Strain-induced surface structures on Sb-covered Ge(111): Epitaxial Ge films on Si(111):Sb

Abstract

STM images of surface structures of an Sb-covered Ge film growing on Si(111):Sb are presented, showing the (√3 × √3) structure on Si(111):Sb, a (6√3 × 6√3) structure consisting of hexagons with a size of 40 Å with triangular subunits of (1 × 1) structure for the three-monolayer Ge film, and a (2 × 1) Sb-structure for the thick relaxed Ge film. Using an ab initio total energy and force method, we have investigated the stability of the different structures of Ge(111):Sb(1 ML) as a function of the lateral lattice constant. We find that the (2 × 1) chain-reconstruction of Ge(111):Sb has a range of stability between about 5.5% compression and 1% expansion. For larger dilatations the (1 × 1) structure becomes stable, for larger compressions the T4 (√3 × √3) structure does. The observed (1 × 1) structure on top of the hexagons can be explained by an 8% dilatation of the surface (compared to Si bulk) due to the stress exerted by the Sb atoms on the Ge film and at the rim of the finite hexagons.