Adsorption of As on stepped Si(100): Resolution of the sublattice-orientation dilemma

First-principles calculations are used to investigate the energetics of an As overlayer adsorbed on a stepped Si(110) surface. We show that the growth of As directly on top of the Si surface produces a metastable structure, while the replacement of the original top Si layer by As leads to a lower-energy configuration. In the latter case, the rearrangement of the surface is driven by the relaxation of stress by surface steps. This result explains the sublattice-orientation dilemma in GaAs-on-Si heteroepitaxy.