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Journal of Applied Physics

Issue 12 • Date Jun 1999

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Displaying Results 1 - 25 of 78
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Near infrared excited micro-Raman spectra of 4:1 methanol–ethanol mixture and ruby fluorescence at high pressure

    Page(s): 8011 - 8017
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    Near infrared (NIR) lasers, as a new excitation source for Raman spectroscopy, has shown its unique advantages and is being increasingly used for some special samples, such as those emitting strong fluorescence in the visible region. This article focuses on some issues related to high-pressure micro-Raman spectroscopy using NIR excitation source. The Raman spectra of 4:1 methanol–ethanol mixture (4:1 M–E) show a linear variation in both Raman shifts and linewidths under pressure up to 18 GPa. This result is useful in distinguishing Raman scattering of samples from that of the alcohol mixture, an extensively used pressure-transmitting medium. The R1 fluorescence in the red region induced by two-photon absorption of the NIR laser is strong enough to be used as pressure scale. The frequency and line width of the R1 lines are very sensitive to pressure change and the glass transition of the pressure medium. Our results manifest that it is reliable and convenient to use NIR induced two-photon excited fluorescence of ruby for both pressure calibration and distribution of pressure in the 4:1 M–E pressure transmitting medium. © 1999 American Institute of Physics. View full abstract»

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  • Thermosetting enhancement of the light-induced polar orientation stability of molecules in polymers

    Page(s): 8018 - 8022
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    Two kinds of polymers with disperse red 19 pendant groups, a thermal-imidization polyimide and a thermal-crosslinking polyurethane, were used in thermal-assisted optical poling to improve the photostability of the optically induced polar orientation of molecules. During the seeding process, samples heated in an oven were irradiated simultaneously by the coherent superposition of the 1064 nm fundamental and the 532 nm second-harmonic light of a nanosecond-pulsed Nd:YAG laser. The second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature even under illumination of the intense 1064 nm fundamental light. The nonlinear optical coefficient d33 was estimated to be 6.9 pm/V for the azopolyimide film and 12.7 pm/V for the azopolyurethane film, respectively. Experimental results indicated that the optically aligned azodye molecules were fixed by the thermosetting polymer matrix during the thermal-assisted optical poling process. © 1999 American Institute of Physics. View full abstract»

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  • Macro- and microstress analysis in sol-gel derived Pb(ZrxTi1-x)O3 thin films

    Page(s): 8023 - 8031
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    Thin films of Pb[(ZrxTi1-x)1-yMey]O3 (Me=Al, Nb) (abbreviated PZT) have been prepared by spincoating of material synthesized by a sol-gel method. In accordance with the widely used arrangement for ferroelectric random access memories, the following layer sequence served as substrate: Si(100)/SiO2/Ti/Pt. Surface profilometry has been used to characterize the macrostresses in the films. Microstresses have been determined on the basis of grazing incidence x-ray diffraction profiles evaluated by the Warren–Averbach algorithm. The macrostress behavior of the PZT thin films is independent of the doping species, whereas the determined microstress behavior strongly depends on doping species aluminum or niobium and the dopant concentration. Furthermore, the general applicability of grazing incidence x-ray diffraction measurements in combination with microstress determination following the Warren–Averbach method has been proven. © 1999 American Institute of Physics. View full abstract»

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  • Growth mechanism of hydrogenated amorphous silicon studied by in situ scanning tunneling microscopy

    Page(s): 8032 - 8039
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    In situ scanning tunneling microscopy has been used to study the evolution of the surface topography of the growing surface of hydrogenated amorphous silicon (a-Si:H) in order to understand its growth mechanism. The surface is found to possess an island-like structure and the island diameter is found to increase with increasing growth temperature. A Fourier analysis of the surface roughness has an exponent of i=1.17. A comparison of the roughness of films of different thickness gives a dynamic scaling exponent of β=0.28, but the films are not particularly self-affine in character. It is argued that the exponent i is not evidence of a viscous flow regime, but that nonstochastic growth of a random network occurs, caused by a preferential hydrogen abstraction at kink-like and step-like surface sites. A simple simulation of the topography is used to support this conclusion. © 1999 American Institute of Physics. View full abstract»

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  • Structural modifications in ion-implanted silicate glasses

