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HL: Halbleiterphysik

HL 36: Heterostrukturen II

HL 36.1: Vortrag

Donnerstag, 25. März 1999, 16:00–16:15, H3

Formation and stability of self-assembled coherent islands in highly mismatched heteroepitaxy — • Ligen Wang, Peter Kratzer, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschdft, Faradayweg 4-6, D-14195 Berlin, Germany

The strain-induced self-assembly of small three-dimensional (3D) islands during heteroepitaxial growth of mismatched materials has raised intense interest. These 3D islands form after the deposition beyond a critical layer thickness. Usually, this growth is referred to as the Stranski-Krastanov growth mode. In the present work, we study the energetics of island formation in Stranski-Krastanov growth of the highly mismatched heteroepitaxial system InAs/GaAs. We present an expression in which the energy gain by islanding depends on the island density, coverage and island volume. The surface energies for both the island facets and the wetting layer are calculated using density-functional theory. The elastic energy in both the islands and the substrate is calculated within continuum elasticity theory. It is shown that a finite equilibrium island size exists if changes in the wetting layer morphology after the 3D transition are properly taken into account. Our approach reproduces very well the experimental island size dependence on the coverage, and indicates that the critical layer thickness depends on growth conditions. The present study provides a new explanation for the occurrence of a well-defined size distribution of self-assembled coherent islands.