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Journal of Applied Physics

Issue 7 • Date Jul 1983

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Displaying Results 1 - 25 of 98
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Optimization of a heat engine based on a dissipative system

    Page(s): 3651 - 3661
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    A new class of heat engine is analyzed in which the working fluid operates in a dissipative process, never in equilibrium. The conditions are found for stability and for the generation of work. Then the optimal path is found for operating the general dissipative engine by means of optimal control theory. The optimal cycle consists of arcs of constant power and of approximately instantaneous adiabats. If the heat flow is a function of temperature only, then the constant power arcs become isotherms. An upper bound is found to the power output. Two examples are worked out in detail: a light‐driven dissipative engine whose absorption is a step function of temperature, and a light‐driven dissipative engine whose working fluid undergoes a chemical reaction (isomerization), absorbing light in the isomeric form favored at high temperatures. View full abstract»

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  • Uniformity of energy deposition for laser driven fusion

    Page(s): 3662 - 3671
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    Laser driven fusion requires a high degree of uniformity in laser energy deposition in order to achieve the high density compressions required for sustaining a thermonuclear burn. The characteristic nonuniformities produced by laser irradiation, with multiple overlapping beams, are examined for a variety of laser‐target configurations. Conditions are found for which the rms variation in uniformity is less than 1%. The analysis is facilitated by separating the contributions from (1) the geometrical effects related to the number and orientation of the laser beams and (2) the details of ray trajectories for the overlapping beams. Emphasis is placed on the wavelength of the nonuniformities in addition to their magnitudes, as the shorter wavelength nonuniformities are more easily smoothed by thermal condution within the target. It is demonstrated how the geometrical symmetry of the laser system effectively eliminates the longer wavelengths, and how shorter wavelength nonuniformities can be ‘‘tuned out’’ by varying parameters such as the focal position and the radial intensity profile of the beam. The distance required for adequate thermal smoothing of the irradiation nonuniformities is found to be 2 to 3 times smaller than previously estimated due mainly to the relatively small spatial wavelength of the nonuniformities. This is a consequence of the geometrical symmetry of the laser system and is relatively insensitive to the details of overlapping beams. The results are particularly important for irradiation with short wavelength laser light (e.g., 0.35 μm), as the small smoothing distances anticipated for moderate laser intensities are found to produce adequate attenuation of the calculated nonuniformities. View full abstract»

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  • Linear theory and adiabatic wave amplitude variation in the converging guide accelerator

    Page(s): 3672 - 3676
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    A linear numerical analysis of the converging guide accelerator incorporating a radially inhomogeneous beam equilibrium and finite axial magnetic field is conducted. It is shown that these characteristics cannot explain the latest experimental results involving large amplitude waves. The slow phase velocity of these waves rely on nonlinear effects. A study of the adiabatic variation of wave amplitude in the accelerator indicates the importance of using high frequency waves for efficient operation. View full abstract»

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  • Energy loss of 24.8‐MeV electrons by interacting with thick materials

    Page(s): 3677 - 3687
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    Energy spectra of 24.8‐MeV electrons after emerging from C, Al, Cu, and Pb were measured at 0°, 5°, 15°, 30°, 60°, 120°, and 150°. The material thickness ranged from ∼1 to ∼3.6 g/cm2. Total energy spectra, defined as 2π ∫π0 f(E,θ)dE sin θdθ, were composed from these observed energy spectra. Average energy loss was calculated from the total energy spectrum for each material. By plotting the experimental data including the one obtained by Ziegler, an empirical equation estimating the average energy loss per unit path length was obtained. The most probable energy losses at 0° for C and Pb agree well with theoretical predictions, while those for Al and Cu are generally larger than calculated values by ∼6–7%. Discrepancy between the experimental and calculated values of the full width of f(E,0°) at half‐maximum due to electron straggling becomes smaller as Z increases. View full abstract»

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  • Pulsed resonant optogalvanic effect in neon discharges

    Page(s): 3688 - 3698
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    Pulsed resonant optogalvanic effect is investigated in a neon hollow cathode discharges utilizing a nitrogen pumped dye laser. We have studied by the pulsed technique transient effects in the discharge plasma such as fast relaxation of level population density and population inversion. The experimental results are correlated with a four states phenomenological model of the pulsed optogalvanic effect taking into account lumped relevant levels of the 3s and 3p manifolds of neon. The time integration of the pulsed optogalvanic siganls (OGS) yields the previously measured cw signals and explains their sign changes. View full abstract»