    Page(s): 8040 - 8049
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    The structural modifications induced in fused silica and soda-lime glasses by implantation (argon, nitrogen) have been studied using step-height profilometry, Rutherford backscattering spectrometry, transmission electron microscopy, and scanning electron microscopy. The step-height measurements indicated a transformation in structure (-ΔL to +ΔL) at energy depositions on the order of 1023keV/cm3 for both fused silica and soda-lime glasses. This change modifies the three-membered ring structure in fused silica initiated by the lower deposition energy of 1–2×1020keV/cm3. The Rutherford backscattering spectrometry measurements show the initiation of the new structure by changes in the argon peak and a spreading of the argon to greater depths. The scanning and transmission electron microscopy measurements are complementary to these changes. The data presented can be understood in terms of ion-implantation induced stress. © 1999 American Institute of Physics. View full abstract»

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  • Correlation of diffuse scattering with nanocrystallite size in porous silicon using transmission microscopy

    Page(s): 8050 - 8053
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    We use high resolution cross sectional transmission electron microscopy to image the nanostructure of (100) p-type porous Si. A network of pore tracks subdivide the material into nano-islands and nanocrystallites are resolved throughout the material. With distance from the substrate, electron diffraction develops noncrystalline-like diffuse patterns that dominate the coherent scattering in the topmost luminescent layer. Also, with distance from the substrate, crystalline islands evolve such that their size drops to as small as 1 nm in the topmost luminescence material. Although the topmost luminescent layer is very rich in nanocrystallites, it has the strongest diffuse scattering of all regions. This confirms that diffuse scattering is due to size reduction effects rather than to an amorphous state. © 1999 American Institute of Physics. View full abstract»

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  • Ultrashallow thermal donor formation in silicon by annealing in ambient oxygen

    Page(s): 8054 - 8059
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    Czochralski-grown silicon wafers doped with phosphorus (∼1014 cm-3) have been annealed in nitrogen, wet nitrogen, oxygen, argon, and vacuum ambients at 470 °C for times up to 500 h. Sample characterization was made using predominantly electrical techniques such as admittance spectroscopy and thermally stimulated capacitance measurements but also secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy were employed. In all samples, an increasing concentration of free carrier electrons is observed with increasing annealing time, reaching a maximum of ∼1016 cm-3 at 100 h. For durations in excess of 100 h gradual decrease of the free electron concentration takes place except for the samples treated in wet nitrogen and oxygen atmospheres, which display donors stable even after 200 h. These stable centers are found to have shallower donor level positions in the energy band gap (∼25 meV below the conduction band edge Ec) than those of the centers formed in vacuum, argon, and nitrogen atmospheres (∼35 meV below Ec). The latter centers are associated with the well-established shallow thermal donors (STDs) while the origin of the former ones, which are labeled ultrashallow thermal donors (USTDs) is less known. However, on the basis of a wealth of experimental results we show that the USTDs are most likely perturbated STDs modified through interaction with fast-in diffusing oxygen species, possibly oxygen dimers. Further, comparison between the electrical data and the SIMS measurements reveals unambiguously that neither the STD nor the USTD centers involve nitrogen, in contrast to recent suggestions in the literature. © 1999 American Institute of Physics.   View full abstract»

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  • Response of boron carbide subjected to large strains, high strain rates, and high pressures

    Page(s): 8060 - 8073
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    This article presents an analysis of the response of boron carbide (B4C) to severe loading conditions that produce large strains, high strain rates, and high pressures. Experimental data from the literature are used to determine and/or estimate constants for the JH-2 constitutive model for brittle materials. Because B4C is a very strong material, it is not always possible to determine the constants explicitly. Instead they must sometimes be inferred from the limited experimental data that are available. The process of determining constants provides insight into the constitutive behavior for some loading conditions, but it also raises questions regarding the response under other loading conditions. Several Lagrangian finite element and Eulerian finite difference computations are provided to illustrate responses for a variety of impact and penetration problems. © 1999 American Institute of Physics. View full abstract»

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  • Shoulder at the 887 cm-1 infrared band in neutron irradiated Si

    Page(s): 8074 - 8078
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    Infrared spectroscopy was used to study the 887 cm-1 band in neutron irradiated Czochralski-grown silicon arising in the spectra upon annealing of the 830 cm-1 band of the VO defect. Our analysis showed the presence of a 884 cm-1 shoulder in the region of the 887 cm-1 infrared band. The 887 cm-1 band is generally attributed to the VO2 defect formed by the capture of a mobile VO center by an oxygen interstitial impurity. In our study the shoulder at 884 cm-1 is tentatively correlated with the V3O defect. Semiempirical calculations carried out for the vibrational frequency of V3O structure gave a value at 883 cm-1 thus corroborating the latter assignment. This new picture of the spectra in the range of the 887 cm-1 band could explain some so far unaccounted for experimental findings previously reported in literature. © 1999 American Institute of Physics. View full abstract»

