bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature effect in quasiharmonic infrared bands of stressed polymers
Authors: Bretzlaff R. S. , Wool R. P.
Published: February 2003

The effect of temperature on vibrational frequency shifts in mechanically stressed polymer chains is analyzed. A single chain is modeled as a weakly coupled, one-dimensional series of anharmonic diatomic oscillators. The anharmonic potential is described as a perturbation of the harmonic potential with cubic and quartic terms. Expressions are derived for the dominant, quasiharmonic contribution to the temperature-dependent frequency shifting coefficient αc, and distinctions are drawn between the vibrational mode ’’mixing contribution’’ and the ’’anharmonic contribution.’’ αc is derived in terms of the Grüneisen parameter; and the resulting expression is −αc = α0+β0T, where α0 is the extrapolated T = 0 °K value of the frequency shifting coefficient, and β0 is constant. The predicted linear dependence of αc on temperature was found to be in excellent qualitative agreement with experimental studies on stress-induced infrared frequency shifts versus T in polypropylene.
Light modulators and deflectors based on polariton effects
Authors: Skettrup T.
Published: February 2003

The possibility of constructing light modulators and deflectors based on polariton effects is considered. The polariton is a mixed complex consisting of a superposition of a one-photon state and a crystal excitation state. By influencing the crystal excitation state by means of external fields, the polariton, and hence the photon part, can be deflected or modulated. The connection with geometrical optics is established, and it is shown that the deflection is due to a gradient in the refraction index created by the applied external field. Several examples with electric, magnetic, and stress fields, and temperature gradients are shown with orders of magnitude of deflections computed.
Free-to-bound transitions in Si-doped epitaxial Ga1−xAlxAs
Authors: Swaminathan V. , Sturge M. D. , Zilko J. L.
Published: February 2003

We have studied silicon-doped Ga1−xAlxAs by low-temperature photoluminescence as a function of aluminum composition up to x ∼0.4 and as a function of Si doping at x ∼ 0.4. We have identified a donor-to-acceptor pair recombination band due to Si in the spectra at 5.5 K. The Si acceptor energy is determined from the peak position of the corresponding free-to-bound transition, which is observed in the 75-K continuous wave spectra or in the 5.5-K time-resolved spectra. It is found to vary from 35 to 62 meV in the range x ∼ 0 to 0.4 and the acceptor is suggested to be Si occuping arsenic sites. The variation of the ionization energy of SiAs with x is intermediate between that of GeAs which shows strong deviation from the effective mass theory and CAs which shows very little deviation.
The measurement of elastic stresses and energy in cubic single-crystal films by x-ray diffraction
Authors: Rao Satish I. , Houska C. R.
Published: February 2003

Anisotropic elasticity calculations have been made for use in conjunction with strain measurements by x-ray diffraction for sputtered single-crystal films. Only the cubic case has been treated. Data from InSb films with (100) and (111) orientations on similarly oriented GaAs substrates are given. It was found that nearly alike planar strains ε yield lower planar stresses σ′1 and σ′2 and stored energy density U for the (100) orientation. The (100) films exhibit a relatively large strain perpendicular to the film ε3.
Tin doping in Ga0.47In0.53As and Al0.48In0.52As grown by molecular-beam epitaxy
Authors: Cheng K. Y. , Cho A. Y. , Wagner W. R.
Published: February 2003

Transport properties of Sn-doped Ga0.47In0.53As and Al0.48In0.52As epitaxial layers grown lattice matched to InP substrates by molecular-beam epitaxy (MBE) have been studied. Doping levels as high as 2×1019 cm−3 have been achieved for both n-types Ga0.47In0.53As and Al0.48In0.52As. The carrier concentration varies proportionally with the arrival rate of Sn and the sticking coefficient of Sn in these ternary systems is estimated to be unity. For the same Sn arrival rate, the carrier concentrations in both ternary epitaxial layers are identical. Mobility studies showed that the results with MBE grown Sn-doped Ga0.47In0.53As layers are comparable to the best reported with liquid phase epitaxy (LPE). The variations of electron mobility as a function of carrier concentration are in excellent agreement with the results of the theoretical calculations involving the alloy scattering mechanism at both room and liquid-nitrogen temperatures. The electron mobility variation in Al0.48In0.52As epitaxial layers follows the same trend as that in Ga0.47In0.53As epilayers. For the same carrier concentration, however, the value is only 1/6 of that of the Ga0.47In0.53As.
Kinematical x-ray diffraction in nonuniform crystalline films: Strain and damage distributions in ion-implanted garnets
Authors: Speriosu V. S.
Published: February 2003

A kinematical model for general Bragg case x-ray diffraction in nonuniform films is presented. The model incorporates depth-dependent strain and spherically symmetric Gaussian distribution of randomly displaced atoms. The model is applicable to ion-implanted, diffused, and other single crystals. Layer thickness is arbitrary, provided maximum reflecting power is less than ∼6%. Strain and random displacement (damage) distributions in He+-implanted Gd, Tm, Ga:YIG, and Ne+-implanted Gd3Ga5O12 are obtained by fitting the model to experimental rocking curves. In the former crystal the layer thickness was 0.89 μm with strain varying between 0.09 and 0.91%. In the latter crystal a wide range of strain and damage was obtained using successively higher doses. In each case layer thickness was 1900 Å, with 2.49% strain corresponding to 0.40-Å standard deviation of random displacements. The strain distributions were strictly linear with dose. The same, closely linear relationship between damage and implantation-induced strain was determined for both crystals.
Transient photoresponse measurements in x-phase of metal-free phthalocyanine photovoltaic cells
Authors: Popovic Zoran D. , Loutfy Rafik O.
Published: February 2003

