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Journal of Applied Physics

Issue 8 • Date Oct 1995

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Displaying Results 1 - 25 of 72
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • X‐ray focusing optics using flat or bent crystals with two‐dimensionally modulated surfaces

    Page(s): 4823 - 4829
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    Calculations of focus characteristics for x‐ray focusing systems using either flat or bent crystals with two‐dimensional modulated surfaces are presented. Based on the wave‐optics approach, the analytical formulas are derived for elliptical Fresnel zone structures (flat crystals) and linear Bragg zone structures (toroidally bent crystals). It is shown that for a given Si(111) reflection and Ti Kα radiation, a micron‐size focal spot can be achieved by using only one flat crystal with a modulated surface. The peak intensity is then nearly 100 times higher than that of the flat crystal without modulations. However, for a toroidally bent crystal with both Fresnel and Bragg diffraction amplitudes, the latter becomes dominant, since, due to the bending, the rapid oscillations of the Fresnel diffraction amplitude vanish. It is also shown that a focal spot of 0.3 μm for a bent crystal with linear Bragg zone structures is approximately four times narrower than that of an unmodulated surface. From the analysis, the modulated surfaces for cylindrically and spherically bent crystals are deduced to be a combination of Bragg and Fresnel zones. © 1995 American Institute of Physics. View full abstract»

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  • Energy straggling of protons in solids

    Page(s): 4830 - 4834
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    By use of the linear‐response dielectric theory and local electron density approximation, we calculate the energy straggling of protons in solids. The correlation and exchange interaction of electron gas in solids is taken into consideration by introducing a static local‐field‐correction function in the dielectric function. The theoretical results are compared with experimental and empirical data, as well as with other previous theoretical results. © 1995 American Institute of Physics. View full abstract»

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  • Polarimetric scattering from heterogeneous particulate media

    Page(s): 4835 - 4839
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    Electromagnetic (EM) scattering in a medium containing discrete scatterers is a problem with broad interdisciplinary interest. The Mueller matrix solution has been applied to the study of EM polarimetric scattering and the vector radiative transfer from a layer of random medium. In this article, we report the methods to polarimetric scattering from a layer of particulate media containing: randomly dense spherical particles, nonuniformly oriented spheroids, or random clusters of spheroids. The complex scattering amplitude functions and phase matrix are explicitly obtained. Numerical results of the Mueller matrix solution show the properties of completely polarimetric scattering of those random media and its functional dependence on the relevant physical parameters. © 1995 American Institute of Physics. View full abstract»

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  • Holographic recording in photorefractive thin films: Edge effects

    Page(s): 4840 - 4844
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    The initial holographic recording rate has been analytically studied for a photorefractive thin slab. The finite thickness is explicitly taken into account by using a two‐dimensional formulation (coordinates x and z parallel and perpendicular to the slab faces, respectively). It is shown that for a thickness comparable to the grating period, the solution appreciably departs from the usual one‐dimensional result, i.e., edge effects are remarkable. In particular, significant space‐charge fields perpendicular to the slab faces are generated. These effects may substantially modify the diffraction properties of the recorded photorefractive gratings, as exemplified for a GaAs film. © 1995 American Institute of Physics. View full abstract»

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  • Standing‐wave acoustic trap for nonintrusive positioning of microparticles

    Page(s): 4845 - 4849
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    A nonintrusive three‐dimensional trap for microscopic particles in a liquid is described. The trap is based on acoustic radiation forces in an ultrasonic confocal standing‐wave cavity. Experiments at 11 MHz demonstrate the concept and verify the theoretically calculated forces. Theoretical calculations for higher‐frequency systems indicate a significant potential for low‐rms‐displacement trapping of submicrometer particles, making the trap suitable for nonintrusive scanning near‐field optical microscopy. © 1995 American Institute of Physics. View full abstract»

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  • Wave‐to‐plasma power transfer in magnetically assisted high‐frequency discharges in argon

