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Showing papers in "Journal of Applied Physics in 1980"


Journal ArticleDOI
TL;DR: In this article, the maximum efficiency of ideal solar cells for both single and multiple energy gap cells using a standard air mass 1.5 terrestrial solar spectrum was calculated using a simple graphical method, which clearly exhibits the contributions of various intrinsic losses.
Abstract: The maximum efficiencies of ideal solar cells are calculated for both single and multiple energy gap cells using a standard air mass 1.5 terrestrial solar spectrum. The calculations of efficiency are made by a simple graphical method, which clearly exhibits the contributions of the various intrinsic losses. The maximum efficiency, at a concentration of 1 sun, is 31%. At a concentration of 1000 suns with the cell at 300 K, the maximum efficiencies are 37, 50, 56, and 72% for cells with 1, 2, 3, and 36 energy gaps, respectively. The value of 72% is less than the limit of 93% imposed by thermodynamics for the conversion of direct solar radiation into work. Ideal multiple energy gap solar cells fall below the thermodynamic limit because of emission of light from the forward‐biased p‐n junctions. The light is radiated at all angles and causes an entropy increase as well as an energy loss.

1,011 citations


Journal ArticleDOI
TL;DR: In this paper, a model for the shear modulus and yield strength as functions of equivalent plastic strain, pressure, and internal energy (temperature) was presented for high-strain rate.
Abstract: A model, applicable at high‐strain rate, is presented for the shear modulus and yield strength as functions of equivalent plastic strain, pressure, and internal energy (temperature) The parameters needed to implement the model have been determined for 14 metals Using this model, hydrodynamic computer simulations have been successful in reproducing measured stress and free‐surface‐velocity–vs–time data for a number of shock‐wave experiments

974 citations


Journal ArticleDOI
TL;DR: In this article, a small concentration of suitably chosen noble gas to a reactive plasma is shown to permit the determination of the functional dependence of reactive particle density on plasma parameters, and examples illustrating the simplicity of this method are presented using F atomic emission from plasma-etching discharges and a comparison is made to available data in the literature.
Abstract: The addition of a small concentration of suitably chosen noble gas to a reactive plasma is shown to permit the determination of the functional dependence of reactive particle density on plasma parameters. Examples illustrating the simplicity of this method are presented using F atomic emission from plasma‐etching discharges and a comparison is made to available data in the literature.

796 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the degree of order in the B site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing.
Abstract: In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B‐site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well‐ordered by long annealing, dielectric measurements on single crystals show a normal first‐order ferroelectric phase change at 13 °C and a maximum low‐temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low‐frequency dielectric dispersion in the transition range. X‐ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single‐crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.

769 citations


Journal ArticleDOI
TL;DR: In this paper, two general classes of explanations for such non-Ohmic effects are presented: thermal and electronic. But, as discussed in Section 2.1, the use of the terminology electrothermal encompasses predominantly thermal and predominantly electronic processes as well as all intermediate cases, and therefore should not prejudice the casual observer into concluding that both effects are necessarily important.
Abstract: The application of sufficiently high electric fields to any material eventually results in deviations from linearity in the observed current-voltage I(V) characteristic. There are two general classes of explanations for such non-Ohmic effects— thermal and electronic. Thermal effects arise because the electrons accelerated by the field always emit phonons in an attempt to return to equilibrium. Electronic effects are due to changes in the response of the charged carriers to high applied fields. In general, both effects must be considered in any quantitative analysis, and the two can produce a coupled response ofter called “electrothermal.” The use of the terminology electrothermal encompasses predominantly thermal and predominantly electronic processes as well as all intermediate cases, and therefore should not prejudice the casual observer into concluding that both effects are necessarily important. In a discussion of the physical mechanism in a particular sample, the major parameters controlling its operation must be identified and separated out from the less significant features.

