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Journal of Applied Physics

Issue 12 • Date Dec 1989

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Displaying Results 1 - 25 of 84
  • On the thermodynamics of the up‐conversion and fluorescence of light

    Page(s): 5685 - 5690
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    Frequency doubling of light, made possible by the laser, has precipitated a host of anti‐Stokes fluorescence activities. In this work, a criterion based on the principle of the increase of entropy in adiabatic processes is presented. This principle relates to the nature of the light rather than to the substances performing the harmonic generation. It is shown that changes in the spectral entropy can be used to discriminate which radiation is suitable for up‐conversion. The spectral entropy of a blackbody has a maximum with respect to frequency at any given temperature. If the final state of a process is located at this maximum, then a critical minimum temperature, below which no up‐conversion may be expected, can be found. A definition of the effective temperature of highly nonequilibrium sources such as the laser is presented. Fluorescence in the low‐pressure mercury lamp is treated in the context of thermodynamics. Examples of practical light sources are discussed, and it is shown that up‐conversion is, rather exclusively, the purview of the laser. View full abstract»

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  • Magnetic fields generated by axially symmetric systems

    Page(s): 5691 - 5701
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    A coherent and systematic multipole formulation of the magnetic field generated, both in the near and remote regions, by axially symmetric field and gradient systems is presented. These include an open spherical winding, an arbitrary number of coaxial coils, and a combination of coils and spherical or solenoidal windings. Optimum configurations for maximum uniformity of the field or field gradient are discussed and illustrated by numerical results. Legendre series resulting from the multipole expansion are analyzed at the system’s boundary where convergence is very slow, using a summation method particularly suitable for numerical computation. View full abstract»

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  • Temperature effect on a tilted birefringent filter in a tunable laser: A limitation for Raman spectroscopy

    Page(s): 5702 - 5706
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    The temperature effect on the wave number selected by a tilted birefringent filter inside a dye laser cavity is measured and theoretically discussed. For a quartz plate at Brewster angle, the wave‐number shift is observed between 1.1 and 1.35 cm-1 K-1 according to the angle between the crystal optical axis and the incident plane. A thorough calculation is fully in agreement with these results: the main part of the shift is related to the variation of refractive indices, but both the thickness expansion and the wavelength disperson of indices moderate the temperature effect. The observed shift is still larger than the width at half height of the exciting line necessary for Raman spectroscopy. A filter with three plates whose thicknesses are in ratio 1:4:16, which transmits a band of satisfactory width, cannot be used however if a rigorous temperature stability is not achieved. A practical solution is found by combining a 1:4 filter and a Fabry–Perot étalon. View full abstract»

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  • A comprehensive kinetic model of the electron‐beam‐excited xenon chloride laser

    Page(s): 5707 - 5725
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    A new kinetics model capable of simulating performance of electron‐beam‐pumped xenon chloride lasers over the full range of experimental evidence is presented. The model comprises 202 chemical processes employing 41 species. Its operation is described and the full set of rate equations given. Calculations of stimulated emission and absorption cross sections for XeCl are presented, and simulations of various lasing results are shown in the context of explicating dominant processes. Major kinetics issues are examined, particularly those leading to the model’s rates for vibrational excitation of HCl and for electron quenching of the excited excimer molecule. View full abstract»

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  • A new composite‐cavity laser with two different waveguide cores for stable longitudinal mode operation

    Page(s): 5726 - 5730
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    We have developed a new composite‐cavity laser with two different waveguide cores connected near the front mirror in the same cladding. This composite cavity has a built‐in structure that is capable of giving high mode selectivity because of strongly modulated reflectivity of the front mirror. The laser shows very stable single longitudinal mode operation in a temperature range as wide as about 50 °C for output powers from 3 to 100 mW without mode hopping. View full abstract»

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  • Phase locking laser diodes using photorefractive coupling