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  • An approach to the defect structure analysis of lithium niobate single crystals

    Page(s): 8079 - 8082
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    A formula for calculating the soft mode frequency and Curie temperature (using ion mass, charge, and the distances between them) was applied to the analysis of the defect structure of nonstoichiometric lithium niobate. Four compositions from near stoichiometric to highly Li2O deficient, including congruent, were studied. The Curie temperatures were calculated for three possible types of defects: (1) oxygen vacancies, (2) niobium vacancies, and (3) lithium vacancies. A comparison between the calculated and experimental values showed that the oxygen and niobium vacancy models did not agree with experimental data. Good quantitative agreement between the calculated and experimental data for the lithium vacancy model allowed us to conclude that this model best describes the defect structure of nonstoichiometric lithium niobate LiNbO3. © 1999 American Institute of Physics. View full abstract»

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  • Characterization of lead zirconate titanate piezoceramic using high frequency ultrasonic spectroscopy

    Page(s): 8083 - 8091
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    Doped piezoceramic lead zircanate titanate has been characterized in the frequency range of 20–60 MHz using ultrasonic spectroscopy. Theoretical analyses were performed for the reflection and refraction of acoustic waves at the interface of water-piezoelectric ceramic. The incident directions of the wave were chosen to be appropriate for ultrasonic spectroscopy measurements. Shear wave spectrum was obtained through mode conversion using a pair of longitudinal transducers submerged in water. The phase velocity shows linear dependence on frequency while the attenuation may be described by a second order polynomial of frequency in the frequency range investigated. The Kramers–Kronig relation between ultrasonic phase velocity and attenuation was compared to measured results. © 1999 American Institute of Physics. View full abstract»

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  • Energy-dispersive x-ray diffraction and Raman scattering of Zn1-xMnxSe bulk crystals at high pressure

    Page(s): 8092 - 8096
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    Energy-dispersive x-ray diffraction experiments were carried out to investigate the structure of phase transitions under high pressure. It was found that the zinc blende (B3) to rock salt (B1) phase transition pressures of Zn0.93Mn0.07Se and Zn0.76Mn0.24Se bulk crystals are found 11.8±1.5 and 9.9±0.5 GPa, respectively. The respective bulk moduli are 61.8±0.8 and 60.5±0.8 GPa. The pressure-induced zinc blende (ZB) to rock salt (RS) structure phase transition is interpreted as a signature of the semiconductor to metal transition for Zn1-xMnxSe. The above interpretation is further corroborated by the observation of the disappearance of the longitudinal optical phonon at the pressure where the ZB to RS structure transition occurs. © 1999 American Institute of Physics. View full abstract»

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  • Oxygen precipitation in silicon: Experimental studies and theoretical investigations within the classical theory of nucleation

    Page(s): 8097 - 8111
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    Quantitative measurements of the oxygen precipitate rate as a function of annealing were made in Czochralski-grown silicon wafers that contained different initial concentrations of oxygen. All wafers were annealed at 1000 °C for 15 min to ensure that the initial cluster-size distributions were identical in all samples of the same composition prior to the multi-step annealing treatments used for the precipitation studies. The experimental data are compared with numerical predictions for time-dependent nucleation within the classical theory of nucleation. Quantitative agreement is obtained between the measured and calculated densities of oxygen precipitates for nucleation temperatures greater than 600 °C, but only over a narrow range of oxygen composition. Below 600 °C, the measured density for all samples is orders of magnitude larger than is predicted from the model. Further, the measured data show an anomalously small temperature dependence for the induction time for nucleation that does not scale with the diffusion coefficient, as expected from the classical theory of nucleation. Fundamentally, the classical theory of nucleation cannot explain the time-dependent nucleation of oxygen precipitates for temperatures below 650 °C. A possible reason is given. © 1999 American Institute of Physics. View full abstract»

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  • Nd2O3 doped low silica calcium aluminosilicate glasses: Thermomechanical properties

    Page(s): 8112 - 8118
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    The effects of Nd2O3 doping on the thermal and mechanical properties of vacuum melted, low silica, calcium aluminosilicate glasses are presented. For the doped glasses, the vitrification limit was found to correspond to a maximum load of 5 wt % Nd2O3. The influence of the rare earth doping on the thermal diffusivity, thermal conductivity, and Vickers hardness was such that all these physical parameters decreased by roughly the same amount, namely 8%, between the undoped and the 5 wt % doped sample. The dependence of these parameters, as a function of the Nd2O3 doping, strongly supports the idea that the Nd3+ act as network modifiers. © 1999 American Institute of Physics.   View full abstract»