    Page(s): 4850 - 4854
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    A simplified discharge model for the prediction of the wave‐to‐plasma power transfer in high‐frequency collisional argon plasmas in the presence of a static magnetic field is presented. The study is based on the solutions to the homogeneous electron Boltzmann equation for an oscillating electric field composed of a right‐ and left‐hand‐side rotating parts, moving around the magnetic‐field lines. The mean absorbed power per electron to maintain the plasma is calculated for a container with nonconducting surfaces and the results are then compared with an experiment in the literature. © 1995 American Institute of Physics. View full abstract»

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  • Ion energy distributions in dual‐ and single‐mode microwave/radio‐frequency plasma

    Page(s): 4855 - 4858
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    Ion energy distribution functions (IEDF) were measured at the surface of a grounded or a rf‐powered electrode exposed to a microwave (MW, 2.45 GHz) or a rf (13.56 MHz) discharge in argon. The IEDFs measured on the grounded electrode in both the rf and the MW modes show a higher contribution of low‐energy ions when the pressure is raised. The maximum ion energy Em decreased from 12.0 to 8.5 eV in the MW plasma, but remained at 26±0.5 eV in the rf plasma. The mean ion energy Ē decreased from 6.1 to 3.8 eV (MW) and from 16.0 to 12.0 eV (rf) when the pressure was raised from 30 to 210 mTorr. The IEDFs in the rf mode exhibit a single peak, while a bimodal structure is observed in the MW mode. When the electrode is rf powered to achieve a negative dc bias voltage VB, the Em values reach ∼1.2eVB (rf) and ∼1.1eVB (MW), respectively. The IEDFs in the rf mode display a multiple peaked structure which is associated with a rf‐modulated sheath. In the dual‐frequency MW/rf mode the IEDF is single peaked, narrow, and centered around eVB. A nearly tenfold increase in the ion flux is observed when increasing the MW input power, while the ion energy remains unchanged for a constant VB value. This allows an independent control of ion energy and ion flux, suitable for the control of material properties in plasma processing. © 1995 American Institute of Physics. View full abstract»

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  • Energy deposition in the cathode layer of transient high pressure glows derived from interferograms of the emanating pressure wave

    Page(s): 4859 - 4866
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    The large electric fields in the cathode sheath of high pressure glow discharges lead to localized energy deposition in the gas, which drives a gas dynamic pressure wave into the region where the transient high pressure glow is homogeneous. For a range of parameters typical for discharge pumped XeCl‐lasers the gas density profiles of these waves have been measured interferometrically with high spatial resolution (20 μm). From comparisons with gas dynamic model calculations the amplitude and the spatial profile of the initial temperature distribution resulting from the energy deposition during the formation of the cathode sheath have been determined. These data can be used to verify assumptions to be made in future improvements of self consistent discharge models of the cathode sheath formation. © 1995 American Institute of Physics. View full abstract»

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  • Electron density fluctuations in a dusty Ar/SiH4 rf discharge

    Page(s): 4867 - 4872
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    The average electron density and electron density fluctuations in a dusty Ar/SiH4 rf discharge have been studied using a microwave resonance technique. The average electron density increases with rf input power and it has a maximum as a function of pressure at about 30 mTorr. Within the first second of plasma operation the electron density decreases with a factor of ten. This is caused by submicroscopic particles, formed in the discharge, which rapidly absorb electrons. When the particles reach a critical size they are expelled from the plasma. This process is governed by a balance between the Coulomb force, trapping the particles in the positive plasma glow and the neutral drag force, flushing them out. The periodic growth and expulsion of particles, monitored by light scattering, results in an oscillatory behavior of the electron density. From the measured oscillation period (τ), which is in the order of seconds to minutes, and its dependence on the gas flow rate (F) and on the fraction α of SiH4 in the plasma (τ[s]≊4.5×102α-1F-2 [sccm], at 10 W rf power input), the trapping force (FC) on particles can be calculated: FC[N]≊4×10-18r [nm], where r is the radius of a particle. © 1995 American Institute of Physics. View full abstract»

