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  • 11
    Electronic Resource
    Electronic Resource
    Dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3158-3160 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results of a time-resolved photoluminescence study of the dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures (DHs). The carrier dynamics including generation, diffusion, spontaneous recombination, and nonradiative relaxation were studied by examining the time decay of photoluminescence associated with the spontaneous recombination from the samples. The temporal evolution of the luminescence from the GaN active layers of the DH samples was found to be governed by a carrier–diffusion dominated capture process. The determination of the capture time for the carriers drift and diffusion into the GaN active region, in addition to the effective lifetimes of the spontaneous recombination for carriers in the AlGaN cladding layers and the GaN active region, allows an estimation of the diffusion constants for the minority carriers in the AlxGa1−xN cladding layers of the DHs. Our results yield a diffusion constant of 2.6 cm2/s for Al0.03Ga0.97N and 1.5 cm2/s for Al0.1Ga0.9N at 10 K. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366101
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  • 12
    Electronic Resource
    Electronic Resource
    Stimulated emission and gain measurements in molecular-beam epitaxially grown CdTe (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6612-6616 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated emission has been observed in molecular-beam epitaxially (MBE) grown films of cadmium telluride (CdTe), using a nanosecond pulsed dye laser as an excitation source. The films were 2.0–2.4 μm thick. Stimulated emission (SE) is seen to arise at several energy positions of the spectra. The different SE peaks exhibited different gain values. The gain was measured using the single beam method, by varying the length of excitation. The bulk CdTe sample studied exhibited stronger saturation effects than those seen in the MBE films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348874
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  • 13
    Electronic Resource
    Electronic Resource
    Fast magnetization of a high-to-low-beta plasma beam (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2482-2486 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization of a high-beta (plasma energy density/magnetic field energy density≡β≥1) hydrogen-plasma beam injected into a vacuum transverse magnetic field is studied experimentally. Nominal parameters were Ti≈1 eV, Te≈5 eV, n≤3×1013 cm−3, vi≤7×106 cm/sec, tpulse〈70 μsec, Bz≤300 G. Plasma characteristics were measured for a wide beam, a/ρi≤35, and a downstream distance, x≤300ρi, where a is the beam radius, x is the downstream distance, and ρi is the ion gyroradius. A brief initial state of diamagnetic propagation is observed, followed by E×B (magnetized) propagation; E×B propagation is accompanied by beam compression transverse to B with as much as a factor of 4 increase in density and a slight drift of the beam in the ion Lorentz force direction. For Bz=200–300 G the observed magnetization time is much faster than calculated from classical Spitzer conductivity and is more of the order of the magnetization time based on Hall conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859512
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  • 14
    Electronic Resource
    Electronic Resource
    High resolution x-ray analysis of pseudomorphic InGaN/GaN multiple quantum wells: Influence of Si doping concentration (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3006-3008 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the structural properties of InGaN/GaN/AlGaN multiple quantum wells (MQWs) by means of two-dimensional reciprocal space mapping (RSM) of high resolution x-ray diffraction. The influence of Si doping in GaN barriers on the characteristics has been studied for 12-period MQWs grown by metalorganic chemical vapor deposition, which have different Si doping concentrations in the GaN barriers ranging from 1×1017 to 3×1019 cm−3. Information on the structural quality of these MQWs was extracted from the linewidth broadening of the higher-order superlattice satellite peaks, as well as from the presence of Pendellösung oscillations. The measured diffraction curves were modeled using kinematic diffraction theory. From the symmetric and asymmetric RSMs around (0002), (0004) and (112¯4) reflections, we found that the InGaN/GaN/AlGaN MQWs are grown coherently on the GaN base layer. Better interface properties are achieved with Si doping. Our results indicate that Si doping in the GaN barriers affects the interface quality of the InGaN/GaN MQW systems, and thus, also influences the optical properties. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369620
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  • 15
    Electronic Resource
    Electronic Resource
