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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of silicon delta-doped gallium arsenide using the Shubnikov–de Haas effect and theoretical modeling (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3583-3588 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a detailed study of electron sub-band occupancies and saturation effects in silicon delta-doped gallium arsenide samples, using Hall and Shubnikov–de Haas (SdH) measurements in conjunction with numerical modeling. This study extends previous work in two respects. First, the samples, produced by molecular beam epitaxy with a nominal delta doping density of 1×1013 cm−2, were examined over a wide range of growth temperature (395–710 °C) to allow the influence of broadening of the doping profile to be examined. Second, the numerical modeling method, based on a self-consistent solution of Poisson's and Schrödinger's equations, included directly the influence of DX-like donor levels, located at 200 meV above the conduction band edge. Excellent agreement with the individual sub-band occupancies determined by SdH was found for all samples up to a growth temperature of 605 °C, with the total silicon doping density kept constant and dopant broadening as the only adjustable parameter in the fit. Despite the evidence for inclusion of DX-like donor levels based on our modeling, all samples showed only a weak persistent photoconductivity effect. This is in contrast to uniformly doped bulk GaAs, indicating the different nature of the DX level in two and three dimensional doping. Above 605 °C it was not possible to model sub-band occupancies using a constant total doping density, showing that another deactivation mechanism such as autocompensation becomes important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357418
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  • 2
    Electronic Resource
    Electronic Resource
    An investigation of the electrical and chemical properties of intimate metal-InyAl1−yAs(100) interfaces (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2481-2488 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical and chemical properties of the interfaces formed at room temprature, between the surface of epitaxial n-type InyAl1−yAs(100) and a selection of metals have been studied. Highly ideal Au, Ag, Cu, and In diodes exhibiting the highest reported barriers (0.78–0.91 eV), measured by the current-voltage (I-V) technique, have been obtained by forming intimate contacts on atomically clean, lattice matched, molecular beam epitaxy grown InyAl1−yAs/InP(100). The formation of Au- and In-InyAl1−yAs interfaces has been investigated using x-ray photoemission spectroscopy, showing that in both cases the Fermi level is pinned at the surface prior to metal deposition. The deposition of both In and Au overlayers initiated the selective removal of As from the interface to segregate on the metal surface; however the presence of these metals on the semiconductor surface produced no further Fermi shift. These observations, in conjunction with the barrier heights measured by the I-V technique, are discussed in the context of currently supported models of Schottky barrier formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356246
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  • 3
    Electronic Resource
    Electronic Resource
    The growth and electrical properties of silicon on GaAs(110) studied by scanning tunneling microscopy and scanning tunneling spectroscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5636-5641 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A scanning tunneling microscope (STM) has been used to study the structural formation of silicon overlayers deposited at room temperature on GaAs(110). In addition spectroscopic measurements were obtained simultaneously to reveal electrical properties associated with the interface and overlayer formation. The Si coverage varied in thickness from submonolayer growth up to ∼16 monolayers. The height variations of the STM images indicate that silicon islands did not exceed ∼3 Å at either submonolayer growth or thicker coverages. The lack of atomic resolution of the adsorbed silicon suggests that the silicon overlayers are amorphous in nature, confirming soft x-ray photoelectron spectroscopy (SXPS) measurements. The scanning tunneling spectroscopy measurements clearly indicate a Fermi shift of 0.8 eV when silicon was deposited on the clean cleaved surface of p+ GaAs(110). This shift is also observed on regions of the substrate which remained exposed after the silicon deposition. The Fermi shifts and resultant band bending are attributed to the formation of the Si–GaAs heterojunction and correlation with earlier SXPS measurements prove favorable. The possibilities of measuring the band offsets are also considered. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371573
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of fast electrons produced in solid targets by laser intensities of 5×1019 W/cm2 (abstract) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 847-847 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal intensity) and planar multilayer targets (Mo/Sn) to study the generation and transport of electrons with MeV energies. Such fast electrons are of prime importance to many proposed applications, e.g., the fast ignitor fusion concept. X-ray emission spectroscopy is used to study the electron transport. Characteristic K α photon emission produced by the fast electrons in the front (Mo) and rear (Sn) layers of the target is measured with a charge-coupled device detector (single photon counting mode) to infer the electron energy deposition. The electron energy spectrum is measured by varying the thickness of the Mo layer to attenuate the electrons by different amounts. Penumbral imaging of the K α emission is used to give information about the angular distribution of the fast electron emission. Details of the measurement techniques and experimental results will be discussed and compared with modeling calculations.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148451
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  • 5
    Electronic Resource
    Electronic Resource