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  • Tracer diffusion and mechanism of non-Arrhenius diffusion behavior of Zr and Nb in body-centered cubic Zr–Nb alloys

    Page(s): 8119 - 8130
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    Tracer diffusion of 95Zr and 95Nb has been measured in a set of β-Zr-Nb alloys (Zr-5.5 at. % Nb, Zr-16.3 at. % Nb, and Zr-28.1 at. % Nb) in a wide temperature range from 1035 to 1871 K. All experimental concentration profiles revealed a Gaussian-like behavior over two to three decades in logarithm of concentrations. Experimental data were analyzed in terms of the Manning’s random alloy model and the partial correlation factors were calculated as functions of temperature. The partial correlation factors vary smoothly over the whole temperature range, whereas the diffusivity shows a pronounced curvature of the Arrhenius plots. A correlation was found between the degree of deviation from the Arrhenius behavior of the diffusion coefficients of both components and the lattice dynamics features of the measured phonon dispersions in their dependence on the Nb content in these alloys. The temperature dependence of the isotope effect parameter E of Zr diffusion was measured in the Zr-5.5 at.% Nb alloy. E essentially increases with temperature and the energy transfer factor ΔK deduced for the alloy was found to be somewhat larger than the corresponding values for pure β-Zr, especially at low temperatures. The whole set of experimental data leads to the conclusion that only one diffusion mechanism—the vacancy mechanism—is operating in the whole investigated temperature range. © 1999 American Institute of Physics. View full abstract»

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  • Numerical study of diffusion coefficient measurements with sinusoidal varying accelerations

    Page(s): 8131 - 8136
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    The effect of periodic gravitational acceleration on diffusion coefficient measurements was analyzed in terms of material properties in the specimen such as viscosity, density, and specimen configuration. We found that convection is induced in microgravity with sinusoidal varying accelerations because a concentration difference exists even under isothermal conditions. g-jitter with lower frequency produced large error in the accuracy of the diffusion coefficient measurement. The errors increased abruptly with a decrease in the frequency below 0.1 Hz. The error increased monotonously with a decrease in the density ratio of elements in diffusion materials. In order to obtain optimized experimental conditions for experiment planning, the predicted error due to gravitational disturbances was plotted as a function of material properties such as the viscosity, the density ratio, and the specimen configuration. © 1999 American Institute of Physics. View full abstract»

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  • Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon

    Page(s): 8137 - 8144
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    We present a physically based modeling of the transient enhanced diffusion (TED) of boron implanted into preamorphized silicon. We start by describing the nucleation and growth of a supersaturation of Si interstitial atoms into dislocation loops. Our modeling of the nucleation and growth of the dislocation loops is divided into three distinct stages: the nucleation, the “pure growth,” and the Ostwald ripening. The implementation of this modeling into the process simulator IMPACT-4 allows one to correctly predict the size and density evolutions of the dislocation loops observed by transmission electron microscopy for a variety of annealing times and temperatures. This simulation also gives access to the concomitant behavior of the free Si interstitials atoms responsible for TED. Implementation of this model into IMPACT-4 shows that TED in preamorphized Si can be simulated for a variety of experimental conditions by assuming boron diffusion occurs through the coupling of boron atoms with this fast evolving supersaturation. It is shown that while not affecting too much the defect evolution itself, the value of the recombination velocity at the surface is a crucial parameter to correctly estimate the amount of TED after a given annealing. Best fits are obtained for recombination lengths of about 16 nm for annealing under Ar gas. © 1999 American Institute of Physics. View full abstract»

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  • Threshold stress behavior in thin film electromigration

    Page(s): 8145 - 8154
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    Thin film electromigration is simulated using simple models for constitutive relations. Inhomogeneities in the mass deposition and stress fields can explain many features of the phenomenon. They imply that the threshold stress depends on the thin film microstructure and texture. The vacancy Z* parameter derived from the Blech threshold is increased in magnitude, in better agreement with experiments than earlier estimates. The predicted transient vacancy flux displays shorter decay times than the commonly used stress model, possibly in better agreement with experiment below threshold. Finally, nonlinear stress–strain relations are shown to be consistent with the behavior that is seen above threshold in passivated and unpassivated interconnects. © 1999 American Institute of Physics. View full abstract»

