bluuebunny/crossref_metadata_2025 huggingface dataset:
The efficiency of photoluminescence of thin epitaxial semiconductors
Authors: Duggan G. , Scott G. B.
Published: February 2003

General theoretical expressions appropriate to calculating the internal and external quantum efficiency of photoluminescence (PL) are derived for a semiconductor of thickness d and bounded by two surfaces with different surface-recombination velocities. The external efficiency expected from thin and thick layers is compared and contrasted. Under certain conditions and adopting reasonable assumptions, we indicate how a single measurement of the steady-state PL can yield information about the minority-carrier diffusion length.
Photoluminescence measurements in Ge-doped p-type Ga0.60Al0.40As
Authors: Swaminathan V. , Schumaker N.E. , Zilko J.L. , Wagner W.R. , Parsons C.A.
Published: February 2003

Results of photoluminescence and Hall effect measurements of p-type Ge-doped Ga0.60Al0.40As grown by liquid phase epitaxy are reported. The effective segregation coefficient for Ge for growth at 785 °C is estimated to be ∼2×10−3. The photoluminescence spectra at 5.5 K are characterized by two edge emission bands at ∼1.91 and ∼1.88 eV and a broadband at ∼1.55 eV. The edge emission bands are identified to be donor-acceptor pair recombination bands involving the same donor but two different acceptors. The ionization energy of the donor is estimated to be 50–60 meV and the acceptor ionization energies are estimated to be ∼60 and ∼100 meV for the 1.91- and 1.88-eV bands, respectively. The deep acceptor is believed to involve a background impurity, most likely C or Si. It is suggested that the 1.55-eV band arises from a next-nearest neighbor complex consisting of Ge on an arsenic site and an As vacancy. Post-growth annealing treatment at 830 °C is found to decrease the photoluminescence intensity suggesting the presence of annealing induced nonradiative centers.
The electric field distribution associated with prebreakdown phenomena in nitrobenzene
Authors: Kelley Edward F. , Hebner Robert E.
Published: February 2003

The electric field distribution between a prebreakdown tree and the electrode toward which it is propagating is determined. The electric field is measured in nitrobenzene, using the electro-optic Kerr effect. High-speed photography is used to provide a 10-ns resolution of the transient, prebreakdown events. The measurements show that to predict the Kerr fringe pattern, and thus the electric field distribution, it is sufficient to model the prebreakdown tree as a spherical conductor about the same size as the tree and at the potential of the electrode from which the tree is propagating.
Alignment of nematic liquid crystals on ruled grating surfaces
Authors: Nakamura Minoru , Ura Mitsuru
Published: February 2003

Ruled gratings of 0.33–3.33-μm wavelength fabricated with SiO, SiO2, and In2O3-SnO2 are used to study the topographical effects of the surface on the twisted nematic (TN) alignments of liquid crystals (LC’s). The types of LC’s are Schiff base, azoxy, biphenyl, biphenyl ester, and phenyl cyclohexane. All of the LC’s, except the azoxy, used in this study take good homogeneous and TN alignments on all grating films of wavelength less than 0.8 μm. The azoxy takes homeotropic alignment on the SiO and SiO2 grating surfaces. The agreement between experimental results and Frank elasticity theory is fairly good. Topographical effects can take precedence over chemical effects between the LC and surface when chemical anchoring is weak. Making use of the calculated elastic deformation energy of LC’s on grating and rubbed surfaces, we estimate the anchoring energies of homogeneous and homeotropic alignments. The application of grating cells to optical display is limited by the occurence of tilt domains.
Ray-optics of magnetic waves guided by a planar film
Authors: Seshadri S. R.
Published: February 2003

The characteristics of the magnetic waves guided by a planar film of ferrimagnet in free space are investigated by the ray-optical techniques for the case of the magnetization direction lying in a plane normal to the surfaces of the film and containing the propagation direction. The dispersion relation is deduced using the zig-zagging wave-normal directions within the film and analyzed to obtain the main features of the guided magnetic waves. The time delay produced when the wave packet of a magnetic wave is totally reflected at an interface between a ferrimagnetic medium and free space is included and a ray-optical description of the group delay of the guided magnetic wave is developed. The group delay is caused partly in the bulk of the ferrimagnet and partly at the surfaces of the film, and the relative importance of these two contributions are examined. The important features of the direct and the reflected rays within the film are brought out. The optimum directions of magnetization for the devices based on the forward and the backward guided magnetic waves are obtained.
Deep level transient spectroscopy of electron traps and sensitizing centers in undoped CdS single crystals
Authors: Hussein M. , Lleti G. , Sagnes G. , Bastide G. , Rouzeyre M.
Published: February 2003

