Showing papers in "Journal of Applied Physics in 1982"

Semiconducting and other major properties of gallium arsenide

Abstract: This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

Model for solute redistribution during rapid solidification

Abstract: A microscopic model for impurity uptake at a sharp crystal‐liquid interface during alloy solidification is presented in terms of the bulk properties of the liquid and solid phases. The results for stepwise growth and continuous growth at the same interface velocity differ quantitatively but exhibit the same qualitative features. A transition from equilibrium segregation to complete solute trapping occurs as the velocity surpasses the diffusive speed of solute in the liquid. The location of the transition varies little with equilibrium segregation coefficient, and a kinetic limit to solute trapping is found to be quite unlikely. Comparison is made with other models; critical differences are pointed out. Coupled with a growth velocity equation and with macroscopic heat‐ and solute‐diffusion equations, the model forms a complete description of one‐dimensional crystal growth. The steady‐state solution to this system is indicated for the case of a planar interface. The results are applied to describe regrowth from laser‐induced melting. Preliminary comparison with experiment is made. The steady‐state solution for thermal and impurity transport is suggested for use whenever detailed computer calculations are unavailable or are unnecessarily involved.

Efficiency of hot-carrier solar energy converters

Abstract: A single‐threshold quantum‐utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite‐threshold device. Such a hot‐carrier flat‐plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.

Charge collection scanning electron microscopy

Abstract: This review encompasses the application of the scanning electron microscope to the study and characterization of semiconductor materials and devices by the Electron Beam Induced Conductivity (EBIC) method. In this technique, the charge carriers generated by the electron beam of the microscope are collected by an electric field within the material and sensed as a current in an external circuit. When employed as the video signal of the SEM, this collected current image reveals inhomogeneities in the electrical properties of the material. The technique has been used to determine carrier lifetime, diffusion length, defect energy levels, and surface recombination velocities. Charge collection images reveal the location of p‐n junctions, recombination sites such as dislocations and precipitates, and the presence of doping level inhomogeneities. Both the theoretical foundation and the practical aspects of these effects are discussed in a tutorial fashion in this review.

Material parameters of In1−xGaxAsyP1−y and related binaries

Abstract: Various models for calculation of physical parameters in compound alloys are discussed and the results for In1−x Gax Asy P1−y quaternaries are presented. The model used is based on a linear interpolation scheme, and therefore necessitates known values of the parameters for the related binary and ternary alloys. The material parameters considered in the present study can be classified into the following eleven groups: (1) lattice constant and crystal density, (2) thermal expansion coefficient, (3) electronic‐band structure, (4) external perturbation effect on the lowest‐direct gap, (5) effective mass, (6) dielectric constant, (7) Frohlich coupling parameter, (8) elastic properties, (9) piezoelectric properties, (10) deformation potential, and (11) excitonic effect. Of particular interest is the deviation of material parameters from linearity with respect to the alloy composition. It is found that the present model provides generally acceptable parameters, in good agreement with the existing experimental da...

Energy gap versus alloy composition and temperature in Hg1−xCdxTe

Abstract: We have used the data from 22 different studies to derive a new empirical expression for the energy band gap (Eg) of Hg1−xCdxTe: Eg =−0.302+1.93x+5.35(10−4)T(1−2x) −0.810x2+0.832x3. This expression is valid over the full composition range and for temperatures from 4.2 to 300 K. The standard error of estimate is 0.013 eV, which is at least 15% better than that of previously reported expressions.

Conductivity behavior in polycrystalline semiconductor thin film transistors

Abstract: CdSe thin film transistor (TFT) structures which have been ion implanted with 50 keV 52Cr, 50 keV 27Al, or 15 keV 11B have a very steeply rising conductivity above some threshold dose and exhibit modulated transistor characteristics over certain ranges of implant dose, even though there is no thermal annealing during or after ion implantation. These results are interpreted using a model based on grain boundary trapping theory. The dependence of leakage current on implant dose, and of drain current (at a fixed dose) on gate voltage are described very well by this model, when the drain voltage is very small. Using this simple model, the important parameters of the polycrystalline CdSe film, namely the trap density per unit area in the grain boundary, the donor density, grain size, and electron mobility can be deduced. The effect of thermal annealing on implanted and unimplanted CdSe TFT’s has also been studied and the model appears to give a general description of the conductivity behavior in polycrystallin...

