bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-spin-resonance studies of vapor-grown carbon fibers
Authors: Marshik B. , Meyer D. , Apple T.
Published: July 2002

The degree of disorder of vapor-grown carbon fibers annealed at various temperatures has been determined through analysis of their electron-spin-resonance (ESR) line shapes. Higher annealing temperatures result in a greater ordering of the crystallites. Fibers annealed at 2275 K show a standard angular deviation between the fiber axis and the crystallite basal planes of 35°, while fibers annealed at 3375 K exhibit a deviation of 12°. The annular nature of the graphene sheets and the anisotropy of the electrical conductivity produce an inhomogeneous penetration of the microwave field detectable when the fiber axis is not coincident with the oscillating magnetic field. This results in a profound effect upon the ESR intensities for different portions of the sample. In general, a greater relative intensity is observed for crystallites having their c axes parallel to the static magnetic field as compared to crystallites at other orientations. Fibers which are annealed at temperatures above 3275 K exhibit a motional narrowing due to the spiraling diffusion of the electron within the basal planes of the fiber. The motional narrowing indicates the development of longer-range annular order in the fiber.
Role of dislocations in n-type annealed CdHgTe grown by liquid-phase epitaxy
Authors: Pelliciari B. , Baret G.
Published: July 2002

Cd(x)Hg(1−x)Te with x=0.23 was grown on CdZnTe substrates by liquid-phase epitaxy and annealed in a sealed ampoule under controlled Hg pressure. The anomalous behavior found in the electrical transport data of some layers is correlated with defects observed in x-ray topography measurements.
Incorporation of argon in titanium silicon multilayer structures during sputter deposition
Authors: Janssen G. C. A. M. , Wessels P. J. J.
Published: July 2002

Titanium silicon multilayer structures have been produced by alternate sputtering of silicon and titanium in an argon plasma. During the sputter process, part of the titanium and silicon layers react to form a silicide at the interfaces. Because of the argon plasma, a certain amount of argon is incorporated in the growing multilayer. A model is presented in which the amount of argon incorporated in the multilayer is a function of the nominal thickness of the individual silicon layers.
Space-charge-limited-current diode model for the rectifying-to-ohmic transition with Au/Al contacts to CdS
Authors: Partain Larry D.
Published: July 2002

The space-charge-limited-current diode model indicates that the rectifying-to-ohmic transition properties of Au/Al contacts to CdS are controlled by a trap at 0.6 eV below the conduction-band edge of the CdS interface with the metal. The trap densities vary between 4 and 10 (1016) cm−3 and the rectification degrades as the band bending asymmetry in the interface decreases from 0.206 to 0.158 eV with the introduction of the Al. The model provides a good fit of both the forward bias current and the nonsaturating reverse bias current characteristics using parameter values that are consistent with those found by other workers using deep-level transient spectroscopy.
Deep levels as local probes for the study of superlattices
Authors: Deveaud Benoit , Lambert Bertrand , Plot Beatrice , Chomette Andre , Regreny Andre , Bourgoin Jacques C. , Stievenard Didier
Published: July 2002

Two kinds of deep levels have been studied in GaAs/GaAlAs superlattices: electron irradiation-induced defects and manganese. In both cases we confirm the localized character of the wave function by showing the invariance of the energy levels with respect to former band edges of the superlattice constituting materials. We obtain information on the energy levels of the electron and hole bands in the superlattice from the observed ionization energies of these deep levels and compare these results to energy level calculations.
Effective intrinsic concentration n
i
e in degenerately doped silicon
Authors: Silard Andrei P. , Duţă Miron J.
Published: July 2002

Based on the semiconductor fundamentals and using the band-gap-narrowing (BGN) models widely quoted in the literature, a thorough analysis of the effective intrinsic concentration nie dependence on impurity concentration in degenerately doped n+- and p+-silicon is performed. It is shown explicitly that starting from a threshold level of dopant concentration the Fermi–Dirac statistics, associated with the semiconductor degeneracy, gradually cancels the impact of BGN on the (pn) product in both highly doped n+-and p+-silicon, regardless of the BGN model employed. Depending on the magnitude of and uncertainties related to the prevailing BGN models, the results of this work show that the effective intrinsic density nie drops to the value of ni at doping levels of 1020–1021 cm−3 in both types of silicon materials. The main qualitative implications and quantitative consequences of the presented results for bipolar device physics and models are also outlined.
Study of the interfacial structure between Si (100) and thermally grown SiO2 using a ball-and-spoke model
Authors: Ohdomari Iwao , Akatsu Hiroyuki , Yamakoshi Yukio , Kishimoto Koji
Published: July 2002

Structural models of the a-SiO2/(100)Si interface have been constructed using plastic balls and spokes to study the atomic scale structure of the thermally grown a-SiO2/(100)Si interface. Various properties of the models such as distortion energy, composition, and interface undulation have been estimated on the basis of the models. The results of the simulation indicate that the energetically favorable interface is not flat but undulated with (111) facets or has a transition region with partially oxidized Si atoms. High-resolution transmission electron microscopy images have also been simulated for the models.
Ferroelectriclike dielectric behavior in the piezoelectric amorphous copolymer of vinylidenecyanide and vinyl acetate
Authors: Wang T. T. , Takase Y.
Published: July 2002