Data are presented on the characterization of deep electron traps in six different undoped single crystals of CdS and in one alloy of CdS96Se4. The obtained spectra by the capacitance deep level transient spectroscopy (DLTS) of the seven samples are very similar with only two or three distinct maxima observed between liquid nitrogen and room temperature. Detailed analysis of the DLTS and admittance spectroscopy reveals that three deep levels:EL1 (200±10 meV, Se ≃10−14 cm−2), EL2 (430±30 meV, Se≃10−12 cm2), and EL4 (630±30 meV, Se ≃10−14 cm2), are present in almost all samples. Direct measurements of the capture cross sections indicate that the capture of an electron occurs with a small lattice relaxation in the case of EL1 and a large lattice relaxation in the case of EL2. Two other trap levels, EL3 (520±30 meV, Se ≃10−11 cm2) and EL5 (750±40 meV, Se ≃10−11 cm2), are also detected in two respective samples. Comparisons are made with previous data obtained in semi-insulating and semiconducting CdS crystals. Illumination of the sample at low temperatures induces a permanent capacitance change due to electron excitation from a very deep level which cannot be electrically refilled at liquid-nitrogen temperature. The energy threshold E≃1.4 eV of the spectral response of this emptying process is an indication that this level is probably the same as the sensitizing center. Direct measurements of the temperature dependence of its capture cross section, Sc =4×10−23 exp (−0.042/kT) cm2 is direct of the doubly ionized acceptor -like imperfection, probably associated to a cadmium vacancy VCd.
Charge storage and distribution in the nitride layer of the metal-nitride-oxide semiconductor structures
Authors: Kapoor V. J. , Turi R. A.
Published: February 2003

Electronic charge trapping in the low-pressure chemically vapor deposited thin film of Si3N4 has been investigated by internal photoelectric-effect technique. Charge-storage characteristics and the spatial distribution of electrons trapped in the Si3N4 layer of a biased Al-Si3N4-SiO2-Si structure have been determined using photocurrent and high-frequency C-V measurements. Electrons generated by internal photoemission at the Si surface were captured by traps located within the Si3N4 layer which gave rise to a charge-storage mechanism. Some of these trapped charges were then photoionized by photons with an energy of 4.14 eV and removed from the insulator. This resulted in a discharging mechanism. The flatband voltage shifts for various charging and discharging processes were determined and characterized in detail. The total trapped electronic charge was on the order of 3.14×1012/cm2, with a retention time of 48 days in the dark. The etch-back experiments, where the charged Si3N4 layer was etched back in steps, determined the distribution of the trapped electronic charge across the Si3N4 film of the metal-nitride-oxide semiconductor structure. The midfilm concentration of these trapped electrons was 2.8×1017/cm3.
Domain-wall motion and wall bowing in a FeSi picture-frame crystal studied by the time-dependent neutron-depolarization technique
Authors: van Schaik F. J. , Burgmijer J. W. , Rekveldt M. Th.
Published: February 2003

Using the three-dimensional time-dependent neutron-depolarization technique the motion of a 180° domain wall in a (010)[001] picture-frame FeSi (3.5 wt. % Si) single specimen with dimensions 15×10×0.26 mm3 has been studied as a function of the field amplitude of a block-shaped magnetic field. The field ranges from 2 to 40 A/m. The wall velocity and deformation have been measured as a function of the applied field strength and the position of the wall in the crystal. The measurements indicate that up to 27 A/m the wall motion is uniform with a dynamic coercive force of 3±0.5 A/m and wall mobilities of 0.68±0.07 and 0.81±0.08 mm s−1/A m−1, dependent upon the position of the moving wall in the crystal. The measured depolarization owing to wall bowing and wall inclination is less than predicted in the literature for an ideally bowed wall, indicating that imperfections in the crystal cause bowing and tilting on a scale much smaller than the crystal thickness. Nevertheless, the measured critical field above which the wall breaks up and no steady-state motion exists, agrees with the predictions of wall bowing theory.
Temperature dependence of polarization echoes in powder
Authors: Kimura Takashi , Yoshikawa Shokichiro , Motegi Tsuyoshi
Published: February 2003

In the temperature range −200 –+40 °C, polarization echo characteristics of Rochelle salt and LiNbO3 powder are measured. Measurements are carried out on the two-pulse echo and the readout echo, which has a transient relaxation process with time constant T*1. The results are discussed with consideration of the temperature coefficients of the materials. The study suggests a possible relation between the observed echo characteristics and the material constants. It is found that the origins of echo generation in Rochelle salt and LiNbO3 powder are dominantly the dielectricity and the piezoelectricity, respectively. Furthermore, the transient relaxation for the readout echo is considered to originate in a residual mechanical fluctuation induced in the two-pulse sequence application.
Three-dimensional heat flow in the photoacoustic effect-II: Cell-wall conduction
Authors: McDonald F. Alan
Published: February 2003

The three-dimensional treatment of heat flow in the photoacoustic effect is extended to allow for thermal conduction to the cell walls. The typical effect is to reduce the photoacoustic signal when thermal waves extend to the cell wall with appreciable amplitude, although small increases may also occur. Results are in good agreement with recent experimental data. Comparisons with predictions from one-dimensional models are given.
Computer simulation study of the structure of vacancies in grain boundaries
Authors: Brokman A. , Bristowe P. D. , Balluffi R. W.
Published: February 2003

The structure of vacancies in grain boundaries has been investigated by computer molecular statics employing pairwise potentials. In order to gain an impression of the vacancy structures which may occur generally, a number of variables was investigated, including metal type, boundary type, degree of lattice coincidence, and choice of boundary site. In all cases the vacancies remained as distinguishable point defects in the relatively irregular boundary structures. However, it was found that the vacancy often induced relatively large atomic displacements in the core of the boundary. These displacements often occurred only in the direct vicinity of the vacancy, but in certain cases they were widely distributed in the boundary, sometimes at surprisingly large distances. In certain cases the displacements included a large inward relaxation of one, or more, of the atoms  neighboring the vacancy, and the initial vacant site became effectively ″split″. These results were classified and discussed in relation to the variables listed above. Several binding energies to the boundary were also calculated. Finally, the relevance of the results to the mechanism of boundary self-diffusion was discussed.
Range and standard deviation of ion-implanted Si in GaAs
Authors: Onuma Takeshi , Hirao Takashi , Sugawa Toshio
Published: February 2003