604 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that long exposure to light decreases the photoconductivity and dark conductivity of some samples of hydrogenated amorphous silicon (a•Si':'H). Annealing above ∼150°C reverses the process.
Abstract: Long exposure to light decreases the photoconductivity and dark conductivity of some samples of hydrogenated amorphous silicon (a‐Si : H). Annealing above ∼150 °C reverses the process. The effect occurs in the bulk of the films, and is associated with changes in density or occupation of deep gap states. High concentrations of P, B, or As quench the effect. Possible models involving hydrogen bond reorientation at a localized defect or electron‐charge transfer between defects are discussed. An example is shown where these conductivity changes do not affect the efficiency of an a‐Si : H solar cell.

573 citations


Journal ArticleDOI
TL;DR: In this paper, the structural properties of corundum-type oxides have been determined at pressures up to 50 kbar by using simple bonding parameters to predict details of crystal structures under nonambient conditions.
Abstract: Crystal structures of several of the corundum‐type oxides have been determined at pressures to 50 kbars. All materials have linear compression within the pressure range and precision of the techniques used. Compression of Cr2O3 and Al2O3 is essentially isotropic (c/a remains constant), Fe2O3 has a slightly anisotropic compression, with c/a decreasing slightly with pressure, and V2O3 is very anisotropic, with the a axis nearly three times more compressible than c. Similar differences are observed in the structural parameters. Aluminum, iron, and chromium sesquioxides simply scale, whereas atomic positions in V2O3 approach an ideal HCP arrangement with increasing pressure. The differences in structural variation with pressure for these ’’isostructural’’ compounds emphasize the difficulty in using simple bonding parameters to predict details of crystal structures under nonambient conditions.

479 citations


Journal ArticleDOI
TL;DR: In this paper, the electrical and optical properties of undoped and antimony-doped tin oxide films have been studied and the temperature dependence of electron mobility has been analyzed to establish the electron conduction mechanism.
Abstract: Tin oxide films have been prepared on glass substrates by spray pyrolysis technique. The electrical and optical properties of undoped and antimony‐doped tin oxide films have been studied. The temperature dependence of electron mobility has been analyzed to establish the electron conduction mechanism. Optical properties near the plasma edge have been analyzed using Drude’s theory. The dependence of effective mass on carrier concentration has been explained on the basis of nonparabolicity of the conduction band. The shift in the Fermi energy, calculated on the basis of energy dependent effective mass, is consistent with the measured shift in the absorption edge.

474 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new theoretical model for the light-induced migration of charges which mediates the photorefractive effect in barium titanate and other crystals, and the theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field.
Abstract: We propose a new theoretical model for the light‐induced migration of charges which mediates the ’’photorefractive effect’’ (light‐induced refractive index change) in barium titanate and other crystals. We also present experimental results of various effects of this light‐induced charge migration in a single‐domain crystal of barium titanate, specifically, (1) energy transfer between two intersecting optical beams, (2) optical four‐wave mixing and optical‐beam phase conjugation, (3) erasure of spatial patterns of photorefractive index variations, and (4) photoconductivity. The theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions, and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field. Time dependences of transients as well as steady‐state magnitudes are predicted. In this model, identical charges migrate by hopping between adjacent sites, with a hopping rate proportional to the total light intensity at the starting site. The net hopping rate varies with the local electric potential that is calculated self‐consistently from the charge migration pattern. In barium titanate the charges are positive with a density of (1.90.2) ×1016 cm−3 at 514 nm. The origin of the charges and sites is at present unknown. The hopping rate constant determined from optical beam interactions is used to predict the observed photoconductivity of 1.3×10−10 cm Ω−1 W−1 at 514 nm.

426 citations


Journal ArticleDOI
TL;DR: In this article, a simple model is proposed to explain how a breakdown avalanche of secondary emission electrons can lead to surface flashover when an insulator in vacuum breaks down a few nanoseconds after high voltage is applied.
Abstract: A simple model is proposed to explain how a breakdown avalanche of secondary emission electrons can lead to surface flashover when an insulator in vacuum breaks down a few nanoseconds after high voltage is applied. The case of a plane insulator–vacuum interface perpendicular to parallel electrodes is considered. Positive surface charging is assumed to occur almost immediately upon application of the voltage, and the attendent secondary emission avalanche is assumed to be maintained at saturation throughout the prebreakdown time delay by field emission from the cathode electrode. Bombardment of the insulator by avalanche electrons desorbs a cloud of gas, which is partially ionized as it drifts through the swarm of electrons in the avalanche. The electric field at the cathode end of the insulator becomes enhanced as positive ions accumulate, which in turn increases the field emission and the rates of gas desorption and ionization. This and other regenerative processes rapidly lead to breakdown. Field enhanc...

