bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of the threshold voltage of metal-oxide-semiconductor field-effect transistors with Pearson-IV channel doping profile
Authors: Kwong D. L. , Meyers D. C.
Published: February 2003

In this paper, a general analytical expression for the calculation of threshold voltage of an ion-implanted n-channel enhancement-mode metal-oxide-semiconductor field-effect transistor with a Pearson-IV channel dopant distribution is presented. Specifically, the threshold voltage in excess of the flat-band voltage is characterized as an explicit function of the four moments about the mean depth of the dopant distribution, namely, projected range, standard deviation, skewness, and kurtosis. The effects of substrate doping concentration, implant dose, and the body effect on the threshold voltage are also presented.
Effect of interface pinning in multilayer bubble garnet films on the dynamics of domain walls
Authors: Żebrowski J. J.
Published: February 2003

Numerical solutions for domain-wall dynamics are found which take into account interface pinning of magnetic moments at the boundary between sublayers of a multilayer bubble garnet film. Dynamic domain-wall structure and velocity are calculated for drive field values up to 100 Oe. The effect of magnetic-moment pinning at one or both of the bubble layer surfaces on the wall structure and its velocity is discussed. It is found theoretically that a form of stationary motion of the wall may occur when magnetic-moment pinning is present even when the value of the drive is high. The results of the theory are compared with high-speed photography data on bubble expansion in self-biasing double layer garnet films and in ion-implanted double-layer self-biasing (triple layer) films. It is concluded that the high drive stationary motion may occur in the ion-implanted films and, also, that the exact structure of the sublayer accompanying the bubble layer is of secondary importance to domain-wall dynamics in multilayer bubble garnet films. Pinning due to ion implantation is seen to be stronger than that induced by an liquid phase epitaxy biasing layer with perpendicular anisotrophy.
Y3Fe5O12 single-crystal growth by top seeded solution growth method
Authors: Oka Kunihiko , Unoki Hiromi
Published: February 2003

Single crystals of yttrium iron garnet have been grown by the top seeded solution growth (TSSG) method with Fe2O3 as the solvent. The starting materials consist of 79%–82% Fe2O3 and 21%–18% Y2O3. Crystals of approximately 38×35×8 mm in size and about 12 g in weight were obtained. The ferromagnetic resonance, magnetization, Néel temperature, and Mössbauer measurements, and the etch-pattern observation have been performed on crystals growth by the TSSG method and are compared to similar measurements on crystals grown by the slow cooling method from a PbO flux.
Theory of eddy currents induced by a nonsymmetric coil above a conducting half-space
Authors: Beissner R. E. , Sablik M. J.
Published: February 2003

A solution is presented for the boundary value problem posed by a current-carrying coil of arbitrary shape in air above the plane surface of a conductor of semi-infinite extent. Two special cases are also treated: a circularly-symmetric coil at an arbitrary tilt angle with respect to the surface normal, and an infinitesimal coil, a magnetic dipole, also at an arbitrary tilt angle. Numerical results are presented for dipole orientations parallel and perpendicular to the surface.
Cathodoluminescence emission from LiNbO3 single crystals
Authors: Llopis J. , Ballesteros C. , González R. , Chen Y.
Published: February 2003

Cathodoluminescence (CL) emission from as-grown, thermochemically reduced and mechanically damaged LiNbO3 single crystals has been studied in the scanning electron microscope. Three emission bands at 410, 525, and 580 nm have been observed. The CL spectra strongly depend on the deformation at the surface region. An intense emission with its peak in the infrared region has been observed. Severe damage is induced by irradiation with the electron microscope beam at very high current intensities.
Growth solution baking effects on the residual impurities in GaAs liquid- phase-epitaxy layers
Authors: Garrido J. , Castaño J. L. , Piqueras J.
Published: February 2003

Unintentionally doped liquid phase epitaxial GaAs layers have been grown from different Ga solutions baked for times between 6 and 48 h. From photoluminescence measurements C and Si have been identified as the main residual impurities. Hall-effect measurements show a reduction of the overall impurity concentration and an increase of the compensation ratio with the baking time. The combination of photoluminescence and Hall-effect results suggests a decrease of the contamination by carbon and probably by silicon of the grown layers as the duration of the heat treatment increases.
The temperature dependence of liquid-crystal tilt angles
Authors: van Sprang H. A. , Aartsen R. G.
Published: February 2003

The temperature behavior of various liquid crystals has been studied on obliquely evaporated SiOx (α°) layers. The structure of such layers is discussed and the competition between the effects of two inherent anisotropies of these layers is indicated as the possible origin of the observed temperature dependence of the tilt angle. Attention is also paid to the structure of liquid-crystal layers close to the nematic to isotropic transition temperature (clearing point). Experimental results for tilt angles as a function of temperature have been adapted to a two-torque model, which is suggested by the above considerations. This allows comparison between the structural data for SiOx and the parameters from the two-torque model. It is found that indeed one of the directions of preference is connected roughly with the columnar axis of the SiOx.
Amorphous-Si/crystalline-Si facet formation during Si solid-phase epitaxy near Si/SiO2 boundary
Authors: Kunii Yasuo , Tabe Michiharu , Kajiyama Kenji
Published: February 2003

