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Journal of Applied Physics

Issue 4 • Date Aug 1987

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Displaying Results 1 - 25 of 76
  • A simple formula for diffusion calculations involving wall reflection and low density

    Page(s): 1141 - 1148
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    Diffusion theory is often employed to calculate the effects of wall destruction on the local concentration of an active species immersed in a scattering gas. In many situations the spatial dependence of the concentration is given to a good approximation by the fundamental diffusion mode, and the local loss frequency can be calculated using the container’s fundamental mode diffusion length Λ. The additional assumption that the density of the active species may be taken to be zero at the container boundaries gives a value of Λ=Λ0 which depends only on the container dimensions, but use of Λ0 can be seriously in error if the diffusion mean free path λm is comparable to the dimensions, or if the particle reflection coefficient R becomes of significance. An improved boundary condition may be written simply in terms of the linear extrapolation length λ, whose inverse is the logarithmic gradient of the particle density at the boundary. The equation λ=2(1+R)λm/3(1-R) allows the representation of the full range of possible values of the particle reflection coefficient, 0≪R≪1, and extends the usefulness of the diffusion approximation to low scatterer densities. In the collisionless limit, the predicted particle loss frequency is identical to that predicted from the average chord length. Using this boundary condition, the dependence of Λ on λ/Λ0 has been computed for a range of simple container shapes, by solving the transcendental equations involved. This has allowed the identification of a dimensionless scaling variable, l0λ/Λ20, where l0 is the ratio of the container volume to its surface area. For all cases considered the simple empirical approximation Λ2=(Λ20+l0λ) is accurate when λ is very l- arge or very small compared to Λ0, and disagrees most with the numerical solutions in the region where λ and Λ0 are comparable, with the worst case error being 11%. View full abstract»

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  • Spherical aberrations of multipoles

    Page(s): 1149 - 1153
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    It is demonstrated in this article that for an electromagnetic 2n-pole system with n=odd, the only existing symmetric aberration which could be used to correct the spherical aberrations of a round lens is the order of 2n-3. Thus, a 2n-pole corrector can only be used to cancel the aberration of round lenses of order 2n-3. View full abstract»

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  • A continuous representation of the acoustic surface‐wave mode shape in arrays of reflecting grooves

    Page(s): 1154 - 1161
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    A variational analysis of the reflection of surface waves by arrays of reflecting grooves is presented. The variational condition results in a system of linear algebraic equations relating the amplitudes of the waves on both sides of the edge of a groove. The influence of transverse moding, which is a result of the finite lateral dimension of the grooves, is included in the treatment, but scattering into bulk waves is not considered. Application of the linear algebraic equations across both edges of a typical groove results in a system of transmission equations, which constitutes a linear difference system for the periodic array. A closed‐form continuous representation of the mode shape along the transmission path is obtained from the solution of the system of linear difference equations for the periodic array. The continuous representation is particularly convenient for use in the evaluation of perturbation integrals that arise in the calculation of the change in frequency of surface‐wave resonators due to biasing states and for many other purposes. When the resonant surface‐wave mode has been found, the reduced resonant frequency and phase velocity are obtained by means of a perturbation procedure. Calculated results are presented for grooved arrays on ST‐cut quartz. View full abstract»

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  • Photoacoustic measurements of the thermal conductivity of some bulk polymer samples

    Page(s): 1162 - 1166
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    Thermal parameters such as thermal diffusivity and thermal conductivity of the polymers nylon 66, cellulose acetate, polyacetal, Teflon, and polystyrene have been determined using the photoacoustic technique. Samples having thickness of the order of 25–50 μm have been specially prepared from bulk solid samples for measurements. The experimental method involves the determination of the characteristic frequency fc by measuring the variation of the amplitude and phase of the photoacoustic signal as a function of the chopping frequency for a monochromatic incident beam. Front surface illumination geometry has been used in the measurements. The measured thermal properties agree with the existing values in literature. View full abstract»

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  • Temperature runaway of microwave irradiated materials

    Page(s): 1167 - 1170
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    A numerical procedure for calculating the steady‐state temperature distribution generated by microwave absorption is described. The procedure can be applied to the case of material for which the permittivity is nonlinearly temperature dependent and can be used to simulate the conditions when temperature runaway occurs. The criteria for temperature runaway are explicitly given for a cylindrical sample which is irradiated with a uniform electric field and is simultaneously cooled by convection. The results illustrate the method of predicting runaway and avoiding it by changing the experimental conditions as a function of the characteristics of the irradiated materials. View full abstract»

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  • Variable collision frequency effects on hose and sausage instabilities in relativistic electron beams