380 citations


Journal ArticleDOI
TL;DR: In this paper, the effective elastic moduli of randomly oriented aggregates of hexagonal, trigonal, and tetragonal crystals are derived using the variational principles of Hashin and Shtrikman.
Abstract: Bounds on the effective elastic moduli of randomly oriented aggregates of hexagonal, trigonal, and tetragonal crystals are derived using the variational principles of Hashin and Shtrikman. The bounds are considerably narrower than the widely used Voigt and Reuss bounds. The Voigt‐Reuss‐Hill average lies within the Hashin‐Shtrikman bounds in nearly all cases. Previous bounds of Peselnick and Meister are shown to be special cases of the present results.

Journal ArticleDOI
TL;DR: In this paper, a three-dimensional heat transfer model for laser material processing with a moving Gaussian heat source is developed using finite difference numerical techniques, which is physically defined as follows: a laser beam, having a defined power distribution, strikes the surface of an opaque substrate of infinite length but finite width and depth moving with a uniform velocity in the positive x direction.
Abstract: (Received 19 September 1979; accepted for publication 12 October 1979)A three‐dimensional heat transfer model for laser material processing with a moving Gaussian heat source is developed using finite difference numerical techniques. In order to develop the model, the process is physically defined as follows: A laser beam, having a defined power distribution, strikes the surface of an opaque substrate of infinite length but finite width and depth moving with a uniform velocity in the positive x direction (along the length). The incident radiation is partly reflected and partly absorbed according to the value of the reflectivity. The reflectivity is considered to be zero at any surface point where the temperature exceeds the boiling point. This is because a ’’keyhole’’ is considered to have formed which will act as a black body. Some of the absorbed energy is lost by reradiation and convection from both the upper and lower surfaces while the rest is conducted into the substrate. That part of the incident r...

Journal ArticleDOI
TL;DR: In this paper, the dopant segregation at grain boundaries in polycrystalline silicon has been investigated, and a theory of segregation in systems of small particles has been developed, using this theory, the heat of segregation of arsenic and phosphorus, and the number of active dopant atoms within the grain boundaries as a function of annealing temperature.
Abstract: Dopant segregation at grain boundaries in polycrystalline silicon has been investigated. Arsenic, phosphorus, and boron were ion implanted into low‐pressure, chemically‐vapor‐deposited polycrystalline‐silicon films. All films were then annealed at 1000 °C for 1 h, and some were subsequently further annealed at 800, 850, or 900 °C for 64, 24, or 12 h, respectively. For phosphorus and arsenic the room‐temperature resistivity of the films was found to be higher after annealing at lower temperatures. By successively annealing the same sample at lower and higher temperatures, the resistivity would repeatedly increase and decrease, indicating reversible dopant segregation at the grain boundaries. Hall measurements were used to estimate the number of active dopant atoms within the grains and the number of atoms segregated at the grain boundaries as a function of annealing temperature. A theory of segregation in systems of small particles has been developed. Using this theory, the heat of segregation of arsenic and phosphorus in polycrystalline silicon was calculated. For boron no appreciable segregation was observed.