Transient response of In/x phase of metal-free phthalocyanine Schottky barrier photovoltaic cells as a function of the applied reverse bias has been investigated under pulse and step illumination conditions. In both cases the dependence of the photoresponse on the applied bias showed the change in shape when the light wavelength was changed. This can be interpreted in the framework of the local carrier generation model in which it is assumed that the carrier generation is dominated by the contribution from the barrier region. In the constant illumination mode, it was clearly demonstrated that the photocurrent has two components—the true photocurrent component and the component caused by changes in the barrier properties. For the true photocurrent component, using strongly absorbed red light for illumination, a saturation was observed which enabled the determination of quantum efficiency of carrier generation in the barrier of 70%.
Optical and electrical characterization of high-dose ion implanted, laser-annealed silicon solar cells
Authors: Ostoja P. , Solmi S. , Zani A.
Published: February 2003

n +/p and p+/n/n+ solar cells were fabricated by using ion implantation and pulsed laser annealing. With these techniques it is possible to obtain emitters which are doped well beyond the solubility limit and present lower sheet resistivities for equal junction depth. The dopants used were phosphorus, arsenic, and boron, and the implanted doses ranged from 2×1015 at/cm2 up to 5×1016 at/cm2. Measurements of diffusion length, quantum efficiency, and reflectivity enabled us to demonstrate that the supersaturated layers are characterized by high values of the absorption coefficient, which determines a poor short-circuit current and consequently a low conversion efficiency. This effect seems to be very marked for concentrations higher than 1021 at/cm3. Also, the reflectivity depends on the surface doping, showing a considerable decrease for the highest concentrations examined.
Effect of various substrates on the hydrogen sensitivity of palladium-semiconductor diodes
Authors: Yamamoto N. , Tonomura S. , Matsuoka T. , Tsubomura H.
Published: February 2003

The effect of hydrogen at various partial pressures in air on the current-potential (I-U) curves for various palladium-semiconductor diodes were studied. The diodes were prepared by depositing Pd on TiO2, ZnO, CdS, GaP, or Si. The onset potentials of the I-U curves in the forward bias region were very sensitive to hydrogen for the TiO2 and ZnO diodes, but those of other semiconductors were insensitive. The substrates in the hydrogen-sensitive diodes are ionic semiconductors and those in the hydrogen-insensitive diodes are covalent semiconductors. The large variation in the hydrogen sensitivity of various diodes is explained by the degree of change in their barrier heights which are produced by the change in the palladium work function caused by hydrogen.
Fluxon propagation in long Josephson junctions with external magnetic field
Authors: Olsen O. H. , Samuelsen M. R.
Published: February 2003

The reflection of a single fluxon propagating in a Josephson line cavity influenced by an external magnetic field is examined numerically. We find a single reflected fluxon, an antifluxon, collapse of the incident fluxon, fission into a higher number of antifluxons or fluxons, and formation of breather-like waves depending on the velocity of the incident fluxon and the magnitude of the external magnetic field. Approximations based on energy analysis describing the border lines between regions of different processes are presented.
The contoured-oxide monolithic series-array solar battery
Authors: Murray E. M. , Warner R. M.
Published: February 2003

The monolithic series-array solar battery (MSASB) combines integrated circuit and solar battery technology. The contoured-oxide MSASB offers an improvement in cell response over previous dielectrically isolated MSASB designs. The devices discussed in this paper demonstrated the feasibility of the contoured-oxide approach, exhibiting power conversion efficiencies of 7.5%. This low value is attributed in part to high series resistance caused by a process omission. In addition, it has been determined that shunting, attributable to poor device isolation, is a problem. Corrective modifications to this process have been detailed.
Degradation properties in metal-nitride-oxide-semiconductor structures
Authors: Suzuki Eiichi , Hayashi Yutaka , Yanai Hisayoshi
Published: February 2003

Degradation properties in metal-nitride-oxide-semiconductor (MNOS) structures are investigated using mainly p-channel MNOS transistors. A model is proposed on the basis of various experimental results, attributing the degradation to the passage of hole current through the SiO2 layer, followed by creation of hole traps in the SiO2 layer, and creation of interface states at the Si-SiO2 interface. A theoretical treatment of the enhancement of hole conduction in the degraded SiO2 layer of the p-channel thick-oxide MNOS transistor is performed, and the hole traps created in the SiO2 layer appear to be E′ centers when the experimental results are fitted to the theoretical calculations. The nature of the interface states created by write-erase (W/E) cycling is also discussed, comparing the experimental results using a p- and an n-channel MNOS transistor.
Heterodyne analysis of metal-oxide-metal diodes
Authors: Augeri R. C.
Published: February 2003