Carrier-concentration profiles of Si in semi-insulating GaAs have been obtained by C-V measurement techniques. Si+ or Si++ ions were implanted at energies ranging from 50 to 600 keV, and annealing was carried out with Si3N4 encapsulants. Range parameters such as the projected range Xp and the projected standard deviation ΔXp were experimentally determined by use of depths at the peak carrier concentration and at the 1/√e value of the peak carrier concentration of the profiles. It was found that ΔXp was strongly dependent on the Cr contents of substrates while Xp was not. The measured carrier concentrations could be approximated by the Gaussian distribution, and values of Xp were in good agreement with the theoretical value of the projected range Rp. However, ΔXp tended to saturate as the incident energies increased and deviated from the theoretical value of the projected standard deviation ΔRp.
Study of longitudinal acoustic modes and other low frequency vibrations in a solid n-alkane by means of incoherent inelastic neutron scattering
Authors: Kaji K. , Kollmar A. , Ewen B. , Stockmeyer R. , Fischer E. W.
Published: February 2003

Incoherent inelastic neutron scattering experiments have been performed in order to establish the longitudinal acoustic modes (LAM) in orthorhombic n-C32H66 crystals by a method different from Raman scattering. Besides the Raman active first order of LAM, the second order of LAM, which is Raman inactive, has been observed. No dispersion of the LAM’s was to be seen. It is masked completely by effects resulting from the absence of optical selection rules. In addition to the LAM’s, the antiparallel translational mode in chain direction, which is optical inactive, was identified. Its assignment was confirmed from the Q dependence of the scattering intensity.
Structural investigation of thin films of diamondlike carbon
Authors: Vora H. , Moravec T. J.
Published: February 2003

Diamondlike carbon films produced both by ion-beam technique and by radio-frequency (rf) plasma decomposition of hydrocarbon gases (C4H10, C2H6, C3H8, and CH4) have been examined using the technique of transmission electron microscopy. Although these examinations indicate that these films are predominantly amorphous, both single-crystal and polycrystalline diffraction patterns have been obtained from films of both types that indicate formation of several different phases. Some of these phases appear to be cubic and could be new forms of carbon. The results of secondary ion mass spectrometric analysis of carbon films produced by rf plasma decomposition of hydrocarbon gases are also discussed.
A study of deep level in bulk n-InP by transient spectroscopy
Authors: McAfee S. R. , Capasso F. , Lang D. V. , Hutchinson A. , Bonner W. A.
Published: February 2003

We report a study of bulk n-InP by deep level transient spectroscopy. Measurements were made on p+n junction diodes and Schottky barriers in which both electron and hole traps were present. The effects of Zn diffusion, phosphorus partial pressure, and relatively low-temperature heat treatment were studied. Results indicate the presence of uniformly distributed traps as well as nonuniform traps with higher concentration near the junction in the presence of Zn diffusion. Results further indicate significant changes in the thermally induced trap concentration associated with the removal of excess phosphorus. Significant changes in the trap spectra were also seen at temperatures below that typically used for Zn diffusion and may have important consequences in device fabrication.
Bias field dependence of domain drag propagation velocities in GdCoAu bubble films
Authors: DeLuca J. C. , Gambino R. J. , Malozemoff A. P. , Berger L.
Published: February 2003

The bias field dependence of the velocity of bubble propagation by the domain drag effect was studied in a GdCoAu amorphous film. Bubbles in close-packed arrays were propagated by pulsing currents directly through a stripline of the material fabricated by photolithography and ion-beam milling. As bias field is increased, at given current and pulse width, the velocity decreases, passes through a minimum, then increases again. The domain drag drive field at a given bias is derived both from the critical current at which motion begins and from the slope of velocity with current. A theory for the domain drag drive field Hd of a bubble raft with infinite length along the current direction is derived, giving the simple result Hd /βjD = 1/2(d0/D) −(π/4√3)(d0/D)3, where β is the Hall angle, j is the current density, d0 is the bubble diameter, and D is the nearest-neighbor spacing. Experimental results from critical current agree approximately with the theory, but results from velocity slope with current are a factor of 3 too high.
Conformational defects and associated molecular motions in crystalline poly(vinylidene fluoride)
Authors: Lovinger Andrew J.
Published: February 2003

Electron-diffraction investigation of single crystals of γ-poly (vinylidene fluoride) grown from the melt has revealed streaking of 0k0 reflections. The three-dimensional structure of the spikes was studied by specimen tilting during electron diffraction; streaking is maximized in the b*c* view and disappears in the a*b* view, indicating that the reciprocal-lattice spikes are directed parallel to c. After exclusion of effects associated with the shape transform of our γ crystals, the streaks are attributed to stacking faults parallel to the ab plane; such faults are consistent with incorporation of α sequences as defects within γ chains during crystallization. Conformational changes between α and γ arrangements are examined using a number of models. The simplest motions (flip-flops or rigid crankshafts) require simultaneous rotation about two noncolinear axes and are, therefore, less favored than mechanisms involving flexible chain motions as described in this report.
Piezoelectricity in γ-form Nylon 11
Authors: Scheinbeim J. I.
Published: February 2003

