulsed CO2 laser
Authors: Yoshida S. , Sasaki J. , Arai Y. , Lei M. P. , Tateishi K. , Uchiyama T.
Published: July 2002

The effect of UV preionization on the optical gas breakdown induced by a CO2 laser pulse is studied experimentally. In the present work a UV spark plug and a pulsed CO2 laser are used as the UV and IR sources, respectively. The experiments are carried out for helium and some other common gases in the pressure range of 10–1000 Torr to determine the breakdown probability. For all of the gases under study the probability appears higher when the gas is UV preionized. These results show the importance of the seed electrons for the IR-induced gas breakdown supporting the theory that the cascade ionization process is dominating in the IR region requiring seed electrons to initiate the process. Oscilloscopic waveforms of the optical breakdown spark fluorescence are also observed which shows the optical breakdown occurs more rapidly when the gas is UV preionized.
Kinetics and morphology of erbium silicide formation
Authors: Knapp J. A. , Picraux S. T. , Wu C. S. , Lau S. S.
Published: July 2002

The growth kinetics and surface morphology of erbium silicide formation from Er layers on Si(100) substrates are examined using both fast e-beam annealing and furnace annealing. Very smooth erbium silicide layers have been grown using a line-source e beam to heat and react the Er overlayers with the substrate. This contrasts to the severe pitting observed when Er layers are reacted with Si in conventional furnace annealing. The pitting phenomenon can be explained by a thin contaminant layer at the interface between Er and Si. Our results suggest the contamination barrier is not due to oxygen, as usually assumed, but may be related to the presence of carbon. Rapid e-beam heating to reaction temperatures of ∼1200 K permits dispersion of the barrier layer before substantial silicide growth can occur, allowing smooth silicide growth. Heating to shorter times to just disperse the interface barrier allows uniform layer growth by subsequent furnace annealing and has permitted measurement of the kinetics of erbium silicide formation on crystalline Si. The reaction obeys (time)1/2 kinetics but is shown to be not totally diffusion limited by the ability to sustain multiple interface growth from a single Si source. The growth rates are nearly an order of magnitude slower for the Er/Si(100) interface than for the Er/amorphous-Si, but with a similar activation energy near 1.75 eV in both cases.
X-ray diffraction studies of thermal treatment of GaAs/InGaAs strained-layer superlattices
Authors: Joncour M. C. , Charasse M. N. , Burgeat J.
Published: July 2002

We analyze in this paper the effect of thermal treatment on structural properties of GaAs/InGaAs strained-layer superlattices grown by molecular beam epitaxy. The superlattices are analyzed using double-crystal x-ray rocking curves. In order to model the satellites intensity variation as a function of the heat treatment time at a temperature of 850 °C, we have calculated the structure factors of the superlattices, taking into account both composition and lattice spacing modulation. The latter is found to be more influent in the calculation in this particular case. The deduced values of the diffusion coefficient, about 2×10−18 cm2/s, is discussed and compared to those determined on GaAs/AlAs structures.
Characterization of microstructural defects in BF+2 -implanted silicon
Authors: Wu I. W. , Chen L. J.
Published: July 2002

A systematic study on the nature and evolution of the postannealing defects in BF+2 -implanted silicon with implantation doses ranging from 5×1014 to 1×1016 cm−2 is reported. The type, nature, size, distribution, and density of the defects were determined by transmission electron microscopy. Formation mechanisms of the microstructural defects are discussed.
High electric field resistivity and pyroelectric properties of vinylidene fluoride-trifluoroethylene copolymer
Authors: Olsen Randall B. , Bruno David A. , Briscoe Joseph M. , Jacobs Everett W.
Published: July 2002