    Stimulated emission in GaN thin films in the temperature range of 300–700 K (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1792-1795 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of an experimental study on stimulated and spontaneous emission from high-quality single-crystal GaN films grown on 6H-SiC and (0001) sapphire substrates in the temperature range of 300–700 K. We observed edge-emitted stimulated emission (SE) at temperatures as high as 700 K for samples grown on both SiC and sapphire substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with temperature and empirical expressions for the energy positions are given. We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanism in this temperature range. The temperature sensitivity of the SE threshold for different samples was studied and the characteristic temperature was found to be 173 K in the temperature range of 300–700 K for one of the samples studied. We suggest that the unique properties of SE in GaN thin films at high temperatures could potentially be utilized in optoelectronic devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369325
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  • 16
    Electronic Resource
    Electronic Resource
    High-spectral-resolution pulsed photoluminescence study of molecular-beam-epitaxy-grown GaAs/AlxGa1−xAs multi-quantum-well structures using a very-low-power tunable pulsed dye laser (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1740-1744 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultralow-power, high-resolution, pulsed-laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular-beam-epitaxial GaAs/AlxGa1−xAs multi-quantum-well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy-hole and light-hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337268
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  • 17
    Electronic Resource
    Electronic Resource
    Room-temperature deep-ultraviolet-stimulated emission from AlxGa1−xN thin films grown on sapphire (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 245-247 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature deep-ultraviolet-stimulated emission (SE) has been observed from optically pumped metalorganic chemical vapor deposition grown AlxGa1−xN thin films. SE has been observed for Al concentrations as high as x=0.26, with a resultant SE wavelength as low as 328 nm at room temperature. The results obtained for the AlxGa1−xN layers are compared with InxGa1−xN layers of comparable alloy concentration and GaN reference layers. The incorporation of Al into GaN is shown to result in AlxGa1−xN layers with similar high excitation-density emission behavior as GaN, in contrast to InxGa1−xN layers, which exhibit markedly different SE behavior. The observation of room-temperature SE from AlxGa1−xN layers of significant Al concentration illustrates the suitability of AlxGa1−xN based structures, not only for use in deep-ultraviolet detectors, but also as a potential source of deep-ultraviolet laser radiation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123269
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  • 18
    Electronic Resource
    Electronic Resource
    Well-thickness dependence of emission from GaN/AlGaN separate confinement heterostructures (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3890-3892 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low-pressure metalorganic chemical vapor deposition. The SCH wells are unstrained and lattice-matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1378047
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  • 19
    Electronic Resource
    Electronic Resource
    Study of gain mechanisms in AlGaN in the temperature range of 30–300 K (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4101-4103 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of an experimental study of the stimulated emission (SE) properties of AlGaN epilayers grown by metalorganic chemical vapor deposition under high optical excitation conditions in the temperature range of 30–300 K. The band gap and energy position of spontaneous and SE peaks were measured over the entire temperature range studied. Through an analysis of the temperature dependence of the relative energy positions and the SE threshold, combined with absorption and time-resolved photoluminescence measurements, we estimated the carrier density at threshold to be ∼1019 cm−3 throughout the temperature range studied. Such a high carrier density indicates that an electron-hole plasma is responsible for the generation of gain in this material system from 30 to 300 K. Issues related to the development of short-wavelength AlGaN-based light emitting devices are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333692
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  • 20
    Electronic Resource
    Electronic Resource
    Time-resolved study of yellow and blue luminescence in Si- and Mg-doped GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 840-842 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved photoluminescence has been employed to study the donor-acceptor pair recombination kinetics of the yellow (∼2.3 eV) and blue (∼2.8 eV) luminescence bands in Si- and Mg-doped GaN layers, respectively. As the Si doping concentration in Si-doped GaN increases, the lifetime τ1/e of the yellow luminescence decreases, indicating that a shallow Si donor is the origin of the yellow luminescence. The blue luminescence is most likely due to a shallow Mg acceptor and a deep donor composed of a Mg acceptor-nitrogen vacancy complex, as seen by the independence of τ1/e on the Mg concentration measured by secondary ion mass spectroscopy in the range (2.5–6.0)×1019 cm−3. As the temperature is increased from 10 to 300 K, the lifetimes for the yellow and blue luminescence remain nearly constant, indicating that the distribution of electrons and holes bound to donors and acceptors does not change much with increasing temperature. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125602
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