201 research outputs found
Crossover from strong to weak confinement for excitons in shallow or narrow quantum wells
Get PDFWe present a theoretical study of the crossover from the two-dimensional (2D, separate confinement of the carriers) to the three-dimensional (3D, center-of-mass confinement) behavior of excitons in shallow or narrow quantum wells (QW's). Exciton binding energies and oscillator strengths are calculated by diagonalizing the Hamiltonian on a large nonorthogonal basis set. We prove that the oscillator strength per unit area has a minimum at the crossover, in analogy with the similar phenomenon occurring for the QW to thin-film crossover on increasing the well thickness, and in agreement with the analytic results of a simplified δ-potential model. Numerical results are obtained for GaAs/Alx Ga1-xAs and InxGa1-xAs/GaAs systems. Our approach can also be applied to obtain an accurate description of excitons in QW's with arbitrary values of the offsets (positive or negative) and also for very narrow wells. In particular, the crossover from 2D to 3D behavior in narrow GaAs/AlxGa1-xAs QW's is investigated: the maximum binding energy of the direct exciton in GaAs/AlAs QW's is found to be ∼26 meV and to occur between one and two monolayers
Die extraartikuläre proximale Femurfraktur des alten Menschen — DHS oder intramedulläre Hüftschraube zur Frakturversorgung?
No full textA randomised controlled trial comparing highly cross-linked and contemporary annealed polyethylene after a minimal eight-year follow-up in total hip arthroplasty using cemented acetabular components
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Optical investigation of a strain-induced mixed type-I–type-II superlattice system: CdTe/ Cd 1 − x Zn x Te
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Reconstruction of the iliac bone using the homolateral femur after resection for pelvic tumor
No full textReconstruction de l’os iliaque à l’aide du fémur homolatéral après résection pour tumeur pelvienne
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