The alternating copolymer of vinylidenecyanide and vinyl acetate is the first amorphous polymer to show a combination of excellent properties among the several known piezoelectric polymers, e.g., high piezoelectric activity (d31=7 pC/N), high electromechanical constant (kt=0.38), and high thermal stability (glass transition temperature, Tg=170 °C). Our dielectric studies have uncovered for the first time several unusual characteristics which strongly suggest the copolymer to be a ferroelectric glass. The ferroelectric nature is manifested in the dielectric anomalies (a fourteenfold increase in the dielectric constant), the Curie–Weiss behavior and, more importantly, the positive and negative divergence of the third-order dielectric susceptibility around the transition temperature. Significantly, these transitional phenomena occur at temperatures slightly above the Tg of the copolymer. The microscopic origin of the dielectric anomalies has been attributed to the cooperative interactions of C≡N dipoles which turn active only after the main chains become mobile.
D
X centers in AlGaAs p-n heterojunctions and heterojunction bipolar transistors
Authors: Nathan M. I. , Tiwari S. , Mooney P. M. , Wright S. L.
Published: July 2002

D X centers are found to cause the capacitance of an AlGaAs/GaAs p-n heterojunction at 77 K to behave like that of a p-i-n diode. Exposure to light causes the capacitance to behave like a normal p-n junction. It is argued that the presence of DX centers has only a small effect on the switching properties heterojunction bipolar transistors.
Growth and modeling of highly doped, thin-layer silicon-modulation-doped superlattices by intermittent solid-phase epitaxy
Authors: Ahlers E. D. , Allen F. G.
Published: July 2002

Earlier results determined the diffusion coefficients of Ga in both amorphous and crystalline silicon. Computer modeling shows that growth of silicon n-i-p-i superlattices with high doping and narrow layer width by either conventional molecular-beam epitaxy or solid-phase epitaxy leads to smearing of the Ga profile because of its relatively large diffusion coefficients in both the amorphous and crystalline states. A method of sequential amorphous deposition and crystallization is presented that minimizes the Ga diffusion. Superlattices with Ga and Sb doping of ≊5×1018 cm−3 and layer thickness of ≊25 nm are shown. The crystal surface after all regrowths produces very sharp low-energy electron diffraction patterns, and Auger electron spectroscopy shows the numerous growth interfaces to be clean to better than 1% of a monolayer of O or C.
Absolute values of the nonlinear susceptibility of dye solutions measured by polarization spectroscopy
Authors: Marcano O. A. , Aranguren L.
Published: July 2002

The absolute value of the thermal grating portion of a polarization spectroscopy signal of acetone solutions of malachite green and 1,3′-diethyl 1-2,2-quinolythiarcarbocyanine iodide is measured. The data are compared with the values calculated from a macroscopic description of the thermal modulation of the refraction index using a thermal susceptibility formalism. A method for the measurement of the resonant third-order electronic susceptibility of the dyes through comparison with the thermal grating susceptibility is proposed.
Electrical properties of Be+ ion-implanted AlxGa1−xAs p-n junctions
Authors: Yamahata Shoji , Adachi Sadao , Ishibashi Tadao
Published: July 2002

The quality of the AlxGa1−xAs (x=0, 0.3) p-n junctions fabricated by Be+ ion implantation (2×1014 cm−2, 100 keV) is investigated by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements. The annealing temperature dependence of the I-V characteristics indicates that the anneals at 600–850 °C for the GaAs diodes and 650–950 °C for the Al0.3Ga0.7As ones result in the lowest values of the ideality factor (about n=1.8). The C-V characteristics indicate that the Be+ -implanted GaAs diodes have graded junctions, independent of annealing temperatures. The junction shape of the Al0.3Ga0.7As diodes, on the other hand, strongly depends on annealing temperatures.
Textured back-surface reflectors for thin-film solar cells
Authors: Paulick Thomas C.
Published: July 2002

A textured interface between α-Si:H and silver is modeled as a periodic corrugation by using the exact extinction theorem. Light is reflected from such a surface into grating modes, which may be either propagating or evanescent. Deeper textures place the reflected light preferentially into modes of higher-order number. The higher-order propagating modes are absorbed with increasing strength by the α-Si:H. The evanescent modes have effective extinction coefficients that may be many orders of magnitude greater than the ‘‘bulk’’ value for α-Si:H. Numerical results suggest the texture dimensions that would most increase the long-wavelength solar cell efficiency. The surface-plasmon polariton dispersion relation is calculated for the interface between α-Si:H and silver. This is used to interpret published photoconductivity data for α-Si:H backed by textured silver.
A study of pulsed energized particle collection in a bench-scale cylindrical electrostatic precipitator
Authors: Tardos Gabriel I. , Snaddon Robert W. L. , Schwabe Robert J. , Walsh Kevin A. , Salasoo Lembit , Nelson J. Keith
Published: July 2002

Careful laboratory measurements have been conducted on a 5-cm-diam wire-cylinder electrostatic precipitator (ESP) in order to examine and understand the salient electrical behavior, particle charging, and collection characteristics for pulse powering under clean plate conditions. The importance of electrical parameters has been examined experimentally to determine the variation in performance for medium width pulses up to 250 μs. Operation at reduced current levels is shown to be possible only when the dc pedestal voltage is below corona inception. A good fit of the experimental data to predictions given by a spatiotemporal model indicates that the physics can be effectively described for both dc-powered and pulsed systems. In particular, the impact and interplay of particle diffusivity and electron charging is investigated. For ESPs of small size, electron charging appears to be significant.
New photoreceptor charging method by rubbing with magnetic conductive particles
Authors: Tetsutani Nobuji , Hoshino Yasushi
Published: July 2002

A new photoreceptor charging method without corona discharge is proposed in this paper. The charging is carried out by rubbing a photoreceptor with magnetic conductive particles having applied potential. Using this method, the photoreceptor is charged to more than 80% of its applied potential. The surface potential is found to be high and stable when the conductivity of particles and the peripheral velocity of the sleeve carrying the conductive particles are high. The charging mechanisms are assumed to be carrier-injection assisted by the rubbing, and injection-carrier trapping.
Effective mobility of electrons in surface layer of semi-insulating and p-type InP substrates
Authors: Takagi Shinichi , Sugano Takuo
Published: July 2002

Effective mobility of electrons in the channel of InP metal-insulator-semiconductor field-effect transistors (MISFETs) fabricated on semi-insulating (SI) or p-type InP substrates was measured in terms of surface electron density and temperature and found to be in fairly good agreement with a model based on the theoretical values calculated by three scattering mechanisms: polar optical-phonon scattering, delta-function-like potential scattering, and screened Coulomb scattering. The effective mobility of electrons in the channel of MISFETs on p-type substrates was lower than that on SI substrates, and this was attributed to a higher density of Coulomb scattering centers in the channel of MISFETs on p-type substrates.
Current versus voltage measurements on GaAs doping superlattices
Authors: Ruden P. P. , Engelhardt D. C. , Walterson R. A. , Hibbs-Brenner M. K.
Published: July 2002

We report results of current versus voltage measurements on GaAs doping superlattices with current flow parallel to the superlattice symmetry axis, i.e., perpendicular to the layers. The material was grown by low-pressure metalorganic chemical vapor deposition and characterized by excitation intensity-dependent photoluminescence spectroscopy. The luminescence results show the superlattices to be of high quality. Four samples with nominally identical doping densities and layer thicknesses but different total numbers of superlattice periods were investigated. The electrical measurements demonstrate the strong dependence of the current on the number of superlattice periods. Our results agree semi-quantitatively with a simple model which attributes the current to thermionic emission over the multiple built-in space-charge potential barriers.
Phase formation and dissociation in the thin-film Pd/Al system
Authors: Colgan E. G.
Published: July 2002

Phase formation has been investigated for thin films in the following systems: Al/Pd, Pd2Al/Al and Pd/PdAl/Al between 200 and 450 °C. The films were prepared by sequential evaporation and coevaporation, annealed under vacuum, and analyzed by Rutherford backscattering and x-ray diffraction. Pd2Al3 is the dominant growing phase in the initial stages of the reaction for these samples. Al is the dominant moving species during the formation of Pd2Al3.
Cu deposition on Al2O3 and AlN surfaces: Electronic structure and bonding
Authors: Ohuchi F. S. , French R. H. , Kasowski R. V.
Published: July 2002

We report a photoelectron spectroscopy study of the interaction of copper with Al2O3 and AlN model systems processed under ultrahigh vacuum conditions and compared the intrinsic electronic interactions between the two cases. The evolution of the electronic structure and bonding of Cu to AlN has been further studied using ab initio total energy pseudofunction techniques.
Low-temperature heteroepitaxial film growth of Si on sapphire by reactive ion beam deposition
Authors: Yamada Hiroshi , Torii Yashuhiro
Published: July 2002

Heteroepitaxial film growth of Si on sapphire (SOS) using ionized species was investigated. These ionized species are produced from reactive gases, such as SiH4, and controlled in the low-energy region, less than 500 eV. SOS films can be grown at 700 °C, at ion energies of 100–300 eV, and at growth rates greater than about 0.04 nm/s. At this temperature and energy level, no microtwins are included in the film surface layers. SOS film growth at 600 °C can also be achieved by increasing the ion energy to 300 eV, but microtwins begin to appear.
Fermi level and current transport of Bi12GeO2
Authors: Braun Christian M. , Fujishima Akira
Published: July 2002

A photoelectrochemical resistor was constructed using a bismuth germanium oxide electrode and a liquid junction. Current transport consists of the oxidation and reduction of water by holes and electrons, and the device exhibits ideal current voltage characteristics with a ratio of light to dark current greater than 104. By comparison of the flat-band potential in the dark and under irradiation it is concluded that the intrinsic Fermi level of our sample is in the center of the band gap at −310 mV vs SCE (pH=5). Deep trap levels at 0.20 and 0.33 eV above the valence band can be present in varying concentrations and facilitate the trapping and recombination of electrons and thereby decrease conductivity.
Ultraviolet photoelectron spectroscopy of sputter-formed Re-1% Pd
Authors: Gordon R. L.
Published: July 2002