    Page(s): 1171 - 1180
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    A relativistic electron beam propagating in a dense gas typically ionizes the gas weakly, and the resulting plasma conductivity evolution strongly influences beam stability properties. We note in this paper that the electric field E and the plasma electron temperature Te usually decrease with distance ζ behind the beam head; as a result, the plasma electron neutral collision frequency νm decreases with ζ, which depresses the conductivity σ in the front of the beam and increases σ further back in the beam. We find that this variation of νm, which has generally been ignored in previous models, substantially modifies beam instability evolution. Hose instability growth tends to increase very rapidly in the beam head and taper off to an asymptotic value for large ζ, in contrast to the pure power law growth seen when νm and dσ/dζ are assumed to be constant. A second effect arises from local decreases in the perturbed conductivity σ, produced by perturbed electric field driven increases in the local collision frequency. This destabilizing effect causes the beam to behave as if the monopole conductivity σ0 were replaced by σ*=σ0 [1-(E/νm)(∂νm/∂E)]≡σ0(1-q¯). Analytical models for the case of constant q¯ illustrate the pattern of rapid hose instability growth in the beam head followed by a ‘‘plateau’’ in hose amplitudes that is also observed in hose simulations with the VIPER model. The destabilizing effect of variable νm on the perturbed conductivity also occurs for the resistive sausage instability. However, the model calculation presented here shows that the threshold for sausage instability is not likely to be reached for reasonable beam and plasma parameters. View full abstract»

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  • Ionization and radiation dynamics of carbon ablation plasmas

    Page(s): 1181 - 1188
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    A computational model that can be used for studying the ablation physics of medium z targets by ion beams is presented. In particular, the interaction of a proton beam as it heats and ablates a carbon target is analyzed. Because the radiation emitted during the interaction can carry away a significant amount of the total target energy, the radiation and ionization dynamics is treated carefully. This is accomplished by incorporating a collisional‐radiative equilibrium model into the ionization dynamics package of a one‐dimensional hydrodynamics model. Cold target energy deposition is assumed, thus eliminating the need for resolving the energy deposition after each time step. The errors incurred by this assumption are discussed. The computer simulation is applied to a general parameter study that involves varying the initial beam conditions to see effects upon the evolution of the target. In addition, the amount of Kα radiation produced by the direct interaction of the beam particles with the individual target atoms is calculated. This information is useful for diagnostic purposes since it is highly dependent upon the ionization state of the target. View full abstract»

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  • The structure of Ni5Si2 formed in Ni‐Si thin‐film lateral diffusion couples

    Page(s): 1189 - 1194
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    The microstructure of the nickel silicide, Ni5Si2, which forms during solid‐state reactions using self‐supporting Ni‐Si lateral‐diffusion couples, has been studied using high‐resolution electron microscopy (HREM) and selected‐area electron diffraction. Two different structures for Ni5Si2 have been identified, one of which is consistent with the crystal structure which has been reported to have an actual composition of Ni31Si12. There is evidence for the existence of a third structure. Variations in the distribution of these structures and the presence of planar defects may account for the reported composition range of Ni5Si2 in the Ni‐Si phase diagram. The observed HREM images are compared with computer simulated images. View full abstract»

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  • Analysis of the effect of thermal nitridation of silicon dioxide on silicon interstitial concentration

    Page(s): 1195 - 1201
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    The thermal nitridation of SiO2 has been analyzed in order to understand how the process results in large interstitial supersaturations in the silicon substrate as manifested by the greatly enhanced diffusivity of substitutional impurities such as phosphorus and boron and the growth of stacking faults. It is postulated that the interstitial injection is due to the growth of a thin oxygen‐rich layer at the dielectric/silicon interface and is magnified by the presence of a nitrogen‐rich layer near the interface which constrains the interstitials to the interface region. Because of the slow rate of growth of the oxide‐rich layer, an initial transient period exists during which many of the interstitials created at the interface are injected into the substrate, raising the concentration in the silicon. For long times, a steady‐state analysis shows that almost all of the interstitials generated at the interface diffuse back into the oxide. By extending a previous analysis for standard oxidation of silicon, a quantitative model was developed for interstitial supersaturation in the silicon which incorporates the transient regime and successfully predicts the diffusion enhancement of phosphorus with time. In addition, nitrogen incorporation in the bulk of the oxynitride and oxidation at the dielectric/silicon interface were modeled by an exponential decay to an equilibrium structure with a common time constant. View full abstract»

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  • Real‐time x‐ray topography on the growth of an Al crystal from melt