Amorphous-Si (a-Si)/crystalline-Si (c-Si) interface facet formation was found during Si solid-phase epitaxy (SPE) near the Si/SiO2 boundary. A (110) facet is formed during (010)b-[100]SPE (SPE growth in the [100] direction and near the (010) boundary between a-Si and SiO2). A (111) facet is formed during (011)b-[100]SPE. The facet formation is explained with an atomistic model wherein an a-Si atom must complete at least two undistorted bonds to attain SPE growth, and the boundary condition wherein an a-Si atom cannot form undistorted bond to Si/SiO2 boundary.
Two-dimensional metallic aggregates in β alumina-type structure
Authors: Boilot J. P. , Collin C. , Comes R.
Published: February 2003

In β alumina used as a solid electrolyte in Na/S batteries, the formation of metallic centers is probably at the origin of the degradation. In silver β ferrite ( β alumina-type compound), silver metallic centers are directly formed by reduction of Ag+ by Fe2+ and consequently the mechanism of metallic precipitation can be studied. X-ray diffuse scattering investigation shows that the silver atoms cluster together into two-dimensional aggregates, which are surrounded by regions poor in Ag. With heating, the clusters first grow in size, silver atoms remaining on the sites along the honeycomb lattice. Then, the silver precipitation arises and is probably enhanced by collapse of the β alumina structure into the spinel one.
Single-crystal Ge films on SiO2-coated Si wafers by laterally seeded heteroepitaxy
Authors: Nishioka Takashi , Shinoda Yukinobu , Ohmachi Yoshiro
Published: February 2003

Germanium film crystallization with W encapsulation has been performed by using rf zone-heating slider system. With the laterally seeded heteroepitaxy technique, (100) single-crystal Ge is obtained on SiO2 islands as large as 280×510 μm on Si(100) substrates. The Ge surface morphology represents growth-velocity anisotropy, indicating a {111}-faceted liquid-solid interface during crystallization. It has been shown that a mixture of Ge crystal and polycrystalline Si2W exists at the peripheral region of the SiO2 island and at the Si opening. Si2W formation is explained by diffusion of substrate Si atoms in Ge followed by reaction with the encapsulant W. The crystalline quality of Ge near the seed is poor because of the Ge lattice deformation due to Si2W. Lateral epitaxy, however, is successfully performed to provide a good-quality Ge single-crystal film on the SiO2 island.
The effects of hydrogen partial pressure on reactively sputtered amorphous silicon
Authors: Ross R. C. , Messier R.
Published: February 2003

Hydrogenated amorphous silicon films have been reactively sputtered under various hydrogen partial pressures (pH2) from 0 to 3 mTorr in which the partial pressure of argon (pAr) also was varied so as to give a range of bombardment conditions and film microstructures. As pH2 is increased, H is initially incorporated primarily as monohydride. The density of monohydride reaches a maximum and then decreases while the density of dihydride continues to increase. The H/Si atomic ratio increases throughout the entire range of pH2 whereas the density of hydrogen reaches a broad maximum and thereafter decreases. The effects of pH2 and pAr are largely independent, but both have substantial control over film properties. Depostion rate, intrinsic stress, H content and bonding, optical properties, and Pd Schottky barrier photoresponse were measured.
Pulsed admittance spectroscopy
Authors: Pautrat J. L.
Published: February 2003

A new method of assessing the capture cross section of deep centers is described. The pulsed admittance spectroscopy technique is essentially an admittance spectroscopy experiment fed with electrical pulses. The main features are simplicity and extended range of available time constants (10−8–10−3 s). Experimental results are presented concerning gold and copper impurities in CdTe.
Current-controlled nonequilibrium processes in semiconductors
Authors: Manifacier J.-C. , Moreau Y. , Henisch H. K.
Published: February 2003

The paper gives a unified overview of the four nonequilibrium processes (injection, exclusion, extraction, accumulation) which occur when current is passed through a semiconductor boundary. Concentration and field contours are provided for the situations which occur in semiconductors, as well as local resistivity versus current relationships for both directions of current flow.
Investigation of diffusion length and lifetime in lead chalcogenides by electron-beam-induced-current measurements at low temperatures
Authors: Eisenbeiss A. , Heinrich H. , Jakubowicz A. , Maurer W. , Palmetshofer L. , Preier H. M. , Bachem K. H. , Böttner H.
Published: February 2003

The electron-beam-induced current (EBIC) mode of the scanning electron microscope has been used to study the temperature dependence of the minority-carrier diffusion length in PbTe and other IV-VI compounds (PbSnSe, PbSSe, PbCdS). The temperature dependence of the minority-carrier lifetime for PbTe has been deduced from diffusion-length measurements. Lifetime values of the order l×10−9–5×10−8 s have been found. Diffusion lengths and lifetimes as a function of carrier concentration have been studied. Discrepancies in the form of the EBIC signal have been found between PbTe diodes and ternary compound laser structures. A memory effect for PbSSe and PbCdS has been observed.
Response of potential probes to nonequilibrium situations
Authors: Manifacier J.-C. , Moreau Y. , Henisch H. K. , Rieder G.
Published: February 2003