Journal ArticleDOI
TL;DR: In this article, a time-of-flight atom-probe field-ion microscope has been developed, which uses nanosecond laser pulses to field evaporate surface species.
Abstract: A time‐of‐flight atom‐probe field‐ion microscope has been developed which uses nanosecond laser pulses to field evaporate surface species. The ability to operate an atom‐probe without using high‐voltage pulses is advantageous for several reasons. The spread in energy arising from the desorption of surface species prior to the voltage pulse attaining its maximum amplitude is eliminated, resulting in increased mass resolution. Semiconductor and insulator samples, for which the electrical resistivity is too high to transmit a short‐duration voltage pulse, can be examined using pulsed‐laser assisted field desorption. Since the electric field at the surface can be significantly smaller, the dissociation of molecular adsorbates by the field can be reduced or eliminated, permitting well‐defined studies of surface chemical reactions. In addition to atom‐probe operation, pulsed‐laser heating of field emitters can be used to study surface diffusion of adatoms and vacancies over a wide range of temperatures. Examples demonstrating each of these advantages are presented, including the first pulsed‐laser atom‐probe (PLAP) mass spectra for both metals (W, Mo, Rh) and semiconductors (Si). Molecular hydrogen, which desorbs exclusively as atomic hydrogen in the conventional atom probe, is shown to desorb undissociatively in the PLAP. Field‐ion microscope observations of the diffusion and dissociation of atomic clusters, the migration of adatoms, and the formation of vacancies resulting from heating with a 7‐ns laser pulse are also presented.

Journal ArticleDOI
TL;DR: In this article, the longitudinal elastic strain was measured for electric fields applied along the 〈100〉 direction in single crystals of lead magnesium niobate [Pb(Mg1/3Nb2/3)03], using a bonded strain gauge technique.
Abstract: Transverse and longitudinal elastic strain have been measured for electric fields applied along the 〈100〉 direction in single crystals of lead magnesium niobate [Pb(Mg1/3Nb2/3)03], using a bonded strain gauge technique. A quadratic electrostrictive relation holds between induced elastic strain and electric polarization for temperatures near the low‐frequency dielectric maximum. The electrostriction coefficients are almost temperature independent with values Q11=2.50×10−2 m4/C2 and Q12=−0.96×10−2 m4/C2. To check the direct measurements, the hydrostatic Q coefficient was determined independently by measuring the pressure dependence of the dielectric permittivity. The value Qh =0.60×10−2 m4/C2 obtained is in good agreement with that calculated from the direct measurements.

Journal ArticleDOI
TL;DR: In this article, a theory of optical beam deflection near a heated surface was introduced as a method of photothermal spectroscopy and applied to the measurement of thermal diffusivity of gases.
Abstract: Optical beam deflection near a heated surface was recently introduced as a method of photothermal spectroscopy. Photothermal spectroscopy (PTS) is closely related to photoacoustic spectroscopy (PAS) in its ability to measure optical properties of opaque solids and liquids. This paper develops a theory of this effect and compares this theory with extensive experimental observations. Both are in excellent agreement. The relationship between this form of PTS and PAS is explicitly developed. Applications to the measurement of thermal diffusivity of gases is described.

Journal ArticleDOI
TL;DR: In this article, the authors derived the spatial configuration of the domains in BaTiO3 ceramics from etch patterns, which can be described by two types of domain configurations: 90'° and 180'° domain walls.
Abstract: The domain structures in BaTiO3 ceramics differ from those of single crystals. The spatial configuration of the domains in the ceramics has been derived from etch patterns. All observed etch patterns can be described by two types of domain configurations. Thin layered domains separated by 90 ° walls are piled up to form sloped stacks. Neighboring stacks are bounded by two types of boundaries. One of them is made up of 90 ° and 180 ° domain walls. The other type has a more complex structure which is not free of polarization charge. In this case the pattern accounts for a head to side relation of polarization vectors. Both structures allow the grain, merely by wall motion, to be easily squeezed to arbitrary deformations up to strains of the order of the spontaneous strain. The elastic energy stored in a mixed wall has been estimated. It shows order of magnitude agreement with the energy of the 90 ° walls if the observed domain size is taken into account.