    Page(s): 5731 - 5737
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    Several authors have reported strong frequency pulling while coupling laser diodes using phase conjugation. However, to our knowledge, no one has proven stable phase locking by interfering the laser outputs to show stable fringes. A stable phase lock has been obtained, and the geometry used is compared with those proposed previously. View full abstract»

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  • Temperature distributions produced in an N‐layer film structure by static or scanning laser or electron beam with application to magneto‐optical media

    Page(s): 5738 - 5748
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    The classic problem of heat flow in multilayer film structures has been revisited from the perspective of engineering applications for fields such as optical storage media design, laser annealing of semiconductor materials, electron beam lithography, and ion implantation. A compact recursive structure N‐layer Green’s function is developed from the coupled partial differential equations of thermal conduction. Temperature profiles are calculated for the absorption of normally incident continuous and pulsed‐Gaussian‐beam irradiation, on both static and moving media, with variable absorption across the source layer. General beam, amplitude‐time dependencies can be calculated with this formalism; however, only simple rectangular pulses are treated in the text. General N‐layer solutions are developed, and compact, recursive‐integral formulas, whose evaluation is enhanced with modern computer languages such as c and apl, are derived. In addition, we offer a clear physical interpretation of the results expressed by the mathematics, which is a key element that aids successful application of the results to engineering design problems. The physics illuminated by the mathematics suggests a path toward optimal design of the media for enhanced performance, irrespective of the specific application. View full abstract»

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  • On the thermal dissociation of hydrogen

    Page(s): 5749 - 5755
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    The important role atomic hydrogen plays in the low‐temperature and pressure deposition of diamond has renewed interest in the dissociation processes of hydrogen. Following a method originally developed by Langmuir and co‐workers, the voltage‐current characteristics of refractory filaments in vacuum and reduced‐pressure gaseous environments are analyzed. Using hydrogen, deuterium, and helium, it is concluded that the difference in the power consumption by the filament in hydrogen and in vacuum is a good measure for the rate of hydrogen dissociation. This rate is shown by experiments and mathematical modeling to depend on the geometry of the refractory heater element. Relatively high dissociation rates, normalized per heater area, are obtained for small‐diameter wires, and it is argued that this is indicative of a nonequilibrium dissociation process. View full abstract»

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  • Emission spectroscopy of cw CO2 laser‐sustained argon plasma: Effects of gas‐flow speed

    Page(s): 5756 - 5762
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    The effects of elevated gas‐flow speed were studied for the cw CO2 laser‐sustained argon plasma in a chamber of 1‐atm pressure using the argon emission spectrum. Electron temperature distribution was obtained from the 415.8‐nm Ari line‐to‐continuum intensity ratio. This temperature distribution was further utilized to calculate the fraction of laser power absorbed by the plasma, and the amount of radiation loss from the plasma. The experiments were performed for laser powers of 2.5 and 5 kW with an f/7 lens focusing scheme, and gas‐flow speeds of 2–10 m/s. The results show that as high as 86% of incident laser energy can be absorbed by the plasma. Accounting for the plasma radiation loss, 41%–62% of the laser energy can still be retained as the gas thermal energy, which is a significant increase over the previously reported results for lower flow speed and smaller focusing f number. View full abstract»

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  • Solving the spatially dependent Boltzmann’s equation for the electron‐velocity distribution using flux corrected transport

    Page(s): 5763 - 5774
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    Boltzmann’s equation(BE) for the electron‐velocity distribution (EVD) in partially ionized plasmas is not usually directly integrated as an initial value problem using finite differences. This circumstance is a result of numerical effects which blur sharp density boundaries in the position‐velocity plane. To address this issue, we have applied flux corrected transport (FCT) to solving BE and demonstrated the method by calculating the EVD in the cathode fall of a He glow discharge by direct integration. Unidirectional and bidirectional EVDs are considered, and comparisons are made to conventional multibeam and Monte Carlo simulations to validate our method. We find that using FCT to solve BE is a significant improvement over conventional finite difference methods, being both more accurate and computationally faster. View full abstract»

