The energetics of site exchange in surfactant-mediated epitaxial growth is investigated using first-principles calculations for the homoepitaxy of Si/Si(001) with an As monolayer. We find that the interaction between Si dimers on the As-terminated Si(001) surface repels the Si dimers from each other and initiates site exchange between the top-layer Si atoms and the second-layer As atoms. The origin of the site exchange is the second-layer rebonding in the resulting geometries. These chemical effects of the As surfactant prevent Si islanding
this is also valid for Ge/Si heteroepitaxy. © 1994 The American Physical Society.