The heterodyne analysis of a metal-oxide-metal (MOM) diode is presented. The analysis is based upon the equivalent circuit and antenna models of the MOM diode. Expressions are derived for the noise equivalent power per Hz (NEP/Hz) for two sources of limiting noise. The first noise limitation considered is shot noise of the current in the diode due to a dc bias voltage of ∼0.2 V. The second noise considered is the shot noise associated with local oscillator (LO) induced current. For a temperature of 300 °K and circuit parameters chosen to optimize the tunnel diode operation, the theoretically ideal NEP/Hz is estimated for the LO and bias voltage noise to be 2×10−18 and 6.7×10−17, respectively.
A demonstration of the decrease of fast-electron preheat from laser-produced plasmas with increasing pulse length
Authors: Hares J. D. , Kilkenny J. D.
Published: February 2003

It is demonstrated that the coupling of laser energy into fast-electron preheat beneath the focal spot decreases with increasing pulse length. An examination of published data corroborates this observation. Tentative theoretical interpretations are advanced.
The analysis of exponential and nonexponential transients in deep-level transient spectroscopy
Authors: Kirchner P. D. , Schaff W. J. , Maracas G. N. , Eastman L. F. , Chappell T. I. , Ransom C. M.
Published: February 2003

One of the major motivations for using computerized waveform capture for deep-level transient spectroscopy is the capability to employ methods of analysis more accurate and informative than boxcars and correlators. Accordingly, we have adapted the fast Fourier transform method and the method of moments to analyze single and multiple exponential decays, respectively. We present relevant details of our experimental system, and compare the boxcar method with the new analyses on both simulated and experimental data. The new analyses have given conclusive, accurate results in cases where the boxcar is ambiguous or directly misleading.
Synchrotron-Čerenkov radiation in the vicinity of an atomic absorption edge
Authors: Rynne T. M.
Published: February 2003

Under the joint action of homogeneous magnetic fields and ambient media, relativistic charged particles emit synchrotron-Čerenkov radiation. The behavior of this radiation in the vicinity of an atomic absorption edge is studied in detail. Theoretical estimates indicate that synchrotron-Čerenkov radiation can be exploited for the measurement of dispersive interactions in the x-ray region of the spectrum in parameter ranges not accessible by other techniques. The K edge of krypton appears to be a conceptually clean-cut case which is particularly suited for experimental tests; detailed predictions for the intensity of synchrotron-Čerenkov radiation in the vicinity of this K edge are given. With 20-GeV electrons and fields of the order of a few kilogauss, it should be possible to measure deviations from unity of the index of refraction to a precision of 1 part in 109 at photon energies of 14.3 keV.
Light scattering from a glass thin-film optical waveguide
Authors: Imai M. , Koseki M. , Ohtsuka Y.
Published: February 2003

Measurements were made of the light scattered out of the Corning 7059 glass thin-film optical waveguide sputtered onto substrates of pyrex glass. The angular distributions of the scattered light can be explained by the waveguide imperfections not only of surface roughness of air-film-substrate interfaces but of refractive-index inhomogeneities. The measured scattering patterns are consistent with the theory taking account of both imperfections, assuming a correlation length of bx/λ ∼ 0.05 and bz/λ ∼1.0, where bx and bz are the correlation lengths in the directions perpendicular and parallel to the waveguide surface.
Characterization of point-plane corona pulses in SF6
Authors: Van Brunt Richard J. , Leep David
Published: February 2003

The properties of streamer or electron avalanche pulses have been investigated for point-plane, and positive and negative dc corona discharges in gaseous SF6 over the pressure range of 50–500 kPa. Measurements were made of the voltage and pressure dependence of electrically detected corona pulse-height distributions, pulse shapes, and repetition rates. Positive corona pulses appear at onset as low-level electron avalanches which, at higher voltages, develop into large streamers usually followed by a burst of many smaller pulses. The burst characteristics of positive corona show a definite dependence on pressure and voltage which is evident in the pulse-height distribution data. Negative corona displays characteristics which are sensitive to cathode surface conditions. For a point electrode that is either exposed to UV radiation or has been conditioned by prior discharges, the negative corona appears predominantly in a quasiglow mode consisting of relatively low-level pulses of high repetition rate.
The diffusion length for gas discharge columns with electron production and loss rates linear and quadratic in electron density
Authors: Rogoff Gerald L.
Published: February 2003

Steady-state positive column calculations can sometimes be simplified by writing the electron diffusion rate in terms of an effective length, thereby replacing a Laplacian with an algebraic quantity. When the electron continuity equation is purely linear in electron density, the characteristic diffusion length is useful for this purpose, since it can be used to relate the electron diffusion loss rate to the dimensions of a plasma and to calculate the electron temperature or operating electric field. If additional, nonlinear processes are introduced, the characteristic diffusion length is no longer appropriate for representing the diffusion rate. This paper presents a simple yet exact definition of a generalized diffusion length for calculations of the spatially averaged electron density in plasmas with electron production and loss rates linear and quadratic in electron density. This generalized effective diffusion length properly accounts for the average effect of electron diffusion for all possible signs and relative magnitudes of the linear and quadratic rates. Some properties of the effective diffusion length differ significantly from those of the characteristic diffusion length, which represents a special limiting case. Problems with other definitions of an effective diffusion length are discussed.
The quaternary alloy system AlxGayIn1−x−ySb
Authors: Zbitnew Kim , Woolley John C.
Published: February 2003

