Monolayer growth and structure of ga on si(111)

The vertical position of Ga on Si(111) for coverages in the monolayer range has been quantitatively established using the x-ray standing-wave technique. The experimentally determined position is in good agreement with first-principles total energy minimization calculations using the local-density functional approach. Gallium atoms substitute for silicon in the outer half of the (111) double layer at the surface. The low-energy electron-diffraction pattern shows an incommensurate superstructure which is not associated with Ga adsorbed in the substitutional sites, but with Ga weakly bound to the surface.