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  • 1
    Electronic Resource
    Electronic Resource
    Physical criteria for the direct-to-indirect gap crossover in AlxGa1−xAs alloys (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 704-706 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: AlxGa1−xAs alloys undergo a direct-to-indirect gap transition when the Al concentration x is increased, or when hydrostatic pressure P is applied to a direct-gap sample of fixed composition. It is usually assumed that either hydrostatic pressure or alloying produce a Γ–X conduction band crossing responsible for the change in the nature of the gap. A critical discussion regarding this widely adopted criterion for the direct-to-indirect gap transition is presented. Alloying and pressure effects in the electronic properties of AlxGa1−xAs are determined through the small crystal approach with a 64-site basic cluster. Finite-size effects are discussed. The photoluminescence emission intensity is calculated as a function of x and P, and physically reliable criteria for the transition from the direct-to-indirect gap regimes based on these results are proposed. A critical concentration consistent with experimental results associated to this change of regime is obtained from our data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106543
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  • 2
    Electronic Resource
    Electronic Resource
    Optical effects of interdiffusion in GaAs/AlAs heterostructures: Atomic scale calculations (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2423-2425 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the effects of atomic interdiffusion in the optical properties of AlAs/GaAs quantum wells through tight-binding model calculations. Ensembles of supercells, each cell containing up to ∼104 atoms with periodic boundary conditions, are used to simulate the heterostructures. The oscillator strength f of optical transitions at the absorption threshold is calculated as a function of the quantum-wells width W and the diffusion length L. As L increases, f undergoes a discontinuous transition to zero, indicating indirect-gap behavior for L larger than a critical value of the diffusion length. A unified behavior of f as a function of L/W1.7 is found. This permits relating optical properties to structural properties through simple fitting formulas. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117658
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  • 3
    Electronic Resource
    Electronic Resource
    Pressure and composition effects on the gap properties of AlxGa1−xAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5531-5537 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Effects of pressure and composition on the gap properties of AlxGa1−xAs randomly disordered alloys are investigated theoretically and experimentally. The analogy between pressure and alloying effects is explored. Special attention is given to the direct-to-indirect gap transition region, where the gap sensitivity to both pressure and composition variations is shown to be strongly enhanced. A 30% decrease in luminescence intensity is produced on a x=0.46 sample under applied pressure of 0.7 kbar, while a similar effect in GaAs would require pressures of several tens of kbar. Calculations are performed within the small crystal approach using 64-, 216-, and 1000-atoms basic cluster sizes, with periodic boundary conditions. Convergence of the calculated properties with the cluster size is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354211
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  • 4
    Electronic Resource
    Electronic Resource
    Localized states in polymeric molecules. I. The transfer matrix for long range interactions (1981)
    Springer
    Theoretical chemistry accounts 60 (1981), S. 11-17 
    Details
    ISSN: 1432-2234
    Keywords: Polymer ; Localized states ; Band states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have extended the transfer matrix technique to determine the Green's function for 1-dimensional systems with long range interactions. The formalism is applied to study the density of states and impurity modes of linear chains; calculations are presented for nearest and next nearest neighbors interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00554383
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