bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of ultrathin tungsten filaments via selective low-pressure chemical vapor deposition
Authors: Busta H. H. , Feinerman A. D. , Ketterson J. B. , Wong G. K.
Published: July 2002

A new technique for the formation of ultrathin tungsten filaments is described. It is based on the selective deposition of tungsten via the silicon reduction of WF6 along the sidewall of a photolithographically defined undoped polycrystalline silicon/SiO2 step. The width of the filament is determined by the tungsten deposition parameters and the thickness by the thickness of the polycrystalline film. Filaments with a cross section of 600×2000 Å and 67.5, 140, and 265 μm lengths have been fabricated by this method. Initial low temperature resistance measurements of nonimplanted and Si-implanted (1×1015 cm−2, 20 keV) filaments show localization/electron-electron interaction behavior.
Diode current detection of extended x-ray absorption fine structure in gallium arsenide
Authors: Boehme R. F. , Cargill III G. S. , Weber W. , Jackson T.
Published: July 2002

Measurement of diode photocurrent represents a new method for obtaining extended x-ray absorption fine structure (EXAFS) information specific to the junction region of a diode. EXAFS measurements at Ga and As K edges of an aluminum-on-GaAs Schottky diode have been used to demonstrate this new technique. The spectra observed in the diode current arise mainly from x-ray absorption events within 2 μm of the diode junction, i.e., within a minority carrier diffusion length of the approximately 600-Å-wide depletion region. The diode current EXAFS are consistent with EXAFS obtained from fluorescence measurements.
Kinetic modeling for hydrogen passivation of polycrystalline silicon
Authors: Ginley D. S. , Hellmer R. P.
Published: July 2002

The introduction of monatomic hydrogen into polysilicon grain boundaries has great potential for improving photovoltaic device efficiencies for thin-film and ribbon material. To optimize this process a more complete understanding of the relevant chemistry and kinetics is required. We discuss here two kinetic models of the passivation process: a one-dimensional Fickian model which is computationally easy and produces diffusion coefficients in good agreement with those in the literature and a two-dimensional model which though computationally complex provides a more accurate physical representation of the passivation process and more realistic grain-boundary diffusion coefficients for monatomic hydrogen. Both models appear to have practical utility for optimizing and understanding the passivation process. The nature of the site filling reaction is also discussed.
Steady-state and time-resolved photoluminescence in microcrystalline silicon
Authors: Komuro Shuji , Aoyagi Yoshinobu , Segawa Yusaburo , Namba Susumu , Masuyama Akio , Kruangam Dusit , Okamoto Hiroaki , Hamakawa Yoshihiro
Published: July 2002

A systematic investigation has been made on steady-state and time-resolved photoluminescence (PL) in microcrystalline silicon (μc-Si) at liquid-helium temperature. The steady-state PL spectra on various grain sizes and volume fractions are examined. It is found that the low-energy emission (∼0.76 eV) arises only from the amorphous phase and not from the crystalline phase and the grain boundary regions. The results indicate that the origin of the luminescence is considered to be due to defects created in the amorphous phase resulting from the microcrystallinity which increase with the grain size and/or the volume fraction. It has been shown from the analysis of the time-resolved PL measurement that the recombination transition of carriers of the low- and the high- (∼1.24 eV) energy emissions can be interpreted by a new model.
Photoluminescence study of confined electron hole plasma in GaxIn1−xAs heterostructures
Authors: Gal M. , Viner J. M. , Taylor P. C. , Kuo C. P. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

A low-energy photoluminescence (PL) emission is observed in GaxIn1−xAs heterostructures. The emission originates from an electron-hole plasma (EHP) confined in a 500 Å GayIn1−yAs layer between the InP substrate and a wider band gap GaxIn1−xAs layer. A line-shape analysis of the EHP emission yields electronic temperatures which essentially coincide with the bath temperature. Linear polarization of the PL was observed which indicates a degree of strain in the confining layer. Studies in a magnetic field indicate that the carrier transport in the heterostructure studied is via free carriers and not via excitons.
Comparative study of intermetallic phases formed by direct ion implantation and radiation enhanced diffusion of tin in two kinds of steel
Authors: Dionisio P. H. , de Barros B. A. S. , Baumvol I. J. R.
Published: July 2002

The surface layers of high-carbon and stainless steel samples, treated by both direct ion implantation of Sn+ ions and radiation enhanced diffusion of tin, are analyzed by means of Rutherford backscattering and 119Sn and 57Fe conversion electron Mössbauer spectroscopy. The intermetallic phases formed in the treated surfaces are determined and their thermal evolution is established. The compositions and phase transformations observed in the surfaces of the samples treated by both direct ion implantation and radiation-enhanced diffusion are very similar, and this similarity indicates that these two treatment processes are essentially equivalent for practical applications.
Photoinduced fixed oxide charge modification in SiO2 films
Authors: Fiori C. , Devine R. A. B. , Meilland P.
Published: July 2002