Copolymers of vinylidene fluoride-trifluoroethylene P(VDF-TrFE) exhibit large piezoelectric and pyroelectric effects. In addition to the most common application of the pyroelectric effect (radiant detection) it is possible to convert heat directly into electrical energy by pyroelectric conversion. This study reports the first measurements of high (constant) field pyroelectric effects of P(VDF-TrFE) which are relevant to pyroelectric conversion. Electric displacement changes which result from temperature changes of the copolymer were measured for thermal cycling from room temperature to 90 °C at fields up to 1 MV/cm. The displacement changes (0.1–0.3 μ C/cm2) were dependent upon the molar ratio of the constituent monomers. The resistivity of the copolymer was also measured in the temperature range 20 to 90 °C and was found to vary from 1012 to 1016Ω cm depending on monomer ratio, temperature, field, and time. The resistivity and displacement change data are discussed in terms of predicted pyroelectric energy conversion performance.
Excimer laser etching of polyimide
Authors: Brannon J. H. , Lankard J. R. , Baise A. I. , Burns F. , Kaufman J.
Published: July 2002

It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength-dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.
Evaluation of interface potential barrier heights between ultrathin silicon oxides and silicon
Authors: Horiguchi Seiji , Yoshino Hideo
Published: July 2002

Interface potential barrier heights for ultrathin silicon oxides (15– 44 Å) on silicon and effective electron masses in some of these oxides are evaluated. Evaluation is performed using a new technique of analyzing the charging characteristics of metal-nitride-oxide-semiconductor capacitors. Oxides thicker than 36 Å have the same potential barrier heights as those for thick oxides, assuming the effective electron mass of the oxides is the same. However, for oxides thinner than 31 Å, the potential barrier heights decrease and the effective electron masses increase as the oxide thickness decreases. These results suggest that oxides at least thicker than 36 Å can be applied to metal-oxide-semiconductor field-effect transistors as gate oxides.
Low-temperature photoluminescence in AlxGa1−xAs grown by molecular beam epitaxy
Authors: Reynolds D. C. , Bajaj K. K. , Litton C. W. , Singh Jasprit , Yu P. W. , Henderson T. , Pearah P. , Morkoç H.
Published: July 2002

We report the first observation of free exciton transitions (X), as well as donor and acceptor bound exciton transitions (D0X, D+X, and A0X), in the high-resolution photoluminescence (PL) spectra of high-quality AlxGa1−xAs layers grown by molecular beam epitaxy (MBE) over the composition range 0.01≤x<0.2. This observation contrasts markedly with several previous investigations of AlxGa1−xAs samples of somewhat higher composition (x>0.2) in which only one or two bound exciton transitions have been reported together with the typically observed carbon free-to-bound transitions (e,A0). From a systematic study of MBE growth and PL spectral characterization, we find that both the free and bound exciton transitions of the AlxGa1−xAs layers correlate to their counterparts in high-purity MBE GaAs layers and that their photon energies increase linearly with increasing x value, as expected for these low AlAs mole fraction samples. At compositions as low as 2.1%, and as high as 12.5%, spectral linewidths of D0X transitions were found to be as narrow as 0.3 and 2 meV, respectively, in reasonably good agreement with the recent PL linewidth predictions of Singh and Bajaj which are based on a theory of alloy scattering. These observations confirm the high quality of the low x-value AlxGa1−xAs samples which were grown to thicknesses between 1 and 2 μm at substrate temperatures approaching 700 °C in a MBE system having low background impurity contamination.
A comparison of single- and double-carrier injection in amorphous silicon alloys
Authors: Hack M. , den Boer W.
Published: July 2002

We present results from both experimental and theoretical studies of single and double carrier injection into amorphous silicon alloys. For biases above approximately half the built-in potential double carrier injection in forward biased p-i-n diodes leads to higher currents than are obtained for single carrier injection in n-i-n diodes. Single carrier injection was found to depend mainly on the density and distribution of localized states in the gap, whereas double injection currents are also very dependent on the recombination kinetics and the carrier band mobilities. Analysis of experimental results suggests that for an electron band mobility of 20 cm2/V sec the hole band mobility is approximately 4 cm2/V sec.
Formation and thermal stability of CoSi2 on polycrystalline Si
Authors: Vaidya S. , Murarka S. P. , Sheng T. T.
Published: July 2002

