By using first-principles total-energy calculations, an analysis was made of the behavior of Ga and Al adatoms on the GaAs(001)-β2 surface. As well as the adsorption site, 2 diffusion channels were identified which were characterized by differing adatom/surface-dimer interactions. Both of the latter paths affected adatom migration. In one channel, the adatom jumped across the surface dimers and left the dimer bonds intact. In the other case, the dimer bonds were broken. Both channels were taken into account in order to derive effective adatom diffusion barriers. A marked diffusional anisotropy was found for both Al and Ga adatoms and, in agreement with experiments, the diffusion barriers were higher for Al than for Ga.

A.Kley, P.Ruggerone, M.Scheffler: Physical Review Letters, 1997, 79[26], 5278-81