The influence of UV irradiation (λ=248 nm) on fixed oxide charges in wet and dry SiO2, with and without postgrowth anneal, is reported. In annealed samples, the density of positive fixed oxide charge increases with accumulated UV dose, more rapidly in dry SiO2 than in wet. In unannealed oxides, the positive fixed oxide charge decreases and becomes negative in wet oxide. Tentative explanations are presented.
Trapping effects in thin oxynitride layers in metal-insulator-semiconductor devices
Authors: Faigon A. , Shappir J.
Published: July 2002

The trapping characteristics of thin oxynitride films obtained by the oxidation of a thermally nitrided silicon surface were studied under both tunneling and hot electron injection. Comparison with standard oxide layers yields the following differences: No net positive charge generation is observed in the investigated layers, and the rate of surface states generation is about one order of magnitude smaller. The electron trap density is estimated to be ∼6×1017 cm−3 with a capture cross section of ∼10−17 cm2.
Simple model of the magnetic interaction between grains in construction steel
Authors: Szpunar J. A. , Szpunar B.
Published: July 2002

A simple model is suggested which enables the calculation of the relationship between the domain length and the domain wall spacing in constructional steel. The magnetic interaction between domains in neighboring grains is measured from the observed domain patterns and a coefficient is proposed which makes possible such a calculation for antiparallel domains. The calculated results compare favorably with experiments.
Electron temperature and average density in spherical laser-produced plasmas: Ultraviolet plasma spectroscopy
Authors: Goldsmith Samuel , Seely J. F. , Feldman U. , Behring W. E. , Cohen Leonard
Published: July 2002

The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high-Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 μm) and the frequency-tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15–200 Å. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency-tripled laser irradiation, Te=2600±600 eV and Ne>6×1020 cm−3. This is consistent with a ‘‘flux limit’’ smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 μm) irradiation.
Studies of Au-GaAs (001) interfaces prepared by molecular beam epitaxy. I. Overlayer growth and Schottky barrier formation
Authors: Kobayashi Keisuke L. I. , Watanabe Nozomu , Narusawa Tadashi , Nakashima Hisao
Published: July 2002

Evolution of Au-GaAs (001) interface structures with increasing Au exposure was studied. This study utilized photoelectron spectroscopy, electron diffraction, and He-ion Rutherford backscattering spectrometry. This was accomplished with the aid of molecular-beam epitaxy for surface preparation. The thermal stability of Au-GaAs (001) interfaces are presented in the following paper [N. Watanabe, K. L. I. Kobayashi, T. Narusawa, and H. Nakashima, J. Appl. Phys. 58, 3766 (1985)]. New phenomena were observed on overlayer growth, electronic structure change, and Schottky barrier formation. The present results apparently differ from previous Au-GaAs (110) system results; however, they support the surface defect model for Schottky barrier formation by W. E. Spicer, I. Lindau, P. Skeath, C. Y. Su, and P. Chye [Phys. Rev. Lett. 44, 420 (1980)].
Nuclear magnetic resonance studies of 143Nd and 145Nd in Nd-Fe-B type alloys
Authors: Potenziani II Ernest
Published: July 2002

Nuclear magnetic resonance of 143Nd and 145Nd in Nd2Fe14B and Nd15Fe77B8 at 4.2 K by zero-field spin-echo nuclear magnetic resonance has been used to determine hyperfine fields, magnetic moments, and relaxation times for the two inequivalent Nd crystal sites. It was found that the Nd spin-echo spectra of Nd2Fe14B and Nd15Fe77B8 are essentially identical, which is consistent with the Nd signal arising from the Nd2Fe14B phase in Nd15Fe77B8. The calculated Nd moments are higher than those obtained by neutron diffraction by 15 to 20%. The relaxation time mechanism appears to arise both from first-order quadrupolar broadening and from anisotropies in the hyperfine field distribution.
Comment on ‘‘Recent results on hydrogen passivation of silicon sheet solar cells’’ [J. Appl. Phys. 5
7, 5523 (1985)]
Authors: Hanoka J. I. , Dubé C. E.
Published: July 2002

Tsuo and Milstein [J. Appl. Phys. 57, 5523 (1985)] recently reported observations of hydrogen passivation of dislocations in silicon sheet solar cells. We dispute their claim of prior discovery on this and also question the validity of a deep channeling model to explain their results.
Reactive ion beam etching with chlorinated gases: Beam characterization and etching of aluminum
Authors: Steinbrüchel Ch.
Published: July 2002

Particle beams generated in a Kaufman-type ion gun from CC12F2, CCl4, and BCl3 have been characterized with a mass spectrometer. The composition of ionic and neutral species emanating from the gun varies strongly with the gun operating conditions. For all three gases major components are Cl+2 and Cl+ among the ions, and Cl2 among the neutrals. Various other ions and neutral fragments of the form CClx Fy, CClx, and BClx are also observed. Changes in the gas composition versus the magnetic field in the gun and versus gas pressure are related to corresponding measurements of the etch yield of aluminum. These results, together with data on the etch yield versus ion energy and incident angle, suggest that the overall etching includes contributions from physical sputtering, direct reactive ion etching, and, especially with CCl4 and to some extent with BCl3, from chemical sputtering. The implications of the beam diagnostics for other experiments, etching such materials as III-V compounds, silicon, and silicides are also discussed.
Longitudinal-mode stabilization in semiconductor lasers with wavelength-selective feedback
Authors: Agrawal Govind P.
Published: July 2002