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  • Elasticity of ultrathin copper-phthalocyanine Langmuir–Blodgett films by picosecond ultrasonics

    Page(s): 8155 - 8159
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    The picosecond ultrasonic technique is used to investigate the elasticity of Langmuir–Blodgett submicronic films of copper (II) octabutoxyphthalocyanine. The amplitude of the acoustic echoes is measured against the number of monolayers (1–24, i.e., from a pure bidimensional behavior to a tridimensional one). The longitudinal sound velocity and the ultrasonic attenuation for frequencies up to about 40 GHz are deduced from this behavior. For the thinnest samples, the acoustic echoes are observed with a delay whose origin is analyzed. We show that the accuracy of the method is only limited by the precise knowledge of the density of the material. © 1999 American Institute of Physics. View full abstract»

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  • Zn0.85Cd0.15Se active layers on graded-composition InxGa1-xAs buffer layers

    Page(s): 8160 - 8169
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    We investigated the structural and optical properties of Zn0.85Cd0.15Se epilayers for blue optical emission on lattice-matched InxGa1-xAs buffer layers. Both the II–VI layers and the III–V buffers were grown by molecular beam epitaxy on GaAs(001) wafers. A parabolic In concentration profile within the graded-composition InxGa1-xAs buffers was selected to control strain relaxation and minimize the concentration of threading dislocations. Dislocation-free II–VI growth was readily achieved on the graded buffers, with a Rutherford backscattering yield ratio reduced by a factor of 3 and a deep-level emission intensity reduced by over two orders of magnitude relative to those observed following direct II–VI growth on GaAs. The surface morphology of the materials, however, was found to replicate the crosshatched pattern of the underlying InxGa1-xAs substrates. © 1999 American Institute of Physics. View full abstract»

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  • Electric field induced surface modification of Au

    Page(s): 8170 - 8177
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    We discuss the role of localized high electric fields in the modification of Au surfaces with a W probe using the interfacial force microscope. Upon bringing a probe close to a Au surface, we measure both the interfacial force and the field emission current as a function of separation with a constant potential of 100 V between tip and sample. The current initially increases exponentially as the separation decreases. However, at a distance of less than ∼500 Å, the current rises sharply as the surface begins to distort and rapidly close the gap. Retraction of the tip before contact is made reveals the formation of a mound on the surface. We propose a simple model, in which the localized high electric field under the tip assists the production of mobile Au adatoms by detachment from surface steps, and a radial field gradient causes a net flux of atoms toward the tip by surface diffusion. These processes give rise to an unstable surface deformation which, if left unchecked, results in a destructive mechanical contact. We discuss our findings with respect to earlier work using voltage pulses in the scanning tunneling microscope as a means of nanofabrication. © 1999 American Institute of Physics. View full abstract»

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  • Impact ionization rate calculations in wide band gap semiconductors

    Page(s): 8178 - 8185
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    An algorithm for calculating impact ionization rates in the semiclassical Fermi’s Golden Rule approximation which is efficient close to threshold is presented. Electron and hole initiated rates are calculated for three semiconductors with particular band structure characteristics, as are the distributions of the generated carriers. Simple analytic expressions of the form R=A(E-E0)P are fitted to the calculated rates. The role of the matrix elements in influencing the distribution of final states is investigated. In the direct gap materials, they act to significantly enhance the low-q transitions, while in the indirect gap case they have a lesser effect on the distribution. Results for GaAs obtained here and by several other workers are compared and possible causes of the discrepancies examined, including differences in band structure and approximations made in evaluation of the matrix element. It is found that these differences do not influence the rate sufficiently to account for the wider variation between authors, and so it is concluded that differences in the implementation of the rate integration algorithm are the main cause. © 1999 American Institute of Physics. View full abstract»

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  • Characteristics of impact ionization rates in direct and indirect gap semiconductors

    Page(s): 8186 - 8192
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    Impact ionization rates for electrons and holes in three semiconductors with particular band structure characteristics are examined to determine underlying factors influencing their qualitative behavior. The applicability of the constant matrix element approximation is investigated, and found to be good for the indirect gap material studied, but overestimates threshold softness in the direct gap materials. The effect that final states in the Γ valley have in influencing characteristics of the rate in the direct gap materials is investigated, and it is found that they play a significantly greater role than the low density of Γ valley states would suggest. The role of threshold anisotropy in affecting threshold softness is examined, and it is concluded that it plays only a small part, and that softness is controlled mainly by the slow increase in available phase space as the threshold energy is exceeded. © 1999 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory