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  • Articles  (4)
  • Articles: DFG German National Licenses  (4)
  • American Institute of Physics (AIP)  (4)
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  • Articles  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Optical characterization of Mg-doped GaN films grown by metalorganic chemical vapor phase deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3470-3478 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning electron microscopy, micro-Raman, and photoluminescence (PL) measurements are reported for Mg-doped GaN films grown on (0001) sapphire substrates by low-pressure metalorganic chemical vapor phase deposition. The surface morphology, structural, and optical properties of GaN samples with Mg concentrations ranging from 1019 to 1021 cm−3 have been studied. In the scanning micrographs large triangular pyramids are observed, probably due to stacking fault formation and three-dimensional growth. The density and size of these structures increase with the amount of magnesium incorporated in the samples. In the photoluminescence spectra, intense lines were found at 3.36 and 3.31 eV on the triangular regions, where the presence of cubic inclusions was confirmed by micro-Raman measurements. The excitation dependence and temperature behavior of these lines enable us to identify their excitonic nature. From our study we conclude that the interface region between these defects and the surrounding wurtzite GaN could be responsible for PL lines. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289794
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  • 2
    Electronic Resource
    Electronic Resource
    Raman scattering and infrared reflectivity in [(InP)5(In0.49Ga0.51As)8]30 superlattices (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6382-6387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured far-infrared and infrared reflectivity as well as Raman scattering in an [(InP)5(In0.49Ga0.51As)8]30 superlattice grown by molecular beam epitaxy. A numerical model for calculating the reflectivity coefficient for complex systems which includes superlattice, buffer layer, and substrate has been developed. The far-infrared reflectivity spectra consists of the superlattice confined and interface modes as well as the modes from the buffer layer (In0.49Ga0.51As) and the substrate (InP). In the infrared spectral range above 1000 cm−1 we observe only interference fringes from the buffer layer. A good agreement between calculated and experimental spectra is achieved. The folded longitudinal acoustic phonon doublet appears at about 39 cm−1 in the Raman scattering spectra. The frequency agrees well with a continuum model calculation. In the optical phonon spectral region we observe confined modes corresponding to both constituents. The modes representing vibrations of atoms at both interfaces: InP/InGaAs (230 cm−1 mode) and InGaAs/InP (240 and 260 cm−1 modes) have also been observed. The geometrical parameters of the sample, obtained from the fitting of the reflectivity data, agree well to the values of the layer thickness obtained by double crystal x-ray diffraction. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287133
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  • 3
    Electronic Resource
    Electronic Resource
    Residual strain effects on the two-dimensional electron gas concentration of AlGaN/GaN heterostructures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4735-4740 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ga-face AlGaN/GaN heterostructures with different sheet carrier concentrations have been studied by photoluminescence and Raman spectroscopy. Compared to bulk GaN, an energy shift of the excitonic emission lines towards higher energies was observed, indicating the presence of residual compressive strain in the GaN layer. This strain was confirmed by the shift of the E2 Raman line, from which biaxial compressive stresses ranging between 0.34 and 1.7 GPa were deduced. The spontaneous and piezoelectric polarizations for each layer of the heterostructures have been also calculated. The analysis of these quantities clarified the influence of the residual stress on the sheet electron concentration (ns). Possible causes for the discrepancies between the calculated and experimentally determined sheet carrier densities are briefly discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408268
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  • 4
    Electronic Resource
    Electronic Resource
    Role of defect centers in recombination processes in GaN monocrystals (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2824-2826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A confocal fluorescence microscopic study was carried out on GaN monocrystals grown by molecular beam epitaxy and doped with Mn. The samples were irradiated with mid band gap radiation (488 nm) rather than ultraviolet, and it was found that a strong yellow radiation was emitted by defect centers. Three-dimensional images clearly reveal not only the size and the form of the illuminating defect centers but also their orientations with respect to the plane on which these defects were grown. This is a direct evidence for the radiative recombination at the defect centers when excited by the midgap radiation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1471938
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