Ultraviolet photoelectron spectroscopy has been used to obtain electron energy distribution curves (EDC’s) from samples of a Re-1% Pd alloy formed by high-rate sputter deposition. The shape of He-i-induced EDC’s was found to depend on surface concentration of Pd. For surfaces with Pd/Re<0.014 the EDC is nearly identical to that of a pure Re reference sample and shows structure attributable to the calculated rhenium density of states. With Pd/Re>0.28 the EDC shows reduced occupation in states near the Fermi level, and exhibits a peak at 2.3 eV below the Fermi level, characteristics of the EDC from a clean Pd reference sample. The EDC from the Pd-covered alloy surface cannot be duplicated by a simple linear superposition of EDC’s from Re and Pd reference samples. The increase in occupation of the 2.3-eV level at the expense of higher-lying levels in both pure Re and in the low-Pd-coverage alloy is thought to be responsible for the increase in work function of the alloy which accompanies segregation of Pd to the surface.
Compressive epitactic layers on single-crystal components for improved mechanical durability and strength
Authors: Marion John E. , Gualtieri Devlin M. , Morris Robert C.
Published: July 2002

Compressive epitactic layers grown on single-crystal substrates are shown to substantially improve mechanical durability. In this study, neodymium-substituted gadolinium gallium garnet (GGG) layers are grown on undoped GGG substrates. The layers are found to dramatically improve the abrasion resistance of the substrates, but to have only a slight effect on strength. Abrasion treatments, which cause up to 20 times decrease in the strength of substrates without epitactic layers, do not cause a significant decrease in the strength of substrates with these compressive surface layers. This permits the high strength of specially prepared strong substrates to be retained after abrasion.
Quick extraction of microwave pulses from a cavity by a superconducting polycrystalline BaPb1−xBixO3 thin film
Authors: Minami Kazuo , Saeki Koshiro , Kubo Hideyuki , Ohtsuka Mieko , Awano Mitsuru , Takai Hiroyuki
Published: July 2002

A superconducting polycrystalline BaPb1−xBixO3 thin film of 300 nm thickness is studied as a quick microwave switch. The film is installed in a cylindrical TE111-mode cavity made of copper with a resonant frequency of 2.84 GHz; the cavity is evacuated and immersed in liquid helium. Transition from the super- to normal conducting state of the film is made by a pulse current through the film with a current density of the order of 3×107 A/m2. The microwave pulse power, which is 1.2 times the cw input to the cavity, is extracted in a short time of less than 200 ns. The time response of the film switch is less than 30 ns, which is the limit of our measuring system. The observed output powers are compared with numerical analyses, and the possibilities for improving the pulse power gain are discussed.
Appropriate use of the strength parameter in solid-state slab laser design
Authors: Marion John E.
Published: July 2002

The manner in which the strength parameter is used in the design process for high-average-power slab lasers is examined. Fracture toughness, an intrinsic measure of the strength of brittle materials, is adopted as the appropriate parameter for comparison of different materials in a selection process. Conversely, an estimate of actual component strength is used in fixing a safe operating stress for the laser by a weibull scaling of fracture data. Measurement methods for characterizing these two strength parameters are examined for both laser glasses and crystals. Experimental results illustrating these techniques are given.
Buried GaAs/GaAlAs laser with p-dopant implanted stripe as a mask for liquid-phase-epitaxy regrowth
Authors: Menigaux L. , Sansonetti P. , Brandon J. , Henoc P.
Published: July 2002

Buried GaAs/GaAlAs double heterostructure lasers have been realized by combining a double heterostructure grown by metalorganic chemical vapor deposition, p-dopant implantation, stripes chemical etching, and liquid-phase epitaxy (LPE) regrowth of n− GaAlAs. Although the p-implanted top of the stripes were thermally annealed during the LPE burying, no regrowth occurred on them. Buried lasers were thus directly obtained while p-ohmic contact properties were good. The causes of such a phenomenon have been studied by transmission electron microscope and electron diffraction techniques. Typical threshold currents of 12 mA for a 270-μm cavity length were obtained. This technology offers the potential of low ohmic contact resistivity.
Rapid thermal annealing of hydrogenated amorphous silicon grown at low temperature
Authors: Fiorini P. , Haller I. , Nocera J. J. , Cohen S. A. , Brodsky M. H.
Published: July 2002

Hydrogenated amorphous silicon with different levels of phosphorous doping has been deposited by plasma-enhanced chemical vapor deposition at a temperature of 125 °C. Its electrical properties are largely inferior to those of standard material grown at 275 °C, but they can be improved by a rapid thermal annealing process. The change in electrical conductivity depends on the doping level and is better for 0.1% than 1% or undoped samples. In this case the electrical conductivity, after annealing, increases by three orders of magnitude and is only a factor of 10 less than that of the best conducting material produced at 275 °C. The improvement in electrical properties is not causatively related to the loss of hydrogen. This low-temperature material, after annealing, forms relatively low resistance contacts with molybdenum or aluminum and is suitable for application in thin-film transistor technology.
On the gate capacitance in n-channel inversion layers on ternary semiconductors under magnetic quantization
Authors: Ghatak K. P. , Mondal M.
Published: July 2002

An attempt is made to derive a generalized expression of the magnetogate capacitance in the n-channel inversion layers on ternary semiconductors without any approximations of weak or strong electric-field limits and taking into account the influences of electron spin and Dingle temperature, respectively. It is found on the basis of the three-band Kane model and taking n-channel inversion layers on Hg1−xCdxTe as an example, that the gate capacitance exhibits oscillations with the changing magnetic field and the oscillatory behavior is in qualitative agreement with the experimental observation reported in the literature for metal-oxide-semiconductor structures of the same semiconductor.
Electron trapping during high-field tunneling injection in metal-oxide-silicon capacitors: The effect of gate-induced strain
Authors: Hook Terence B. , Ma T.-P.
Published: July 2002