When a metal contact is placed on a semiconducting material which is not in electronic equilibrium, a floating potential (difference) is developed between the metal and the bulk semiconductor. This is analogous to the open circuit voltage of a solar cell. Floating potentials can cause substantial errors when associated with probes used for the determination of potential contours. Their magnitude is here calculated by numerical and analytic techniques, as a function of the departure from equilibrium and the characteristics of the contact barrier structure. Criteria are established for a safe use of potential probes.
Electroluminescence studies in silicon dioxide films containing tiny silicon islands
Authors: DiMaria D. J. , Kirtley J. R. , Pakulis E. J. , Dong D. W. , Kuan T. S. , Pesavento F. L. , Theis T. N. , Cutro J. A. , Brorson S. D.
Published: February 2003

Electroluminescence from metal-insulator-semiconductor structures with silicon dioxide (SiO2) layers containing varying amounts of excess silicon (Si) in the form of tiny Si precipitates have been studied in detail. Bulk insulator emission from the Si islands is shown to dominate over emission from either the SiO2 matrix material or the metallic gate material by studies of oxide or metal gate material, voltage polarity, and insulator thickness dependencies. Several distinct spectral peaks are observed in the energy range from 1.5 to 5 eV which cannot be attributed to optical interference effects. The higher-energy peaks show a strong dependence on electric field relative to that at the lowest energy (1.7–2 eV). The entire spectral amplitude shows a strong dependence on high-temperature annealing and excess Si content, decreasing drastically with increasing Si or decreasing annealing temperature. These results are shown to be consistent with light emission during electronic transitions between discrete energy levels associated with Si islands and/or their interface with the SiO2 host matrix material. Quantum size effects, similar to those observed in semiconductor superlattices, are proposed as one possible explanation.
Transport properties of multilayered Cr/SiOx thin films
Authors: Tanielian M. H. , Willhite J. R. , Niarchos D.
Published: February 2003

A series of multilayered Cr/SiOx thin films with 1.8<x<2 were rf deposited from a Cr and SiO2 target in an alternating fashion. The film thicknesses were nominally 600 Å made up by six Cr and six SiOx layers with a nominal period of 100 Å. The films were analyzed using x-ray diffraction and Auger spectroscopy. The sheet resistance of the films was measured between 8–330 K and showed that films with more than 50% metal had positive temperature coefficient of resistance (TCR) and those with less than 50% had negative TCRs. The films with more than 50% metal showed a minimum in the resistance in the range of 30–70 K which we associate with localization effects and also a maximum in the resistance around 270 K which we tentatively attribute to their multilayered structure.
Coherent sidelobe cancelling
Authors: Peterson Kenneth M. , Weiss Neil A.
Published: February 2003

Coherent sidelobe cancellers have been and continue to be of interest for radar, sonar, and communication system applications. Typical sidelobe cancellers employ an adaptive antenna array to produce spatial nulls in the direction of interference sources. These nulls are usually formed by optimally adjusting the coefficients of a transversal filter, one filter being used with each array element. In this paper a necessary and sufficient condition is given for a filter to exist so as to produce complete cancellation of weakly stationary interference sources. It is then shown how this optimal filter may be approximated by a transversal filter.
Effect of lateral energy transport on the momentum transfer to targets in laser produced plasmas
Authors: Gupta P. D. , Naik P. A. , Pant H. C.
Published: February 2003

We have studied the ablation driven momentum transfer to single and layered planar targets, irradiated by a 1-GW, 5-nsec Nd:glass laser in the intensity range 1011–1013 W/cm2. The results show an effect of lateral energy transport on the scaling of momentum with laser intensity. Corroborative evidence for this is presented from experiments on thin foil targets.
Two-dimensional continuum percolation and conduction
Authors: Nakamura Mitsunobu
Published: February 2003

In physical systems, we encounter phenomena well described by the continuum percolation as often as those characterized by the lattice percolation. However, the conductivity data of the continuum percolation are scarce compared to those of the lattice percolation. With this situation in mind, we consider here two types of two-dimensional continuum percolation problem and compute, by the finite element method, the critical volume fractions of the metallic elements for the metal-insulator transition. We also compute the conductivities. The geometrical configuration of the first (or second) type is formed by random deposits of square metals (or holes) of the same size and orientation on an insulator substrate (or on a metal). The critical volume fractions are calculated to be, respectively, 0.58 and 0.42. We compare the computed conductivities with results from the effective-medium approximation and from the extended Watson–Leath equation, with the measurement of Smith and Lobb and with the conductivities of composite materials having a regular structure.
Numerical analysis of thermomagnetic generators
Authors: Kirol Lance D. , Mills James I.
Published: February 2003

