Binding sites and diffusion barriers of a Ga adatom on the GaAs(001)-c(4X4) surface from first-principles computations

The Ga adatom adsorption and diffusion processes on the GaAs(001)-c(4x4) surface were studied using ab initio density-functional-theory computations in the local density approximation. Two distinct sets of minima and transition sites were discovered for a Ga adatom relaxing from heights of 3 and 0.5 angstrom from the surface. These two sets show significant differences in the interaction of the Ga adatom with surface As dimers. An electronic signature of the differences in this interaction was identified. We computed the energetic barriers to diffusion for various adsorption sites. From these, we propose three pathways for diffusion of a Ga adatom on this surface which indicate anisotropic diffusion along different directions.