Ingots of AlxGayIn1−x−ySb were grown using a directional freeze technique. Slices were cut from these ingots and their compositions determined by an x-ray fluorescence method. X-ray powder photographs were taken of the slices to check for single phase condition and hence lattice parameter values were determined. Optical energy-gap values were also obtained from standard transmission measurements. Empirical equations were then derived to fit the lattice parameter and energy-gap data as functions of composition.
Properties of zinc oxide films prepared by the oxidation of diethyl zinc
Authors: Roth A. P. , Williams D. F.
Published: February 2003

Polycrystalline transparent semiconducting zinc oxide films have been deposited by the oxidation of diethyl zinc. The film growth rate is controlled by a complex multistep oxidation process which is dominated by radical reactions. The effect of substrate temperature and gas pressures have been studied. Samples deposited between 280 and 350 °C have a conductivity varying from 10−2 to 50 Ω−1 cm−1. The electrical properties of the films which are typical of polycrystalline material with small crystallites are shown to depend very closely on the film growth conditions. A study of oxygen chemisorption at grain boundaries confirms the importance of grain boundary effects in ZnO polycrystalline films.
Diffusion coefficient of electrons in silicon
Authors: Brunetti R. , Jacoboni C. , Nava F. , Reggiani L. , Bosman G. , Zijlstra R. J. J.
Published: February 2003

This paper reports an experimental and theoretical analysis of the diffusivity of electrons in Si as function of temperature, field strength, and field direction. Results for the longitudinal diffusion coefficient have been obtained experimentally for fields applied along 〈111〉 and 〈100〉 directions with time-of-flight and noise measurements. Calculations have been performed with the Monte Carlo procedure. The theoretical analysis, which includes an extensive discussion of the intervalley diffusion process, has yielded a revised version of the silicon model which correctly interprets both the new diffusion data and other well-established electron transport properties. The revision of the model is mainly concerned with the relative weights of f and g intervalley scattering mechanisms. In fact the interpretation of the anisotropy of the diffusion allows separate estimates of the two types of scattering through their different effects on the intervalley diffusion which comes about when electrons have different drift velocities in different valleys.
Electrical properties of epitaxial indium phosphide films grown by metalorganic chemical vapor deposition
Authors: Yang Jane J. , Ruth Ralph P. , Manasevit Harold M.
Published: February 2003

Charge transport properties of epitaxial indium phosphide films deposited on semi-insulating single-crystal InP:Fe substrates by metal-organic chemical vapor deposition were investigated by means of Hall effect and resistivity measurements made over a range of temperature from ∼420 °K down to liquid-nitrogen temperature. The activation energies characteristic of both undoped and acceptor-doped films were found from the variation of carrier concentration in the films with sample temperature. For undoped n-type InP films grown on InP:Fe substrates of the three orientations (100), (111A), and (111B) very small activation energies, ranging from 0.006 to 0.009 eV, were found, although some evidence of deeper levels was also obtained. Zn-doped and Cd-doped InP films were also characterized. The activation energy of Zn in p-type InP was 0.023 eV for (100)- and (111B)-oriented films, and Cd energies were 0.049 eV for (100)-oriented films and 0.067 eV for (111A)-oriented films.
Computation of photoconductivity in insulators in the space charge and recombination regime: Application to PbO films
Authors: Hughes R. C. , Sokel R. J.
Published: February 2003

Exact solutions for the photoconductivity of insulators with space charge (caused by deep trapping) and recombination require numerical methods for solving coupled, nonlinear differential equations. A method for obtaining computer solutions is outlined and the parameters required for fitting existing data for the photoconductor PbO are given. The carrier lifetimes are found to be much longer than previously assumed and the recombination coefficients for free with trapped carriers are found to be very large, close to diffusion controlled. The predictions for the time required to achieve steady state were found to be unexpectedly long, a result of the feedback between trapping and recombination.
Amplitude-dependent velocity of vortices in long Josephson junctions estimated from microwave-induced dc voltages
Authors: Hamasaki K. , Enpuku K. , Irie F. , Yoshida K.
Published: February 2003

The microwave-induced dc voltage in long Josephson tunnel junctions in the absence of dc bias currents is studied to obtain the velocity of a moving vortex train driven by a microwave. Detailed experiments for the induced dc voltage are carried out for the experimental configuration where the amplitude and the length of the vortex train can be controlled by the magnitudes of the applied microwave and the dc magnetic field. An analysis of the induced dc voltage is made on the basis of Whitham’s averaged Lagrangian method, which explains well the observed dependences of the induced dc voltage on the microwave power and the dc magnetic field. The velocity of the vortex train is estimated from the observed dc voltage, and is shown to be strongly dependent on the amplitude as is predicted from the theory.
The generation of acoustic harmonics by dislocation dipoles and loops
Authors: Beshers D. N. , Oppenheim Alan
Published: February 2003