It is shown that the electron trapping during Fowler–Nordheim tunneling in metal-oxide-semiconductor capacitors is a function of the gate-induced strain. The trapping probability is modulated by the strain induced by the gate electrode. A larger induced compressive strain results in a smaller probability of trapping. A silicon-rich silicon-dioxide injector stack was utilized to obtain spatially uniform injection under both positive and negative gate bias. Devices without the injector exhibited perimeter-dominated current under negative gate bias because of the field enhancement near the edges. The electron trapping dependence on the gate-induced strain is invoked to explain the sublinear dependence of the perimeter-related current. It is shown that only traps of capture cross section greater than 10−18 cm2 are affected by this strain, apparently by modulating the capture cross section.
Thermal expansion and flow model for pit formation in laser marking of polymeric film optical disks
Authors: Wissbrun Kurt F.
Published: July 2002

A mechanism for the formation of a pit by laser marking of a polymer/dye medium is proposed. The absorbed radiation melts the medium and increases its volume, causing formation of a protruding bulge of molten polymer. This protrusion flows out and levels under the driving force of surface tension. Subsequent cooling and contraction leave a depression surrounded by a rim. Approximate calculations to support the plausibility of the proposed mechanism are presented.
Field emission effect on the rise time of small spark-gap switches for N2 lasers
Authors: Ishikawa Kazuhito , Muto Shinzo , Matsuzawa Hidenori , Suganomata Shinji
Published: July 2002

It has been shown that the power of a low-pressure, Blumlein-type N2 laser increases with decreasing separation of the electrodes of spark-gap switches and that the laser pulse width decreases at the same time. This is primarily due to field emission current from those electrodes. The field emission current steepened the buildup of spark-gap current and of laser tube discharge by preionizing the atmosphere in the spark-gap chamber and in the laser tube.
Anodized niobium as barrier for Josephson tunnel junctions
Authors: Aponte J. , Rivera E. , Sa Neto A. , Octavio M.
Published: July 2002

We have fabricated Nb-NbOx-Pb Josephson tunnel junctions in which the barrier is formed by anodization of the niobium electrode. The anodized barrier is made thick (>100 Å) to then be sputter etched to the desired thickness. The geometry of the niobium electrode is defined by a selective anodization process and the lead electrode is patterned by chemical etching. The I-V characteristics of 10−6-cm2 rectangular junctions have been measured at 4 K. Our junctions exhibit large leakage current and low ICRN product, making them less attractive for practical applications than junctions made by other techniques. However, the ease of fabrication and reasonable reproducibility of the electrical characteristics of our junctions make our method of fabrication quite useful when high quality of the barrier is not a stringent requirement. Noise measurements in our junctions and electron diffraction analysis of niobium-oxide films grown by anodization confirm the presence of a large number of defects in the barrier.
Strength of long optical glass fibers
Authors: Phani K. K.
Published: July 2002

The tensile strength of optical fibers has been analyzed in terms of a modified Weibull-type function having lower and upper strength limits with two-shape parameters. The function provides reasonable predictions of the long length strengths.
Direct observation of the composition of A and B {111} faces of GaP by using x-ray photoemission
Authors: Frommer M. H.
Published: July 2002

X-ray photoemission from Ga 2p3/2 electrons was used to investigate the two polar {111} faces of a polished, single-crystal GaP wafer. It is shown directly by examining, for the first time, the contributions to the photoemission from electrons involved in Ga–Ga, Ga–P, and Ga–O bonds, that one of these faces consists solely of Ga atoms and the reverse face solely of P atoms. The same experiments on both faces of a similar {100} wafer showed that both {100} faces are the same.
Microstructural observations of RBa2Cu3O7 (R=Gd, Y, and Tm) superconductor thin crystals between 15 and 1000 K
Authors: Gasgnier M. , Ruault M.-O.
Published: July 2002

Small crushed crystals of the new superconductor materials of the type RBa2Cu3O7 (R=Gd, Y, and Tm) were studied by conventional transmission electron microscopy between 15 and 1000 K. Between 15 and 300 K a He-liquid cold stage was used, while temperatures between 300 and 1000 K were obtained by focusing the electron beam. The thin-edge areas unambiguously show the formation of the classical orthorhombic structure. The orthorhombic-tetragonal transition, in the course of the cooling, was not observed. Electron diffraction results show the presence of various unknown structures and the BaCuO2 compound. The crystals present few defects: Only some twins and dislocations have been observed.
Supermode behavior of coupled two-stripe AlxGa1−xAs-GaAs quantum-well heterostructure lasers
Authors: Jackson G. S. , Holonyak N. , Hall D. C. , Epler J. E. , Burnham R. D. , Paoli T. L.
Published: July 2002