On tunneling in metal‐oxide‐silicon structures

Abstract: The analysis of Fowler‐Nordheim tunneling data in metal‐oxide‐silicon structures is reviewed. It is concluded that a parabolic dispersion relation for SiO2 and an electron effective mass of mox = 0.5m provide the best description of the experimental results, this conclusion is consistent with recent band structure calculations for SiO2. Also included is a brief discussion of the transverse momentum conservation issue for tunneling from silicon of 〈100〉, 〈110〉, and 〈111〉 orientation into SiO2.

Growth kinetics of planar binary diffusion couples: ’’Thin‐film case’’ versus ’’bulk cases’’

Abstract: It is proposed that interfacial reaction barriers in binary A/B diffusion couples lead to the absence of phases predicted by the equilibrium phase diagram, provided that the diffusion zones are sufficiently thin (thin‐film case). With increasing thickness of the diffusion zones the influence of interfacial reaction barriers decreases and the simultaneous existence of diffusion‐controlled growth of all equilibrium phases is expected (bulk case). Selective growth of the first and second phases and the effect of impurities are discussed with the influence of interfacial reaction barriers and with references to the known cases of silicide formation.

A photoelectrochemical determination of the position of the conduction and valence band edges of p‐type CuO

Abstract: Lithium‐doped p‐type CuO is a low mobility semiconductor with an indirect band gap of 1.35 eV and a flatband potential of +0.55 V, with respect to the saturated calomel electrode (SCE), when in contact with an electrolyte at a pH of 9.4. Its valence band lies 5.42 eV below the vacuum level and is made up mainly from the Cu2+−3d wavefunctions. An oxygen‐2p type band is at 7.33 eV, in agreement with a semi‐empirical estimate. Its performance as a photoelectrode for the solar photoelectrolysis of water is rather poor, due to the presence of recombination centers in the band gap and its chemical instability. As photoelectrolysis electrodes, oxides with 3d‐type valence bands may have advantages over the more common oxides with 2p‐type valence bands.

Properties and structure of a‐SiC:H for high‐efficiency a‐Si solar cell

Abstract: A series of experimental investigations on optical and optoelectronic properties of methane‐ and ethylene‐based a‐SiC:H films has been made. The chemical bonding structure of two kinds of a‐ SiC:H films has also been explored from infrared (IR) absorption structural analysis. An experimental verification for the wide gap window material in the amorphous silicon solar cell is shown on methane‐ and ethylene‐based a‐SiC:H. The methane‐based a‐SiC:H film shows one or two orders of magnitude larger photoconductivity recovery effect of doping than the ethylene‐ based one. IR absorption analysis shows that the methane‐based a‐SiC:H film is recognized as a rather ideal amorphous SiC alloy as compared with the ethylene‐based one. It has been found through these investigations that the methane‐based a‐SiC:H film is superior to the ethylene‐ based one as a window material. Utilizing the methane‐based a‐SiC:H, an 8% efficiency barrier has been broken through with an a‐SiC:H/a‐Si:H heterojunction structure.

Hall measurement studies and an electrical conduction model of tin oxide ultrafine particle films

Abstract: The Hall effect has been measured for ultrafine particle films of tin oxide (particle size 50–200 A) in contact with reducing gases. Both the carrier concentration and mobility increased with an increasing concentration of reducing gas. As a result, conductivity, the product of the carrier concentration and mobility, shows a large gas concentration dependence. This means the ultrafine particle films are highly sensitive to gases. The variation of the carrier mobility with the gas concentration is interpreted in terms of a model in which the width of a long, thin channel, determined by particle size and Debye length, increases with a decrease in the number of O− ions desorbed by a chemical reaction with the reducing gases.

