STABLE AND UNSTABLE GROWTH IN MOLECULAR-BEAM EPITAXY

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