X-ray studies of unpoled and poled γ-form Nylon 11 films indicate that the polarization mechanism is not due to a field-induced crystal transformation from the γ to the α form, suggesting the existence of a polar γ form. The temperature dependence of d31 shows no decrease in polarization at the α-γ transition temperature (∼95 °C), indicating that the hydrogen bonds in the poled film are not able to randomize. These results suggest the possibility that our understanding of the γ-form structure of Nylon 11 is incomplete.
Viscoplastic behavior of a glass at high pressures
Authors: Questad D. L. , Pae K. D. , Scheinbeim J. I. , Newman B. A.
Published: February 2003

The glass transition pressure Pg for a polyurethane elastomer (Solithane 113, 50/50 resin-catalist ratio, manufactured by Thiokol Chemical Co.) is located at 2.5 kbar at room temperature and the glass transition temperature Tg is at −20 °C. Mechanical behavior of the elastomer, namely the tensile and the compressive stress-strain behavior, in the glassy state as well as in the rubbery state has been determined. The Young’s modulus increases from ∼107 dyn/cm2 in the rubbery state to ∼1010 dyn/cm2 in the glassy state. The tensile fracture strain increases rapidly from 60% at atmospheric pressure to greater than ∼200% at 1 kbar and higher. In the glassy state, the samples exhibit yielding, yield drop, and cold drawing. The yield drop is not accompanied by necking. Rather the samples undergo uniform drawing throughout the entire gage length. A series of sequential loading, unloading, and reloading tests in the plastic range was also conducted in the glassy state. It was observed that the plastic strain recovers as a function of time, that the yield maximum reappeared and grew after a delay time, and that the Young’s modulus in subsequent loadings was higher than the initial values and increased steadily with time. Various loading histories can be completely erased upon returning to a rubbery state by removal of applied pressure. The recovery of the plastic deformation, or the viscoplastic behavior, occurs at essentially the same rate at all pressures tested, and thus the data were superimposable to form a master curve near Pg. A molecular explanation for the various new phenomena observed is given.
Flat band potential determination of an electrolyte/semiconductor junction by an electro-optical method
Authors: Lemasson P. , Dalbera J. P. , Gautron J.
Published: February 2003

When excitons have a lifetime sufficiently large at room temperature and when the semiconductor presents a uniform dopant distribution in the near surface region, if a convenient doping level is used it is possible to demonstrate an excitonic interference phenomenon. The latter may be modulated by varying the dc polarization bias V of the semiconductor/electrolyte junction and then oscillations of the ΔR/R electroreflectance response versus V appear. In this particular case of junctions, it is possible to correlate simply the period of the observed oscillations with (V−Vfb )1/2, where Vfb is the flat band potential value. A comparison of values obtained for Vfb in this way with those obtained by classical methods for three different semiconductors (CdS, GaAs, and ZnSe) shows the interest of this electro-optical method.
Interface recombination velocity and misfit strain in molecular-beam epitaxy double heterostructures of GaAs/GaxIn1−x P(0.47<x<0.51)
Authors: Scott G. B. , Duggan G. , Roberts J. S.
Published: February 2003

Within an experimental uncertainty of ±2.5%, the photoluminescence yield of the central GaAs layer in a GaAs/GaxIn1−xP double heterostructure grown by molecular-beam epitaxy remains constant as the alloy composition varies in the range 0.47 <x<0.51. In contrast to results obtained on vapor phase epitaxy structures, these data imply that the interface recombination velocity between the active region and the confining layers has only a weak dependence on the misfit strain ε present at the growth temperature, where −3.0×10−3<ε<1.4×10−4. This situation is attributed to the absence of misfit dislocations in the molecular-beam epitaxy (MBE) heterostructures in a strain range where misfit dislocations are observed in those produced by vapor phase epitaxy.
Levitational end effects in a cylindrical magnetic suspension
Authors: Bird J. F.
Published: February 2003

An analytical calculation is presented for the effects of finite length on the magnetic levitation of a cylindrical metal shell encircling an alternating-current filament, which system was treated previously by ignoring end effects. The levitational end corrections are calculated by analyzing the differences in magnetic-field distribution between the finite-length and endless geometries. This approach yields a new eigenvalue equation, and expansion of the magnetic-field corrections in corresponding eigenfunctions leads, after some reduction, to a compact set of equations determining the expansion coefficients. From this formulation, the levitation force is expressed solely in terms of field coefficients for the region bounded by the shell inner surface and end planes. An approximation for these coefficients is then developed from the basic equations, yielding an anlytical formula for the levitational end corrections. The approximation formula is shown to give satisfactory results for representative cases. The exact solution for the magnetic field in the equilibrium configuration is appended.
Molecular recombination in laser media. I. Theoretical study of NF2+F+Ne→NF3+Ne
Authors: Smith G. P. , Huestis D. L.
Published: February 2003

