Dresden 2009 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 3: Heterostructures
HL 3.9: Vortrag
Montag, 23. März 2009, 12:30–12:45, BEY 154
Inhomogeneous and homogeneous broadening of excitonic spectra due to disorder — •Noemi Gögh1, Peter Thomas1, Irina Kuznetsova1, and Torsten Meier2 — 1Department of Physics and Material Sciences Center, Philipps University Marburg — 2Department of Physics, University Paderborn
In a disordered semiconductor heterostructure the excitonic line is both homogeneously and inhomogeneously broadened. While it is evident that disorder is responsible for inhomogeneous broadening, it is less obvious that disorder also contributes to homogeneous broadening (disorder-induced dephasing). We apply a one-dimensional tight-binding model of a disordered semiconductor. The optical polarization is calculated for a large number of configurations of the disorder potential and an ensemble average is performed at the end. We focus on homogeneous broadening due to disorder. Excitonic states in a disordered semiconductor are mutually coupled in the sense of Fano-resonances. At a certain spatial position the dominant energetic low-lying transition (corresponding to the 1s-exciton in an ordered three-dimensional situation) may be degenerate with the center-of-mass continuum of neighbouring excitonic transitions. Coupling of these states due to disorder, leading to homogeneous broadening, can be identified by Two-Dimensional-Fourier-Transfom-Spectroscopy (2DFTS), a variant of Four-Wave-Mixing. In order to illustrate the spectral features originating from such Fano situations, 2DFT-spectra are calculated first for conventional Fano situations. Then spectra of the disordered semiconductor model are interpreted in terms of Fano-coupling.