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  • 1
    Electronic Resource
    Electronic Resource
    Lateral redistribution of excitons in CdSe/ZnSe quantum dots (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 473-475 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1432743
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  • 2
    Electronic Resource
    Electronic Resource
    Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 685-687 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two well distinguishable classes of nanoscale islands were identified in CdSe/ZnSe quantum dot structures by optical spectroscopy and transmission electron microscopy. For 2.1 to 3.1 monolayer CdSe deposition, coherent three-dimensional (3D) islands, formed in the Stranski–Krastanow (SK) mode, are found with typical diameters of ∼16 nm and a coverage-dependent density of up to 3×1010 cm−2. Simultaneously, small islands with lateral extensions below 10 nm and a density of ∼5×1011 cm−2 are formed by strain-modified island growth. Whereas the 3D SK islands dominate the emission properties at room temperature, the latter smaller islands determine the optical properties at temperatures below 120 K. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125861
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  • 3
    Electronic Resource
    Electronic Resource
    The origin of optical gain in cubic InGaN grown by molecular beam epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2832-2834 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical properties of cubic InGaN samples with varying In content are investigated to provide insight into the processes responsible for optical amplification. The samples were grown by molecular beam epitaxy on GaAs substrates. The structural and optical properties were studied by means of time-resolved and time-integrated photoluminescence spectroscopy and cathodoluminescence microscopy, as well as gain measurements at various temperatures. From these measurements, localized states are proposed to be responsible as recombination mechanism. The cathodoluminescence measurements evidence a direct correlation of the degree of In fluctuation and the efficiency of optical amplification of the samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126488
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Resonant Raman scattering in self-organized InAs/GaAs quantum dots (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3746-3748 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exciton-phonon coupling in self-organized InAs/GaAs quantum dots (QDs) is investigated under resonant excitation of the ground-state transition. First- and second-order phonon sidebands of the TO (30.3 meV) and LO (33.2 meV) modes of the strained InAs QDs as well as an interface (35.9 meV) mode are resolved. Huang–Rhys factors of 0.012, 0.026, and 0.006, respectively, indicate enhanced polar exciton-phonon coupling in such strained low-symmetry QDs. Time-resolved measurements support the local character of the phonon modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329321
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  • 6
    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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  • 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
    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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  • 9
    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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  • 10
    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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