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  • Interaction of an edge dislocation with a wedge crack

    Page(s): 4873 - 4880
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    The elastic interaction of an edge dislocation with a wedge crack is investigated using Muskhelishvili’s complex potential treatment of elasticity. The stress intensity factors induced by the dislocation, the strain energy, and the image force acting on the dislocation are formulated, calculated, and plotted. Especially, the influence of wedge angle on the shielding effects and on image forces is investigated. The results show that the radial component of the image force is inversely proportional to the distance from the crack tip to the dislocation and the tangential image force increases with increasing wedge angle as the dislocation position is kept unchanged. When the slip plane passes the crack tip, whether the edge dislocation shields or antishields the crack tip depends on its Burgers vector. In this case, the slip plane of the edge dislocation of Burgers vector b1+ib2=beiθmax inclined at an angle θmax with respect to the positive real axis corresponding to the maximum mode I crack shielding increases slightly to a maximum and then decreases with increasing wedge angle. Regardless of wedge angle, the maximum mode II shielding (or anti‐shielding) occurs when the dislocation is located at the positive real axis. © 1995 American Institute of Physics. View full abstract»

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  • Chemical transformations of the polyimide Kapton brought about by ultraviolet laser radiation

    Page(s): 4881 - 4887
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    By the use of ultraviolet laser pulses of microsecond and millisecond duration it is shown that the chemistry of the transformations of Kapton by UV laser radiation is strongly dependent on the intensity (power/unit area) of the laser beam. With these long pulses, the polymer was not ablated. The decomposition resulted in 51% of the polymer weight being converted to gaseous products consisting mostly of CO (67%), HCN (15%), C2H2 (12%), and some (≪5%) CO2. The major solid product that remained was ‘‘glassy’’ carbon which was identified from its Raman spectrum. This material can be viewed as the product of the secondary addition reactions of the residue that is left after the loss of the gaseous products listed above. With 20 ms pulses, the evolution of the gaseous products increased linearly with intensity and the product composition was constant within the experimental uncertainty over a 12‐fold range of intensity up to 50 kW/cm2 (≡1 kJ/cm2). These results show that pulses of duration much greater than ns do not lead to ablation even at fluences that are 104 greater than the threshold for ablation using nanosecond pulses. It is therefore more appropriate to view the ablation of this polymer by UV laser pulses of nanosecond duration as being due to the scaling of an intensity threshold rather than a fluence threshold as has become the practice. © 1995 American Institute of Physics. View full abstract»

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  • Methods for calculating electrostatic quantities due to a free charge in a nanoscale three‐dimensional tip/base junction

    Page(s): 4888 - 4894
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    The exact solutions for fully three‐dimensional electrostatic quantities due to a free charge in a nanoscale tip/base junction, such as the scanning‐tunneling microscope, are given for the problem as modeled in the prolate‐spheroidal coordinate system. These exact solutions consist of summation series of integrals of conical functions, and methods for calculating these exact solutions with high accuracy are described in detail in this paper. Calculated results for the surface‐charge distribution on the tip and the base due to a free electron in a nanoscale tip/base junction are also presented. This analysis has important implications for the ultimate objective of quantifying electron tunneling, from first principles, in nonplanar geometries such as sharp vacuum field emitters. © 1995 American Institute of Physics.   View full abstract»

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  • Identification of the common electrically detected magnetic resonance signal from a Si diode

    Page(s): 4895 - 4898
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    Structure in the electrically detected magnetic resonance signal from a common type of Si diode has been resolved and measured for different orientations of the magnetic field in the (111) plane. The center is found to have C3v symmetry with Δg≳0 and Δg≊0. It is proposed that the signal is due to a broken bond, or combination of colinear broken bonds, in a vacancy cluster which acts as a recombination center. The most likely cluster is the divacancy which has captured an electron in the antibonding state formed from the most distant broken bonds and a hole in a bonding state associated with the divacancy. © 1995 American Institute of Physics. View full abstract»

