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

The Ga adatom adsorption and diffusion processes on the $\text{GaAs}(001)\text{\ensuremath{-}}c(4\ifmmode\times\else\texttimes\fi{}4)$ 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 $0.5\text{ }\text{\AA{}}$ from the surface. These two sets show significant differences in the interaction of the Ga adatom with surface $\text{As}$ 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.