The high temperature stability of CoSi2/polycrystalline-Si/SiO2 structures has been explored by techniques of Rutherford backscattering, scanning, and transmission electron microscopy. Results indicate that the silicide formed by reacting 400 Å of Co with 3300 Å of poly-Si is metallurgically stable up to 30 min at 900 °C. A 30-min 1000 °C sinter causes intermixing of the silicide/Si phase, although the SiO2 layer is not visibly damaged. More severe forming-gas anneals result in Si loss from the metallization and a complete destruction of the multilayered geometry. This Si loss can be prevented by sintering in a partially oxidizing ambient, which forms an encapsulating SiO2 surface layer. The stability of co-sputtered films on Si is critically dependent on the as-deposited Si/Co ratio. Si/Co2 are both unstable for temperature excursions in excess of 800 °C. In contrast, Si/Co≂2 composites form stable co-sputtered silicides with thermal characteristics similar to those of thin Co on polycrystalline Si.
Photoenhanced metalorganic chemical vapor deposition of ZnSe films using diethylzinc and dimethylselenide
Authors: Ando Hideyasu , Inuzuka Hajime , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

ZnSe thin films have been grown on (100)-oriented GaAs and glass substrates by photoenhanced metalorganic chemical vapor deposition from diethylzinc and dimethylselenide with a low-pressure mercury lamp as a light source. Process temperatures have been varied between 500 and 200° C. Without irradiation of the ultraviolet (UV) light, the growth rate decreases rapidly below 400 °C, whereas with irradiation, the growth occurred in the whole temperature range investigated, and the enhancement of the growth rate was observed above 400 °C. Furthermore, the enhancement of the preferential orientation of ZnSe films grown on glass substrates by the UV irradiation was also observed.
Optical properties of ZrN as a function of temperature
Authors: François J. C. , Casset J. , Chassaing G. , Gravier P. , Sigrist M.
Published: July 2002

Reflectance of stoichiometric ZrN was investigated from 0.22 to 5.50 eV as a function of temperature between 20 and 700 °C. The complex dielectric function was calculated by a Kramers–Kronig analysis and split to find the interband and intraband contributions, using Drude’s theory. This decomposition showed an interband maximum at 2.5 eV which became less pronounced with increasing temperature. Temperature increase had two main effects, first to increase the damping term of the conduction electrons without a significant change of the plasma frequency, second to shift the screened plasma frequency towards lower energies.
Spectroscopic measurements of He2 in the afterglow of a dense Z-pinch plasma
Authors: Tucker J. E. , Brake M. L. , Gilgenbach R. M.
Published: July 2002

Visible emission spectroscopy (330–650 nm) has been performed radially and axially on a Z-pinch plasma. During the peak compression, continuum and He ii line emission (468.6 nm) predominated. We report the first observation of He2 in the post-pinch phase of a dense helium Z-pinch discharge. Axial measurements of this afterglow plasma also revealed pronounced absorption bands which cannot be identified with He2, He i, He ii, or impurities.
Impurity-induced enhancement of the growth rate of amorphized silicon during solid-phase epitaxy: A free-carrier effect
Authors: Licoppe C. , Nissim Y. I.
Published: July 2002

The study of solid-phase epitaxy in ion-implanted amorphized silicon is presented via optical reflectivity measurements. The effect of impurities on recrystallization is studied in detail through accurate measurements of growth rate. Enhancement of the growth rate and decrease of the activation energy are shown. These parameters are studied as a function of the impurity concentration. This phenomenon is understood in terms of an original model which introduces band bending and an electric field at the disordered layer-crystalline substrate interface. The electric field acts on recrystallization through the enhancement of defect migration at the interface. The agreement of the model with experimental results is shown to be excellent, and a parallel is drawn with the phenomenon of enhanced dislocation mobility with doping, which behaves in a strikingly similar way.
Some remarks on annealing and doping in CuInS2
Authors: Lin J. L. , Liu L. M. , Lue J. T. , Yang M. H. , Hwang H. L.
Published: July 2002

