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O: Oberflächenphysik
O 12: Postersitzung (Struktur und Dynamik reiner Oberfl
ächen, Grenzfl
äche fest-flüssig, Nanostrukturen, Teilchen und Cluster, Halbleiteroberfl
ächen und Grenzfl
ächen, Zeitaufgelöste Spektroskopie, Rastersondentechniken, Methodisches)
O 12.23: Poster
Montag, 24. März 2003, 18:00–21:00, P1
Combined density-functional and tight-binding approach to vicinal GaAs and InAs surfaces — •Dengke Yu, Peter Kratzer, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
Spontaneous formation of nanostructures on surfaces is often governed by a delicate interplay between relaxation of surface stress and long-range strain fields in the substrate. For atomically thin films or islands only a few nanometer in size, the theory of elastic continua is no longer applicable. Moreover, a quantum-mechanical treatment of dangling bonds and rehybridization of surface atoms is required to reproduce correctly the effects of surface energy and surface stress on the elastic relaxation in nanostructures. Here we propose a mixed approach which combines calculations employing density-functional theory (DFT) with tight-binding calculations for situations that involve so many atoms that they become untractable by the first-principles method.
We present total energy calculations based on an empirical sp3s* tight-binding model for GaAs and InAs with nearest-neighbor interaction and scaling functions for hopping parameters and pairwise repulsion. The tight-binding calculations of elastic constants, surface energies and surfaces stress of GaAs and InAs surfaces are in excellent agreement with DFT calculations. We apply the method to the study of surfaces vicinal to GaAs(001), using tight-binding to add finite-size corrections to step energies calculated in DFT slab models. The effect of medium-range strain relaxation near steps on pure GaAs surfaces, as well as on GaAs surfaces covered by a monolayer film of InAs, will be discussed.