Thermomagnetic generators allow direct conversion of heat energy to electrical energy. Temperature cycling about or near the Curie temperature causes changes in magnetization, resulting in time variant magnetic flux and induced voltage in a surrounding conductor. Numerical analyses of regenerative thermomagnetic generators with perfect regeneration have been performed for three working materials: iron, gadolinium, and Ho69Fe31. Power density above 20 W/kg of shunt material and efficiency approaching Carnot limits are possible over temperature differences of 50 K. Analytical studies performed during the 1950s predicted maximum power density less than 7 W/kg and efficiency less than 1% for nonregenerative cycles.
Electric-field-modulated, infrared internal-reflection study of the silicon-electrolyte interface
Authors: Palik E. D. , Holm R. T. , Stella A.
Published: February 2003

The electric-field modulation of the internal-reflection response of a Si-electrolyte interface is shown to give information both about accumulation of free carriers, interface states, and about molecular species in the oxide or in the Helmholtz or Gouy layer. Measurements were made in either a 0.1-M KOH or 0.1-M H2SO4 solution and evidence of electromodulation of vibration bands of H3O+, OH, and H2O was obtained.
1/N expansion for Dirichlet boundary problems
Authors: Epele L. N. , Fanchiotti H. , García-Canal C. A.
Published: February 2003

Dirichlet problems posed by boundaries with a symmetry CN are studied via 1/N expansion. The characteristic impedance of a coaxial system consisting of a regular polygon concentric with a circle is explicitly computed as a typical application of the method.
Power/energy limiter using reverse saturable absorption
Authors: Harter D. J. , Shand M. L. , Band Y. B.
Published: February 2003

In materials with an excited-state absorption cross section larger than the ground-state absorption cross section, increasing the incident light intensity (thus populating the excited state) increases the absorption. We show that such a reverse saturable absorber can function as a power limiter and pulse smoother for long pulses and as an energy limiter and pulse shortener for short pulses. The necessary properties for such a material are described. Reverse saturable absorption is demonstrated at 488 nm in alexandrite. A simple model describing these effects is presented.
Stacked thin-film photoelectrode using iron oxide
Authors: Itoh K. , Bockris J. O’M.
Published: February 2003

For photoanodes of materials with low mobilities it is advantageous to use several layers of thickness less than the space-charge region, thereby decreasing recombination. To compensate losses due to lack of absorption, several layers should be placed successively in the light path. Some experimental verification is described.
Analysis of fluctuating signals from a multichord interferometer
Authors: Rusbridge Michael G. , Jacobson Abram R.
Published: February 2003

Fluctuating signals from multichord interferometers contain information about the spatial structure of the corresponding plasma perturbations. We present results from the interferometer used with the reversed-field pinch device ZT-40M, and discuss methods of systematically surveying the spectrum of fluctuations so as to search for patterns representing coherent spatial structures in the plasma. Three such structures or ‘‘modes’’ are identified, and it is shown how the amplitude distributions of each can be separated out from the general background due to other modes. Knowledge of the amplitude distributions is then used to construct linear combinations of the eight interferometer signals, which represent the time variation of each of the coherent modes; power spectra of these linear combinations show prominent peaks at frequencies characteristic of the modes even when the spectra of the individual interferometer signals are bland and featureless. From an analysis of the amplitude distributions it is shown that the three modes comprise (a) a broad-band symmetric (m=0) mode concentrated in the outer quarter of the plasma; (b) an antisymmetric (m=1) mode at ∼30 kHz confined to the discharge core; and (c) a second antisymmetric mode at ∼100 kHz confined to the outer region of the plasma.
Copper-related deep acceptor in quenched germanium
Authors: Kamiura Y. , Hashimoto F. , Nobusada T. , Yoneyama S.
Published: February 2003

New deep acceptors (DA) at Ev+80 meV together with contaminating substitutional copper (Cus) were produced in Ge by the quenching from 700 °C. Annealing around 260 °C caused these acceptors to disappear leaving an equal additional Cus density, giving rise to a decrease in hole mobility at 77 K. The annealing process obeys first-order kinetics with an activation energy of 1.3 eV. Annealing behavior consistently explains the so-called reverse annealing of quenching-induced conductivity changes that have often been observed by various investigators. In the as-quenched state, the DA density is completely proportional to the Cus density, which was varied at 700 °C from 3×1013 to 3×1015 cm−3 using the techniques of gettering and diffusion of copper. The 1.5 MeV electron irradiation to a total dose of 5×1014 electrons/cm2 slightly below room temperature induced the DA acceptors once annihilated by the preceding annealing to reappear in a density of 2×1013 cm−3. The most probable defect model for the DA acceptor which best fits the data is a pair consisting of a substitutional copper atom and a mobile defect, which may possibly be a vacancy or an interstitial of a neutral impurity like carbon, silicon, or oxygen.
Ledge growth, strain accommodation, and stacking fault formation during silicon oxidation
Authors: Hirth John P. , Tiller William A.
Published: February 2003

A detailed ledge model is presented to describe the oxidation of single-crystal silicon. Volume strains are completely accommodated as a consequence of the model. Interface dislocations at the silicon-oxide interface result with attendant short-range strain fields. The model leads to an explanation of the observed anisotropic stacking fault distributions among available {111} planes when orientations slightly removed from low index surfaces are oxidized.
Sputter deposition of platinum films in argon/oxygen and neon/oxygen discharges
Authors: Aita C. R. , Tran Ngoc C.
Published: February 2003

