Arsenic adatom structures for Ge(111) and Si(111) surfaces: First-principles calculations

The (1 x 1) and (root 3 x root 3)R30 degrees (T4) structures of As adatoms on the Ge(111) and Si(111) surfaces are studied using first-principles calculations. Comparing the adsorption energies per As atom, we find that on the Si(lll) surface, the T4 configuration is favored against the (1 x 1) structure by 0.5 eV per As adatom. The same preference is found on the Ge(lll) surface, but only by 0.1 eV As adatoms. The (root 3 x root 3)R30 degrees structure (1/3 ML coverage) is nevertheless unstable, and the energetics favor its transformation into domains with 1 ML coverage, and areas of a clean, reconstructed surface. The relaxed adatom structures and the redistribution of the electronic charge densities are also presented and discussed.