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  • Design of rotationally symmetrical electrostatic mirror for time‐of‐flight mass spectrometry

    Page(s): 3699 - 3703
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    In order to be able to use it in time‐of‐flight mass spectrometry, we have tried to find a mirror with as few spherical and chromatic aberrations as possible. We have studied the characteristics of the mirror with charged particles whose initial energy varies by ±1% around a central value and which go through an imaginary input pupil of radius 0.2 ρ (ρ being the radius of the three cylinders which go to make up the mirror). The best operating conditions are calculated for different source points on the axis, taking into account separate residual chromatic and spherical aberrations, and also in the case of simultaneous chromatic and spherical aberrations. The second part of the paper deals with flight time (internal mirror flight time and object‐image flight time). The data enable us to establish that this convergent mirror plays an essential compensating role; it eliminates not only the initial energy spread effects, but also those of the ion bunch divergence. Consequently, all the above‐mentioned particles have a flight time which is virtually constant. View full abstract»

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  • Particle sizing in two‐phase flows from scattered laser power spectra and laser attenuation

    Page(s): 3704 - 3709
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    Diagnostic measurements have been made on a two‐phase flow of carbon particles suspended in nitrogen gas, in conjunction with another experiment. Experimental data on particle size distribution were obtained from scanning electron microscopy of samples, laser extinction, and laser scattering in the flow. Two independent nonintrusive laser measurements indicated ‘‘average’’ particle diameters of 1.5 and 3.4 μm. Predictive calculations show that these experimental measurements can be used to indicate the degree of agglomeration in the flow and provide restrictive boundaries to a priori size distributions which are computationally consistent with the observed data. View full abstract»

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  • Ablative organic films for optical recording

    Page(s): 3710 - 3711
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    This work presents a new type of optical recording medium for a diode laser which is three times more sensitive than a chalcogenide thin film. This medium has a tetralayer structure of n–hexatriacontane, zinc stearate, Sb2S3 and Bi. The Bi layer absorbs a recording light beam and organic layers are ablated by heat evolved in the Bi layer. The high sensitivity characteristic of this medium is attributed to the use of low‐melting‐point material as the ablating layer and the effective use of the incident beam. View full abstract»

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  • A general theory of the Raman‐type free‐electron laser

    Page(s): 3712 - 3722
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    A general theoretical consideration is given for the stimulated Raman scattering in a finitely magnetized relativistic electron beam on which the operation of the Raman‐type free‐electron laser is based. After some preliminary discussion, the coupled mode equations are derived which relate the pump wave (assumed to be an electromagnetic wave), the scattered wave and the electron plasma wave (negative‐energy wave). From the coupled mode equations obtained above, the linear growth rate for the scattered and electron plasma waves is found. Then, the energy relations are formulated for the three waves involved in the process of the stimulated Raman scattering, together with the discussion on the energy balance among these waves. A special attention is paid to the behavior of the scattered wave in the vicinity of the cyclotron resonance. Some of the important features brought about by the cyclotron resonance are as follows: (a) According to the conditions imposed on the frequency and wave number of the pump wave, the scattered wave becomes either the electromagnetic wave mode or the electron cyclotron wave mode, or it is not excited. (b) In the presence of a finite static magnetic field, the spatial growth rate for the electromagnetic wave mode takes a maximum value for a particular set of various parameters, and the maximum growth rate becomes one order of magnitude or more as large as the growth rate for the case that there is no static magnetic field applied. View full abstract»

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  • A kinetic model of the sustained discharge HgBr laser