We have investigated the resistivity, crystallography, and chemistry of films sputter deposited from a platinum target in argon and neon discharges containing small amounts of oxygen. The results presented here indicate that the oxidation behavior of platinum is strongly dependent upon the type of rare gas used for the deposition. A comparison of the dependence of platinum-oxygen bond formation on cathode voltage and deposition rate suggests that oxide formation in the films is controlled by a reaction which occurs at the target surface and is enhanced when neon carrier gas is used. A large increase in resistivity above that of bulk platinum metal is always correlated with platinum-oxygen bond formation in the film.
Effect of specimen size on photoplastic effects in anthracene crystals
Authors: Kojima Kenichi , Suzuki Kinichi , Okada Isamu , Chijiwa Eiko
Published: February 2003

The photoplastic effect (PPE) in anthracene crystals, which is a photoinduced hardening, has been studied by shear deformation. The PPE is produced at wavelengths ranging from less than 300 to 440 nm, with a maximum effect at 430 nm. The PPE is a bulk effect; it can be produced by light that has travelled more than 2 mm into a crystal. When PPE occurs with short wavelength (≤400 nm) small attenuation length (∼10−4 cm) illumination, it is not produced directly by the intrinsic light absorption, but rather by longer wavelength fluorescence radiation from the near-surface region. The photoproducts that interact with dislocations to increase the flow stress are most likely physical dimers near defect sites.
Microstructural observations of sputtered silicon-tin-hydrogen alloys
Authors: Jones K. M. , Williamson D. L. , Yacobi B. G.
Published: February 2003

Structural and compositional properties of hydrogenated silicon-tin alloys have been investigated as a function of tin content, sputtering pressure, and presence of hydrogen. Transmission electron microscopy, energy dispersive x-ray microanalysis, and scanning electron microscopy were used to detect compositional and structural inhomogeneities in these materials.
Commensurate and incommensurate structures in molecular beam epitaxially grown GexSi1−xfilms on Si(100)
Authors: Fiory A. T. , Bean J. C. , Feldman L. C. , Robinson I. K.
Published: February 2003

The transition between commensurate and incommensurate growth of GexSi1−x alloys on Si is observed directly by means of ion channeling and x-ray diffraction measurements. Molecular beam epitaxial films of thickness h up to 2500 Å thick show commensurate epitaxy for x≲50% and h≲hc, a critical thickness dependent upon x. The observed values of hc are discussed in terms of a model invoking the maximum theoretical interfacial shear strength and a barrier to misfit dislocation formation.
An extension of the model for the extracurrent in almost ideal silicon junction diodes
Authors: Cerofolini G. F. , Polignano M. L.
Published: February 2003

The model which ascribes the deviation from ideality of the behavior of almost ideal silicon junction diodes to a current due to donor-acceptor twins is (1) substained by the analysis of the reverse current-voltage characteristics of diodes with different substrate concentrations, and (2) extended to take into account the spatial variation of the electric field in the depletion layer.
Low resistance polycrystalline silicon by boron or arsenic implantation and thermal crystallization of amorphously deposited films
Authors: Becker F. S. , Oppolzer H. , Weitzel I. , Eichermüller H. , Schaber H.
Published: February 2003

Polycrystalline silicon films with high surface smoothness, good step coverage, and a relatively large grain size of ∼0.3 μm have been prepared by low-pressure chemical vapor deposition in the amorphous state and subsequent crystallization in a furnace. The final grain size achieved does not significantly depend on the initial annealing temperature used to crystallize the layer. For heavily boron implanted films, a clear correlation between sheet resistance and average grain size is found and the resistivity is close to the single crystal value for the amorphously deposited films. In contrast, only a minor resistivity reduction relative to standard polycrystalline silicon could be achieved by amorphous deposition for arsenic implanted films.
Graphite strip rapid isothermal annealing of tantalum silicide
Authors: Li B. Z. , Jones R. E. , Daneshvar K. , Davis J.
Published: February 2003

Silicon-poor tantalum silicide films cosputtered on polycrystalline silicon over thermal oxide on silicon were rapidly annealed for various temperatures and times using a graphite strip heater. Rutherford backscattering and x-ray diffraction showed rapid formation of a stoichiometric tantalum disilicide via Si diffusion from the polycrystalline Si. This was accompanied by significant grain growth and a reduction in resistivity. Sheet resistances comparable with those of furnace-annealed samples were obtained.
On the double cantilever beam technique for studying crack propagation
Authors: El-Senussi A. K. , Webber J. P. H.
Published: February 2003

The problem of a semi-infinite elastic plate loaded along its straight boundary is pursued to develop an analytical and realistic Double Cantilever Beam Model which accounts for the end deflections associated with deformation beyond the crack tip. Deformation of the uncracked portion allows each arm to rotate about the built-in end, producing an end deflection in addition to those caused by bending and shear. Comparisons with the predictions of existing models show reasonable agreement, but comparisons with some available experimental results reveal that the theoretical end deflection is underestimated. This was shown not to be unreasonable when the limitations of the theory were considered.
Monte Carlo treatment of impurity diffusion in polycrystalline films
Authors: Lavine J. P. , Losee D. L.
Published: February 2003