Journal ArticleDOI
TL;DR: In this article, the formation of supersaturated substitutional alloys by ion implantation and rapid liquid phase-epitaxial regrowth induced by pulsed laser annealing has been studied using Rutherford backscattering, ion channeling analysis.
Abstract: The formation of supersaturated substitutional alloys by ion implantation and rapid liquid‐phase‐epitaxial regrowth induced by pulsed laser annealing has been studied using Rutherford backscattering, ion channeling analysis. Group‐III (Ga, In) and group‐V (As, Sb, Bi) dopants have been implanted into single‐crystal silicon at doses ranging from 1×1015 to 1×1017/cm2. The samples were annealed with a Q‐switched ruby laser (energy density ∼1.5 J/cm2, pulse duration ∼15×10−9 sec). Ion channeling analysis shows that laser annealing incorporates these dopants into substitutional lattice sites at concentrations far in excess of the equilibrium solid solubility. Channeling measurements indicate the silicon crystal is essentially defect free after laser annealing. Also values for the maximum dopant concentration (Cmaxs) that can be incorporated into substitutional lattice sites are determined for our annealing conditions. Dopant profiles determined by Rutherford backscattering are compared to model calculations wh...

Journal ArticleDOI
TL;DR: In this article, the theory of piezoelectric photoacoustic spectroscopy for condensed-matter samples is developed for condensedmatter samples, treating the sample as an elastic layer and neglecting the transducers effect on the sample, the three-dimensional uncoupled quasistatic thermoelastic equations are solved using a Green's function for the stress.
Abstract: The theory of piezoelectric photoacoustic spectroscopy is developed for condensed‐matter samples. Treating the sample as an elastic layer and neglecting the transducer’s effect on the sample, the three‐dimensional uncoupled quasistatic thermoelastic equations are solved using a Green’s function for the stress. An expression for the dependence of the signal on absorption, modulation frequency, thermal properties, and mechanical properties of the sample is derived. The theoretical predictions are experimentally verified, the sources of noise are analyzed, and the noise equivalent power is estimated. Finally, considerations for detector optimization are discussed.

Journal ArticleDOI
TL;DR: In this paper, a set of curves are given which allow the determination of ND•NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample.
Abstract: Semi‐insulating GaAs materials, undoped or doped with concentration of chromium varying from 6×1015 to 4×1017 cm−3, have been studied using both Hall effect measurements and optical absorption measurements. It is definitively concluded that compensation comes from the presence of the deep donor EL2 in undoped materials, and from both this deep donor and the deep acceptor related to chromium in Cr‐doped materials. Sets of curves are given which allow the determination of ND‐NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample. Such curves can be a working tool for assessing any piece of semi‐insulating GaAs in a routine way.

Journal ArticleDOI
TL;DR: In this article, a unified view of thermodynamic energy conversion efficiencies is presented from a unified point of view, including the distinction between temperatures based on fluxes and temperatures ∂U/∂S based on standard thermodynamics.
Abstract: Much recent work on thermodynamic energy conversion efficiencies is here presented ab initio and from a unified point of view. New considerations are offered and previous work is analyzed in light of the unified presentation. The energy conversion processes discussed include, for example, the conversion into light in a laser or light-emitting diode and the direct or indirect conversion of solar radiation into work. The thermodynamic limiting efficiencies of these various processes are derived by applying simple balance equations to a generalized energy convertor. The new work includes the distinction between temperatures based on fluxes and temperatures ∂U/∂S based on standard thermodynamics, etc., and their application in the correct context. Also the use of standard entropy formulas is justified without relying on thermodynamic equilibrium and the results are then applied to nonequilibrium situations in energy conversion.

Journal ArticleDOI
TL;DR: In this paper, the elastic behavior of manganin gauges was investigated in a series of plane shock wave experiments and the calibration curve obtained is linear in the 0.5 to 1.5 GPa range and curves for higher stresses (1.5-18.1 GPa).
Abstract: Commercial manganin gauges were calibrated in a series of plane shock wave experiments. The calibration curve obtained is linear in the 0–1.5‐GPa range and curves for higher stresses (1.5–18.1 GPa). The linear portion is attributed to the elastic behavior of the gauge. This was confirmed by experiments which included rarefactions from free surfaces. The onset of hysteresis was found to be at 1.5 GPa. The experiments demonstrated that the gauge’s response does not depend on the target material in which the gauge is embedded. Also the thickness of the insulating layer which surrounds the gauge does not have any influence on its relative resistance changes.

