Surface-morphology evolution during unstable homoepitaxial growth of GaAs(110)

The time evolution of the surface morphology during growth of GaAs(110) by molecular-beam epitaxy is studied using Nomarski and atomic force microscop y. Depending on the growth temperature and As-4 over-pressure, different ty pes of growth instabilities are observed: large three-dimensional pyramidal features develop under As-deficient growth conditions, whereas step bunchi ng takes place under As-rich conditions. In addition, a crossover from step bunching, attributed to a negative step-edge barrier, to unstable growth t ypical of a positive step-edge barrier, takes place under As-deficient cond itions as the film thickness increases. Under suitable growth conditions, s elf-organization of the microscopic features during growth leads to the cre ation of a highly unusual, well-ordered pattern on the surface. We, discuss the microscopic origin of the observed instabilities with the help of rece nt theoretical and experimental results. [S0163-1829(99)05803-8].