The recombination reaction NF2+F+M→NF3+M has been investigated theoretically using a RRKM approach. Adequate agreement is found with the available association and decomposition data in low pressures of He or Ar. The recombination in 4 atm of Ne is calculated to be much slower than would be expected from extrapolation of the low-pressure, three-body rate constant. In particular, little recombination should occur during a discharge or electron-beam laser excitation pulse (≲1 μs), but reformation of NF3 should be the dominant loss mechanism for F and NF2. The theoretical techniques used here should be equally applicable to other important recombination processes in laser media.
Molecular recombination in laser media. II. Experimental study of NF2+F+Ne→NF3+Ne
Authors: Tang K. Y. , Hunter R. O. , Huestis D. L.
Published: February 2003

The recombination reaction NF2+F+Ne→NF3+Ne has been investigated experimentally in electron-beam-excited Ne/Xe/NF3 mixtures. The results obtained are in excellent agreement with the theoretical predictions.
A new structure for high-powered injection lasers
Authors: Small M. B. , Lynch R. T.
Published: February 2003

New laser structures have been fabricated which distribute the optical power generated within a wide injecting stripe among a multiplicity of lateral modes. This was done with the objective of increasing the life of such lasers at high power by reducing the optical stress on the facets. The levels of catastrophic optical breakdown have been measured and the very high levels achieved (≳300 mW for a 3-spot device) have been taken as an indication of our success. These lasers were also very efficient and the mode pattern was stable to the point of breakdown. In contrast to these useful properties, it was found that intrinsic to these structures is a poor temperature coefficient of threshold, which would make them more useful for pulsed rather than cw operation.
Frequency stability of a small scale HF cw laser
Authors: Bertrand L. , Monchalin J-P. , Pitre R. , Gagné J.M.
Published: February 2003

A small laboratory scale cw HF laser has been built and its frequency stability is studied using a Fabry-Perot interferometer. Performances of the free-running laser, of the Lamb dip stabilized laser, and of the laser stabilized on a Fabry-Perot resonance (side of a mode and derivative zero crossing) are reported. In this last case, stability close to 10−9 has been observed.
Ion-electrostatic instabilities in current-carrying magnetized plasmas
Authors: Willett Joseph E. , Mehdian Hassan
Published: February 2003

A fluid analysis of the stability of obliquely propagating ion-electrostatic waves to current flow along the magnetic field in a fully ionized, collisional plasma is presented. The stabilizing or destabilizing effects of frictional force, collisional energy transfer, electron and ion viscosity, electron and ion thermal conductivity, and thermal force are investigated. Simple analytical expressions for the growth rate arising from each dissipative mechanism are derived for ion-cyclotron, cosine ion-acoustic, ion-acoustic, and cosine ion-cyclotron waves.
Composition and thickness of the surface segregation region of a binary alloy system determined by a quantitative Auger electron spectroscopy method
Authors: Tokutaka H. , Nishimori K. , Tanaka K. , Takashima K. , Le Héricy J. , Langeron J. P.
Published: February 2003

Let us consider the surface composition of the binary alloy, where the surface composition R1 is considered to be different from the bulk inside composition R2 and also the segregation region thickness is T. In this model it is possible to count the Auger signals considering the contributions of an attenuating primary beam and the secondary electrons which are backscattered and forwardscattered. Using the theory, we have calculated these R1 for the reported experimental results of the Ag-Au binary alloy as a function of T. The calculated Ag composition R1 are compared with the ISS (Ion Scattering Spectroscopy) results that are said to be the most surface sensitive technique. When the bulk Ag content is less than 50 at. %, the Ag segregation region thickness T is considered to be one monolayer (2.58 Å ∼ an average layer spacing, d3 = M/6.02×1023ρ, where M = atomic mass and ρ = specific mass or density). However, when the bulk content is greater than 50 at. %, T lies between one and two monolayers (2.58 and 5.16 Å). The usual method that uses a relative sensitivity factor only estimates the surface average composition in the depth of the mean free path of the Auger electrons. However, this method can estimate the surface composition R1 as well as the segregation region thickness T.
Single-crystal growth and characterization of LiGaSe2
Authors: Kuriyama K. , Nozaki T.
Published: February 2003

Single crystals of a new ternary lithium chalcogenide LiGaSe2 were grown by an improved directional solidification technique. The typical as-grown crystal has dimensions of about 4 mm cubed and shows a transparent light yellow color. We infer that LiGaSe2 crystallizes in the β-NaFeO2 structure having an orthorhombic unit cell (a = 6.833 Å, b = 8.227 Å, and c = 6.541 Å) by powder x-ray diffraction. The melting point was determined by differential thermal analysis to be 846 °C. The energy band gap of LiGaSe2 at room temperature was determined by optical reflectance measurements to be 3.65 eV.
Carrier generation efficiency measurements on dispersions of photoconductive particles
Authors: Popovic Zoran D.
Published: February 2003

A method for determining quantum efficiencies of carrier generation of photoconductive particles dispersed in inert polymer matrices is proposed. It has been applied to study generation efficiencies in x phase of x-metal-free phthalocyanine dispersed in a polystyrene n-butylmethacrylate copolymer matrix. Data for pigment concentration from 1% to 20% by weight give consistent values for the generation efficiencies, confirming the value of the proposed method.
Carrier-collection efficiencies in amorphous hydrogenated silicon Schottky-barrier solar cells
Authors: Viktorovitch P. , Moddel G. , Blake J. , Paul William
Published: February 2003