    Hard x-ray production from high intensity laser solid interactions (invited) : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 265-269 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Intense laser (〉1021 W/cm2) driven hard x-ray sources offer a new alternative to conventional electron accelerator bremsstrahlung sources. These laser driven sources offer considerable simplicity in design and cost advantage for multiple axis views and have the potential for much higher spatial and temporal resolution than is achievable with accelerator sources. We have begun a series of experiments using the Petawatt laser system at LLNL to determine the potential of these sources for radiography applications. Absolutely calibrated spectra extending to 20 MeV and high resolution radiographs through a ρr≥150 g/cm2 have been obtained. The physics of these sources and the scaling relationships and laser technology required to provide the dose levels necessary for radiography applications will be discussed. Diagnostics of the laser produced electrons and photons will be addressed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149442
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  • 6
    Electronic Resource
    Electronic Resource
    Nuclear diagnostics for petawatt experiments (invited) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 767-772 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: With the operation of successively more intense and powerful lasers, such as the NOVA petawatt laser with I∼3×1020 W/cm2, several novel (to laser physics) nuclear diagnostics were used to determine the nature of the laser/matter interaction at the target surface. A broad beam of hot electrons, whose centroid varied from shot to shot, width was remarkably constant, and intensity was about 40% of the incident laser energy was observed. New nuclear phenomenon included photonuclear reactions [e.g., (γ,xn)], photofission of 238U and intense beams of ions. Photonuclear reactions were observed and quantified in Cu, Ni, and Au samples, and produced activation products as neutron deficient as 191Au [a (γ,6n) reaction!], requiring gamma rays exceeding 50 MeV in energy. The spectral features of the gamma-ray source have been investigated by comparing activation ratios in Ni and Au samples, and angular distributions of higher energy photons have been measured with activation of spatially distributed Au samples. Extraordinarily intense beams of charged particles (primarily protons) were observed normal to the rear surface of the target and quantified using the charged particle reaction 48Ti(p,n)48V, radiochromic film and CR39 plastic track detectors. Approximately 3×1013 protons, with energies up to 55 MeV were observed in some experiments. Collimation of this beam increases with increasing proton energy. Correlations of activation with laser performance will be discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319355
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  • 7
    Electronic Resource
    Electronic Resource
    Energetic proton generation in ultra-intense laser–solid interactions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 542-549 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An explanation for the energetic ions observed in the PetaWatt experiments is presented. In solid target experiments with focused intensities exceeding 1020 W/cm2, high-energy electron generation, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. In this report, an attempt is made to explain the physical process present that will explain the presence of these energetic protons, as well as explain the number, energy, and angular spread of the protons observed in experiment. In particular, we hypothesize that hot electrons produced on the front of the target are sent through to the back off the target, where they ionize the hydrogen layer there. These ions are then accelerated by the hot electron cloud, to tens of MeV energies in distances of order tens of μm, whereupon they end up being detected in the radiographic and spectrographic detectors. © 2001 American Institute of Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333697
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  • 8
    Electronic Resource
    Electronic Resource
    Stimulated Raman backscatter in ultraintense, short pulse laser–plasma interactions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 274-279 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stimulated Raman backscatter instability that occurs when short (∼50–100 fs), intense (I(approximately-equal-to)2×1017 W/cm2) laser pulses are focused into a high density, low temperature plasma is reported on in this article. Results from linear theory, numerical differencing of the coupled mode equations, and one-dimensional particle-in-cell simulations will be discussed. It is found that the growth rate is a function of position along the pulse, and that the maximum growth rate at the peak of the pulse is reduced from the homogeneous long pulse value, γ0 by a factor of 1/(square root of)2. A criterion is obtained that predicts when the product of the pulse length and the growth rate is large enough so that the backscatter instability will heat the background electrons to a significant amount above the initial temperature. The usual hot electron component associated with this instability will also be discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871097
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  • 9
    Electronic Resource
    Electronic Resource
    Laser beam propagation and channel formation in underdense plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2825-2834 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results are presented which show the formation of density channels in a preformed plasma by a 100 ps laser beam focused with different f/number lenses. The density channels are diagnosed by an interferometer. The experiments are made with both line foci and circular foci up to intensities of 5×1016 W/cm2. The experimental channel size and density perturbation compare favorably with the predictions of two-dimensional theoretical models. The limited axial extent of the channels is shown to be due to the onset of the filamentation instability. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871180
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  • 10
    Electronic Resource
    Electronic Resource
    Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1800-1810 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been shown that there are at least three ways in which ion waves can be stimulated in these plasmas and have a significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of stimulated Brillouin scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersects, ion waves can be excited at the "beat" frequency and wave number of the intersecting beams, causing the sidescatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et al., Phys. Rev. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by stimulated Raman scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et al., Phys. Rev. Lett. 77, 2706 (1996)]. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872293
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