A Monte Carlo method for a random walk on a lattice is used to model impurity diffusion in a polycrystalline thin film. This approach permits the modeling of diffusion in films with more than one grain vertically. Numerical results illustrate the effects on the diffused impurity profile of a multiple-grain structure that resembles a brick wall.
Trapping kinetics in high trap density silicon nitride insulators
Authors: Bibyk Steven B. , Kapoor Vikram J.
Published: February 2003

An analytical method has been developed to investigate the trapping kinetics of multiple trap levels in a silicon nitride insulator under very complex conditions. Solutions for the trapped-charge distribution are given for the case of a nonuniform single carrier current in an insulator having very strong charge trapping and various detrapping mechanisms such as Poole-Frenkel emission or photoionization. The trapped-charge distribution is given in terms of a series in the position and time variables, and is given for a single trap level, several trap levels, and an energy distribution of traps. In the more complex models, the series are terminated after a finite number of terms and are used to calculate the trapped-charge centroid as a function of the total trapped charge. The trapped-charge centroid calculations are shown to be useful for studying silicon nitride or other strong trapping insulating materials used for long term charge storage applications.
Numerical study of an n-gallium arsenide diode distributed oscillator
Authors: Aishima Asuo , Fukushima Yoshifumi
Published: February 2003

The dynamic electron velocity, electron temperature, etc., in an n-gallium arsenide ballistic diode have been calculated by solving the Boltzmann equation under a hydrodynamic approximation. It has been found from the results that an n-gallium arsenide ballistic diode exhibits a negative conductance at a fairly high frequency range and over a wide frequency range from 1500.0 to 2300.0 GHz. From the small signal analysis using a simplified diode model, it has been shown that the negative conductance arises as a result of density modulation effects of the carriers, namely, space-charge transit time effects. High growth rate, up to 300.0 Np/cm, has been predicted in an n-gallium arsenide ballistic diode distributed oscillator. The diode can be expected to act as a new solid-state source at a far infrared frequency range.
Free carrier absorption in quantum well structures for polar optical phonon scattering
Authors: Adamska Halina , Spector Harold N.
Published: February 2003

The free carrier absorption is calculated for quantum well structures fabricated from III-V semiconducting materials where polar optical phonon scattering is important. The free carrier absorption coefficient is found to be an oscillatory function of the photon frequency for the case where the free carriers are confined in a quasi-two-dimensional structure such as superlattice heterostructures or quantum wells. The absorption is found to depend upon the polarization of the electromagnetic radiation relative to the plane of the layer or quantum well and is enhanced by going to layers or quantum wells of decreasing thickness over its value in bulk III-V semiconducting materials. The oscillatory behavior of the absorption is explained in terms of phonon assisted transitions between the quantized subbands which arise from the confinement of the carriers in these quasi-two-dimensional structures.
Photovoltaic study of the substrate-layer interface for Sn-doped GaAs grown by metalorganic vapor phase epitaxy
Authors: Fortin E. , Charbonneau S. , Meikle S. , Roth A. P.
Published: February 2003

Photovoltaic spectra have been obtained for Sn-doped GaAs epitaxial layers grown by metal-organic vapor phase epitaxy (MOVPE) on Cr-doped semi-insulating GaAs substrates with a view to studying the substrate-layer interface characteristics. The photoresponse was found to be relatively strong and extended into the near infrared to λ≂2 μm. The photosignal is due to carrier excitation at the interface, where a high density of deep traps creates a depletion region and a potential barrier. The shape of the spectral response can be analyzed to yield information on the nature of these traps. They are found to be EL2 and Cr-related electron and hole traps in concentrations which depend on the layer growth conditions. The barrier height deduced directly from the spectra is about 0.6 eV, and is attributed to Fermi level pinning at the Cr2+ electron trap level.
Peripheral photoresponse of a large p-n junction in a thick semiconductor
Authors: Brailsford A. D. , Holloway H.
Published: February 2003

Two approximate analytic methods are given for deriving the laterally collected photocurrent in a mesa diode all of whose dimensions are large compared to the minority carrier diffusion length in the surrounding semiconductor, whose thickness is also large by comparison with the diffusion length. The better of these methods yields a laterally collected photocurrent equal to 0.53 times that of a thin-film device, in excellent agreement with the exact result of 0.50 derived by numerical techniques.
Theory of light scattering from a random metal surface: Excitation of surface plasmons in a Ag film
Authors: Nakayama Jun-ichi , Mitzutani Kiyoshi , Ogura Hisanao , Hayashi Shinji
Published: February 2003

The scattering of light by a silver film with a random rough surface and the excitation of surface plasmon modes at the metal surface are theoretically studied in detail by means of the new stochastic treatment. The silver film is assumed sandwiched between the air and a crystal and a plane wave is incident through the crystal to excite the surface-plasmon mode. The stochastic formulation is developed for the stated problem and approximate solutions are obtained for the coherent and incoherent scattered waves involving the optical theorem. Details of the scattering characteristics are numerically calculated for various combinations of film thickness, surface roughness, and correlation length. The angular pattern of incoherent scattering into the crystal is shown to have two sharp resonant peaks due to the excitation of the surface plasmon, which are directly observable by an experiment.
Quadratic electro-optic (Kerr) effects in zincblende-type semiconductors: Key properties of InGaAsP relevant to device design
Authors: Adachi Sadao , Oe Kunishige
Published: February 2003