In optical communication systems operating near the zero-dispersion wavelength of the fiber, the wavelength of semiconductor lasers should remain stabilized to minimize the effects of fiber dispersion. We analyze theoretically the requirements for mode stabilization when external dispersive feedback is used to select a longitudinal mode. The feedback bandwidth should be less than the external-cavity mode spacing to avoid the excitation of side modes corresponding to the longitudinal modes of the external cavity. By a suitable choice of laser parameters, a multimode laser can remain stabilized in the vicinity of the feedback-selected wavelength even when the free-running wavelength has drifted by more than 10 nm.
Mathematical model for the calculation of magnetization in anisotropic materials
Authors: Furlani Edward P. , Baker Alan G.
Published: July 2002

A three-dimensional formalism has been developed that can be used to compute the anhysteretic magnetization of anisotropic materials. The formalism represents a statistically based mean-field model in which the material is characterized as an ensemble of pseudodomains. The magnetization of the ensemble is obtained using a Maxwell–Boltzmann distribution with an energy dependence that includes both interactive and anisotropic terms. The model is applied to a single crystal of cobalt and excellent agreement with experimental data is obtained.
Laser initiation of an electrical discharge channel in cesium contained gas
Authors: Tamura H. , Horioka K. , Kasuya K.
Published: July 2002

A high power laser light tuned to the resonance line (455.5 nm) of the cesium atom induced photoionization in argon buffer gas and initiated a channel discharge of 60 cm length. The time lag from the laser injection to the channel breakdown was observed and compared with numerical result based on a simple model of the discharge channel. It was confirmed that good agreement was obtained between both time lags. A simple model well described the fundamental characteristic of the channel breakdown.
Imaging of radio-carbon clusters in high-purity germanium using a self-detection scheme
Authors: Luke P. N. , Haller E. E.
Published: July 2002

A new isotope-specific and quantitative technique based on self-detection in a position-sensitive detector has been developed for the imaging of radio-carbon clusters in high-purity Ge. Using a novel position-sensitive detector concept, a one-dimensional spatial resolution of ∼200 μm FWHM and a sensitivity of ∼6×107 14C atoms per cluster has been obtained. This technique can be applied to other semiconductors which can be used to fabricate self-counting position-sensitive nuclear radiation detectors.
Lattice-graded epitaxial layers
Authors: Cook Melvin S.
Published: July 2002

Lattice-graded epilayers may be grown without defects due to lattice misfit by controlling lattice constant changes and by growing the layers over curved surfaces. The critical layer thickness and the defect count of a lattice-graded layer can be related to similar quantities for a heteroepitaxial layer. The effect of the differences in coefficients of thermal expansion in the layer does not have a significant effect on its elastic strain. Product layers with a uniform composition can be grown over the lattice-graded layers, e.g., a GaAs layer can be grown over a Si–Ge lattice-graded layer formed on a silicon substrate. Convex-shaped surface features can be formed on a silicon wafer by reactive-ion etching.
Degradation of the electrical characteristics of the Si–SiO2 interface induced by electron injection
Authors: Falcony C. , Salas F. H.
Published: July 2002

The effects of electron injection on the electrical characteristics of the Si–SiO2 interface have been studied on metal-oxide-semiconductor type structures incorporating very thin oxide films (≲200 Å). Electron current across the oxide is obtained by Fowler–Nordheim tunneling in Al:SiO2:Si structures or by enhanced Fowler–Nordheim tunneling in Al:Si-rich-SiO2:SiO2:Si devices. The changes induced by charge injection in these structures were monitored by measuring the 1-MHz and the quasistatic capacitance versus voltage characteristic curves. In both structures negative charge trapping in the oxide and positive charge accumulation were observed as well as generation of interface states at approximately 0.6 eV from the top of the Si valence band. However, in structures with Si-rich-SiO2 layers an anomalous peak in the quasistatic capacitance curves was observed to be induced by the injection of electrons. The role of the Si-rich-SiO2 layer in these phenomena is discussed.
High dopant and carrier concentration effects in gallium arsenide: Band structure and effective intrinsic carrier concentrations
Authors: Bennett Herbert S.
Published: July 2002

The quality and reliability of predictions from numerical simulations of GaAs/AlGaAs devices, such as heterojunction bipolar transistors, depend on model parameters. These parameters include the variations with doping and carrier concentrations of the valence- and conduction-band edges and of the effective intrinsic carrier concentrations for heavily doped p- and n-type gallium arsenide. The Klauder self-energy method is used to calculate the effects of interactions among carriers and dopant ions in heavily doped GaAs at 300 K. The carrier-carrier interactions of exchange and correlation are estimated by interpreting optical-absorption measurements and by calculations based on degenerate theory. When densities exceed 1019 cm−3 in p-type and 1017 cm−3 in n-type gallium arsenide, carrier-dopant ion interactions and carrier-carrier interactions become of the same order of magnitude and should be included in calculations of band-structure changes and of properties which depend on the density of states, such as carrier transport and effective intrinsic carrier concentrations.
Tests for the gelation of solutions of atactic polystyrene
Authors: Plazek Donald J. , Altares Timothy
Published: July 2002

