Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 12: Quantum dots and wires: Optical properties I
HL 12.1: Vortrag
Montag, 26. März 2007, 14:45–15:00, H17
Origin of the excitonic dipole moment in InAs/GaAs Quantum Dots: A Tight-Binding Study — •Alexander Kleinsorge1, Thomas Hammerscmidt1, Peter Kratzer2,1, and Matthias Scheffler1 — 1Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin, Germany — 2Fachbereich Physik, Universität Duisburg-Essen, D-47048 Duisburg, Germany
With the help of electronic structure calculations, the electronic and optical properties of quantum dots (QDs) can be related to their atomic structure. We employ the empirical sp3s* tight-binding approach, including 2nd-nearest-neighbor interactions and spin-orbit coupling, preceded by structural relaxation using a potential of the Abell-Tersoff type. We are able to treat large systems (up to 106 atoms, folded-spectrum method). We apply our method to buried InAs QDs in GaAs, comparing different inverted pyramid shapes and composition profiles. Because of the different shape of the electron and hole wavefunctions (WF), the exciton is associated with a dipole moment which causes the experimentally observed Stark shift. We investigate how the relative position of an electron or hole state in a QD depends on its size in different inverted-pyramid shape boundaries. The presence of the wetting layer (WL) is found to affect the localization of the hole WF and thus the magnitude of the dipole moment, and for flat QD (height < 4nm) even its sign. If an inversion of the dipole is observed experimentally for flat quantum dots, we interprete this as indication that the WL below the QD must have been dissolved.