We report the results of a systematic study of correlations in the collection efficiency, collection length, depletion width, midgap density of states and energy-band gap in sputter and silane-decomposition-produced amorphous hydrogenated silicon Schottky diodes. Films produced by sputtering have a collection length Lc, which is less than the depletion width W, unlike silane-decomposition-produced films for which Lc≃W. We show that the relatively weak variation of the deduced hole-mobility-lifetime product with midgap state density and temperature is consistent with the holes becoming immobilized before recombining. The collection efficiency is found to be controlled dominantly by the field-assisted diffusion of carriers in the depletion region, and not limited by geminate recombination.
Molecular field coefficients and cation distribution of substituted yttrium iron garnets
Authors: Röschmann P. , Hansen P.
Published: February 2003

The saturation magnetization Ms(T) of Ga, Al, Sc, and CaVBi substituted Y3Fe5O12 (YIG) single crystals and of polycrystalline Ca/Ge and Ca/Ti substituted YIG has been investigated for 4.2 K ⩽T⩽TC. The samples were repeatedly annealed and quenched at different equilibrium temperatures 773 K⩽Te ⩽1523 K. The attained site exchange of Fe and the substituents between the a and d sites resulted in considerable changes of Ms(T). From a fit of the Néel molecular field theory to the Ms(T) data the dependence of the magnetic moments at T = 0 K and of the molecular field coefficients on the amount of nonmagnetic substitutions on the a and d sites were determined. It turned out that ion-specific sets of equations are required accounting for the ’’particular ion effect’’ of different cation species. The cation distributions inferred from the magnetic data have been analyzed along with a thermodynamic equilibrium model. The derived site stabilizing energies for the mixed Fe–Ga and Fe–Al garnets agree well with recently reported data. New results are presented for the site stabilizing energies in Ca/Ge:YIG and for the substituents Sc and Ti with octahedral site preference.
Vanadium-substitution effect on the first-order magnetic and electrical transition in NiS
Authors: Anzai S. , Futami T. , Sawa T.
Published: February 2003

The cell volume ν of the NiAs-type Ni1−xVxS increases with increasing x below the solubility limit xL = 0.076±0.003. The following results of the V substitution are discussed on the basis of the strongly perturbed dilute-alloy model which is modified to the splitting eg -band diagram for NiS. (1) The transition temperature Tt and the heat-of-transition decrease with increasing x in the high x region below xL. This behavior is in contrast with the volume effect (∂Tt/∂ν ≳ 0) deduced from the previous pressure experiment. (2) The susceptibility at 300 K ( ≳ Tt) is enhanced with increasing x. (3) Below Tt, dominant carriers are holes in the sample with x = 0.02, while they are electrons in x = 0.05.
Vacuum ultraviolet properties of beryllium fluoride glass
Authors: Williams R. T. , Nagel D. J. , Klein P. H. , Weber M. J.
Published: February 2003

The reflectivity of pure and multicomponent BeF2 glasses has been measured in the spectral range 8–50 eV. Optical transmission and ultraviolet photoelectron spectroscopy are also described. The data are interpreted to indicate that pure BeF2 glass has a 13.8-eV band gap and an exciton peak at 12.8 eV. An alternative interpretation of the spectra in terms of a direct-forbidden band edge analogous to SiO2 would suggest a smaller band gap. BeF2 should ultimately be capable of an ultraviolet transmission range comparable to that of LiF, though extrinsic factors now limit the transparency range.
Theory of structure and conformation of polyacetylene
Authors: Good Brian S. , Taylor P. L. , Hopfinger A. J.
Published: February 2003

An investigation of the structure of polyacetylene is carried out taking into account intrachain interactions. The distribution of torsional angles along the polymer chain is obtained using a transfer integral method. The most stable configuration at low temperature appears to be the cis-transoid conformation.
The effect of annealing on the properties of silicidized molybdenum thin films
Authors: Chow T. P. , Steckl A. J. , Brown D. M.
Published: February 2003

The effect of isothermal and isochronal annealing on the structural and electrical properties of silicidized Mo thin films is reported. The silicidation of Mo with SiH4 resulted in Mo films with increasing hexagonal MoSi2 content as the reaction time increased. Post-reaction annealing was performed in various ambients (hydrogen, nitrogen, and vacuum) at temperatures from 800 to 1000 °C for times up to 1 h. Annealing in H2 at 1000 °C for only 5 min results in the virtual disappearance of the original components and the formation of intermediate silicide phases (Mo5Si3 and Mo3Si) and the tetragonal MoSi2 phase. This structural transformation leads to a significant increase in resistivity. The reaction kinetics are considerably slower in the case of N2 ambient, where even after a 60-min anneal at 1000 °C a substantial percentage of Mo remains. This slower rate of phase change is reflected in a more gradual increase in the sheet resistance. The characteristics of vacuum-annealed films followed the N2 case for short-term anneals (t≲10 min), but resembled the H2 case longer-term anneals (t≳15 min). The dependence of reaction mechanisms on various ambients is discussed.
Superconductor-insulator-superconductor mixing with arrays at millimeter-wave frequencies
Authors: Rudner S. , Feldman M.J. , Kollberg E. , Claeson T.
Published: February 2003