The shear creep and recovery behavior of narrow molecular weight atactic polystyrene (APS) (6.7×105Mw) solutions (27.3 wt. %) in two solvents (n-amyl and n-butyl acetate) were studied at various temperatures down to −83 °C above and below reported thermoreversible gel points (∼−50 °C). In both cases viscous flow was measured above and below the reported gel points. The resulting compliance curves for two solutions (n-amyl and n-butyl acetates) were successfully reduced to T0=−82 and −61 °C, respectively, indicating viscoelastic liquid response down to −82 °C. These solutions were clear. A solution of 18.7% APS (3.9×105 Mw) in iso-amyl acetate was also studied. It responded similarly to the first solutions until T=−49 °C when it became cloudy, indicating phase separation. At lower temperatures the viscosity increased dramatically, suggesting gel-like behavior.
Application of AlAs-GaAs superlattices to step-index and graded-index waveguide separate-confinement heterostructure laser diodes
Authors: Tokuda Yasunori , Ohta Yasumi N. , Fujiwara Kenzo , Nakayama Takashi
Published: July 2002

AlAs-GaAs superlattices were utilized for the waveguides in separate-confinement heterostructure laser diodes. A significantly low threshold current density Jth of 200 A/cm2 was achieved at a cavity length of about 500 μm for a graded-index superlattice-waveguide separate-confinement heterostructure laser diode. By photoluminescence measurements taken under a direct excitation condition, it was clearly demonstrated that the advantage of using the superlattice waveguide, i.e., the reduction of Jth value, is due to the improvement of heterointerface quality of the GaAs active layer. Moreover, a result on an all-binary SCH laser composed of the only AlAs and GaAs revealed that the Jth as considerably low as 400 A/cm2 was achieved at a cavity length of 400 μm.
Computerized analysis of thermal correlations using Peltier ac heating
Authors: Johansen Tom H.
Published: July 2002

Estimating uncontrolled thermal gradients between a system thermometer and a sample mounted in some measurement cell is a problem recognized in many experimental situations. To demonstrate a solution we describe a computer based low-frequency ac method for determining the relevant thermal impedances in a high-resolution capacitance dilatometer/oven system. Heat generated sinusoidally in time from a Peltier element allows measurements of complex transfer functions relating the response of thermometers placed at different locations. In particular, letting thermal expansion of a mounted sample represent its temperature has permitted a precise frequency analysis of the thermal separation from the primary system thermometer. The results characterizing the apparatus are compared to simple models for heat transport where the frequency response is described in terms of a relaxation time or an effective thermal diffusivity. The method is adaptable to a wide variety of measurement cells.
Photoelectron spectra of amorphous SixHy alloy films: The effect of microstructure on the Si-2p level shift
Authors: Das S. R. , Webb J. B. , de Castro S. C. , Sundaram V. S.
Published: July 2002

Depending on the deposition conditions, amorphous SixHy alloy films prepared by planar rf reactive magnetron sputtering exhibit one of three types of microstructure: (i) type A with no discernible microstructural features down to the 20-Å level and with a smooth uniform density; (ii) type B consisting of high-density regions of 50–200-Å lateral dimensions separated by a low-density network; and (iii) a two-level (type C) microstructure consisting of 300–500-Å dimensions columns separated by a pronounced low-density network. The columns, in turn, are composed of 50–200-Å dimension high-density regions interspersed with low-density network. The Si-2p level in these alloy films, determined by x-ray photoelectron spectroscopy, is observed to be strongly influenced by the microstructure of the film. A shift in the Si-2p level, systematically varying with the hydrogen concentration, is observed in alloy films with type B and type C microstructures. No shift is observed, irrespective of the hydrogen concentration, in alloy films with type A microstructure. The photoelectron spectra are examined in the light of the vibrational spectra of the films as measured by Fourier transform infrared techniques. The dependence of the Si-2p level shift on the microstructure and the variation with hydrogen concentration are explained qualitatively in terms of the differences in the silicon–hydrogen bonding in amorphous SixHy films with dissimilar microstructures.
Electron-beam-induced current near the localized defects in a polycrystalline semiconductor
Authors: Romanowski A.
Published: July 2002

The short-circuit current in a polycrystalline semiconductor may be distorted by the local defects or by the local interface defects (variation of the effective recombination velocity at the grain boundary). These defects can be determined from the steady-state electron-beam-induced current. The expression for the contrast coefficient C for the above defects are given. In the analysis, the generation of the excess carriers is assumed to be uniform in a sphere tangent to the semiconductor surface. The p-n junction is placed on the surface of the semiconductor.
Time constants and reaction cross sections characterizing film deposition by beam-induced polymerization
Authors: Fritzsche C. R.
Published: July 2002