    Page(s): 3723 - 3731
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    A kinetic model of the sustained discharge Ar/HgBr2 laser is developed from an experimental base. The choice of Ar as the buffer gas is supported by measurements of the specific fluorescence and laser efficiency in the buffer mixtures (Ar, Ar+5% Xe, Ne+10% Xe, Ne+10% N2). A computational treatment of the coupled photon and kinetic equations is described. Gain measurements determine a peak HgBr (B‐X) stimulated emission cross section of 1.6×10-16 cm2±20% at 502 nm. Absorption measurements between 515 and 530 nm show the presence of a large, broad band absorption tentatively assigned to HgBr+2 with a cross section of 2×10-18 cm2. An upper bound of 5×10-9 cm3 sec-1 is placed on the rate constant for electron collisional quenching of the HgBr(B) state. The laser extraction efficiency of 65% is modeled by a lower level collisional deactivation by Ar with a rate constant 6.0×10-12 cm3 sec-1. Discharge impedance is measured as a function of E/N and the ionizing electron beam current density. Using the new data a good description of laser efficiency is demonstrated if the ratio of HgBr(B‐X) fluorescence power to discharge input electical power is set to 6.1%, for 0.8% HgBr2 in Ar at E/N=8×10-17 V cm2. View full abstract»

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  • Comparison of N2, Xe, Kr, and ArF excimer flashlamps with respect to their suitability for pumping TlI

    Page(s): 3732 - 3734
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    The far UV spectra of a flashlamp with a rise time of 30 ns filled with either N2, Xe, Kr, or Ar, F2, He mixtures at 1 bar have been recorded. Emission of these flashlamps are compared in a band ranging from 190 to 220 nm. It is shown that the N2 and ArF flashlamps produce an nearly identical output and are best suited for TlI photodissociation. The light energy in this band with respect to the total emission from 190 nm to 4.5  μm amounts to 7% for N2 and 15%–25% for ArF. View full abstract»

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  • Surface roughness and the attenuation length of guided waves in optical fibers

    Page(s): 3735 - 3742
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    We consider the influence of surface roughness on the attenuation length of electromagnetic waves guided by a dielectric cylinder. Fluctuations in the radius of the cylinder allow the guided wave to radiate energy into the vacuum outside the guide. We find that a perfectly sinusoidal modulation of the radius of the guide leads to a contribution to the attenuation coefficient propertional to ω2, if the wavelength of the guided mode is small compared to the radius of the guide, and if the spatial period of the sinusoid is in the appropriate range. Random fluctuations in the radius on a spatial scale small compared to the wavelength of the mode lead to a contribution proportional to ω3, in the limit of large guide radius. Our theoretical results will be compared to the data reported by Harrington, who studied the scattering produced by waves with wavelength in the 2–10 μm range in thallium halide fibers. View full abstract»

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  • Fundamental defect centers in glass: Electron spin resonance and optical absorption studies of irradiated phosphorus‐doped silica glass and optical fibers

    Page(s): 3743 - 3762
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    Defect centers induced by ionizing radiation (50–100‐keV x rays, 60Co γ rays) in high purity P‐doped silica glass have been observed and elucidated by ESR spectroscopy. Four generic species are well characterized on the basis of the observed 31P hyperfine splittings and g values as defects analogous to PO2-3 (phosphoryl), PO4-4 (phosphoranyl), PO2-2 (phosphinyl), and PO2-4 radicals. The latter species, also termed the phosphorus‐oxygen‐hole center (POHC), is shown to occur in two variants comprising holes trapped on one or two nonbridging oxygens. Radiation‐induced Si E′ centers with and without P next‐nearest‐neighbors were also identified, and a singlet resonance S due to E′ type defects such as (OSi2)Si∙ and/or (O2Si)Si∙ was observed to grow in with annealing above ∼800 K, regardless of whether or not the sample was irradiated. The structures, formation mechanisms, and precursors of these defects have been determined or inferred for all centers. Radiation‐induced optical absorption spectra over the range 0.5–6.2 eV have been obtained for bulk glass and fiber samples after irradiation and following anneals to various temperatures up to 1250 K. Gaussian resolutions of the spectra into component bands have been performed and isochronal anneal data have been used to identify optical absorptions of the PO2-3, PO4-4, PO2-2, POHC, and S centers. The PO2-3 defect was found to absorb at ∼0.8 eV in the region of interest for fiber optic communication. Oscillator strengths are calculated for all bands. View full abstract»

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  • Bonding pad induced stresses in (Al,Ga)As double heterostructure lasers