By combining the first- and second-order Stark effects of the electronic energy-band structures with well-defined optical susceptibility, we have obtained an expression for the dispersion of quadratic electro-optic (QEO) coefficients in zincblende-type materials. It has been found that the calculated QEO coefficients show very strong dispersion at a region near the direct-band edge. The theoretical prediction has been compared with recently reported QEO dispersion data in materials of InGaAsP quaternaries. It has been found that the present model provides generally acceptable values, in quite good agreement with the experimental data. The present results allow us to design a wide variety of optoelectronic devices for use in optical-fiber communications.
Separation of the Helmholtz equation in prolate spheroidal coordinates
Authors: Jen Lang , Hu Chuanshui , Sheng Kemin
Published: February 2003

This paper deals with the solution of Maxwell’s equations in prolate spheroidal coordinates when the excited fields are not axially symmetrical. It is demonstrated that, by the introduction of a suitable transform, the method of separation of variables may be employed. This provides a new solution of the more general problem of forced oscillations of a metallic prolate spheroid with asymmetrical axial excitation.
Effects of shock waves on the performance of a cw supersonic HF chemical laser
Authors: Stricker J. , Waichman K.
Published: February 2003

The effects of oblique shock waves on the gain and the output power of a cw supersonic HF chemical laser are theoretically investigated. A one-dimensional model is used to solve the flow of a premixed H2–SF6–He or H2–F2–He mixture through the resonator, allowing the presence of oblique shock waves in the flow. It is shown that a shock wave significantly affects the laser performance due to the gas compression at the shock front and due to acceleration of the chemical and energy transfer processes. It was found that immediately behind the shock front the gain coefficients and the photon energy sharply increase and further downstream they fall off rapidly, thus the profiles of the gain and radiation flux become narrower along the flow direction. Integration of the radiation flux along the cavity coordinate reveals that in some cases the total available power is significantly higher than the available power obtained in the undisturbed flow. For HF lasers pumped by the chain reactions it was found that choking occurs over a wide range of flow parameters including very weak shock waves. This is due to the large amount of heat released by the exothermic reactions.
Temperature variation of acoustic attenuation and nonlinearity constant in Ge and GaAs
Authors: Rajagopalan S. , Joharapurkar D. N.
Published: February 2003

The temperature dependence of the nonlinearity constant in pure germanium has been estimated for longitudinal waves along [110] and [111] directions and for shear waves along [110] direction with polarization along [11̄0] and [001] directions in the temperature range 25–293 K. The nonlinearity constant estimated from second order elastic constants and third order elastic constants has been further used to evaluate the ultrasonic attentuation at 475 MHz in Ge for (i) longitudinal waves along the [110] direction and (ii) for shear waves along the [110] directions. We have also estimated the nonlinearity constant and ultrasonic attenuation for longitudinal waves at 306 MHz along the [111] direction. The estimated values of attenuation have been compared with the experimental values of attenuation available in the literature. They are found to be in good agreement with the experimental values. The estimated values of nonlinearity constant increases with temperature for longitudinal waves whereas it shows a negative temperature coefficient for shear waves. The results are similar for Si and Cu. The nonlinearity constant for GaAs at 298 K is estimated from elastic moduli data for longitudinal waves along [111] direction and for shear waves along [110] direction with polarization along [001] direction and then the frequency dependence of ultrasonic attenuation have been estimated. Comparison with the experimental values available in literature shows that the results are quite satisfactory. It is worthwhile to mention that the Mason’s nonlinearity constant D is deceptively similar to the nonlinearity parameter β defined by Breazeale and coworkers. The nonlinearity constant D is evaluated from the knowledge of the Gruneisen number γ ji for various modes and directions and other data, whereas the nonlinearity parameter β is the negative ratio of coefficients of nonlinear term to the linear term of the (dissipationless) nonlinear wave equation. Both D and β are in general temperature dependent.
Blackbody radiation from cubes and spheres with application to rapid solidification of microspheres
Authors: Kalensher Bernard E.
Published: February 2003

By taking into account all of the standing electromagnetic wave frequencies inside cubical and spherical cavities, generalized expressions for the spectral and total radiation from cubical and spherical blackbodies are derived. It is found that the Stefan–Boltzmann law becomes valid only when χT≫hc/k, where χ denotes the length of a cube edge or the diameter of the sphere, T is the blackbody temperature, h is Planck’s constant, c is the speed of light, and k is Boltzmann’s constant. When χT≲hc/k, the radiated power per unit area is less than that predicted by the SB law. The theory is applied to the radiative cooling of micron-size, spherical, liquid-metal droplets. It is found that the cooling rate, when calculated at temperatures exceeding the melting temperature, experiences an absolute maximum at droplet diameters that are of the order of 1 μ. A comparison is made between the extent of the crystallization observed in several hundred submicron solidified aluminum droplets and the degree of crystallization predicted by the theory. The experimental and theoretical results are found to be consistent.
Thermal detectors as x-ray spectrometers
Authors: Moseley S. H. , Mather J. C. , McCammon D.
Published: February 2003