The generation of acoustic harmonics by nonlinear dislocation motion is studied using several models in which the dislocations are initially bound in asymmetric potential wells from which they mas escape at large amplitudes of vibration. The models are the edge dipole, the glide loop stabilized by a center of dilation, and variants of these, each subjected to a sinusoidal stress of circular frequency ω = 2π×22.5×103 s−1; in each case inertia-like terms were negligible at this frequency. For each model we found the steady-state response by numerical integration. The corresponding dislocation strain was expressed as a Fourier series, the nth term having the form An sin(nωt−φn). We obatined the variation of the An as a function of the amplitude of the vibrational stress. Certain features are common to all the solutions: (i) for dislocations trapped in a potential well An∝An1; (ii) on escape from a well at higher amplitudes there is a peak in An/A1 and a sharp fall in An/An1; (iii) a change in the effective symmetry of the motion on escape is reflected in a change in the relative proportions of even and odd harmonics. Our results are not inconsistent with the previous theoretical work. Comparison with the available data, although hampered by the lack of a really complete set, indicates that such behavior is observed. These patterns are expected only at fairly low values of ω, such that the damping force does not overshadow the dislocation restoring force.
The dependences of electroluminescent characteristics of ZnS:Mn thin films upon their device parameters
Authors: Sasakura Hiroshi , Kobayashi Hiroshi , Tanaka Shosaku , Mita Juro , Tanaka Toshihiko , Nakayama Hirofumi
Published: February 2003

The dependences of brightness, emission efficiency η, average electric field EA, conduction current JA, and emission lifetime τ upon the device parameters such as film thickness, substrate temperature during evaporation, and Mn concentration have been systematically investigated in ZnS:Mn thin-film electroluminescent devices. The value of η increases rapidly with film thicknesses below 3000 Å but EA decreases slowly. These results can be explained by the increase of the crystallinity of the ZnS:Mn films. The value of η increases with the Mn concentration and reaches its maximum at about 0.45 wt %. At above this Mn concentration, η and τ decrease rapidly, EA increases, and JA decreases slowly. These results may be attributed to a decrease of hot electron energy and/or an increase of the nonradiative transition probability of the excited Mn centers. The brightness-voltage (B-V) hysteresis characteristic is observed in this Mn concentration region. This memory effect is also discussed.
Dependence of minority carrier diffusion length on illumination level and temperature in single crystal and polycrystalline Si solar cells
Authors: Mathur P. C. , Arora J. D. , Sharma R. P. , Saxena P.
Published: February 2003

The minority carrier diffusion length L has been measured in the intensity range 0–200 mw cm−2 in the base region of diffused junction n+p single crystal and polycrystalline Si solar cells at various ambient temperatures (77–335 K). It has been found that L increases monotonically with intensity at low temperatures in both types of cells. However, in case of single-crystal cells, it shows a peak at an intensity ∼0.4 sun for temperatures above 200 K and further decreases with the increase of intensity. The results have been interpreted in the light of various recombination mechanisms involved.
Low frequency capacitance characterizations on indium/x-phase of metal free phthalocyanine solar cells
Authors: Shing Y. H. , Loutfy R. O.
Published: February 2003

The low-frequency oscillographic capacitance measurements have been employed to characterize indium/x-phase of metal-free phthalocyanine Schottky-barrier solar cells. The capacitance-voltage relationships (1/c2 vs V) measured at various frequencies in the dark and under simulated solar illumination can be described by an approximation of two intersecting lines. The slope of these lines showed strong dependence on both frequency and light intensity. The frequency, bias potential, and light intensity dependence of the capacitance of the cell was attributed to shallow traps and deep acceptor states which have a long relaxation time. The shallow trap and deep acceptor state densities were determined to be 6.3×1016 and 2×1016 cm−3, respectively.
Triggered-avalanche detection of optical photons
Authors: Ekstrom Philip A.
Published: February 2003

In a suitably cooled and biased semiconductor diode, individual photoevents will trigger avalanche discharges which can be detected and quenched by external circuitry. The resulting triggered-avalanche detector (TAD) is a solid-state analog of the Geiger counter, and can be used to detect individual visible and infrared photons. TAD operation in commercially available silicon avalanche photodiodes was found to be limited by carrier-trapping effects to a noise-equivalent power (NEP) of 7×10−16 WHz−1/2 for continuous signals at 0.8-μm wavelength, but can achieve 7×10−18 WHz−1/2 for optimally pulsed signals. Interfering avalanches triggered by trapped carriers have been used to investigate exactly those traps which affect TAD operation in a given diode structure and material. Substantial NEP improvement is possible in diodes optimized for TAD operation. The usual requirement for disparate carrier ionization rates in avalanche diode materials does not apply to TAD operation, and a wide range of narrow-band-gap materials can be considered for infrared photon-counting detectors.
The effect of germanium ion implantation dose on the amorphization and recrystallization of polycrystalline silicon films
Authors: Komem Y. , Hall I. W.
Published: February 2003

Polycrystalline Si films have been amorphized by implantation with 130-KeV Ge ions and subsequently recrystallized by conventional heat treatment. It is found that, after amorphization with a low ion dose, recrystallization produces a structure which is morphologically similar to the original film. By contrast, after high Ge dose implantation, recrystallization proceeds dendritically. An initial rationale for this behavior is proposed in terms of the lattice disorder introduced by ion implantation.
Orientation effects on doping profiles in gallium arsenide implanted with selenium
Authors: Inada T. , Sugiyama T.
Published: February 2003

