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HL: Fachverband Halbleiterphysik
HL 48: Quantum dots and wires: preparation and characterization II
HL 48.1: Vortrag
Donnerstag, 29. März 2007, 16:15–16:30, H13
Evidence for Reduction of the Critical Nucleus in InAs/GaAs Quantum Dot Stacks — •Thomas Hammerschmidt1, 3, Peter Kratzer2, 3, and Matthias Scheffler3 — 1Department of Materials, University of Oxford, Oxford, UK — 2Fachbereich Physik, Universität Duisburg-Essen, Duisburg, Germany — 3Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
Growth of quantum dot (QD) stacks is a possible route to influence the lateral arrangement of self-assembled semiconductor QDs. In stacks of InAs QDs in GaAs, the QDs in a new layer form preferably right above those in the previous layer. Is is surprising, how the weak interactions of surface atoms with the buried QD trigger this `correlated' growth. In this work we offer a quantitative explanation based on the influence of elastic interactions on the critical nucleus for QD formation.
In particular, we apply a recently developed Abell-Tersoff potential to realistic QD nanostructures. For the formation of a new layer of QDs on a capping layer above a layer of buried QDs, we study systematically the formation energy as a function of lateral distance of buried and free-standing QD. We find it to be minimal if the free-standing QD is placed exactly vertically above the buried QD, in line with the growth correlation observed in most experiments of stacked QD growth. The elastic interactions observed in our calculations lower the energy barrier for QD nucleation by up to 2 eV per QD as compared to nucleation in a single QD layer. The size of the critical nucleus thereby reduces from approximately 70 to not more than 25 InAs units.