Experimental values are reported for parameters employed in the theory of film deposition from organic vapors by irradiation with charged particles. Direct evidence is given for the known assumption that for ion-beam-induced deposition the activation cross section is much larger than for electron-beam-induced deposition. It is shown that this cross section is a complex quantity presumably including energy transfer within the macromolecules and excitation by secondary particles. The other parameters were found to be consistent with their simple interpretations in the theory as the lifetime of an activated state and area per polymerization center.
Transmission electron microscope observation of a NbN/Nb oxide/NbN trilayer structure
Authors: Miyamoto N. , Tarutani Y. , Hirano M. , Shimotsu T. , Kawabe U.
Published: July 2002

A NbN/Nb oxide/NbN trilayer film was fabricated and its cross-sectional structure was observed by a transmission electron microscope. The NbN oxide thickness was taken to be as thin as that (∼4 nm) of a typical Josephson junction in order to clarify the tunnel barrier structure. It was proven that the Nb oxide layer was not uniform and this nonuniformity was correlated with the crystal structure, grain boundary, and crystal orientation of the lower NbN film. A variety of oxide thicknesses may be responsible for the local distribution of tunneling currents within the Josephson junction.
Electron and hole transport in a-Si1−xGex:H alloys
Authors: Karg F. , Krühler W. , Möller M. , Klitzing K. v.
Published: July 2002

Amorphous Si1−xGex:H films and p-i-n diodes were fabricated by decomposition of SiH4/GeH4 mixtures in a triode glow-discharge reactor. The photoconductivity under AM1 illumination in these alloys was constant over a range of band gaps between 1.8 (x=0) and 1.5 eV (x=0.25), while the solar cell conversion efficiency decreased at the same time from 8.6% to 4.3%. This can be explained by a reduction in the μτ product for holes with rising x in undoped samples as revealed by time-of-flight experiments. In contrast to μτ, the hole drift mobility μD,h remains constant. The opposite behavior is observed for electrons, whose drift mobility μD,e decreases as the mobility activation energy EA increases. The relation between EA and μD,e for variable x is suggestive of the Meyer–Neldel rule for the conductivity. In conjunction with space-charge-limited current and sub-band-gap absorption data we conclude that only the conduction-band tail is widened by the incorporation of Ge while the valence-band tail remains unaffected. The transport data for x>0 can no longer be explained by a purely exponential conduction-band tail. The rising density of midgap states shows an increasing capture cross section for holes and a decreasing one for electrons.
Graphical analysis of processes with multiple activation energies
Authors: Lachter Jalil , Bragg Robert H. , Close Elon
Published: July 2002

The activation energies characterizing a kinetic process are derived from the slopes of the Arrhenius diagrams obtained by plotting rate constants versus reciprocal temperature. Those rate constants correspond to the shifts along the time axis needed to superpose the successive isotherms. A general method based on Chebyshev interpolation is proposed for the optimization of the superposition of the experimental data points. This method is applied to determine the activation energies of the graphitization kinetics of the interlayer spacings of pitch coke and pyrocarbon samples.
On the occasion of the 80th birthday celebration for Clarence Zener: Saturday, November 12, 1985
Authors: Seitz Frederick
Published: July 2002

The author traces the affiliations, associations, and interests of Zener throughout a long career.
Zener’s contribution to solid-state electronics and magnetism
Authors: Carr W. J.
Published: July 2002

A brief account is given of Zener’s contributions to solid-state electronics and magnetism, and of the impact several simple ideas have had on these subjects. Four topics are singled out for discussion: the theory of ferromagnetism, the temperature dependence of magnetic anisotropy, the Zener diode, and the optical Wood–Zener effect.
Recording process on an optical recording medium with thermal coloration
Authors: Morinaka Akira , Oikawa Shigeru
Published: July 2002

Laser recording on optical recording media with thermal coloration was investigated. The basic recording principle is a thermally induced hole opening following the chemical reaction between a coloring reagent layer and a coupler reagent layer. Sensitivity dependence on light absorbers in this optical recording medium was investigated. Almost equalized sensitivity for the three-colors recording was achieved by adjusting the thicknesses of the light absorbers.
Spatially resolved lifetime measurements in neutron-transmutation-doped polycrystalline silicon
Authors: Damaskinos S. , Dixon A. E. , Roberts G. D. , Dagg I. R.
Published: July 2002

Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels between 1013 and 1017 atoms/cm3. The carrier lifetime was measured using a contactless microwave absorption technique to monitor the decay of photoconductivity which allowed us to perform either isothermal or isochronal annealing to remove the damage caused by irradiation. An optimum anneal of 30 min at 700 °C resulted in almost full recovery to the lifetime before irradiation. A short laser pulse of wavelength 900 nm was focused to a 0.3-mm-diam spot on the samples. Lifetimes of two different sets of carriers were measured, the bulk carrier lifetime at the center of a grain and the carrier lifetime at a grain boundary. This latter carrier lifetime involves both fast and slow recombination mechanisms. The slow decay mechanism is due to interface states at the grain boundary. The fast recombination lifetime was found to be of the same order as the bulk recombination lifetime (of the order of 1 μs) and the slow one was of the order of 1 ms. Doping levels up to 1016 atoms/cm3 show no significant effect on the measured bulk carrier lifetime.
Magnetic and strain field splitting of the emission lines in the 1.5040–1.5110 eV range in GaAs
Authors: Reynolds D. C. , Bajaj K. K. , Litton C. W. , Yu P. W. , Huang D. , Klem J. , Morkoç H.
Published: July 2002