Data are presented on the simplest form of multiple-stripe laser array, a gain-guided two-stripe configuration of wide spacing (∼15 μm, weak or moderate coupling), showing the effects of the two forms of supermode oscillation on the laser’s L-I characteristic, far-field emission pattern, and radiation spectrum. Measurements of the spatial dependence of the gain, at various currents, for a modified (antireflection-coated) two-stripe AlxGa1−xAs-GaAs quantum-well heterostucture laser diode provides a basis for explaining the onset of oscillations of both forms of supermodes (n=1, symmetric or ‘‘even,’’ and n=2, antisymmetric or ‘‘odd’’). These results agree with the significant band filling of the single quantum well and the supermode energy splitting of ∼15 meV in high-level laser operation. The data and results presented are obtained by operating antireflection-coated diodes in a tunable external grating cavity and by taking gain measurements on and between the stripes at the Fabry–Perot facets.
A microscopic model of energy deposition in silicon slabs exposed to high-energy protons
Authors: Azziz N. , Tang H. H. K. , Srinivasan G. R.
Published: July 2002

A parameter free, microscopic model has been formulated to study the energy deposition due to protons bombarding silicon samples. The model is based on a Monte Carlo technique and uses two sets of essential and fundamental quantities from nuclear physics and condensed matter physics, the energy spectra and angular distributions of light fragments and heavy recoil nuclei from proton induced reactions, and the stopping power of ions through condensed media. Our model calculations are found to agree very well with the pulse-height spectra measured by McNulty, Farrell, and Tucker [IEEE Trans. Nucl. Sci. NS-28, 4007 (1981)] and by Farrell and McNulty [IEEE Trans. Nucl. Sci. NS-29, 2012 (1982)] for thin slabs of silicon (8.7–200 μm) exposed to protons at various energies (86–158 MeV). We present a critical analysis of the contributions of various spallation products to the total spectra and discuss the physical implications of such results for semiconductor devices.
A new system for vacuum deposition of refractory materials using an atmospheric-pressure inductively coupled plasma
Authors: Merkle B. D. , Kniseley R. N. , Schmidt F. A.
Published: July 2002

We have successfully developed a technique utilizing an atmospheric-pressure inductively coupled plasma combined with a low-pressure deposition chamber for deposition of thin films. The equipment and method of operation are discussed. Refractory powders (Nb and Y2O3) were injected into the plasma and deposited as Nb and substoichiometric yttrium oxide, YO1.49, onto Fe and Cu substrates. The substoichiometric yttrium oxide deposit adhered well to the Fe and Cu substrates, while the Nb deposit adhered well to the Fe only. The Nb deposit on the Cu substrate flaked and peeled probably because of stresses induced from the thermal expansion mismatch between the Nb and Cu. Further studies will be undertaken to better understand the processes occurring in this type of plasma-coating system in order to optimize the instrumental parameters for particular coating applications.
Square loop antenna with a dielectric core
Authors: Casey John P. , Bansal Rajeev
Published: July 2002

An experimental investigation of the input impedance of a square loop antenna with a dielectric core is reported. The effects of the dielectric constant and the height of the core on the loop impedance are given. A comparison between the measured and theoretical results is included.
Polarization competition in quasi-index-guided laser diodes
Authors: Amann Markus-Christian , Stegmüller Bernhard
Published: July 2002

The mechanism of polarization competition in laser diodes with a lateral quasi-index-guiding (QIG) structure is analyzed generally by way of the effective index approximation using a simplified QIG laser model. The influence of the relevant waveguide parameters on the polarization-dependent threshold current of QIG laser diodes is investigated in detail by example of λ=1.3-μm ridge-waveguide lasers. Thereby, it is found that for intermediate values of the effective index step, the TM mode exhibits a higher gain and lower threshold current, whereas for pure gain guiding or strong index guiding, the TE mode prevails. This behavior, which compares excellently to published experimental results, is proven as a basic feature of the two-dimensional waveguiding mechanism in QIG devices. Accordingly, the effect of stress-induced anisotropy of the optical gain has been found to be of minor importance as the origin for TM-polarized QIG lasers made from lattice-matched heterostructures. It is further demonstrated that, for certain device parameters, the QIG lasers with a small effective index step exhibit somewhat higher threshold currents than the purely gain-guided devices of identical geometry.
Characteristics of a laser triggered spark gap using air, Ar, CH4, H2, He, N2, SF6, and Xe
Authors: Kimura W. D. , Kushner M. J. , Seamans J. F.
Published: July 2002

A KrF discharge laser (248 nm) has been used to laser trigger, by volume preionization, a spark gap switch (38–65 kV, >10 kA, 100 ns pulse duration) filled with 20 different gas mixtures using various combinations of air, Ar, CH4, H2, He, N2 SF6, and Xe. A pulsed laser interferometer is used to probe the spark column. Characteristics studied include the internal structure of the column, the arc expansion rate, and evidence of any photoionization precursor effect. Our results show that the rate of arc expansion varies depending on the average molecular weight of the mixtures. In this experiment, pure H2 has the highest rate (≊9.5×105 cm/s) and air has one of the lowest (≊7×105 cm/s) for the same hold-off voltage. A computer model of the spark column formation is able to predict most of the structure observed in the arcs, including the effect of mixing gases with widely different molecular weights. The work suggests that, under proper circumstances, the spark gap switch performance may be improved by using gases lighter than conventional switch gases such as SF6.
Nonlinear piezoelectricity in poly(vinylidene fluoride)
Authors: Fukada E. , Date M. , Neumann H. E. , Wendorff J. H.
Published: July 2002

