Surface and bulk equilibrium structures of silicon-germanium alloys from Monte Carlo simulations

The technologically important alloy of silicon and germanium is known to have no long-range order in the bulk. Whether there is any short-range order in the bulk and the nature of the structure of the surface and near-surface regions remains the subject of some debate. We present a method of Monte Carlo simulation that is effective for studying the equilibrium structural properties of the bulk and strained-superlattice alloys. The simulations of the bulk alloy indicate that there is no short-range order and that the Si-Ge alloy is a true random alloy at room temperature and above. The surfaces of these alloys experience segregation of germanium to the surface, with no long-range order observed in the slightly silicon-rich subsurface layers, in agreement with recent experiments.