We report high-frequency mixing at 75 GHz using superconductor-insulator-superconductor (SIS) tunnel junction arrays of various length and composition. Short (6-junction) arrays, both of Pb (In) and of Pb, and long (36-junction) arrays of Pb are used. The array geometry and antenna coupling can be scaled to 300 GHz with existing technology. Comparing the experiments to each other and to theory provides criteria for SIS mixer design. The measured single side band (SSB) conversion loss is as good as 2.0±0.9 dB. This is marginally the best published conversion result for any resistive mixer without image rejection, and quantitatively agrees with the quantum theory of mixing. We examine Josephson effect noise in this device and give a rough upper frequency limit for single-junction SIS mixers. Conversion maxima are also noted close to the half-gap singularity present in Pb (In) junctions.
The temperature independence of Grüneisen’s gamma at high temperature
Authors: Steinberg Daniel J.
Published: February 2003

Within the accuracy of the data on thermal expansion, bulk modulus, and specific heat, Grüneisen’s gamma at constant volume for 21 metals is shown to be independent of temperature, at least to a substantial fraction of the melt temperature.
Lattice constant values in the (Cu1−xAgx)(In1−yGay)Te2 alloys
Authors: Avon Julie E. , Woolley John C. , Asbjornsen Ampai , Chatraphorn Somphong , Ratanathammapan Kiranant , Yoodee Kajornyod
Published: February 2003

It has been shown that single phase solid solution occurs throughout the composition range of the system (Cu1−xAgx)(In1−yGay)Te2, the structure throughout being tetragonal chalcopyrite. Values of lattice parameters a and c have been determined as functions of x and y and fitted to power series expressions. Contours of constant a and constant c are plotted, and it is indicated that these parameter values can be used to determine the composition of samples in this alloy system.
Comment on ’’Energy gap in Si and Ge: Impurity dependence’’
Authors: Sterne P. A. , Inkson J. C.
Published: February 2003

A recent paper by Mahan on energy-gap narrowing in extrinsic semiconductors is compared and contrasted with a previous analysis by Inkson. It is found that, contrary to a statement by Mahan, the two papers rely on the same physical basis but use different means of calculation. The source of confusion is identified as the use of an inconsistent terminology.
Effect of pyrolytic Al2O3 deposition temperature on inversion-mode InP metal-insulator-semiconductor field–effect transistor
Authors: Kobayashi Takeshi , Okamura Masamichi , Yamaguchi Eiichi , Shinoda Yukinobu , Hirota Yukihiro
Published: February 2003

The effects of pyrolytic Al2O3 deposition temperature on electrical properties of an inversion-mode InP (MISFET) metal-insulator-semiconductor field-effect transistor were investigated. An Al2O3 gate insulator was deposited using an aluminum isopropoxide organic source on a HCl vapor etched InP surface. An increasing current drift was seen when the insulator was deposited at a temperature below 330 °C. This became exaggerated with decreasing temperature. The observed drift is explained in terms of a time-dependent threshold voltage associated with the polarization of organic molecules or radicals introduced into the insulator by an incomplete decomposition of the source gas during deposition of the dielectric layers at rather low temperatures. The effective electron mobility of the InP MISFET did not show any dependence on the deposition temperature below 350 °C. At higher temperatures, the effective mobility appreciably decreased.
Inverse solution of Maxwell’s equations in plasmas
Authors: Hokenson Gustave
Published: February 2003

Maxwell’s equations, which govern the magnetic, current density, and electric field vector distributions throughout a plasma have been formulated and solved in an inverse manner. The methodology allows the geometrical configuration of those components which bound the plasma to be determined in physical space, given the magnitude of the relevant field vectors on their surfaces (boundaries of the computation region in a transformed plane). To accommodate the required mathematical structure of the analysis, a uniform plasma flow at low magnetic Reynolds number is considered in which ion slip and electron pressure/temperature gradient diffusion effects are negligible.
Electron impact excitation of the helium isoelectronic sequence
Authors: Ganas P. S.
Published: February 2003

A simple analytic central potential with two adjustable parameters is proposed for the helium isoelectronic sequence. The potential parameters are obtained by appealing to the precise values of optical oscillator strengths calculated by Schiff et al. Using the Born approximation we calculate generalized oscillator strengths and integrated cross sections from threshold up to 5 keV for the electron impact excitation of the resonance transition 11S–21P in the helium isoelectronic sequence. The accuracy and the systematics of the results are discussed.
Macroscopic analysis of electromagnetic waves coupling in CdS
Authors: Laurenti J. P. , Rouzeyre M.
Published: February 2003

The uniaxial stress-induced coupling of the optical ordinary and extraordinary modes in CdS is quantitatively investigated by analyzing, at room temperature, the transmitted light spectrum of a sample placed between two polarizers crossed along the natural neutral lines. Experiments are performed in the wavelength range 5200–7000 Å under application of a calibrated (<500 bar) uniaxial stress directed at 45° with respect to the C axis. At the near gap isotropic wavelength 5229 Å the phase matching allows energy transfer. It is shown that the high selectivity of the process is due to the fast rotation of the induced neutral lines. Due to the stress-induced splitting, the actual birefringence exhibits a sharp but nonzero minimum, at the isotropic wavelength, which is a linear increasing function of the pressure. Its linear pressure coefficient is measured, 6.3×10−6 bar−1, and this allows a direct calculation of the corresponding elasto-optic coefficient p44 = 9.9×10−2. The frequency dispersion of p44 is investigated near the fundamental absorption edge where it exhibits a broad maximum and a sharp structure. The main characteristics of a coupled mode band-pass optical filter are calculated and briefly discussed. Finally the residual internal strain field in most ’’as-grown’’ crystals is estimated as 1.5×10−5.
A unified treatment of the Langmuir probe and diode equations
Authors: Sherman Christopher
Published: February 2003