This paper addresses problems associated with thermal annealing and n-type and p-type doping in CuInS2. The results of incorporating impurities like Zn and P in CuInS2 single crystals by different methods are reported. Some evidence has been provided to explain the formation of precipitates being the limiting factor to exhibit the shallow acceptor property. The electron beam annealing of phosphorus-implanted CuInS2 has been shown for the first time to be an effective way for p-type conductivity control by extrinsic impurities in any I-III-VI2 ternary chalcopyrite.
Defect structure in III-V compound semiconductors: Generation and evolution of defect structures in InGaAs and InGaAsP epitaxial layer grown by hydride transport vapor-phase epitaxy
Authors: Chu S. N. G. , Nakahara S. , Karlicek R. F. , Strege K. E. , Mitcham D. , Johnston W. D.
Published: July 2002

The generation and evolution of a novel defect structure in InGaAs single-layer and InGaAsP/InP multilayer laser structures grown by hydride transport vapor-phase epitaxy on (001)InP substrate has been studied in detail using both cross-section and plan-view transmission electron microscopy. Under certain growth conditions, a unique defect structure consisting of a dislocation tangle initiated at the InGaAs/InP interface, having the shape of a pyramid, followed by a bundle of straight dislocations propagating through the InGaAs epitaxial layer near [001] growth direction and along 〈112〉 orientations, is formed. Such defect structure is universal to these materials grown from vapor sources. The pyramidal-dislocation tangles, or PDT defects, are formed as a result of the agglomeration of fine precipitates (500 Å in size) which generate a special type of edge dislocation lying in the (110) plane with the line direction oriented close to the [001] growth direction. X-ray microanalysis indicates that the interfacial precipitate, which induces the generation of the PDT defect, contains excess Ga and P. At the InGaAsP/InP interface, the agglomeration of fine precipitates does not occur even at a density as high as 4×1012 cm2. The possible causes of the formation of the fine interfacial precipitate and PDT defect are discussed. The evolution of the defect structure across successive layers is further investigated in a multilayer structure. The result indicates that the major defects in the quaternary layers are the [001]-oriented dislocations generated from the precipitates at the quaternary/binary interfaces. These dislocations recombine at the second interface after propagating through the layer. The 60° slip-type dislocation is also observed. The replication of dislocations from the substrate is negligible.
Raman scattering by coupled plasmon-phonon modes in n-type Ga1−xAlxAs epitaxial layers
Authors: Kirillov D. , Chai Y. , Webb C. , Davis G.
Published: July 2002

Raman scattering by coupled plasmon-phonon modes in Ga0.75Al0.25As epitaxial layers grown by molecular beam epitaxy and metalorganic chemical vapor deposition was studied. Good agreement between predicted and observed behavior was found. It was concluded that Raman scattering can be conveniently used for nondestructive and fast evaluation of free electron concentration in these materials.
Cross-sectional transmission electron microscopy investigation of Ti/Si reaction on phosphorus-doped polycrystalline silicon gate
Authors: Wong C. Y. , Lai F. S. , McFarland P. A. , d’Heurle F. M. , Ting C. Y.
Published: July 2002

Titanium interaction with phosphorus-doped polycrystalline silicon gate electrodes was investigated by cross-sectional transmission electron microscopy and correlated with sheet resistance measurements. Phosphorus concentration above 1×1016 ion/cm2 in the polycrystalline silicon leads to decreased TiSi2 formation, discontinuous metal silicide layer, and increased sheet resistance. A possible cause could be the formation of titanium phosphide at high phosphorus concentration in the polycrystalline silicon, competing with the total titanium available for silicide formation.