Substrate orientation effects on carrier-concentration profiles have been found for Se implantation in GaAs. Doping profiles formed in both (111)- and (100) -oriented GaAs by Se implantation are examined. For (111) samples, anomalous carrier-concentration profile is obtained near the surface when Se ions are implanted at room temperature. On the other hand, such anomality is not detected for (100) samples. Furthermore, such orientation effect is found lessened for Se implantation at 400 °C.
1/f noise in gate-controlled implanted resistors
Authors: Amberiadis K. , van der Ziel A. , Rucker L. M.
Published: February 2003

We measured 1/f noise in gate-controlled p-type implanted resistors in which the surface could be brought from accumulation to strong inversion. The noise increased by a factor of 150 when the surface was brought from accumulation to strong inversion. The results indicate strongly that the noise is due to the interaction of electrons in the inversion layer with the surface oxide. This gives rise to a fluctuating surface potential which in turn give a 1/f modulation of the surface mobility.
Detection of local heating in impact or shock experiments with thermally sensitive films
Authors: Coffey C. S. , Jacobs S. J.
Published: February 2003

Materials undergoing shock or impact loading experience heating due to that loading. This heating, frequently localized in the form of hot spots, can play a significant role in determining the physical and chemical response of the material to the load. To date this phenomenon has been inadequately investigated due to, at least in part, a lack of experimental techniques. Here we present a simple method for obtaining both spatial and temperature information of the heat generated in shocked or impact-loaded materials. We present some results showing the spatial heat patterns that result when NaCl crystals undergo impact loading.
Reply to ’’Comments on ’Normal modes of semiconductor p-n-junction devices for material-parameter determination’ ’’
Authors: Lindholm Fredrik A. , Sah C. T.
Published: February 2003

This reply provides a perspective on open-circuit voltage decay (OCVD) different from R. Muralidharan and S. C. Jain by emphasizing the connection between their work and our previous publication, and by indicating in what respects their work falls short of a complete solution.
Superconducting transition of multiconnected Josephson network
Authors: Ishida T. , Mazaki H.
Published: February 2003

The response of superconducting Tc with multiconnected structure against a small ac magnetic field is studied in terms of complex susceptibility. It has been revealed that the fundamental susceptibility χ1′−iχ1″ is very sensitive to the amplitude h0 of the ac field; i.e., the superconducting transition width is appreciably broadened as h0 increases, but the onset temperature of the transition holds its value. In addition, χ1″ with respect to temperature has an asymmetric peak. We propose a phenomenological model on the assumption that the multiconnected network behaves like a single loop as a whole due to the coherent nature of the specimen. It has been revealed that the main features of observed characters are well reproduced by this model. Since our model predicts higher harmonics in susceptibility, the third harmonic response of the specimen against a small ac magnetic field is also studied. Measurements with respect to temperature are simultaneously performed for the amplitude of third harmonic susceptibility ‖χ3‖ and χ1″. Observations show that ‖χ3‖ is proportional to χ1″ and forms a peak in the temperature region of the superconducting transition. This finding is in good agreement with our prediction from the weakly connected loop model. Peculiar instability in susceptibility curves of transition (h0≳2 Oe) is first observed.
Melting phenomena and pulsed-laser annealing in semiconductors
Authors: Narayan J. , Fletcher J. , White C. W. , Christie W. H.
Published: February 2003

Annealing of displacement damage (amorphous as well as layers containing only dislocation loops), dissolution of boron precipitates, broadening of dopant profiles, and the formation of constitutional supercooling cells have been studied in laser annealed silicon. These samples were irradiated with laser pulses (λ = 0.485 μm, E = 0.7–1.25 J cm−2, τ = 9 ns), the same as those used by Compaan and coworkers for Raman temperature measurements. In contrast to their conclusion, present results can be interpreted only on the basis of a melting model.
Temperature dependence of amplitude-dependent dislocation damping
Authors: Granato A. V. , Lücke Kurt
Published: February 2003

A theory of the damping due to the break-away of dislocations from pinning points given by the authors for low temperatures has been extended into the high-temperature range by taking into account thermal activation during break-away. It has been found that in the high-temperature range the amplitude dependence is described by the same formula as in the low-temperature range (Granato-Lücke formula) but the parameters have a different meaning.
Internal friction background and peaking effect
Authors: Caro J. A. , Mondino M.
Published: February 2003

Internal friction results on poly- and single-crystalline samples of 5 N Cu during irradiation at 350 K with 1.5 MeV electrons are presented. It is found that the peaking effect is a function of the total number of point defects created in the lattice and that it is independent of the frequency in the range 102–105 Hz. The amplitude dependence of peaking is shown to be related to the background amplitude dependence. Pulsed irradiation experiments indicate that no diffusion mechanism is involved in the initial increase of internal friction. It is then concluded that peaking is due to two effects, one from the bulk, responsible for the increase and the second, associated to the arrival of point defects at the dislocations and reducing their contribution to damping. The observation of peaking in single crystals at ε?10−6 indicates that sample structure only influences the strain amplitude level at which peaking appears but not its presence. A comparison with existing models allows one to conclude that a lattice dynamics approach provides the most satisfactory description of present results.
Characteristics of submicron pores obtained by chemical etching of nuclear tracks in polycarbonate films
Authors: Guillot G. , Rondelez F.
Published: February 2003