Journal ArticleDOI
TL;DR: In this article, the temperature profiles induced by a cw laser beam in a semiconductor are calculated for an elliptical scanning beam and covers a wide range of experimental conditions, and the limiting case of a circular beam is also studied.
Abstract: Temperature profiles induced by a cw laser beam in a semiconductor are calculated. The calculation is done for an elliptical scanning beam and covers a wide range of experimental conditions. The limiting case of a circular beam is also studied. This calculation is developed in the particular cases of silicon and gallium arsenide, where the temperature dependence of the thermal conductivity has been taken into consideration. Using a cylindrical lens to produce an elliptical beam with an aspect ratio of 20, a 1‐mm‐wide area of an ion‐implanted silicon wafer was annealed in a single scan. The experimental data are consistent with the extrapolation of solid‐phase epitaxial regrowth rates to the calculated laser‐induced temperatures.

Journal ArticleDOI
TL;DR: In this paper, the transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material, and the thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.
Abstract: Quantitative experimental measurements have been made in the study of thermoelastic generation of elastic waves in a metal by unfocused laser radiation. A calibrated wide‐band detection system, incorporating a capacitance transducer, has enabled acoustic waveforms to be recorded with a minimum of distortion. From these measurements, a theoretical model has been developed. The transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material. The thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.

Journal ArticleDOI
TL;DR: In this article, a detailed study of these films has been carried out using x-ray diffraction, scanning electron microscopy, reflection electron diffraction and optical measurement, and electromechanical measurement.
Abstract: ZnO films with an excellent crystal orientation and surface flatness have been prepared by high‐deposition‐rate rf planar‐magnetron sputtering. A detailed study of these films has been carried out using x‐ray diffraction, scanning electron microscopy, reflection electron diffraction, optical measurement, and electromechanical measurement. These films have the c‐axis perpendicular to the substrate. The value of the standard deviation angle σ of the c‐axis orientation distribution is smaller than 0.5°, and the minimum value of σ is 0.35°, where the sputtering conditions are that the gas pressure is 5×10−3–3×10−2 Torr of premixed Ar (50%)+O2(50%) and the substrate temperature is 300–350 °C. ZnO films with a thickness up to 48 μm have been reproducibly prepared without the decreases of film quality and surface flatness. The surface flatness of these films is similar to that of a glass substrate. An optical waveguide loss for the TE0 mode of the He‐Ne 6328‐A line is as low as 2.0 dB/cm in a 4.2‐μm‐thick film, ...

Journal ArticleDOI
TL;DR: In this article, the authors examined the preionization level and other initial conditions necessary for the formation of spatially homogeneous pulsed avalanche discharges at high gas pressures and found that the minimum preionisation level required for homogeneous discharge initiation depends on the voltage rise time across the electrodes as well as on the total pressure and various electrochemical properties of the gas mixture which govern the net rate of change of the first Townsend coefficient with respect to the local electric field strength.
Abstract: The preionization level and other initial conditions necessary for the formation of spatially homogeneous pulsed avalanche discharges at high gas pressures are examined. Assuming properly shaped electrodes with no strong edge effects, the minimum preionization level required for homogeneous discharge initiation is found to depend on the voltage rise time across the electrodes as well as on the total pressure and various electrochemical properties of the gas mixture which govern the net rate of change of the first Townsend coefficient with respect to the local electric field strength. Our predictive results are found to be consistent with experimental observations.

Journal ArticleDOI
TL;DR: In this article, a transformation of grain boundary recombination centers to a uniform distribution of such states throughout the grain was proposed, and the effective carrier lifetime was expressed in terms of grain size, allowing calculation of shortcircuit current, open-circuit voltage, and fill factor.
Abstract: Grain boundary states play a dominant role in determining the electrical and photovoltaic properties of polycrystalline silicon by acting as traps and recombination centers. The recombination loss at grain boundaries is the predominant loss mechanism in polycrystalline solar cells. Cell parameters are calculated based on a transformation of grain boundary recombination centers to a uniform distribution of such states throughout the grain. Effective carrier lifetime is expressed in terms of grain size, allowing calculation of short‐circuit current, open‐circuit voltage, and fill factor. Excellent agreement is observed between theory and experiment for almost all device parameters. It is indicated that one could fabricate 10% efficiency polycrystalline solar cells from 20‐μm‐thick material if the grain size exceeds 500 μm.

