Stable adsorption sites and potential-energy surface of a Ga adatom on a GaAs(111)A surface

We theoretically investigated the stable adsorption sites and potential-energy surface of Ga adatoms on a GaAs(111)A surface. Although Ga-vacancy sites on the surface were expected to be the most stable for Ga adatoms, the first-principles calculation results contradict this. Comparing the results with those obtained by the empirical interatomic potential calculations, we found that electronic contributions, such as valence electron redistribution, are crucial for stabilizing Ga adatoms on a GaAs(111)A surface. Based on the energies at several sites, a potential-energy surface was also obtained and the diffusion barrier height of a Ga adatom was estimated. The estimated height was 0.4 eV, which is much lower than that calculated for a GaAs(001) surface. This is consistent with the experimentally observed results. The present calculation results further suggest that mechanisms of Ga-vacancy-site stabilization, such as the self-surfactant effect, play an important role in epitaxial growth processes. [S0163-1829(99)07939-4].