Atomic force microscopy has been used to observe surface morphologies
during growth of GaAs films on GaAs(001) by chemical beam epitaxy. Mou
nd formation is observed at the beginning of GaAs growth as a function
of the surface prior to deposition. GaAs substrates exhibit a large d
ensity of pits and cracks after usual thermal treatment employed for o
xide desorption. On this kind of surface mounds form and coalesce as f
ilm thickness increases; surface planarization is eventually achieved-
at this point, morphologies are typically those expected from two-dime
nsional growth. In this sense we observe that monolayer island size di
stribution is determined by the kinetic conditions used for the growth
; nucleation sites and island spatial distribution, however, are stron
gly 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 theor
etical results where negligible step edge barriers are considered.