Origin of apparent critical thickness for island formation in heteroepitaxy

Simulations of strained-layer growth, using a continuum model that accounts for the alloy compositional degrees of freedom were carried out. It was found that a continuum model of heteroepitaxy exhibited a sharp crossover with increasing coverage, from planar growth to island formation. It was also shown that the surface stiffness could depend sensitively on surface composition. The surface diffusivity could also be different for the two alloy components and could have a nontrivial dependence on composition. It was stated that the transition was kinetic in nature and depended weakly on growth rate.