    Page(s): 1202 - 1207
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    Aluminium crystals grown from melt in an ultrahigh vacuum chamber have been observed in situ and in real time by using white synchrotron radiation [experiments were performed at the Laboratoire pour l’Utilisation du Rayonnement Electromagnétique (L. U. R. E.), Bâtiment 209c, 91405 Orsay, France]. The shape of the solid‐liquid interface is determined by the thermal conditions. The defects are generated by strains extraneous to the fusion‐crystallization process. The interfacial area is free from growth dislocations. The dislocations and subboundaries have a tendency to be parallel to the growth axis. Simple 1/2 ≪011≫‐type dislocations impinge upon the interfacial plane, proving their stability up to the melting point. View full abstract»

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  • Mechanism of crack formation in glass after high‐power laser pulse irradiation

    Page(s): 1208 - 1211
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    We report the observation of crack formation in glass surfaces after high‐power laser pulse irradiation. The damage in the irradiated region was caused by laser ablation and plasma formation, but cracks and liquid drops also appeared outside the irradiated region over a distance of many millimeters. These cracks and liquid drops became clearly visible at 12 h or more after laser irradiation in the surface of both soda‐lime glass and borosilicate crown glass. In contrast, such a delayed formation was not observed in fused silica glass. It is considered that the delayed crack formation is caused by chemical interactions of the components of the glass with atmospheric water vapor at microcracks in the surface induced by laser‐driven shock waves. View full abstract»

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  • Effects of In impurity on the dynamic behavior of dislocations in GaAs

    Page(s): 1212 - 1219
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    The effects of In impurity on the dynamic behavior of dislocations in GaAs crystals are investigated in comparison with those of Si impurity. Indium, even at a concentration of the order of 1020 cm-3, is found to affect the velocity of moving dislocations only slightly while Si impurity at a concentration of the order of 1018 cm-3 reduces it by one or two orders of magnitude. However, α dislocations are easily immobilized by In atoms while they are at rest by gettering the latter. Immobilization of β dislocations due to In gettering is much weaker than that of α dislocations. An interpretation is given of how such a difference in locking by In impurity comes about between α and β dislocations. The function of Si impurity to lock both α and β dislocations is stronger than that of In impurity on α dislocations. Nevertheless, the locking effect due to Si impurity manifests itself only in the high‐temperature range. This seems to be related to the low diffusivity of Si impurity in GaAs crystals. View full abstract»

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  • Effect of small amounts of hydrogen on the elastic behavior of lutetium

    Page(s): 1220 - 1223
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    The elastic constants of a well‐characterized, high‐purity single crystal were measured before and after hydrogen was added to change the hydrogen content from 500 at. ppm (3 wt. ppm) to 6900 at. ppm (40 wt. ppm). Comparison between the two sets of measurements shows that such a small change in hydrogen content has a disproportionately large effect on the elastic stiffness. In this case the increase in hydrogen content produced an increase in all directly measured elastic constants by the order of 0.5%. Further comparison of our data with earlier data indicates that other interstitial elements (e.g., C, N, and O) may also exert an inordinately large influence on the elastic stiffness. View full abstract»

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  • Phase formation and dissociation in the thin‐film Pt/Al system

    Page(s): 1224 - 1231
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    Phase formation has been investigated in the following thin‐film systems: Al/Pt, Pt2Al/Al, Pt8Al21/Pt, Pt/PtAl, and Pt/Pt5Al21/Al, between 225 and 550 °C. The films were prepared by sequential evaporation and coevaporation, annealed under vacuum, and analyzed by Rutherford backscattering and x‐ray diffraction. In all cases, except for Pt/PtAl, the initial phase formed was Pt2Al3, followed by the more Pt‐ or Al‐rich phases, depending on the overall stoichiometry. Al is the dominant moving species during the formation of Pt2Al3. View full abstract»

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  • Stress effects on III‐V solid‐liquid equilibria

    Page(s): 1232 - 1239
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    The general equations that govern the equilibrium of a stressed III‐V ternary compound with a melt are derived and applied to the case of liquid‐phase epitaxy. The stresses are analyzed in detail and the thin‐film approximation is assessed. The deviations of the solid and liquid compositions from their phase diagram values are obtained in the vicinity of the solid composition that gives lattice matching with the substrate. A quantity Q is defined that can be used as an index of the magnitude of the stress effect (sometimes called lattice pulling). The intrinsic properties and growth conditions that may affect Q are discussed. View full abstract»

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  • Hydrogen motion in thermally annealed sputter‐deposited hydrogenated amorphous silicon