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  • The growth dynamics of thick sputtered copper coatings under the influence of surface diffusion: A quantitative atomic force microscopy study

    Page(s): 4899 - 4905
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    The evolution of surface features during the growth of a coating is of vital importance for the resulting overall film structure and morphology. In the low substrate temperature regime (T/TM≪0.3) the growth front of a single component material roughens due to fluctuations in the incoming particle beam (kinetic roughening) and relaxes via surface diffusion. The continuous deposition process thus leads to the evolution of surface features of large lateral extensions compared to the extension of the film‐forming particles. A detailed experimental study of the surface evolution of sputtered copper coatings with thicknesses ranging from 300 to 105 Å for a working gas pressure of 0.4 Pa is presented. The roughening as well as the relaxation of the film growth front is studied by means of atomic force microscopy (AFM). The increasing lateral extension of the surface features during growth (coarsening) can well be described by a deterministic continuum model of surface diffusion. The model is capable of predicting the evolution of the surface profile’s Fourier transform for increasing deposition times (i.e., increasing film thickness). A retransformation from k space to real space allows for a direct comparison of surface profiles obtained from AFM scans with those resulting from the continuum model and gives good qualitative agreement of the profile shapes. © 1995 American Institute of Physics. View full abstract»

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  • Laser‐induced crystallization phenomena in GeTe‐based alloys. I. Characterization of nucleation and growth

    Page(s): 4906 - 4917
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    The laser‐induced crystallization behavior of GeTe‐based amorphous alloy thin films has been quantitatively studied by local reflection measurements with a focused 780 nm laser. The use of multiple laser pulse sequences enables the nucleation rate and crystal‐growth speed to be separately deduced, allowing the compositional variation of both these processes to be followed. This not only gives detailed information on the crystallization mechanism, but also allows the fine tuning of phase change alloy compositions for use in erasable optical recording. The differences between the as‐deposited and melt‐quenched amorphous phases are also discussed. In particular, it is shown that the crystallization speed of the as‐deposited layer can differ by over an order of magnitude from that of the melt‐quenched amorphous layer. The as‐deposited state can, however, be transformed into a modified amorphous state equivalent to that obtained by melt quenching a previously crystalline layer. This allows the determination of the optical constants and crystallization speeds of the amorphous state written during optical recording. © 1995 American Institute of Physics. View full abstract»

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  • Laser‐induced crystallization phenomena in GeTe‐based alloys. II. Composition dependence of nucleation and growth

    Page(s): 4918 - 4928
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    The laser‐induced crystallization behavior of GeTe‐based amorphous alloys has been measured with a novel multipulse laser technique. This enables the composition dependence of the nucleation rate and crystal growth speed to be independently followed. Two types of crystallization are investigated. The first involves single‐phase crystallization of quaternary alloys based on Ge39Sb9Te52, in which the composition dependence of nucleation and growth is followed as Se, S, Sn, and Si are included. Both the nucleation rate and crystal‐growth speed vary exponentially with the composition, and a correlation is found between crystallization behavior and bond strengths. The second involves multiphase crystallization in the GeSbTe ternary system. It is shown that the observed variations in crystallization behavior primarily arise from the composition dependence of nucleation rather than crystal growth. The implications of this finding for the importance of long range diffusion during crystallization in the GeSbTe system are discussed. © 1995 American Institute of Physics. View full abstract»

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  • Measurement of tortuosity of anisotropic acoustic materials