The magnetic field splitting and strain splitting of the emission lines in the 1.5040–1.5110 eV range in GaAs are reported. In the Voigt configuration the lines show doublet splittings in applied magnetic fields. In combined magnetic and strain fields four lines are observed in this configuration. All of the lines show a similar splitting. The splittings agree with what would be expected for shallow donor-acceptor pair centers in a zinc-blende structure.
Photoelastic trends from halides to pnictides by a bond-orbital method
Authors: Lines M. E.
Published: July 2002

The photoelastic effect, or the strain dependence of refractive index n0, essentially controls the details of light scattering in liquids, glasses, and crystals. Some knowledge of its behavior as a function of structure and chemical composition is therefore extremely valuable in a search for devices which seek to maximize or minimize such light scattering mechanisms. This paper derives a bond-orbital theory for the hydrostatic photoelastic effect (or the dependence of n0 on density ρ) for three-dimensionally coordinated crystalline structures (for which density fluctuations are directly related to primary bond length fluctuations) including four-, six-, and eightfold coordinated cations. The theory sets out the manner in which ∂n0/∂ρ depends on such fundamentals as valence, ionic radii, and degree of covalence, and highlights a term not previously derived in any prior theories of linear dielectric response. This term, involving relative anion to cation size, while not inconsequential in an evaluation of n0 itself, is absolutely essential for any understanding of ∂n0/∂ρ and completely dominates the latter in many more-ionic crystals. The final theory contains two parameters which are determined from experiment (essentially in the ionic and fully covalent limits, respectively). When complete it is tested on more than thirty halides, oxides, chalcogenides, and pnictides, for which reliable photoelastic data have been found in the literature. The agreement of theory with experiment is within experimental error for all except the tetrahedrally bonded halides for which direct interband activity by shallow-core d electrons places them outside the theory as presently constituted.
Density of oxidation-induced stacking faults in damaged silicon
Authors: Kuper F. G. , De Hosson J. Th. M. , Verwey J. F.
Published: July 2002

A model for the relation between density and length of oxidation-induced stacking faults on damaged silicon surfaces is proposed, based on interactions of stacking faults with dislocations and neighboring stacking faults. The model agrees with experiments.
Space-charge correction of solenoidal lenses
Authors: Hess G. , Humphries S.
Published: July 2002

A trapped distribution of low-energy electrons was used to alleviate spherical aberration in a solenoidal magnetic lens. The space-charge-correction method has potential application to the focusing of heavy, negatively charged particles such as H− ions. In the geometry investigated, the field contributions from trapped electrons cancel net electric fields along magnetic flux surfaces. The lens magnetic fields therefore define equipotential surfaces. Experimental results were obtained using a 10-keV electron beam as a nondestructive probe in a solenoid lens with 65-G peak field. Annular distributions of trapped electrons were achieved that were stable against the diochotron instability. Deflections of the probe beam were consistent with theoretical predictions. The peak focused current density of the 10-keV beam was improved twentyfold with the addition of trapped electrons in the lens.
Numerical calculations of director patterns in highly twisted nematic configurations with nonzero pretilt angles
Authors: van Sprang H. A. , Breddels P. A.
Published: July 2002

The influence is described of several device parameters, i.e., the total director twist, the pretilt angle, and anchoring energy, on the director pattern in highly twisted samples with nonzero boundary tilt. A difference compared with previous approaches is the inclusion of a finite anchoring energy coefficient in the continuum equations. The results indicate a pronounced influence of the surface anchoring on the hysteresis in the midplane tilt angle as a function of an applied voltage.
Improvements in high-field superconducting performance of V3Ga by a two-stage reaction process
Authors: Takeuchi T. , Iijima Y. , Inoue K. , Tachikawa K.
Published: July 2002

Effects of the heat treatment condition on the high-field superconducting performances of the surface diffusion processed V3Ga have been investigated. Ic at fields near Hc2 depends mainly on the layer thickness and Hc2 of V3Ga. The two-stage reaction process, which consists of the first reaction at the higher temperature to form a thick enough V3Ga layer and the subsequent second reaction at the lower temperature to achieve high values of Tc and Hc2, has been found to improve appreciably the Ic of SDP V3Ga in high magnetic fields. Overall Jc (including copper stabilizer) of about 2.0×104 A/cm2 at 19 T has been obtained for a ∼100-m-long V3Ga tape.
Planar and residual channeling of Si+ implants in GaAs
Authors: Blunt R. T. , Davies P.
Published: July 2002

The influence of planar channeling on the atomic profiles of low-dose Si+ implants into GaAs is demonstrated as a function of wafer rotation angle, ion beam incidence angle, wafer crystallinity, and thickness of dielectric coating on the surface of the wafer during implantation. Use of a controlled wafer rotation angle or implantation through a dielectric layer results in reproducible profiles free of planar channeling effects. However, even these implants still show a significant profile ‘‘tail’’ that is absent for implants into preamorphized material, thus suggesting the existence of significant residual channeling in GaAs.
Sputtered amorphous Fe–Te films: Structural and electrical studies
Authors: Chiba Kiyoshi , Tokumitsu Kazuto , Ino Hiromitsu
Published: July 2002

