Surface morphologies in GaAs homoepitaxy: Mound formation and evolution

Atomic force microscopy has been used to observe surface morphologies during growth of GaAs films on GaAs(001) by chemical beam epitaxy. Mound formation is observed at the beginning of GaAs growth as a function of the surface prior to deposition. GaAs substrates exhibit a large density of pits and cracks after usual thermal treatment employed for oxide desorption. On this kind of surface mounds form and coalesce as film thickness increases; surface planarization is eventually achieved-at this point, morphologies are typically those expected from two-dimensional growth. In this sense we observe that monolayer island size distribution is determined by the kinetic conditions used for the growth; nucleation sites and island spatial distribution, however, are strongly influenced by the topography of the initial surface where the film is deposited even for films thousands of monolayers thick. The final morphologies present wide terraces and few monolayer islands on top of them independent of growth conditions. This picture agrees with theoretical results where negligible step edge barriers are considered.