We show that sensitive thermal detectors should be useful for measuring very small energy pulses, such as those produced by the absorption of x-ray photons. The measurement uncertainty can be very small, making the technique promising for high resolution nondispersive x-ray spectroscopy. We derive the limits to the energy resolution of such thermal detectors. We use these to find the resolution to be expected for a detector suitable for x-ray spectroscopy in the 100–10 000 eV range. If there is no noise in the thermalization of the x-ray, resolution better than 1 eV full width at half maximum (FWHM) is possible for detectors operating at 0.1 K. Energy loss in the conversion of the photon energy to heat is a potential problem. Statistical fluctuations of lost energy would reduce the energy resolution of the detector. The loss mechanisms may include emission of photons or electrons, or the trapping of energy in long-lived metastable states. Fluctuations in the phonon spectrum could also limit the resolution if phonon relaxation times are very long. We give conceptual solutions for each of these possible problems.
Element and isotope separation in a vacuum-arc centrifuge
Authors: Geva M. , Krishnan M. , Hirshfield J. L.
Published: February 2003

Centrifugal separation of elements and isotopes in a rotating, magnetized column of highly ionized plasma is described. Such a centrifuge differs from prior plasma centrifuges in that the source of plasma is a laser-initiated vacuum arc, rather than a gas discharge. Detailed measurements are presented of the axial evolution of the radial plasma flux and separation profiles. Centrifugal separation increases rapidly with distance from the cathode plasma source, reaching an asymptotic value about 60 cm downstream. The separation is observed to increase exponentially with the square of the radius. The potential profile across the column was measured and found to be parabolic with radius. These observations are accounted for by a steady-state, multispecies, fluid model of the rotating plasma.
Ion-induced solid solution and ordered compound formation in Au/Cu bilayers
Authors: Hung L. S. , Nastasi M. , Mayer J. W.
Published: February 2003

Ion mixing of Au/Cu bilayers has been investigated using He ion backscattering, x-ray diffraction, and transmission electron diffraction techniques. When Au/Cu bilayers are subjected to Ar or Xe ion irradiation at doses of about 1016 ions/cm2 at room temperature, Cu is completely mixed with Au to form a substitutional solid solution with a graded composition. There was no evidence for the presence of crystal compounds. The formation of ordered compounds is achieved either by the mixing of Au/Cu bilayers with Ar ions at 200 °C or by a He ion irradiation of the mixed layers at 60 °C. Similar results have been observed when the mixed samples were subjected to heat treatment at 350 °C. The observations indicate that the phase formation by ion mixing is related to the atomic mobility at the target temperature during implantation.
Ultrasonic attenuation in p-type GaSb
Authors: Sakurai Hiromi , Yamanaka Fusao , Yoshida Kohichi , Ohshima Naoto , Suzuki Katsuo
Published: February 2003

We have measured the temperature dependence of the ultrasonic attenuation in undoped p-type GaSb at 55–650 MHz in the temperature range 2–40 K. It is found that the attenuation depends strongly on temperature only for the [111] longitudinal and the [110] fast transverse modes, which is due to the interaction with mobile holes in the valence band or similar conductive states via the piezoelectric coupling. The experimental results are discussed based on the Hutson–White theory. The interaction between bound holes and ultrasonic waves via the deformation potential coupling is very small.
Surface studies of epitaxial β-SiC on Si(100)
Authors: Kaplan Ray
Published: February 2003

The surface properties of β-SiC epitaxial layers on Si (100) have been studied. As-grown layers showed submonolayer coverage of both O and excess C, with the former bonded as SiO. Suitably cleaned surfaces were C terminated with no observable excess C, and gave SiC 1×1 low-energy electron diffraction patterns. A well-defined structure was observed in the SiLVV and CKLL Auger spectra of clean, ordered surfaces. This structure was apparently characteristic of SiC bonding and was absent for disordered surfaces.
Photoconductivity of CdS powders by microwave loss measurement
Authors: Dierssen G. H. , Sahyun M. R. V.
Published: February 2003

We have studied the room-temperature photophysics of variously doped CdS and Cd(Hg)S powders by the microwave photoconductivity technique. Accordingly, we infer that both Cu and Ag are effective hole traps, the rate of hole trapping being limiting for the first order decay of photoconductivity. In CdS:Cu, states 0.14 and 0.33 eV below the conduction band are important to the photophysics of the powders; these have been demonstrated to be associated with sulfide vacancies. The presence of a (neutral) donor state associated with mercury appears to be a useful working hypothesis in the interpretation of observations made on Cd(Hg)S powders. Combination of donor (Ga or Eu) and acceptor (Cu or Ag) dopants leads to formation of spectroscopically detectable charge-transfer complexes in the CdS lattice; the conduction band can be populated directly from the acceptor state of the complex on irradiation.