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  • Radio‐frequency probe for plasma conductivity measurement. I. Theoretical study

    Page(s): 5775 - 5785
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    Radio‐frequency impedance variation of a finite length coil surrounding a plasma column is theoretically related to plasma complex conductivity. Calculations use two dimensions and do not need perturbation approximation. Their application range is discussed and methods are proposed to deduce from measurements the plasma electron density and effective collision frequency. View full abstract»

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  • Radio‐frequency probe for plasma conductivity measurements. II. Application to an electron beam created plasma in oxygen

    Page(s): 5786 - 5790
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    Calculations establishing the principles of a radio‐frequency coil to measure the electron characteristics of a plasma column have been discussed in the previous article. They are illustrated by an application to a low‐pressure oxygen plasma created by an electron beam of some keV. Original experimental apparatus and methodology are described. Electron densities of the order of 1011 cm-3 and electron temperatures around 0.15 eV are readily measured. View full abstract»

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  • Empirical model of breakdown in SF6: Corona‐shielding effect

    Page(s): 5791 - 5797
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    An empirical relationship for the breakdown voltage in a nonuniform field in SF6 is derived with the help of a correlation of experimental data for a rod‐plane geometry. The model is based on the hypothesis that the corona shielding radius and the critical corona length are related by a simple formula. In the first approximation this formula depends on the rod radius and the critical corona length at critical pressure; for small gap lengths a correction term, dependent on the gap length, is suggested. View full abstract»

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  • Electron paramagnetic resonance study on the p‐type doping of copper indium disulfide by phosphorus implantation

    Page(s): 5798 - 5800
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    High doping efficiencies have been observed in phosphorus‐implanted CuInS2 single crystals by pulsed electron‐beam annealing, which could not be achieved by the conventional furnace annealing method. This paper presents the investigations by using the electron paramagnetic resonance measurement on this p‐type doping effect. The electron paramagnetic resonance signal from the phosphorus interstitials was observed in the as‐implanted crystals. The same signal appeared in the subsequently thermally annealed samples but disappeared in the pulsed electron beam annealed ones. This shows the superiority of melting crystal surfaces in the pulsed electron‐beam annealing on eliminating the implantation‐induced defects to obtain high doping efficiencies. View full abstract»

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  • Defect generation in silicon‐implanted gate insulators of insulated gate field‐effect transistors

    Page(s): 5801 - 5804
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    In this paper, the effects on insulated gate field‐effect transistor device characteristics due to implantation of silicon into the gate insulator have been studied. Contrary to what one might have expected in an oxygen‐deficient insulator, the primary defects generated, as detected by optically assisted injection of electrons into the gate insulators of damaged devices, are large quantities, as much as 1.3×1012 cm-2, of neutral electron traps (NET). Secondary types of defects found appear to be fixed negative charge, approximately 2.3×1011 cm-2 in the worse case, and a smaller amount of fixed positive charge (FPC), approximately 1.7×1011 cm-2 in the worse case. It was found that none of these defects could be removed by employing conventional postmetal annealing conditions in forming gas (10% H2, 90% N2) at 400 °C for up to 60 min. The defects created by ion implantation appear to be quite different from those created by x‐ray or electron irradiation, where large quantities of FPC and NET are generated which can be annealed in a similar postmetal annealing cycles. View full abstract»

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  • The hardness and Young’s modulus of amorphous hydrogenated carbon and silicon films measured with an ultralow load indenter

    Page(s): 5805 - 5808
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    With an ultralow load indenter the hardness H and the Young’s modulus E of amorphous hydrogenated carbon and silicon films, prepared under different conditions, were determined. The values of the hardness of a‐C:H, corrected for the elastic recovery, are about 1/3 of the values measured by the Knoop method. The results show that the hardness of a‐C:H and a‐Si:H are proportional to Young’s modulus [(H/E)C =0.115, (H/E)Si =0.093]. In previous works a proportionality of H and E for metal and metal‐metalloid glasses, respectively, already has been found. View full abstract»