Semiconductors for high‐voltage, vertical channel field‐effect transistors

Abstract: The influence of material parameters upon the characteristics of vertical channel power field effect transistors is examined. It is demonstrated that for devices with the same breakdown voltage and device structure, the on‐resistance is inversely proportional to the third power of the energyband gap and inversely proportional to the mobility. In addition the frequency response of these devices increases in proportion to the mobility and the energyband gap. Calculated device parameters for III–V semiconductor compounds, as well as their alloys, have been compared to those of a silicondevice with the same breakdown voltage. It is found that devicesfabricated from GaAs,InP, and GaP are expected to have a current handling capability which is a factor of 12.7, 5, and 1.85 better than that of the silicondevice with the same breakdown voltage. In addition, the current handling capability of devicesfabricated from the alloy semiconductors GaAlAs, GaAsP, and InGaP are even superior to those of a GaAsdevice with the same breakdown voltage.

Piezoelectricity of a high‐content lead zirconate titanate/polymer composite

Abstract: A binary system consisting of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) powder was investigated to determine its dielectric constant, piezoelectric constant, and Young’s modulus. An expression was obtained for the piezoelectric constant, and expressions for the dielectric constant and Young’s modulus were also mentioned. The calculated values had good agreement with the observed values for the composite with a large PZT volume fraction. The dielectric constant and the piezoelectric constant were 152 and 48.3×10−12 C/N, respectively, for the composite with the PZT volume fraction of 0.67. Changing the mixing ratio of PVDF and the fluorine elastomer, Young’s modulus was varied without changing the piezoelectric constant.

Estimation of wavenumber and frequency spectra using fixed probe pairs

Abstract: We introduce the concept of the local wavenumber and frequency spectral density, which can be estimated using spatially fixed, point data sources (’’fixed probe pairs’’), and discuss the relationship of this spectral density to the conventional wavenumber and frequency spectral density and the cross‐power spectral density. The local wavenumber and frequency spectral density is shown to be equivalent to the conventional wavenumber and frequency spectral density when the fluctuation is stationary and homogeneous and consists of a superposition of wave packets; such a fluctuation is the basic model used in many turbulence theories. A digital method for estimating the local wavenumber spectrum is described and applied to the study of drift‐wave turbulence in an rf‐excited discharge. The statistical dispersion relation and wavenumber spectral width, computed from the local wavenumber and frequency spectrum of the drift‐wave turbulence, are compared with the conventional spectral moments computed using the correlation method of Iwama and Tsukishima; good agreement is found over a wide range of frequency. A frequency‐integrated wavenumber spectrum is computed; both frequency and wavenumber spectral indices are found independently. The local wavenumber and frequency spectrum is a completely new approach to the use of fixed‐probe data, and we believe it can greatly extend the quantity of information available from fixed probes, which are the principle tools in many, if not most, fluctuation experiments.

The response of solids to elastic/plastic indentation. I. Stresses and residual stresses

Abstract: A new approach for analyzing indentation plasticity and for determining indentation stress fields is presented. The analysis permits relations to be established between material properties (notably hardness, yield strength, and elastic modulus) and the dimensions of the indentation and plastic zone. The predictions are demonstrated to correlate with observations performed on a wide range of materials. The indentation stress fields are computed along trajectories pertinent to three dominant indentation crack systems: radial, median, and lateral cracks. The peak load and residual tensile stresses are shown to be consistent with observed trends in indentation fracture.

Strained-layer superlattices from lattice mismatched materials

Abstract: Results are presented from the first theoretical study of the electronic properties of strained‐layer semiconductor superlattices made from lattice mismatched materials. The energy gaps and electronic states of GaAs‐GaAs0.2P0.8 (100) superlattices are studied as a function of layer thicknesses using a tight binding model. The superlattice band gaps are found to depend on the layer thicknesses through quantum mechanical effects and through the strains in the layers.

Local inertial effects in dynamic fragmentation

Abstract: A general definition of dynamic fragmentation can encompass any impulsive process which partitions a body of material into discrete domains. Two examples are fragmentation due to brittle fracture under impact loading and fragmentation due to shear banding in shock‐compression plastic deformation. In application, prediction of fragment size or shear band spacing is frequently either the objective, or else requisite to understanding the process. An approach is presented whereby surface or interface area created in the fragmentation process is governed by an equilibrium balance of the surface or interface energy and a local inertial or kinetic energy. Fragment size can be approximately related to surface or interface area. Relations provided by the analysis compare well with experimental dynamic fracture and shock‐wave shear‐band results.