Journal ArticleDOI
TL;DR: In this paper, it has been shown that an electric arc can be added to the interaction between a laser beam and a material surface in such a way that in welding and cutting it produces an effect similar to that from a more powerful laser.
Abstract: It has recently been found that an electric arc can be added to the interaction between a laser beam and a material surface in such a way that in welding and cutting it produces an effect similar to that from a more powerful laser. The experimental results are discussed together with an analysis of the process mechanism. In particular it appears that the arc strikes the work piece at the same interaction zone as the laser, and in so doing undergoes a contraction in width to near the same size as the laser beam. It also seems probable that some of the arc energy penetrates the laser generated keyhole. So far the experimental results have shown that arc augmentation of the laser by some 2 kW of arc power in the work piece can be achieved without unduly spoiling the high quality of the cut or weld that would be made by a laser alone of similar total power.

Journal ArticleDOI
TL;DR: In this article, a detailed study of interdiffusion in (GaAs)n(AlAs)m multilayer structures grown by molecular beam epitaxy was made, where the time dependence of the Fourier components of the composition modulation at a constant annealing temperature was obtained by measuring the intensities of the superlattice satellites by x-ray diffraction.
Abstract: A detailed study has been made of interdiffusion in (GaAs)n(AlAs)m multilayer structures grown by molecular beam epitaxy. The subscripts n and m indicate that the structure is a repeating sequence of n monolayers of GaAs followed by m monolayers of AlAs. The time dependence of the Fourier components of the composition modulation at a constant annealing temperature was obtained by measuring the intensities of the superlattice satellites by x‐ray diffraction. For a sample with (n,m) = (12,9) at a temperature of 860 °C, the data can be fit by a composition‐dependent diffusion coefficient of the form D (C) =8.8×10−20 exp(αC) cm2/sec, where α=2.06 and C is the gallium concentration. The parameter α is proportional to the difference in the diffusion activation energy in GaAs and AlAs. An α of 2.06 at 860 °C corresponds to an energy difference of 0.201 eV. Calculations which assume vacancy diffusion via the arsenic sublattice give an energy difference of 0.25 eV in reasonable agreement with the experimental valu...

Journal ArticleDOI
TL;DR: In this paper, a detailed statistical theory of normal grain growth has been constructed by extending the theory of Feltham and combining it with the work of Rhines and Craig, and complete solutions are found for the grain growth kinetics of each class, as well as the transfer rates between classes.
Abstract: By extending the theory of Feltham and combining it with the work of Rhines and Craig, a detailed statistical theory of normal grain growth has been constructed. The theory exhibits all four attributes of normal grain growth: uniformity, scaling, stability, and lognormality. A prime new feature of the theory is the division of the grains into topological classes (14 planar, 34 spatial), each with a lognormal distribution of grain sizes. Growth is found to be controlled by the rate of loss of grains from the lowest topological class. Complete solutions are found for the grain growth kinetics of each class, as well as the transfer rates between classes. The latter result is used to explain how the median diameter of those classes in which grains are shrinking still manages to increase in the manner required to keep their number a constant fraction of the total population. A parabolic growth law is found for the median grain size of the whole population as well as the median grain size in each topological class. The growth constant for each class is found to increase approximately as the cube of the planar topological parameter or the square of the spatial topological parameter. The Rhines‐Craig structural gradient is shown to be independent of time and hence a basic constant of normal grain growth. Stability is due to a maximum in the grain boundary velocity with increasing grain size. The ratio of the maximum to median grain diameter is found to be e(=2.718). A comparison of the present theory is made with that of Hillert. Possible origins of the lognormality are discussed.