Critical role of the surface reconstruction in the thermodynamic stability of (105) Ge pyramids on Si(001).

We show by molecular dynamics simulations on a scale comparable to experimental dimensions that a peculiar surface reconstruction of the (105) facets is responsible for the stability of Ge pyramids on Si(001). This finding is confirmed by ab initio total energy calculations for competing surface reconstructions and a very satisfactory comparison of the corresponding charge density maps to scanning tunneling microscopy measurements of the facets, both for filled and empty states.