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  • Out‐diffusion of Ga and As atoms into dielectric films in SiOx /GaAs and SiNy/GaAs systems

    Page(s): 5809 - 5815
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    Residual Ga and As atoms in SiOx and SiNy dielectric films deposited on GaAs were investigated by Rutherford backscattering spectroscopy and particle‐induced x‐ray emission techniques. Both Ga and As atoms were detected in the films after high temperature heat treatment, and even in the films as‐deposited. The magnitude of the residual atoms presumably out‐diffused from GaAs substrates was of the order of 1×1019 /cm3. The concentration of Ga atoms prevails over that of As atoms in SiOx/GaAs systems as is generally known, and vice versa in SiNy/GaAs systems after heat treatment. Dynamic behavior of Ga and As atoms in the films as functions of annealing temperature and annealing time cannot be explained by a simple diffusion mechanism. A model is proposed that the damaged layer around the interface of the systems is responsible for the anomalous out‐diffusion phenomena. View full abstract»

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  • Diffusion and self‐gettering of ion‐implanted copper in polyimide

    Page(s): 5816 - 5820
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    The diffusion of ion‐implanted Cu in Kapton films has been studied by Rutherford backscattering. At low temperatures, diffusion is thermally activated with an energy of 0.41 eV and a diffusion constant D of about 10-18 cm2/s at room temperature. Above 460 K the implanted profiles narrow dramatically instead of continuing to spread, a process interpreted in terms of cluster nucleation at the polymer’s β’ transition temperature. Subsequent diffusion of the clusters above 525 K has an activation energy of 1.91 eV. The ion implantation causes discernible surface damage to the polyimide. View full abstract»

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  • Defect‐accelerated donor diffusion and layer intermixing of GaAs/AlAs superlattices on laser‐patterned substrates

    Page(s): 5821 - 5825
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    Data are presented showing that donor diffusion and Alx Ga1-x As‐GaAs layer intermixing are greatly enhanced in the presence of defects created by crystal overgrowth on locally laser‐melted substrates. Accelerated defect and impurity‐induced layer disordering, and donor diffusion from a solid source (SiO2 ), a vapor source (Ge), and from a grown‐in source (Se) are observed in regions of high defect density. The enhanced donor diffusion and crystal self‐diffusion are attributed to an increased density of column‐III defects and dislocations in the crystal. View full abstract»

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  • Preparation of epitaxial ABO3 perovskite‐type oxide thin films on a (100)MgAl2O4/Si substrate

    Page(s): 5826 - 5832
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    Epitaxial thin films of ABO3 perovskite‐type oxides, including PbTiO3, (Pb0.90La0.10) (Zr0.65Ti0.35)0.975O3,BaTiO3, and SrTiO3, have been successfully obtained by rf magnetron sputtering on (100)Si substrate with an intermediate epitaxial layer of MgAl2O4. Only PbTiO3 grew in the tetragonal crystal structure and other materials grew in the cubic structure. The unit axis direction of the perovskite‐type oxide films was coincident with that of the underlying MgAl2O4 films. The tetragonal PbTiO3 films were a mixture of c and a domain. The preferred orientation of the tetragonal PbTiO3 film, that is c to a domain volume ratio, could be controlled by the conditions of sample cooling after the deposition. Highly c‐axis oriented films, which consisted of more than 90% c domains, were produced by cooling the sample at a high cooling rate, typically 30 °C/min, and by maintaining an rf plasma during cooling. The mechanism of the preferred orientation of PbTiO3 film has been explained by a balance of compressive stress due to a self‐bias effect and tensile stress due to the lattice mismatch and due to the lattice anisotropy of tetragonal PbTiO3. View full abstract»

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  • Characterization of Ga out‐diffusion from GaAs into SiOxNy films during thermal annealing