    Page(s): 1240 - 1244
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    It is shown that the bulk hydrogen concentration in radio‐frequency (rf) sputtered films of hydrogenated amorphous silicon (a‐Si:H) can be determined from reflected electron energy‐loss spectroscopy signals obtained even during ion beam etching of the film. As a result, depth profiling, with a 50‐Å depth resolution of the hydrogen concentration, and with 1 at. % accuracy of the a‐Si Hx/a‐Si Hy multilayer, is achieved. Using this technique to depth profile annealed multilayer samples of rf sputter‐deposited a‐Si:H, it was found that despite the loss of hydrogen at elevated temperatures the original interface widths are unchanged even after a 500 °C, 1 h anneal. This result contrasts sharply with previous measurements of hydrogen motion in glow‐discharge a‐Si:H and indicates a significant difference between the two types of a‐Si:H with respect to hydrogen motion at elevated temperatures. View full abstract»

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  • Spreading of Au dots on InP surfaces

    Page(s): 1245 - 1250
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    Circular gold dots, measuring about 200 μm in diameter and either 150 or 300 nm in thickness, have been produced on {100}, {110}, and {111} substrates of indium phosphide by a combination of vapor deposition and photolithographic processing, annealed at temperatures ranging from 420–460 °C, and subsequently examined by optical microscopy. During annealing, a reaction product, bounded by well‐defined crystallographic planes of the substrate, forms, expands parabolically with annealing time, and eventually saturates due to the limited supply of gold. Generally, reactions proceed at least three times faster at {100} and {110} planes than at {111}In planes, in which reactions proceed about three times faster than at {111}P planes. Analysis of concomitant reaction kinetics yields an activation energy of 8.6±3.0 eV for reactions at {111}In planes. Results are interpreted in terms of a preferential interfacial reaction at {111}In planes, which is controlled by solid‐state diffusion and eventual escape of phosphorus. View full abstract»

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  • Metalorganic molecular‐beam epitaxy of ZnSe and ZnS

    Page(s): 1251 - 1256
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    The metalorganic molecular‐beam epitaxial growth of ZnSe and ZnS on (100) GaAs has been demonstrated and characterized. Diethylzinc and diethylselenide were used for the ZnSe growth, while for the ZnS growth both hydrogen sulfide and diethylsulfide (DES) were tested as sulfur sources. The dependence of the growth rate on various growth conditions was investigated to clarify the growth mechanism. When group VI alkyls were used as sources, pyrolysis in a cracking cell was required, unlike metalorganic chemical vapor deposition. Interesting differences in growth kinetics and in crystallinity between H2S‐based and DES‐based ZnS have been found. Photoluminescence spectra of ZnSe layers measured at 4.2 K showed resolved exciton emissions. However, donor‐acceptor pair emission lines attributed to a Li acceptor (LiZn) were also observed. Smooth, monocrystalline ZnS layers could be grown at substrate temperatures above 250 °C by using cracked H2S and DES, and above 150 °C by using uncracked H2S. Photoluminescence spectra of ZnS layers at 74 K were dominated by unidentified blue emissions. These good results reflect the complete absence of a premature reaction. View full abstract»

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  • Silicide formation with codeposited titanium‐tantalum alloys on silicon

    Page(s): 1257 - 1264
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    The formation of disilicides of titanium and tantalum from Ti‐Ta alloys codeposited on silicon and polycrystalline silicon have been investigated using x‐ray diffraction techniques, resistance measurements, and Auger electron spectroscopy. Titanium and tantalum in the Ti‐Ta alloy interacted independently with silicon. There was no titanium/tantalum compound formation and no ternary was detected. The growth of each metal silicide was sustained by continuous out‐diffusion of silicon into the Ti‐Ta alloy film until the metals were consumed in the silicide transformation. This behavior may account for the absence of phase separation and component accumulation. An initial reaction was observed after the 600 °C, 30 min anneal. The stable end phases formed at temperatures ≥800 °C are TiSi2 and TaSi2. High molecular weight intermetallics such as Ta5Si3 and Ti5Si3 that are normally not detected in Ta‐Si and Ti‐Si interaction studies were detected, suggesting a stabilizing effect of the impurities. The sheet resistance of the heat‐treated samples is: (a) a strong function of the titanium content of the Ti‐Ta alloy (low for Ti‐rich alloys); (b) lower on silicon substrates; (c) invariant at temperatures ≫900 °C. The etch rate of the heat‐treated samples in buffered hydrofluoric acid increased with increasing titanium content in the film. View full abstract»

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  • High aspect ratio hole filling by tungsten chemical vapor deposition combined with a silicon sidewall and barrier metal for multilevel interconnection