    Page(s): 4929 - 4932
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    Tortuosity, i.e., the high‐frequency limit of the squared propagation index, has been evaluated with narrow‐band piezoelectric transducers on reticulated plastic foams. The basic procedure was recently reported by J. F. Allard, B. Castagnède, M. Henry and W. Lauriks [Rev. Sci. Instrum. 65, 754 (1994)]. Further experimental work related to the anisotropic nature of these materials has been done by probing the propagation index versus angle. A simple numerical routine has been implemented in order to recover the propagation index along principal directions. These predicted values compare well with measurements taken directly along the principal geometric axes of the samples. Slight angular deviations of the principal axes themselves have been observed. This is the very first account of the anisotropy of tortuosity measured by ultrasonic methods in air‐saturated porous materials. © 1995 American Institute of Physics. View full abstract»

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  • A solution of the doping problem for Ga delta‐doping layers in Si

    Page(s): 4933 - 4938
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    We have studied the incorporation of Ga in silicon during the fabrication of delta‐doping layers. The delta‐function doping profiles were grown by molecular beam deposition following a solid phase epitaxial growth method. Medium‐energy ion scattering, secondary ion mass spectrometry, and Rutherford backscattering spectrometry were used to determine the structure and composition of the grown films. The interface velocity of the crystallization front and the diffusion coefficient of the impurity atoms in the Si matrix, both relevant parameters of the growth process, were measured. Optimum growth conditions were found that yield Ga doping profiles of less than 1.0 nm (full width at half maximum), with more than 95% of the buried dopant atoms on lattice sites. For these optimum growth conditions, a model is derived explaining the observed incorporation of the Ga atoms. © 1995 American Institute of Physics. View full abstract»

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  • Cross‐sectional atomic force microscopy of semiconductor nanostructures

    Page(s): 4939 - 4942
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    We performed imaging of semiconductor nanostructures (quantum wells and quantum wires) by atomic force microscopy of the cleaved edge of the samples under ambient conditions. Selective etching was used to enhance the composition contrast of the semiconductor heterostructure layers, and a procedure for retrieving the nanostructure dimensions from the scanned image is presented. The simple sample preparation and the relatively large (up to ∼100×100 μm2) imaged areas offer advantages over more conventional nanometer resolution techniques such as transmission electron microscopy. © 1995 American Institute of Physics. View full abstract»

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  • Organic molecular beam deposition of highly nonlinear optical 4′‐nitrobenzylidene‐3‐acetamino‐4‐methoxy‐aniline

    Page(s): 4943 - 4947
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    Thin films of the nonlinear optical material 4′‐nitrobenzylidene‐3‐acetamino‐4‐methoxy‐aniline have been prepared using the organic molecular beam deposition technique. High quality homoepitaxial layers have been grown at substrate temperatures of 80 °C and moderate growth rates of 0.1–0.5 Å/s. The samples have been characterized by optical polarization and interference microscopy as well as atomic force microscopy. Growth experiments on inorganic substrates, including silicon and glass, have been performed in a substrate temperature range of -190 to 100 °C and led to amorphous films at low temperatures and polycrystalline films at temperatures above 50 °C. © 1995 American Institute of Physics. View full abstract»

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  • Anisotropic elasticity study of the critical thickness of an epilayer on a substrate with different elastic constants

    Page(s): 4948 - 4957
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    The critical thickness of an epilayer on a substrate with different elastic constants is investigated by following Stroh’s treatment of anisotropic elasticity [Philos. Mag. 3, 625 (1958)]. A closed formula is derived to calculate the critical thickness and an exact solution may involve numerical evaluation of the equation. The results indicate that the self‐energy of the dislocation is controlled by the soft phase between the epilayer and the substrate, while the interaction energy depends only on the elastic constants of the thin film. It is easier for a dislocation to be formed if the substrate is softer than the film, and consequently the critical thickness is smaller. On the other hand, a soft epilayer can have a large thickness without any mismatch dislocation. Explicit equations are given here for the {100}, {110}, and {111} epitaxial planes. The system of a GexSi1-x epilayer on a Si substrate was taken as an example to demonstrate the influence of the difference in elastic constants on the critical thickness. Even though the difference between the elastic constants of the epilayer and the substrate is not very large, ignoring this difference can cause a relative error over 20% in calculation of the critical thickness. For this system, a simplified equation yields sufficiently accurate results. © 1995 American Institute of Physics. View full abstract»