Thin films of an iron–tellurium alloy were prepared by rf sputtering and characterized by means of x-ray diffraction and Mössbauer spectroscopy. In an immiscible range in equilibrium composition, tellurium atoms were incorporated into iron, distorting the lattice to some extent. Beyond 14 at. % of Te, an amorphous structure appeared. Judging from the metastable superstructures formed at higher substrate temperatures and the covalent nature in the bonding, the kinetic hindrance against the redistribution of the elements due to the local atomic forces during rapid quenching plays a critical role in the formation of amorphous structure in this alloy. In addition, beyond some intermetallic range around 60 at. % Te, an amorphous phase also exists in the tellurium-rich region. The thermal stability was examined by a differential scanning calorimetry; the electrical resistivity is also discussed.
A self-consistent analysis of temperature-dependent field-effect measurements in hydrogenated amorphous silicon thin-film transistors
Authors: Schropp R. E. I. , Snijder J. , Verwey J. F.
Published: July 2002

We calculated a more accurate density of states (DOS) profile from field-effect (FE) measurements in hydrogenated amorphous silicon thin-film transistors, taking into account the anomalously changing conductivity prefactor in accordance with the Meyer–Neldel (MN) rule. We present a self-consistent analysis of the density of gap states profile, where the MN rule is, for the first time, properly considered in relation to the nonuniform shift of the Fermi level as induced by the field effect. Moreover, the calculation yields the correct flat-band voltage and the corresponding flat-band activation energy. The determination of conductivity activation energies free from any initial band bending effects is of importance in all types of transport measurements.
Theoretical study on eddy current tests for ferromagnetic materials
Authors: Yi Jae-yel , Lee Sekyung
Published: July 2002

The eddy current tests of ferromagnetic materials are theoretically analyzed employing a Globus model for the magnetization process, and the impedance change of a coil due to the presence of flaws contained in a magnetic conductor is derived employing Green’s function technique. The results show that for an excitation field which is lower than the critical field, the impedance change is maximum when the residual magnetization (or the dc magnetic field applied for the magnetic saturation of the conductor) is absent but for a large field the impedance change becomes maximum when the appropriate dc magnetic field in which the differential permeability reaches its maximum value is applied. For small surface flaws, the volume inhomogeneity mainly contributes to the reactance change of the coil whereas the discontinuity in magnetic permeability contributes to both real and imaginary parts of the impedance change. The dependence of the impedance change on flaw shape is shown explicitly in the derived formula.
The Orbitron as a stimulated-bremsstrahlung glow-discharge maser
Authors: Rosenberg A. , Felsteiner J. , Ben-Aryeh Y. , Politch J.
Published: July 2002

A new physical explanation for the operation of the Orbitron maser is presented. The Orbitron experimental results are shown to be in agreement with the prediction of the theory of amplification by stimulated emission of bremsstrahlung.
A ferrite-loaded autoaccelerator
Authors: Still G. W. , Ivers J. D. , Nation J. A. , Zhang S.
Published: July 2002

An account is presented of the performance of an autoaccelerator in which energy is extracted from the front portion of a relativistic electron beam, via a ferrite-loaded cavity, and stored in an oil-filled transmission line. The extracted energy is returned to augment the energy of the electrons in the latter half of the beam. An increase of up to 33% in the electron beam energy is reported. The device was also used to investigate beam energy recovery. In this application the line was terminated in a matched load and up to 60% of the beam energy recovered. The autoaccelerator performance was limited by current pulse rise time degradation in the ferrite and by the formation of virtual cathodes during the deceleration phase. The latter process also limits the energy recovery.
A model of deep center formation and reactions in electron irradiated InP
Authors: Sibille A. , Suski J. , Gilleron M.
Published: July 2002

We present a model of the production of deep centers and their reactions following electron irradiations in InP. We propose that the dominant hole traps in p-InP and electron traps in p+n InP junctions are complexes between shallow acceptors and a common intrinsic entity, the phosphorus interstitial or vacancy. The reactions observed below and above room temperature are then due to a local mobility of this entity, which can be obtained as well by thermal as by electronic stimulation of the reactions. This model implies the long-range migration (at least down to 16 K) of this entity, and explains the strongly different behavior of n-InP compared to p-InP samples.
Fundamental processes in the laser-triggered electrical breakdown of gases: Unconventional geometries
Authors: Dougal R. A. , Williams P. F.
Published: July 2002

Experimental studies of the laser-triggered electrical breakdown of spark gaps in three nonconventional geometries have been performed. The results of these studies shed new light on the subject of triggered electrical breakdown of gases in general and confirm conclusions we had drawn previously regarding the interaction between the optical beam and the propagating streamer in the conventional laser-triggering geometry (in which the focused beam struck one electrode after passing coaxially through the opposing electrode). In particular, we relate the V-I characteristics of the spark to the triggering conditions and to the system impedance and operating voltage. This relationship defines an upper limit on the initial ionization volume in order to insure prompt collapse of the gap voltage.
Comment on ‘‘Shortening of electron conduction pulses by electron attachers O2, N2O, and CF4’’ [J. Appl. Phys. 5
6, 3169 (1984)]
Authors: Hunter S. R.
Published: July 2002