    Page(s): 5833 - 5836
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    The out‐diffusion of Ga atoms during thermal annealing from a GaAs substrate into an SiOxNy encapsulating film has been studied using secondary ion mass spectrometry. The concentration of Ga atoms detected within the SiOxNy encapsulant annealed at 850 °C is found to increase with increasing the oxygen content of the encapsulant. The results are well correlated with the concentration change of the electron trap EL5 (Ec-ET =0.42 eV) evaluated from deep‐level transient spectroscopy. We conclude that the controlled Ga out‐diffusion by SiOxNy capped annealing causes enhanced electrical activation of Si implants and the generation of the EL5 trap during thermal annealing is ascribed to the Ga out‐diffusion. View full abstract»

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  • A phenomenological description of strain relaxation in GexSi1-x/Si(100) heterostructures

    Page(s): 5837 - 5843
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    We describe how in situ observation of strain relaxation of Gex Si1-x /Si(100) heterostructures in a transmission electron microscope enable us to obtain the fundamental parameters which describe the nucleation, propagation, and interaction of misfit dislocations. Activation energies and prefactors are obtained for the nucleation and propagation processes for x in the range 0.20–0.35, and a simple model to account for dislocation interactions is developed. These measured parameters are then incorporated into a predictive model of strain relaxation which successfully reproduces experimental data. This model relies only upon parameters which can be directly measured. View full abstract»

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  • Formation and characterization of grain‐oriented VO2 thin films

    Page(s): 5844 - 5850
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    Grain‐oriented films of VO2 have been prepared to characterize the effects of film orientation on electrical and optical switching performance. This oriented growth has been achieved by lattice matching to (0001) sapphire, and results in intergranular structures favorable to rapid propagation of the monoclinic‐tetragonal phase transformation. The electrical and optical property changes across this transition are strongly affected by film microstructure, with the oriented structures favoring rapid switching and narrow hysteresis. View full abstract»

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  • Heterogeneous silicon crystal growth on a single‐crystal silicon wafer

    Page(s): 5851 - 5853
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    Using a new process, a large grain polycrystalline silicon layer was grown directly from molten Si on a single‐crystal silicon wafer at a rate 100 times faster than the conventional chemical vapor deposition process. A polycrystalline silicon layer was also produced on a single‐crystal silicon wafer, which had an oxide layer and etched V grooves, through use of an additional ultrasonic wave effect in this process. A layer thickness of 100–600 μm and a grain size of 10 μm–3 mm were controllably obtained. After the growth of the polycrystalline layer, dislocation densities of 4×105 cm-2 for the single‐crystal silicon substrate, and 2×106 cm-2 for the polycrystalline layer were obtained. Some devices were fabricated from the products of this new process, and the characteristics of these devices were investigated. View full abstract»

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  • Passivation and generation of deep level defects in hydrogenated n‐GaAs (Si)

    Page(s): 5854 - 5861
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    Bulk n‐type GaAs wafers (Si doped) have been exposed to a capacitively coupled rf hydrogen plasma at different power densities ranging from 0.01 to 0.2 W/cm2 at 260 °C. The electronic properties of these layers have been investigated by capacitance‐voltage experiments and deep level transient spectroscopy. Besides the neutralization of the silicon donors by the in‐diffused hydrogen atoms, we observe a modification of the deep level transient spectroscopy (DLTS) spectra after hydrogenation. For rf power densities lower than 0.1 W/cm2, the deep levels present in the region of the starting material explored by DLTS are passivated. The absence of electronic states associated with the silicon‐hydrogen complexes in the neutralized donor region indicates that these complexes are either electrically inactive or deeply located in the energy band gap. For rf power densities higher than 0.1 W/cm2, two new deep electronic states appear at 0.41 and 0.55 eV below the conduction band. These levels are the signature of a large amount of defects in the near‐surface region of n‐GaAs (Si) after exposure to a rf hydrogen plasma at such power densities. Trapping of hydrogen on these defects is probably responsible for the accumulation of hydrogen in the near‐surface region observed in the hydrogen diffusion profiles. 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