The piezoelectric strain constant d32 of uniaxially stretched and poled PVDF [poly(vinylidene fluoride)] was found to be a nonlinear function of the applied stress or strain. The nonlinear behavior manifests itself, in good agreement with the predictions of the phenomenological theory of nonlinear piezoelectricity, by a piezoelectric constant d32 which decreases with increasing stress and by the occurrence of the second harmonic component (2f) of the polarization for a sinusoidal stress (frequency f). The nonlinearity has been tentatively attributed to the stress-induced variation of the distance between parallel chains in the PVDF crystals and their interfaces, causing a reduction of the dipolar and nondipolar interchain interactions.
The discharge of charged dipolar insulating materials
Authors: Wintle H. J.
Published: July 2002

The separation of space charge and polarization effects in acoustic pulse observations of dielectrics requires some reliable theoretical models for reference purposes. In the present paper, we have numerically analyzed the behavior of the fields and the space charge during the discharge of a material containing both space charge and fictitious (dipolar) charge in comparable amounts. We show that the relevant time constant is the dipolar relaxation time, and that the two types of charge follow different histories if the sample were initially carrying a space-charge-limited current. This variation may be sufficient for the two sorts of charge to be distinguished experimentally. A system in which the initial fields vary linearly with distance can be worked out by an alternate numerical route. This example serves to confirm the accuracy of our computation, although it would not be useful for comparison with experiment.
Energy-band structure of (AlAs)(GaAs) superlattices
Authors: Takahashi K. , Hayakawa T. , Suyama T. , Kondo M. , Yamamoto S. , Hijikata T.
Published: July 2002

The energy-band structure of (AlAs) (GaAs) short-period superlattices (SLs) has been investigated by using photoluminescence and photoluminescence excitation spectroscopy. In the indirect transition region, both direct and indirect transitions are simultaneously observed and the band structure is elucidated. Indirect-direct crossover occurs in the region of 15–18 Å GaAs thickness for SLs with 10-Å AlAs thickness.
Si-doped GaAs diodes with negative resistance
Authors: Park S. H. , Choe B. D. , Jang S. J.
Published: July 2002

The electrical and optical properties of amphoteric Si-doped GaAs diodes prepared by a single-step liquid-phase-epitaxy technique have been studied. These diodes have a P-P0-N structure and their current-voltage characteristics exhibit a negative resistance near 77 K. Existence of a recombination barrier is confirmed near the P0-P boundary by the spatial distribution of light emission, and a typical onset voltage of the negative resistance is 3 V at a current of 30 mA at 77 K. This low value can be interpreted as due to the relatively high density of thermally generated holes contributed by the shallow acceptors with activation energy of ∼30 meV. The deep acceptor level of ∼100 meV above the valence band edge is considered to be the origin for the negative resistance.
Stress distribution in released vacuum-deposited aluminum films
Authors: van Opdorp C. , Verkerk M. J.
Published: July 2002

We have determined the stress distribution in released vacuum-deposited aluminum films with thicknesses between 350 and 1500 nm. The method used is based on the release of small square segments of the film from the substrate and the subsequent measurement of their curvatures. A simple, idealized stress model is developed, in which tensile stresses are generated during film growth due to the disappearance of grain boundaries; these stresses are inhomogeneous in depth. The theoretical expression for the curvature of the segments derived from this model can be fitted well to the experimental data. This fitting yields the value of 0.06 nm for the decrease in film length due to the disappearance of a single grain boundary. Another adjustable parameter is the film thickness above which significant disappearance of grain boundaries sets in; its value lies between 100 and 200 nm. This result turns out to be consistent with data obtained from the transmission electron microscope. Using these parameter values we were able to calculate the complete stress distribution in the released films.
Barrier modulation deep-level transient spectroscopy on semiconductor-insulator-semiconductor structures: Basic principles and numerical simulations
Authors: Sibille A. , Palmier J. F.
Published: July 2002

A technique is described which allows direct characterization of deep centers in an insulator slab sandwiched between doped semiconducting layers. It is based on transient conductivity measurements, on devices biased in the high-injection regime, and relies on the modulation of the barrier height under carrier trapping or detrapping of deep levels present in the insulator. It offers the advantage of a higher sensitivity than in capacitance techniques if the semiconductor contacting layers are heavily doped, and it allows the determination of the influence of deep centers on current voltage (I-V) curves (e.g., hysteresis) when the sample is leaky. Numerical simulations of the current-transport processes are carried out, in order to demonstrate the validity of the technique and to show the limits of its applicability.
Effects of temperature annealing on charge-injection-induced trapping in gate oxides of metal-oxide-silicon transistors
Authors: Avni E. , Shappir J.
Published: July 2002

Temperature-detrapping-anneal treatments combined with charge-injection effects on gate oxides of transistors are studied by using a recently reported trapping-characterization method. Electron detrapping from repulsive traps, as well as from newly generated trapping sites is observed following the annealing step. It is observed that retrapping in both types of traps is made possible by additional charge injection through the oxide. On the other hand, thermal annealing up to 430 °C does not change the density of both types of trapping sites. Although new trapping sites are generated under charge injection, heat treatment up to 430 °C cannot change their existing density, but only their occupation level. As reported previously, surface states were found to be annealed under temperature treatments, but combined with additional charge injection, surface states show an enhanced nonsaturating generation.
Control of the barrier height of triangular-barrier diodes by doping their intrinsic layers
Authors: Gupta R. S. , Chilana G. S.
Published: July 2002