Negative ion formation in pure CF4 and CF4/N2 gas mixtures is shown to proceed exclusively by dissociative electron attachment mechanisms at electron energies >4 eV in a high-pressure electron swarm experiment. These results are in contrast to a recent swarm study where CF4 was reportedly shown to attach electrons by transient parent anion formation processes at low electron energies ε≊0.5 eV. Possible sources of errors in that study are discussed.
Emitter tests in an open thermionic converter with vapor injection through the collector
Authors: Wriedt Susen , Möller Kenneth , Holmlid Leif
Published: July 2002

Mo and Pt emitters and a Ni collector with 400 laser-bored holes were used in an ‘‘open’’ thermionic converter. The alkali vapor was introduced into the converter through the array of holes in the collector from an adjacent alkali metal reservoir with separately controlled temperature. The overall results from the open thermionic converter are comparable to results from enclosed converters. The results found with a Cs plasma are encouraging, with barrier indices down to below 1.8 eV, at emitter temperatures around 1500 K in the case of a Mo emitter. The output power density was around 3.5 W cm−2. In the case of a Pt emitter, both Cs and K plasmas were used, with power densities up to 5.7 and 1.8 W cm−2, respectively close to 1800 K. The structure of the laser-bored collector may have contributed to these results, as well as the efficient removal of impurities in the ‘‘open’’ converter.
Doping studies using thermal beams in chemical-beam epitaxy
Authors: Tsang W. T. , Tell B. , Ditzenberger J. A. , Dayem A. H.
Published: July 2002

The use of chemical-beam expitaxy instead of chemical vapor deposition allows the incorporation of thermal atomic beams for doping. Dopant profile measurements by a differential capacitance-voltage technique and secondary ion mass spectroscopy technique show that there is no surface segregation with Si dopants in InP at all growth temperatures (<600 °C). On the other hand, Sn and to a lesser extent Be show surface segregation which can be reduced by growing the InP at a lower temperature (<550 °C). From this study, it is seen that Si should be preferred as the n-type dopant in producing InP/InGaAs high electron mobility transistors.
Formation and properties of very high-conductivity CdTe film made by evaporation
Authors: Suzuki K. , Ema Y. , Hayashi T.
Published: July 2002

Very high-conductivity n-type CdTe films with large crystallite size were prepared by vacuum coevaporation of CdTe and Cd and the electrical properties and the structure were investigated. The highest dark conductivity at room temperature of the film obtained was 6.5×103 S cm−1. The conductivity decreased with the increase of the ambient temperature. The electron concentration increased and the mobility decreased with the temperature. The film was a polycrystalline hexagonal phase and the crystallite size was a few tens of μm.
Generalized Poisson integrals and parametric head field equations
Authors: Huang Heui Li , Yen Sun Chung
Published: July 2002

To calculate the head field distribution first we pursue the Poisson integral approach3 using Fourier series method retaining up to 200 terms in the series. The parameters related to the rational approximation to the field equation for both ring heads and pole-keeper heads have been obtained and tabulated. The idea of the Poisson integral is then extended, denoted as Poisson integral II, to enable us to calculate the head fields both within and without the head gap regions. The first Poisson integral II involves eight parameters and enables us to calculate head fields in reasonably good agreement with the direct Fourier series calculations. The second Poisson integral II involves a self-consistent calculation, which is reducible to the rational field equations with five parameters and is highly capable of producing head field distribution anywhere with great accuracy at low spacings. Results of a comparison with a finite element method calculation are excellent.
Growth and surface properties of CuInSe2
Authors: Haneman D. , Kristensen R. D. L. , Hafiz A.
Published: July 2002

It has been found that CuInSe2 polycrystalline material suitable for photoelectrochemical cells can be produced from low grade In, Se, and Cu. Low-energy electron diffraction (LEED) measurements on these samples show that well ordered (112) surfaces can be produced after 35 min Ar ion bombardment at ∼8 μA cm−2, 600 eV, followed by 30 min anneal at temperatures as low as 320 °C. Extra LEED spots are visible at some energies, indicating a clean surface but with possible nonstoichiometric areas. No effects of oxygen are observed at exposures up to 326×103 L.
Single and coupled double-well GaAs/AlGaAs and energy-dependent light-hole mass
Authors: Watanabe Naozo , Kawai Hiroji
Published: July 2002

Photoluminescence spectra of single and coupled double wells were reanalyzed assuming a 62% partition of the band-gap discontinuity to the conduction band and an energy-dependent light-hole effective mass. The photoluminescence peak positions of the single well are little affected when 62% instead of 85% is adopted for the partition value. The photoluminescence spectra of the coupled wells consist of a main peak and its satellites. Energy differences between the peak and its satellites are in good agreement with the calculated values when they are ascribed to transitions between doublet states in the conduction-band well and doublet states in the valence-band well, assuming a 62% partition and reasonable energy dependence of the light-hole mass. This coupled double well offers a first evidence for the energy-dependent light-hole mass.