Reentrant mound formation in GaAs(001) homoepitaxy observed by ex situ atomic force microscopy

A study of the surface morphology of homoepitaxial GaAs(001) by means of ex situ atomic force microscopy in air reveals the reentrance of mounding behavior at low growth temperatures. A transition from statistical roughening to organized mound formation is observed as the growth temperature is reduced. We show by means of growth simulations that the observed morphology is compatible with anisotropic adatom diffusion in the presence of an Ehrlich-Schwoebel barrier. The mechanism leading to this kind of adatom kinetics at low temperatures is interpreted in terms of surfactant acting arsenic condensing on the surface.