An analytic model for the control of the barrier height of a triangular-barrier diode (TBD) is proposed. It is shown that an extra (p- or n-type) doping given to the two intrinsic layers of a TBD changes its barrier height over a wide range (over all 40%). A simple closed-form expression is derived to give the dependence of barrier height on the extra dopings. It is seen that the ideality of the diode is not affected in spite of a wide range of changes obtained in the barrier height. Furthermore, the differential resistance of the device is shown to exponentially decrease with the extra n-type doping given to the structure. Such a strong dependence leads to an improvement in the forward-bias cut-off frequency of the device.
1.5-μm GaInAsP planar buried heterostructure lasers grown using chemical-beam-epitaxial base structures
Authors: Tsang W. T. , Bowers J. E. , Burkhardt E. G. , Ditzenberger J. A. , Wilt D. P. , Dutta N. K. , Napholtz S. G. , Shen T. M. , Twu Y. , Logan R. A.
Published: July 2002

GaInAsP/InP double heterostructures grown by chemical-beam epitaxy have been used in conjunction with liquid-phase-epitaxial regrowth to fabricate high-performance buried heterostructure lasers operating at a wavelength of 1.5 μm. These lasers show room-temperature threshold currents as low as 12 mA, external quantum efficiencies as high as 0.2 mW/mA per facet, and, in general, linear output power up to ∼10 mW/facet. The 3-dB bandwidth at optimal biasing is about 8 GHz and is believed to be limited by the heatsink stud. The relative intensity noise is low, <−150 dB/Hz at 1 GHz for bias currents from 50 mA to above 150 mA.
Effect of interfacial oxide on solid-phase epitaxy of Si films deposited on Si substrates
Authors: Mizushima I. , Kuwano H. , Hamasaki T. , Yoshii T. , Kashiwagi M.
Published: July 2002

The effect of interfacial oxide on defect generation and regrowth rate in solid-phase epitaxy of amorphized Si has been investigated. Si-ion implantation was used to amorphize the chemical-vapor-deposited polycrystalline Si (poly-Si) and to reduce the oxygen concentration at the poly/single-crystalline Si interface. The crystallinity of the epitaxial layers obtained under different conditions, such as surface treatment, Si-ion-implantation dose, and thermal annealing, was examined by high-resolution electron microscopy and Rutherford backscattering spectroscopy (RBS). Experimental results showed that microtwins were induced by inhomogenious oxygen distribution at the interface and that low defect density (the channeling minimum yield in RBS; χmin=7%) could be achieved for specimens with maximum interfacial oxide thickness of about 4 Å.
Distortion of band-edge luminescence in InP due to self-absorption
Authors: Lester S. D. , Kim T. S. , Streetman B. G.
Published: July 2002

Self-absorption is shown to dramatically distort both the intensity and spectral distribution of low-temperature band-edge photoluminescence in InP. The selective reabsorption of bound-exciton emission is shown to give rise to artifactual luminescence peaks in the low-energy portion of the band-edge region that sometimes overwhelm emission from the bound-exciton lines, resulting in dramatic spectral distortions. The severity of these distortions is highly sensitive to excitation power density and surface preparation, both of which affect the fraction of luminescence that escapes from the sample without self-absorption. These effects can easily lead to misinterpretation of luminescence spectra when self-absorption is not taken into account.
Characteristics and surface analysis of ion beam deposition from binary boron platinum (Pt58B42) liquid-metal ion source
Authors: Higuchi-Rusli R. H. , Corelli J. C. , Steckl A. J. , Jin H-S.
Published: July 2002

Characteristics of a eutectic boron platinum (Pt58B42) liquid-metal ion source (LMIS) were analyzed and investigated with a quadrupole mass spectrometer (QMS), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). The source characteristics can be explained by the hydrodynamic model, particularly for needle geometry LMIS. Surface analysis with RBS and AES indicated that more boron is produced in the ion beam than left in the liquid alloy reservoir and more droplets are produced with a 10-μm emitter tip radius, which reduced boron current in the beam. The source instability was associated with droplet formation. AES results show that substantial neutral ions were produced which was not detected by QMS. RBS results on the depleted residual alloy remaining on the carbon ribbon heater indicated that the cause of the alloy system’s short lifetime (33 h) is due to a change in alloy stoichiometry to a higher platinum content. Three different emitter tip radii (2.5, 5, and 10 μm) made of graphite were used in the present investigation. Higher boron current and high stability during ion emission was recorded with 2.5-μm graphite emitter tip radius than with the 5- or 10-μm tip radii.
Impedance-frequency characteristics of metal-oxide-semiconductor structures on polycrystalline silicon
Authors: Lakshmi M. V. S. , Ramkumar K.
Published: July 2002

This paper reports the variations in impedance with frequency of metal-oxide-semiconductor (MOS) structures on polycrystalline silicon. The origin of these impedance-frequency characteristics are qualitatively explained. These characteristics indicate that the MOS structure on polycrystalline silicon can be exploited to realize voltage controlled filters.