Calibrated pores in the range 102–2×103 Å have been obtained by chemical etching of polycarbonate thin films irradiated with high energy krypton ions (500 MeV, Kr25+). Both the amorphous and the crystalline forms of polycarbonate (Makrofol, Bayer), further designated by their respective trade names N and KG, have been investigated up to thicknesses of 60 μm, close to the theoretical ion range of 77 μm. From conductivity studies, three different domains have been separated around the ion track: A highly damaged core of radius ?50 Å with a fast etching rate vT ≊104 Å/min, an intermediate zone of radius ?500 Å with an etching rate vI = 0.9 Å/min, an outer region with an etching rate equal to that of the undamaged material, vG = 0.47 Å/min. These observations are compatible with the delta ray model for track formation in plastic materials. Scanning electron microscope investigations have revealed that the pores formed in the N material are straight cylinders with a narrow distribution of the pore entrance diameters. On the other hand, the pores for the KG type are much less uniform and appear to be tapered, the difference between the two sides of the membrane being as much as 50%. These characteristics could be related to inhomogeneities in the morphological structure due to (i) the finite size of the crystalline domains and (ii) an asymetric manufacturer’s processing of the film surfaces.
Polymorphic transitions in single crystals: A new molecular dynamics method
Authors: Parrinello M. , Rahman A.
Published: February 2003

A new Lagrangian formulation is introduced. It can be used to make molecular dynamics (MD) calculations on systems under the most general, externally applied, conditions of stress. In this formulation the MD cell shape and size can change according to dynamical equations given by this Lagrangian. This new MD technique is well suited to the study of structural transformations in solids under external stress and at finite temperature. As an example of the use of this technique we show how a single crystal of Ni behaves under uniform uniaxial compressive and tensile loads. This work confirms some of the results of static (i.e., zero temperature) calculations reported in the literature. We also show that some results regarding the stress-strain relation obtained by static calculations are invalid at finite temperature. We find that, under compressive loading, our model of Ni shows a bifurcation in its stress-strain relation; this bifurcation provides a link in configuration space between cubic and hexagonal close packing. It is suggested that such a transformation could perhaps be observed experimentally under extreme conditions of shock.
A helical transversely excited copper bromide laser
Authors: Krahn K.-H.
Published: February 2003

The construction and successful operation of a helical transversely excited copper bromide laser is reported. Satisfactory laser performance has been obtained over a wide range of discharge parameters. As a consequence of the helical electrode geometry, the copper laser-beam cross section is circular symmetric and exhibits a radial energy profile that is near to Gaussian.
Relative influence of hydrogen/deuterium donors and driving circuit parameters on the performance of a uv preionized pulsed HF/DF laser
Authors: Marchetti R. , Penco E. , Salvetti G.
Published: February 2003

The influence of the preionizer and initiating discharge circuit parameters on the performance of a UV preionized pulsed HF/DF chemical laser with relatively low active volume (about 20 cm3) has been investigated. The laser has been operated with gas mixtures of SF6 and H2, C2H6, and D2 at pressures ?90 Torr, giving laser output energies up to ∼70 mJ with a maximum efficiency of about 2.2%. We observed that the insertion of a peaking capacitor bank across the main discharge gap strongly affected the laser output characteristics. The laser output energy was seen to vary with the capacitance of the peaking capacitor bank, whose influence is a function of the SF6 partner in the laser mixture, the gas pressure, and the input energy density into the discharge.
Ion response to plasma excitation frequency
Authors: Bruce R. H.
Published: February 2003

The time dependence of the potential distribution in a parallel plate discharge is discussed in terms of a model which indicates the plasma potential oscillates with the applied voltage only over the positive part of the cycle. Measurements of this oscillation have been made, and the response of the ions to the oscillating field has been studied as a function of excitation frequency.
The initial growth of gold on surfaces of oxidized silicon
Authors: Andersson T. G.
Published: February 2003

The initial growth of gold on oxidized silicon has been studied by Auger electron spectroscopy and reflection high-energy electron diffraction. Below 0.4 monolayer (ML) coverage the gold atoms were dispersed on the surface. Thereafter 2D domains dominated the growth up to 3 ML coverage where the bulk Auger signal was fully developed. A very small deficiency of metal was observed at the initial growth which might be an intermixing. For high coverages, 30 ML, a splitting of the Si (L2,3VV) transition was observed indicating silicide formation.
Electrochemical sulfur doping of GaAs grown by molecular beam epitaxy
Authors: Davies G. J. , Andrews D. A. , Heckingbottom R.
Published: February 2003