An argument is presented which justifies the simultaneous use of both the Langmuir Mott-Smith orbit-limited, and the diode space-charge-limited equations for current collection by electrostatic probes. From these two equations the sheath size can be eliminated and the current to a probe obtained for a large range of values of probe potential and Debye length. Numerical solutions are presented for both the spherical and cylindrical cases. Asymptotic properties are considered. Comparison with results of previous probe theoretical treatments are made.
Argon-oxygen interaction in rf sputtering glow discharges
Authors: Aita C. R. , Marhic M. E.
Published: February 2003

Optical emission spectroscopy was used to study the behavior of the excited states of argon and oxygen atoms which occur in glow discharges generated during the rf diode sputtering of a zinc oxide target. The results indicate that there is an interaction between the two gases when the sputtering gas contains less than approximately 15% oxygen. A quasi-resonant transfer of excitation from a metastable argon atom to an excited, repulsive, neutral state of the oxygen molecule, which subsequently dissociates, is proposed as the interaction mechanism. Correlation with mass spectrometry data indicates that the dissociation products increase the relative rate of zinc oxide production at the target surface and therefore promote single (0001) crystallographic orientation zinc oxide film growth.
Models of diffraction from layered ultrathin coherent structures
Authors: Meyer K. E. , Felcher G. P. , Sinha S. K. , Schuller Ivan K.
Published: February 2003

We show how relatively simple diffraction theory can be applied to layered ultrathin coherent structures to yield diffraction patterns with main peaks and satellites. We also discuss how the introduction of lattice strain into the model affects the results, and how this modified model might be applied to a real system.
Effects of rf power and reactant gas pressure on plasma deposited amorphous hydrogenated silicon
Authors: Potts J. E. , Peterson E. M. , McMillan J. A.
Published: February 2003

The properties of amorphous hydrogenated silicon films produced at room temperature by rf glow discharge decomposition of silane have been studied while systematically varying the rf power and the pressure of the reactant gas. The structure and composition of the films were monitored by measuring the optical gap, IR vibrational spectrum, and the hydrogen evolution rate. Evidence is seen for an improvement of film quality at high rf power levels. Such improvement is discussed in terms of energetic ion bombardment of the growth surface. The significance of ion bombardment is emphasized by comparing films grown simultaneously on biased and unbiased electrodes. Increasing pressure moderates the ion bombardment energies and diminishes the film quality.
Quantitative evaluation of structure in coalescence grown discontinuous metal films
Authors: Norrman S. H. , Andersson T. G.
Published: February 2003

A statistical model is presented to describe the structure of discontinous metal films in their coalescence stage of growth. The model is based upon predictions from atomistic adsorption and nucleation theory. The irregular metal particles in the discontinuous films are assumed to be prolate spheroids. Proceeding from these model particles (with log-normal distributed axes) a statistical approach is adopted to calculate the lengths of the radius vector in particles randomly oriented around their centers of gravity. The gradual change in the distribution of the center-to-center (ctc) distance with increased film thickness has been considered. This change has been described in two different ways: by a random walk concept and by statistical considerations of more distant neighbors. The distribution of the computed radius vector together with that of the observed ctc distance (represented as a truncated Gaussian) then serve as a foundation for calculations of edge-to-edge separations between nearest neighbors. Predicted distributions of radius vector, ctc distance, and separation are compared with observed distributions for gold films formed on glass substrates and with thicknesses in the range t⩽4.0 nm. Good quantitative agreement was found between computed and experimental results. Small discrepancies could be accounted for in terms of particle alignment. In the edge-to-edge separation distributions, both the mode and the dispersion were found to increase with film thickness. Finally, when introducing a limited dependence between radius vector and nearest neighbor distance (based upon observations), an excellent agreement was achieved for calculated and observed separation distributions.
Phase-shift analysis of modulated photocurrent: Its application to the determination of the energetic distribution of gap states
Authors: Oheda Hidetoshi
Published: February 2003

In order to determine an energetic distribution of localized states, a new method is proposed. The method is based on the analysis of the phase shift between a sinusoidally modulated excitation light and its inducing photocurrent. The theoretical relation between the phase shift and its relevant localized states is derived assuming a trap-limited band conduction of unipolar photocarriers. The energetic profile of the localized states can be calculated from a modulation frequency dependence of the phase shift. The method has been applied to CdS crystal and the validity has been confirmed. It is suggested that the method is useful for amorphous semiconductors in which the localized states are distributed quasi-continuously in the band gap.
Dielectric function for ultraviolet plasmons in the short-lifetime limit
Authors: Fowler H. A. , Filliben J. J.
Published: February 2003

The ’’inverted’’ Drude-Sellmeier formula, for a two-parameter free-electron-gas spectrum of plasmon excitations, is evaluated for very large values of the line breadth. These function values for 1/ε(ω) characterize a solid dominated by a free-electron plasma with short ’’damping time,’’ over the ultraviolet range. A rounded energy-loss distribution is suggested at the critical damping limit.