Diluted magnetic semiconductors: An interface of semiconductor physics and magnetism (invited)

Abstract: This paper reviews the electrical, magnetic, and optical properties of diluted magnetic semiconductors (sometimes also referred to as ‘‘semimagnetic’’ semiconductors). These materials are ternary semiconductor alloys whose lattice is made up in part of substitutional magnetic ions. Cd1−xMnxTe and Hg1−xMnxTe are examples of such systems. As semiconductors, these alloys display interesting and important properties, such as the variation of the energy gap and of effective mass with composition. They also exhibit magnetic properties which are interesting in their own right, e.g., a low temperature spin glass transition and magnon excitations. Most importantly, however, the presence of substitutional magnetic ions in these alloys leads to spin–spin exchange interaction between the localized magnetic moments and the band electrons. This in turn has rather important consequences on band structure and on donor and acceptor states, leading to dramatic effects in quantum transport, impurity conduction, and magneto‐optics. Specifically, the presence of exchange interaction results in extremely large and temperature dependent g‐factors of electrons and holes; in gigantic values of Faraday rotation; in anomalously large negative magnetoresistance; and in the formation of the bound magnetic polaron.

Electron channeling patterns in the scanning electron microscope

Abstract: This article provides a comprehensive review of the theory, practice, and application of electron channeling patterns in the scanning electron microscope. An atlas of indexed channeling maps for the bcc, fcc, diamond cubic, and hcp systems is included with a bibliography of 240 references containing all known published work on electron channeling for crystallographic studies in the SEM.

Identification of AsGa antisites in plastically deformed GaAs

Abstract: AsGa antisite defects formed during plastic deformation of GaAs are identified by electron paramagnetic resonance (EPR) measurements. From photo‐EPR results it can be concluded that the two levels of this double donor are located near Ec −0.75 eV and Ev +0.5 eV. These values are coincident with the Fermi level pinning energies at Schottky barriers. The upper level can be related to the ’’main electron trap’’ EL2 in GaAs. Photoluminescence experiments before and after thermal annealing suggest that AsGa defects reduce the near band edge luminescence efficiency. A dislocation climb model is presented which is able to explain AsGa formation during dislocation movement. The production of AsGa antisites during dislocation motion under injection conditions in light emitting devices may thus be connected with degradation of the light output.

Simple approximate treatment of unipolar space‐charge‐dominated coronas: The Warburg law and the saturation current

Abstract: Unipolar space‐charge distribution ρ(t) drifting with constant ion mobility μ in gas under time and space dependent electric fields will evolve according to the unipolar charge drift formula [1/ρ(t)]−[1/ρ(t0)] = (μ/e0)(t−t0), neglecting diffusion effects. This general formula is especially useful as a starting point for approximate treatment of space‐charge effects, both in ion drift and diffusion experiments, and in electrical coronas. A first simple derivation of an equivalent of the Warburg cos5ϑ current‐density distribution for point‐to‐plane coronas is given, together with a formula for the maximum possible unipolar ion current (the unipolar saturation current) Is ≊2μe0 V2/d, for a given corona voltage V and point‐to‐plane distance d. It is demonstrated that corona currents in excess of this limit always involve free electron or bipolar conduction phenomena, like streamers.

Defect production and lifetime control in electron and γ‐irradiated silicon

Abstract: A study of the effect of 1‐ and 12‐MeV electron and Co60 γ irradiation has been made on power p‐i‐ n diodes and Schottky barrier diodes fabricated on the same starting material. A comparison of the results from these two types of structures illustrated the influence of device processing on the type of defects formed by subsequent irradiation. Detailed electrical characterization of the defects demonstrated good consistency between certain elements of the structural nature of the defect, inferred from these measurements, and those already obtained from electron spin resonance (ESR) measurements. Lifetime measurements on the p‐i‐n diodes indicated that both the A center and the divacancy were active recombination centers. Finally, data are presented on defect and lifetime annealing.

Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling

Abstract: Thin‐oxide (40–50 A) metal oxide semiconductor (MOS) structures are shown to exhibit, prior to large levels of electron tunnel injection, the near‐ideal behavior predicted for a uniform trapezoidal barrier with thick‐oxide properties. The oscillatory field dependence due to electron‐wave interference at the Si/SiO2 interface indicates an abrupt, one‐monolayer barrier transition (∼2.5 A) consistent with earlier work. After tunnel injection of 1017 –5×1018 electrons/cm2, the barrier undergoes significant degradation leading to enhanced tunneling conductance, with reproducible behavior observed among different samples. This effect is consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (<20 A), where the tunneling electrons emerge into the oxide conduction band. Densities of positive‐charge and interface‐state buildup are also observed from capacitance‐voltage (C‐V) measurements and are found to be consistent with the observed tunneling dependence on positiv...

Properties of AlxGa1−xN films prepared by reactive molecular beam epitaxy

Abstract: Single‐crystal films of the solid solution AlxGa1−xN of the entire composition range have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 700 °C. The properties of the films have been studied by the reflection high energy electron diffraction technique, x‐ray diffraction, and electrical and optical measurements. The lattice constant of the film is not a linear function of the composition, and the fundamental absorption edge also shows nonlinear dependence on the composition. The narrow intense peak of the cathodoluminescence concerned with the band to band or shallow impurity band transition, varies from 3.4 to 6 eV with the composition, which suggests the feasibility of AlxGa1−xN films grown by reactive MBE for optical devices in the ultraviolet spectral region.

Prussian‐blue‐modified electrodes: An application for a stable electrochromic display device

Abstract: An electrochromic display based on a Prussian‐blue‐modified electrode is described. Prussian blues are deposited electrochemically in a solution of ferric‐ferricyanide. Current flow at +0.2 and +1.0 V is due to the reduction of Fe3+ and the oxidation of Fe2+ in the Prussian‐blue coating, respectively. The result is a display that switches from clear to blue, has high stability, and has a response of less than 100 ms.

Electrical and optical properties of tin oxide films doped with F and (Sb+F)

Abstract: This paper presents the structural, electrical, and optical properties of F‐ and (Sb+F)‐doped tin oxide films prepared by spray pyrolysis technique. Resistivity as low as 5.5×10−4 Ω cm with high optical transmission (≳80%) and high infrared reflection (∼90%) have been obtained in F‐doped tin oxide films. The figure of merit ΦTC = T10/Rsh (52.6×10−3Ω−1 at 0.65μm) of these films is the highest amongst the results reported on doped tin oxide films. The variation of mobility with doping concentration has been analyzed to understand the electron–conduction mechanism. The Drude theory has been used to explain the optical properties near the plasma edge.

Optical generation of tunable ultrasonic waves

Abstract: A convenient method of optically exciting and monitoring coherent acoustic waves in transparent or light‐absorbing liquids and solids is described. The acoustic frequency is easily and continuously tunable from ≊3 MHz to at least 30 GHz with our experimental apparatus and in principle over a considerably wider range. In anisotropic materials any propagation direction can be selected. The optically generated acoustic waves can be optically amplified, cancelled, or phase shifted.

Thermal‐wave depth profiling: Theory

Abstract: We have developed a one‐dimensional model for thermal‐wave depth profiling that provides expressions for the temperature at the surface of the sample and for the thermoelastic response beneath the surface. The model shows that elastic wave interference effects produce significant differences between samples with mechanically free and constrained surfaces, and that thermal‐ wave images of thermal conductivity variations are obtainable from the thermoelastic signal only if the front surface is mechanically free. We have also considered the case of subsurface heating and found that for heating occurring at depths of more than a few thermal diffusion lengths, the thermoelastic signal becomes independent of thermal conductivity variations. This has important implications for thermal‐wave image range and resolution.

Temperature profiles induced by a scanning cw laser beam

Abstract: We present calculations of the temperature profiles induced by a moving cw elliptical laser beam with a Gaussian intensity distribution in a semi‐infinite material. Temperature‐dependent thermal diffusivity, conductivity, and surface reflectivity are incorporated in our model, and some aspects of melting are discussed. As an example, we apply the calculations to silicon. For a comparison of stationary elliptical spots of varying eccentricities, we present material‐independent normalized linear temperature profiles. We find that highly elliptical beams can be used to rapidly scan and anneal large areas.