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  • 1
    Electronic Resource
    Electronic Resource
    Photoluminescence and Raman study of compensation effects in Mg-doped GaN epilayers (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5828-5830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The compensation of Mg-doped GaN is systematically studied by low-temperature photoluminescence and Raman spectroscopy using a series of samples with different Mg concentrations. Strongly doped samples are found to be highly compensated in electrical measurements. The compensation mechanism is directly related to the incorporation of Mg. Three different deep donor levels are found at 240±30, 350±30, and 850±30 meV from the conduction band, each giving rise to deep unstructured donor-acceptor pair emission. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368853
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrogen-related local vibrational modes in ZnO:N (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1909-1911 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition (CVD) containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy (SIMS), was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm−1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1461903
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature and pressure dependence of Mg local modes in GaN (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 198-200 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature and pressure dependence of the zone-center phonons and of the local vibrational modes of magnesium in the hexagonal modification of GaN was studied within a valence-force model. The contribution caused by thermal expansion was calculated and compared with the experiment. We find that the frequency shift of the local vibrational modes arises to a much larger extent from anharmonic decay into lower energy phonons than the shift of the GaN host modes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1339848
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  • 4
    Electronic Resource
    Electronic Resource
    Recombination mechanisms in GaInNAs/GaAs multiple quantum wells (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1391-1393 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recombination processes in Ga1−xInxNyAs1−y/GaAs multiple quantum wells (MQWs) were investigated as function of the nitrogen molar fraction. We found a pronounced S-shaped behavior for the temperature-dependent shift of the photoluminescence emission similar to the ternary nitrides InGaN and AlGaN. This is explained by exciton localization at potential fluctuations. Time-resolved measurements at 4 K reveal an increase of the decay time with decreasing emission energy. A model based on lateral transfer processes to lower-energy states is proposed to explain this energy dependence. The formation of tail states in the Ga1−xInxNyAs1−y/GaAs MQWs is attributed to nitrogen fluctuations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355014
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  • 5
    Electronic Resource
    Electronic Resource
    Temporal evolution of resonant Raman-scattering in ZnCdSe quantum dots (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2662-2664 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated ZnCdSe/ZnSe quantum-dot structures which include planar and coherently strained three-dimensional islands with different sizes. Optical excitation of these islands well below the ZnSe band gap leads to a resonant enhancement of the Zn0.7Cd0.3Se longitudinal-optical (LO) phonon-scattering efficiency and makes the 2LO and 3LO multiphonon emission observable. Resonant excitation with a power density of about 1.3 MW/cm2 using a micro-Raman setup results in an exponential decrease of the 1LO, 2LO, and 3LO intensity with irradiation time. This decay behavior is not observed for pure ZnSe crystals and can be avoided for the ZnCdSe/ZnSe structures using much lower excitation densities. The decrease in intensity is accompanied by a shift of the LO mode to higher frequencies resulting from a lower cadmium concentration in the alloy. From these experimental findings, we conclude that resonant excitation at a certain power density leads to cadmium out-diffusion from the planar quantum dots, which shifts the resonance away from the excitation energy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126436
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  • 6
    Electronic Resource
    Electronic Resource
    Lattice dynamics of hexagonal and cubic InN: Raman-scattering experiments and calculations (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2122-2124 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results of first- and second-order Raman-scattering experiments on hexagonal and cubic InN covering the acoustic and optical phonon and overtone region. Using a modified valence-force model, we calculated the phonon dispersion curves and the density of states in both InN modifications. The observed Raman shifts agree well the calculated Γ-point frequencies and the corresponding overtone density of states. A tentative assignment to particular phonon branches is given. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126273
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  • 7
    Electronic Resource
    Electronic Resource
    Micro-Raman and cathodoluminescence studies of epitaxial laterally overgrown GaN with tungsten masks: A method to map the free-carrier concentration of thick GaN samples (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3418-3420 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cathodoluminescence (CL) and micro-Raman spectroscopy were applied to study microscopically the optical and structural properties of two epitaxial-laterally overgrown GaN structures with tungsten masks in 〈11(underbar)00〉 and 〈112(underbar)0〉 direction, respectively. A free-carrier concentration higher than 1019 cm−3 was observed right above the masks, leading to a gradient in free-carrier concentration over the whole layer thickness. We used the normalized longitudinal-optical-phonon intensity and the broad band around 650 cm−1 as a measure for the free-electron concentration, which is a promising method to determine the free-carrier concentration justified by the good correlation with CL results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126665
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  • 8
    Electronic Resource
    Electronic Resource
    Optical microscopy of electronic and structural properties of epitaxial laterally overgrown GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3320-3322 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local strain relaxation as well as inhomogeneous impurity incorporation in epitaxial laterally overgrown GaN (ELOG) structures is microscopically characterized using spectrally resolved scanning cathodoluminescence (CL) and micro-Raman spectroscopy. We correlate the different CL emission spectra with results of spatially resolved Raman-scattering experiments sensing the local strain and free-carrier concentration. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123331
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  • 9
    Electronic Resource
    Electronic Resource
    Local vibrational modes in Mg-doped GaN grown by molecular beam epitaxy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3281-3283 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local vibrational modes in the region of the acoustic and optical phonons are reported for Mg-doped GaN grown by molecular beam epitaxy. The modes, studied by Raman spectroscopy, appear in addition to the known modes in the high-energy region around 2200 cm−1. We suggest disorder-activated scattering and scattering from Mg-related lattice vibrations to be the origin of the low-energy modes. Our assignment is supported by calculations based on a modified valence-force model of Kane. Temperature-dependent measurements between 4 and 300 K exclude an electronic Raman-scattering mechanism. We also report a new line at 2129 cm−1 and discuss the origin of all five observed high-energy modes. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123320
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  • 10
    Electronic Resource
    Electronic Resource
    Time-resolved microphotoluminescence of epitaxial laterally overgrown GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3647-3649 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial laterally overgrown GaN (ELOG) structures are microscopically characterized using spatially resolved microphotoluminescence (micro-PL) and time-dependent spectroscopy. To understand the influence of the different lateral growth mechanisms on the peak position and the temporal behavior of the transition lines, we correlated the different micro-PL emission spectra with results of spatially resolved time-dependent spectroscopy experiments. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125416
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