    Page(s): 3763 - 3768
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    We have studied Au bonding pad induced stresses in (AlGa)As double heterostructure lasers by photoluminescence, x‐ray Automatic Bragg Angle Control measurements, and infrared and optical microscopy. Examination of several devices which have thick (10–12 μm) plated Au bonding pads indicates that stresses approaching the fracture stress can exist in such devices. The high stress induces aggregates of microcracks along 〈100〉 directions in the epitaxial layers. Regions in the stripe where the cracks intersect are nonradiative, causing failure of the device. View full abstract»

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  • Effect of surface relaxation on stress failure in laser‐irradiated glass

    Page(s): 3769 - 3776
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    An analytic study is conducted to determine the effect of stress and structural relaxation on stress failure in laser‐irradiated BK‐7 glass. Both short (10 μs) and long (1 s) pulses of CO2 and DF laser radiation are considered. The model for the glass temperature consists of the one‐dimensional diffusion equation with a source term to account for absorption of energy from the laser beam. Stresses are calculated from an analysis which includes the effect of relaxation at the irradiated surface. The model indicates that the surface stress is strongly dependent on the absorption coefficient of the glass at the laser wavelength and on the laser pulse duration. The implication of these results as to the failure mode in glass subjected to high intensity CO2 and DF radiation is discussed. View full abstract»

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  • Transport coefficients in arc plasma of SF6–N2 mixtures

    Page(s): 3777 - 3787
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    We compute thermal and electrical conductivity coefficients as a function of temperature for different compositions of the N2–SF6 mixture. The method we used was derived from Chapman–Enskog’s. The composition of the plasma is calculated assuming the hypothesis of local thermodynamic equilibrium. Calculations were made for temperatures between 1000 and 15 000 K. We show that the densities of the compounds specifically due to the SF6–N2 mixture (i.e., NF, NS, N2F4, NF3, etc....) are negligible compared with the densities of the products due to SF6 alone and N2 alone. The characteristics of the transport coefficients of the mixture are therefore a combination (depending on the proportions in the mixture) of the characteristics of pure N2 and SF6. These theoretical values allow us to interpret the curves obtained experimentally by measuring, using laser interferometry at two wavelengths, the variation of electron number density in a decaying arc discharge in a SF6–N2 mixture. By substituting the values of the transport coefficients into an energy balance equation, we also determined, in the stationary state the profiles of the temperature and the electric field and the variation of the electron density with the discharge current. View full abstract»

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  • An analysis of the asymmetric part of electron–electron Boltzmann integral

    Page(s): 3788 - 3797
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    A numerical analysis of the asymmetric part of electron–electron collision integral is presented. The results are given in the form of graphs for two commonly considered plasma situations: the collision‐dominated case (symmetric part of electron distribution is Maxwellian) and the field‐dominated case (symmetric part of electron distribution is Druyvesteynian). The importance of the asymmetric part of e‐e collision integral in the Boltzmann equation is also discussed. View full abstract»

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  • Mode conversion and its utilization of degenerating surface wave modes on a plasma column

    Page(s): 3798 - 3806
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    Both mode conversion at degenerating points of dispersion relations for surface wave modes on a discharge plasma column and the methods for their detection and utilization are presented. Mode conversions at three degenerating points become observable by using a surface wave resonator when an azimuthal inhomogeneity of plasma is produced by a static magnetic field of about 1 G applied perpendicular to the column axis. Two of the three detected degenerating points can be utilized for an easy and exact determination of the electron density and its distribution in the discharge tube. View full abstract»

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  • Nonlinear Landau damping of a whistler in a current‐carrying plasma

    Page(s): 3807 - 3809
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    A high‐amplitude whistler wave propagating through a current‐carrying plasma decays into a low‐frequency resistive quasimode and frequency‐upshifted scattered whistler. In this process of nonlinear Landau damping a pump‐wave photon absorbs a quantum of energy from the drifting electrons to generate an upshifted whistler photon. Upconversion occurs only when the drift velocity of electrons exceeds the phase velocity of the quasimode (ω≪k∙vd). View full abstract»

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  • Adverse shielding of the heating field and high ohmic loss introduced by electrostatic shields employed in radio‐frequency heating of plasma