A novel method of intentionally doping molecular beam epitaxy grown GaAs n- type is described. The donor atoms are sulfur, from a beam of S2, generated in a low temperature (200 °C), electrochemical Knudsen cell. The galvanic cell is Pt/Ag/AgI/Ag2S/Pt, where the flow of current through the cell, with the positive pole at the Ag2S is a measure of the sulfur flux effusing from the cell. Net carrier concentrations n between ∼1015 and ∼1018 cm−3 have been obtained. There is no detectable accumulation of S at the surface for high donor concentrations (∼1018 cm−3) in the bulk. This novel method of sulfur generation has a particularly fast (<1 sec) response time—much faster than the thermal equilibration times of conventional thermal Knudsen sources. Complicated doping profiles are shown to be produced relatively easily with a single doping source using this technique. Free-electron mobilities μ300 K = 6000 cm2/V sec and μ77 K = 17 000 cm2/V sec have been obtained for sulfur doped layers with n = 1.1016 cm−3.
Electron beam-induced current in direct band-gap semiconductors
Authors: Akamatsu B. , Hénoc J. , Hénoc P.
Published: February 2003

Monte Carlo calculations are used to compute the generated electron–hole pair distribution and the electron beam-induced current in order to determine the minority carriers diffusion lengths when an electron beam probes a semiconductor specimen in the neighborhood of a p-n junction. It is shown that with direct band-gap semiconductor materials, such as GaAs, the current generated by the reabsorbed recombination radiation must be taken into account. Its contribution can be evaluated by comparison with the cathodoluminescence signal. Three GaAs devices of different doping level are checked. Plots of computed induced current versus probe position for a GaAs p-n junction are presented.
Capture and release of electrons on Na+-related trapping sites in the SiO2 layer of metal-oxide-semiconductor structures at temperatures between 77 and 296 °K
Authors: DiMaria D. J.
Published: February 2003

Electron trapping and detrapping mechanisms on Na+ ions near the Si-SiO2 interface of metal-oxide-semiconductor (MOS) structures and the location of these captured electrons were studied as a function of temperature from 77° to 296 °K. Capacitance-voltage and photocurrent-voltage techniques have been used to show directly that the charge neutralization on the Na+ ions takes place spatially in the immediate vicinity of the ions near the Si-SiO2 interface. Experiments reported here indicated that Na+ ions neutralized at 77 °K by electron capture do not become charged again even under negative voltage stressing conditions if the sample is heated to 296 °K. This applies if the initial areal density of Na+ ions near the Si-SiO2 interface is less than ≊3.7×1012 cm−2. For densities greater than ≊3.7×1012 cm−2, Na+ motion back to the Al-SiO2 interface under negative voltage bias can be observed due to incomplete neutralization. Other experiments have shown that the electron capture process on Na+ related sites (with capture cross sections of 2×10−19 and 5×10−20 cm2) decreases with increasing temperature as the MOS is warmed from 77 °K and stops at ≊158 °K. However, electron capture resumes again when the sample is cooled. This phenomenon appears to depend somewhat on local electric fields near the Si-SiO2 interface and is reversed (trapping increases with temperature) for large initial Na+ ion densities (≊6.1×1012 cm−2). Several models are discussed which are consistent with the overall picture for the neutralization process, and a comparison of this work to the studies by others of the effect of Na+ on inversion layer electrons is made.
The open circuit potential in solar cells
Authors: Khan Shahed U. M. , Bockris John O′M.
Published: February 2003

The relation between Vonset and V0rev in photoelectrochemical situations with p-type semiconductors is considered. The model assumes high surface-state concentration on the semiconductor surface and exchange of electrons between states at the bottom of the conduction band and those in the vibration/rotation levels of the solvated ions. The proposed model gives fair numerical agreement with the experimentally observed: Vonset−V0rev?Constant?0.4 V.
Field-dependent transport through the depletion layer of a semiconducting electrode
Authors: Thomchick John , Buoncristiani A. M.
Published: February 2003

We extend the results of a previous paper dealing with the transport of photo-generated excess charge carriers in a semiconducting electrode by including an explicit dependence on the mean electric field in the depletion layer. A general equation for the flux reaching the electrode surface is derived, and limiting expressions giving the electric field dependence of the quantum yield in both the low field and high field cases are obtained. The relation between these limiting expressions and results based on other models of the charge transport are discussed. A specific advantage of the present approach is that it describes the transport in terms of microscopic scattering and recombination probabilities whose dependence upon the field is specified.
A new structure for a semiconductor-insulator-semiconductor solar cell
Authors: Sen K. , Srivastava R. S.
Published: February 2003

A new structure [S(p+n)IS] is considered for a semiconductor–insulator–semiconductor solar cell. Theoretical considerations predict that the open circuit voltage and efficiency of this structure can be much higher than the [S(n+)IS] type solar cells. Calculations show that for [S(p+n)IS] structure the maximum attainable efficiency and open circuit voltage are of the order of 30% and 1.3 V, respectively.
Photoionization cross section of electron traps in silicon nitride films
Authors: Bibyk Steve B. , Kapoor Vikram J.
Published: February 2003

The internal photoemission and flatband voltage monitored trap-photodepopulation technique has been used to investigate the first order kinetics of trap emptying in the low pressure chemically vapor-deposited thin film of Si3N4 of an Al-Si3N4-SiO2-Si capacitor structure. An effective photoionization cross section associated with a 3.0-eV deep electron trapping center in the bandgap of the Si3N4 film was determined to be 0.3–1.7×10−19cm2 over the photon energy range 2.0–3.4 eV.