We consider the growth of films by molecular beam epitaxy in the presence of step-edge (Schwoebel) barriers using numerical simulation and experiments. We show that the growth of a singular surface is unstable, but that a miscut above a certain critical slope (which depends on growth conditions) leads to stable growth in a step-flow mode. For singular surfaces the instability gives rise to the formation of large mounded structures on the surface for which the slope is in the stable regime. We identify these in GaAs epitaxy using atomic force and scanning tunneling microscopy. We propose a continuum equation which exhibits these features.

• Received 5 August 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.116