    Page(s): 1265 - 1273
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    A newly developed processing for high aspect ratio hole filling by tungsten chemical vapor deposition, combined with a Si sidewall technique and resist etch back is proposed. A high aspect ratio hole (around 3) was completely filled with W and W‐Si alloy without voids. It is also proposed to interpose a TiN/TiSi2 layer between W and Si, in order to suppress rapid silicidation of W at high temperatures above 800 °C. Silicidation rates for W/TiN/TiSi2/Si systems were 2–2.5 orders of magnitude lower than W/Si systems. Electrical contact resistivity was kept to be lower than 1×10-5 Ω cm2 even after 900 °C annealing by suppressing rapid silicidation of W. View full abstract»

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  • Structural measurements on evaporated a‐Si/SiOx superlattices

    Page(s): 1274 - 1277
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    The structure of evaporated a‐Si/SiOx superlattices has been investigated by transmission electron microscopy, Raman scattering, and optical absorption spectroscopy. The layers are smooth and regular, but all three measurements show effects of bond distortions or defects within 1–2 nm of the Si/SiOx interfaces. View full abstract»

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  • High‐resolution x‐ray diffraction studies of InGaAs(P)/InP superlattices grown by gas‐source molecular‐beam epitaxy

    Page(s): 1278 - 1283
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    High‐resolution x‐ray diffraction studies have been carried out to determine the structural perfection and periodicity for a number of high‐quality InGaAs/InP superlattices and one InGaAsP/InP superlattice grown by gas‐source molecular‐beam epitaxy. For comparison, high‐resolution diffraction both with a three‐crystal geometry and with a four‐crystal monochromator was used along with conventional double‐crystal x‐ray diffractometry. The best resolution in the x‐ray satellite patterns was obtained with the four‐crystal monochromator, providing a resolution of one molecular layer in the periodicity of the superlattice. The presence of sharp satellite reflections in the x‐ray diffraction profiles demonstrate smooth interfaces with well‐defined modulated structures which could be derived from a kinematical diffraction step model. For some superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier with ideally sharp interfaces. For other superlattices a thin strained layer had to be assumed on either one or both sides of each quantum well. The comparison of these structures demonstrates the extreme sensitivity of the high‐resolution method in conjunction with the step model, to study very small modifications in superlattice periodicities. View full abstract»

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  • A novel method of selective epitaxial growth of InP by metalorganic chemical vapor deposition

    Page(s): 1284 - 1286
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    A novel method of the selective epitaxy of InP was developed by employing a two‐step growth in atmospheric pressure metalorganic chemical vapor deposition. By this method, selective epitaxy, without ridge and/or lateral growth, and with uniform deposition of the polycrystalline layer on the SiO2 mask, could be achieved. First, a thin uniform InP polycrystalline layer was deposited on a SiO2/InP substrate and a stripe pattern was formed by photolithography, and then selective epitaxial growth was performed. Selective epitaxial layers thus obtained were found to have a photoluminescence half width of ∼40 meV at room temperature, which was comparable to the one reported by other workers in homoepitaxial metalorganic chemical vapor deposition growth of InP. The resistivity of the polycrystalline layer was ∼700 Ω cm at room temperature, which was four orders of magnitude larger than that of the selective epitaxial layer. Therefore, electrical isolation may be sufficient for fabrication of InP planar devices. View full abstract»

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  • Depletion of interstitial oxygen in silicon and the thermal donor model

    Page(s): 1287 - 1289
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    Recent experimental studies which monitor the loss of oxygen interstitials during 450 °C annealing of Czochralski silicon have been argued to be in conflict with the predictions of existing thermal donor (TD) kinetic models. In this paper we show that a recently proposed model predicts an oxygen depletion rate which is in excellent agreement with the experimental findings. View full abstract»

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  • Electron states in two coupled quantum wells—A strong coupling‐of‐modes approach

    Page(s): 1290 - 1297
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    In this paper, coupled‐mode equations for two strongly coupled quantum wells are derived via two methods: (i) a ‘‘reciprocity’’ formulation similar to the reciprocity theorem in electromagnetics, and (ii) a variational formulation. It is shown that both formulations give the same coupled‐mode equations. Numerical results for the electron energy levels and wave functions for two coupled asymmetric or symmetric quantum wells are presented, using both the strong coupling‐of‐modes theory and the conventional weak coupling‐of‐modes theory, and are compared with those of the exact calculations. The two‐coupled‐quantum‐wells model is useful in the study of electron transport in superlattice via hopping or tunneling. 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