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  • 1
    Electronic Resource
    Electronic Resource
    Free excitonic transitions in GaN, grown by metal-organic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7001-7004 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic processes of the free excitonic transitions in GaN grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. The recombination lifetimes of the A and B excitons have been measured at different temperatures and excitation intensities, from which radiative recombination lifetimes of about 0.35 and 0.3 ns for the A and B excitons, respectively, have been obtained. An increase in excitation power has resulted in a drastic enhancement in the radiative decay rate as well as in the exciton photoluminescence quantum yield, suggesting the excitonic transitions may provide gain for laser actions in GaN. The high quality as well as high purity of the investigated MOCVD sample has been demonstrated by the observations of (1) the free A- and B-excitonic transitions, (2) excited states of the free excitons, (3) narrow free excitonic emission linewidths (1.7 meV at 10 K), (4) low electron concentration, and (5) high electron mobilities (∼600 cm2/V s). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362448
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  • 2
    Electronic Resource
    Electronic Resource
    Photoluminescence studies of band-edge transitions in GaN epitaxial layers grown by plasma-assisted molecular beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2675-2683 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Continuous-wave and time-resolved photoluminescence spectroscopies have been employed to study the band-edge transitions in GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. In addition to the neutral-donor-bound exciton transition (the I2 line), a transition line at about 83 meV below the band gap has been observed in an epitaxial layer grown under a lower plasma power or growth rate. This emission line has been assigned to the band-to-impurity transition resulting from the recombination between electrons bound to shallow donors and free holes D0, h+). Systematic studies of these optical transitions have been carried out under different temperatures and excitation intensities. The temperature variation of the spectral peak position of the D0, h+) emission line differs from the band gap variation with temperature, but is consistent with an existing theory for D0, h+) transitions. The dynamic processes of the D0, h+) transition have also been investigated and subnanosecond recombination lifetimes have been observed. The emission energy and the temperature dependencies of the recombination lifetime have been measured. These results have provided solid evidence for the assignment of the D0, h+) transition and show that the motions of the free holes which participated in this transition are more or less restricted in the plane of the epitaxial layer at temperatures below 140 K and that the thermal quenching of the emission intensity of this transition is due to the dissociation of neutral donors. Our results show that time-resolved photoluminescence spectroscopy can be of immense value in understanding the optical recombination dynamics in GaN. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361138
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  • 3
    Electronic Resource
    Electronic Resource
    Electrical evaluation of Al–p+-GexSi1−x ohmic contacts (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3110-3114 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical properties of Al–p+-GexSi1−x contacts were studied using transmission line measurements. For this study the GeSi alloy layers were selectively formed with 30 or 90 keV Ge implantation into Si, a technique which offers a simple, self-aligned process for the fabrication of such layers. Measurements of the current–voltage characteristics showed that the metal–alloy contacts were ohmic over the voltage range examined. The specific contact resistivity was found to be a function of Ge concentration, decreasing with increasing Ge concentration for concentrations below a critical value and increasing with increasing Ge concentration above this value. The initial decrease in specific contact resistivity is attributed to the effect of Ge on the contact barrier height and width, an effect which is caused by the reduction in the band gap of the alloy. The subsequent increase in specific contact resistivity at higher Ge concentrations is believed to be due to the presence of a high concentration of dislocations in the alloy layer. The thermal stability of contacts is also reported. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363121
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and magnetic properties of Fe–N films prepared by ion-beam-assisted deposition (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3299-3302 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe–N films were prepared by ion-beam-assisted deposition at different N/Fe atomic arrival ratios to the substrates. Films consisted of nitrogen-rich α-Fe and different phases of iron nitrides including ζ-Fe2N, ε-Fe2-3N, and γ′-Fe4N were formed. The phase composition of Fe–N films was found to depend sensitively on the N/Fe atomic arrival ratio and deposition temperature. The magnetic properties of the films mainly depends on phase composition. It was found that nitrogen-rich α-Fe films exhibited higher Ms than that of the pure iron film, and their Ms could be increased further by vacuum annealing at relatively low temperatures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360021
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  • 5
    Electronic Resource
    Electronic Resource
    High power laser semiconductor interactions: A Monte Carlo study for silicon (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 1807-1812 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, we use Monte Carlo methods to study the interaction of high power laser pulses with electrons in the conduction band of semiconductors. The laser field is represented by a sinusoidal electric field which tends to cause an oscillatory motion in the electrons. The scattering of electrons from the lattice force the electrons to lose phase coherence with the field. The approach is applied to silicon. We use the approach to examine the carrier energy distribution and material breakdown due to the transfer of energy from the laser to the electrons followed by impact ionization. The impact ionization coefficient, α, and its dependence on the laser frequency and field strength is examined and compared to the values in a dc field. In general, the ac value is smaller than the dc value, but at low frequencies and high field strengths, the ac impact ionization coefficient approaches the dc value at the same rms field value. The importance of collisions in the energy transfer process is elucidated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364037