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  • Film thickness effects in the Ti–Si1-xGex solid phase reaction

    Page(s): 4958 - 4965
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    The effects of film thickness on the Ti–Si1-xGex solid phase reaction were investigated. Thin C49 TiM2 (M=Si1-yGey) films were formed from the solid phase reaction of 400 Å Ti or 100 Å Ti with Si1-xGex alloys. It was determined that for films formed from 400 Å Ti, the nucleation barrier of the C49‐to‐C54 transformation decreases with increasing germanium content, for alloy compositions with up to ≊40 at. % germanium (i.e., x≤0.40). It was also observed that germanium segregates out of the TiM2 lattice, for both the C49 and C54 phases, and is replaced on the TiM2 lattice with Si from the substrate. The germanium segregation changes the Ge index y of the Ti(Si1-yGey)2. For films formed from a 100 Å Ti layer it was observed that the C54 TiSi2 nucleation temperature was increased by ≥125 °C. The addition of germanium to the silicon increased the agglomeration of the C49 phase and caused the C54 TiM2 nucleation barrier to increase further. The results also indicate that the increased temperature required for the transition to the C54 phase, for the 100 Å films, leads to an increased rate of germanium segregation. © 1995 American Institute of Physics. View full abstract»

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  • Improvement of microstructure of amorphous silicon–germanium alloys by hydrogen dilution

    Page(s): 4966 - 4974
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    The microstructures of two sets of hydrogenated amorphous silicon–germanium (a‐Si1-xGex:H) alloys prepared by the plasma‐enhanced, chemical‐vapor‐deposition technique with and without hydrogen dilution of the source gases (silane and germane) have been analyzed by small‐angle x‐ray scattering (SAXS), infrared vibrational spectroscopy, and flotation density measurements. Optoelectronic properties of codeposited films have also been characterized. Hydrogen dilution suppresses dihydride/polyhydride formation, reduces bonded H content, and reduces the SAXS‐detected microstructure for x≳0. Studies of anisotropy in the SAXS intensity indicate an increased amount of oriented microstructure as Ge is added, consistent with a trend toward columnarlike growth in both undiluted and hydrogen‐diluted films, but the diluted films have a significantly reduced degree of such oriented microstructure. The improvement in the microstructure of a‐Si1-xGex:H films by H2 dilution correlates with concomitant improvement of optoelectronic properties. The modification of microstructure due to H2 dilution of the source gases is discussed in terms of growth mechanisms of alloy films. © 1995 American Institute of Physics. View full abstract»

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  • Effect of growth conditions on the structural properties of ion beam sputter deposited SiGe epilayers

    Page(s): 4975 - 4981
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    Structural properties of Si1-xGex layers epitaxially grown on Si(100) by Ion Beam Sputter Deposition were studied as a function of growth temperature and film thickness. It was shown that the structure of defects strongly depends on the growth temperature, Tg. The dislocations cross grid which is observed at the SiGe/Si interface for layers grown at high (700 °C) Tg is missing in layers grown at low (≲550 °C) Tg, while a new type of defects parallel to {001} and {113} lattice planes appear at these temperatures. The optimal Tg for a Ge content of 20‐25 at. % was found to be close to 550‐625 °C. Surface roughness for all the growth temperatures was found to be less than that for such a ‘‘smooth’’ technique as MBE. Photoluminescence studies revealed, to the best of our knowledge for the first time, two peaks on the low energy side in the neighborhood of the Si(TO) peak of the epilayers. The evolution of the intensity of these peaks is strongly correlated with the dynamics of strain relaxation and can be attributed to a set of dislocations at the SiGe/Si interface extending both to the epilayer and to the bulk Si. © 1995 American Institute of Physics. View full abstract»

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Aims & Scope

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

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Editor
P. James Viccaro
Argonne National Laboratory