| Ab initio self-consistent total energy calculations using second order Møller-Plesset perturbation theory and Hay-Wadt effective core potentials for gallium and arsenic have been used to investigate the chemisorption properties of atomic oxygen and atomic aluminum on the Ga-rich GaAs(100)-(2 x 1) and β(4 x 2) surfaces. Finite sized hydrogen saturated clusters with the experimental zinc-blende lattice constant of 5.654 Å and the energy optimized Ga dimer bond length of 2.758 Å have been used to model the semiconductor surface. The energetics of chemisorption on the (100) surface layer including adsorption beneath the surface layer at two interstitial sites for the oxygen adatom are investigated. For aluminum, the energetics of chemisorption on the (100) surface layer including adsorption beneath the surface layer at a single interstitial site are investigated. Chemisorption energies, nearest surface neighbor bond lengths, Mulliken population analysis, and highest occupied molecular orbital, lowest unoccupied molecular orbital (HOMO-LUMO) gaps are reported for all considered sites of chemisorption. For oxygen, possibilities of transition of the surface to a semi-insulating state are discussed. |