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  • 6
    Electronic Resource
    Electronic Resource
    Metastability and persistent photoconductivity in Mg-doped p-type GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1808-1810 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical properties of Mg-doped p-type GaN grown by metalorganic chemical vapor deposition have been investigated by Hall effect and conductivity measurements. Metastability and persistent photoconductivity effects have been observed in GaN. It was found that at low temperatures, it takes several hours for the free hole concentration to reach its equilibrium value in the dark as well as in the photoexcited state, implying a bistable nature of impurities in p-type GaN. Temperature dependence of these behaviors have been studied, from which the energy barrier for free hole capture by ionized impurities as well as between the metastable and the stable states of neutral impurities have been obtained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116020
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  • 7
    Electronic Resource
    Electronic Resource
    Persistent photoconductivity in a two-dimensional electron gas system formed by an AlGaN/GaN heterostructure (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 1227-1230 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Persistent photoconductivity (PPC) effect associated with a two-dimensional electron gas (2DEG) in an AlGaN/GaN heterojunction device has been observed. As a consequence, the device was observed to be sensitive to light and the sensitivity was associated with a permanent photoinduced increase in the 2DEG carrier mobility and density. By formulating the PPC buildup and decay kinetics, we attributed the observed increase in the 2DEG carrier density and mobility to the photoionization of deep level impurities (DX like centers) in the AlGaN barrier material. In the PPC state, we were able to continuously vary the 2DEG carrier density in a single sample through photoexcitation and it has been found that the 2DEG carrier mobility increases almost linearly with the carrier density in the 2DEG channel. At 10 K, an electron mobility of 5800 cm2/V⋅s has been obtained in a PPC state. Implications of these observations on the device applications based on AlGaN/GaN heterojunctions have also been discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365893
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic and structural properties of epitaxially grown FeTaN thin films (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 5955-5966 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial FeTaN films (∼1500 Å) were grown as a function of nitrogen flow rate on epitaxial Cu(001) buffer layers (∼2000 Å) on Si(001) single crystal substrates to investigate the effect of Ta and nitrogen on the magnetocrystalline anisotropy and magnetostriction. Detailed structural investigation by transmission electron microscopy and x-ray diffraction showed that the FeTaN films were epitaxial with the Pitsch orientation relationship of FeTaN(110)(parallel)Cu(001) and FeTaN〈111〉(parallel)Cu〈110〉, which allows four different in-plane variants to coexist in the film. It was found that the saturation magnetization did not change with nitrogen addition (∼1600 emu/cc) up to 2% lattice dilation. The values of K1 and λ100 of Fe decreased slightly (20% and 10%, respectively), while λ111 increased with increasing nitrogen content and eventually changed sign at ∼2% normalized lattice dilation. These results qualitatively agree with our earlier findings on (001) oriented FeTaN epitaxial films on MgO single crystal substrates. Also, our calculated saturation magnetostriction for nanocrystalline samples agrees very well with published data on the same FeTaN composition. Based on Hoffmann's ripple theory the ripple constant is calculated for nanocrystalline films using the Doyle–Finnegan model for the local average anisotropy and our measured single crystal constants. It was found that the effect of nitrogen on reducing the average anisotropy through the fundamental constants is not significant, and therefore the major factor in achieving a low ripple constant (i.e., soft magnetic properties) is the grain size, the number of grains across the thickness and the thin film stress. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367460
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  • 9
    Electronic Resource
    Electronic Resource
    Thickness dependence of the magnetic percolation threshold in as-deposited and annealed Fe–SiO2 granular thin films (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5693-5697 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties and microstructure of as-deposited and annealed Fe–SiO2 granular thin films were studied. As-deposited films have a maximum in coercivity at an Fe volume fraction (Fe vol %) ∼62% independent of film thickness. Iron grains in as-deposited films are well defined, nearly equiaxial and ∼5 nm in diameter. From 66 to 90 Fe vol %, some as-deposited films showed an unusual well defined in-plane uniaxial anisotropy. The magnetic percolation threshold, xp, as indicated by the maximum in the Hc vs Fe vol % curve, changed after the films were annealed. The percolation threshold (xp) of films annealed at 420 °C for 30 min shifted to ∼47 Fe vol % except for the 5 nm films, whose xp remained unchanged. After annealing at 510 °C for 3 h, a strong thickness dependence of the percolation threshold was revealed in films thinner than 40 nm, with values ranging from 78 Fe vol % to less than 44 Fe vol %. The shifts of xp in both 420 and 510 °C annealed films can be explained by the effects of reduced dimensions in very thin films. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368832
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  • 10
    Electronic Resource
    Electronic Resource
    Acceptor-bound exciton recombination dynamics in p-type GaN (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3295-3297 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dynamics of the neutral-acceptor-bound exciton transition (the I1 line) in a Mg doped p-type GaN epitaxial layer grown by metalorganic chemical vapor deposition (MOCVD) have been studied by time-resolved photoluminescence emission spectroscopy. Two emission lines in the I1 transition region have been resolved in the time-resolved spectra, possibly due to the existence of two energy states of the Mg impurities after postgrowth thermal annealing. The recombination lifetimes of the acceptor-bound exciton transition have been measured under different conditions including temperature, excitation intensity, and emission energy. From these measurements, a value of about 450 ps for the radiative recombination lifetime has been obtained, which is an important physical quantity for optoelectronic device applications based on GaN. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115225
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