    Page(s): 3810 - 3817
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    The electrostatic shields now commonly employed to shield antennas in the heating of plasma in the ion cyclotron frequency range are shown to reduce the specific radiation resistance of a long narrow antenna in the presence of plasma by a significant factor (on the order of 2/3 for a typical double‐array shield) due to the effect of magnetic shielding of the magnetosonic polarization. An allied change in antenna specific inductance is also found. These effects are shown to diminish with increase in antenna width and should pose no major problem for the wide antennas projected for use in fusion experiments. In addition to the foregoing effects which are not ohmically dissipative in essence, electrostatic shields are also shown to introduce surprisingly high ohmic loss, this being of potential importance in shield design. The dependences of the above magnetic and ohmic phenomena on shield parameters are given and a shield design minimizing them is presented. Their repercussion on coupling efficiency and on the excitation voltage necessary for a given power flux from the antenna is discussed. View full abstract»

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  • Analysis of the cathode region of a free‐burning high intensity argon arc

    Page(s): 3818 - 3824
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    This paper is concerned with analytical/numerical studies of the cathode region of an atmospheric pressure, free‐burning high intensity argon arc. The cathode region is divided into two model zones: the ionization zone and the space‐charge zone. The former accounts for the generation of ions while the latter is responsible for the sheath formation. The governing equations for each zone are established by taking the dominant physical processes into account. Employing boundary conditions from the results of previous studies of the flow‐affected region, one‐dimensional solutions of the governing equations are obtained. The results indicate a net positive space charge in front of the cathode surface and the electron and ion fluxes are mainly driven by the potential gradient. A significant fraction of the total current is carried by positive ions which is important for establishing the energy balance at the cathode surface. View full abstract»

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  • Intrinsic defects in ZnO varistors

    Page(s): 3825 - 3832
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    Theoretical calculations are presented for equilibrium concentrations of zinc and oxygen vacancies in ZnO. Results are presented at the sintering temperature, and also at room temperature. Theoretical calculations of reaction constants show that the intrinsic donor is the oxygen vacancy, rather than the zinc interstitial. The depletion of vacancies in the surface region, as the ZnO is cooled from the sintering temperature, is also calculated. Homojunction effects which are caused by such depletion are shown to be small. View full abstract»

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  • Creation and annealing kinetics of magnetic oxygen vacancy centers in SiO2

    Page(s): 3833 - 3838
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    Dose and energy dependence of the E1 defect density/cm2 created in SiO2 by implantation of Ar ions has been determined by electron paramagnetic resonance. A dose dependent region followed by a saturated, dose independent region is found for all energies studied (50–150 keV). In the low dose limit for 100‐keV Ar ions we estimate E1 creation to be 35/implant ion. The defect density/cm2 is found to be a linear function of the longitudinal atomic collisional damage distribution consistent with a picture of overlapping lateral damage distributions. A simple model for defect creation and annihilation gives a good quantitative explanation of the observed energy and dose dependence of the defect density. Isothermal annealing studies have been performed and the results do not follow those expected for a simple exponentially activated process. A model assuming correlated defect/interstitial recovery gives a better description of the experimental results and suggests an activation energy for recovery of approximately 0.85 eV. View full abstract»

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  • Defects in Q‐switched laser annealed silicon

    Page(s): 3839 - 3848
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    This paper describes the characterization of residual defects using transient capacitance spectroscopy for ion‐implanted Si annealed with a Q‐switched Nd‐glass laser. The deep‐level defect levels observed in this study were similar to those obtained in low‐fluence ion implanted samples. The spatial distributions of deep‐level defect concentrations were obtained for conditions using different anneal energy densities. From the difference of the distribution profiles, it is concluded that the greater the annealing laser energy densities, the lower the defect concentration near the junction.The reduction of the defect concentration is partly due to the inward movement of the junction. Thus the defects detected are those which lie further down in the tail of the defect distribution profile and have a lower concentration. Other reasons for the reduction of the defect concentration can be due to thermal annealing as heat propagates into the substrate during laser radiation. The reduction of the defect concentration agrees with the improvement of the measured I–V characteristics. Annealing with multiple shots of laser radiation was performed and the annealing model was established. The junction movement was confirmed by an electron beam induced conductivity technique. The carrier diffusion length measured in the region, where a surface layer of 2–3 μm was etched, decreases as the annealing energy density increases. This may be explained by the fact that the native defects generated thermally in the melts at the surface diffuse into the bulk and subsequently are trapped by the impurities in Si. 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