First-principles study of GaAs(0 0 1)-β2(2 × 4) surface oxidation

Oxygen atom adsorption on GaAs(0 0 1)-β2(2 × 4) during initial surface oxidation is studied by density functional theory (DFT). The results show that one or two oxygen atom adsorption at back-bond sites satisfy the bond saturation conditions leading to no effect on the surface gap states. However, for an oxygen replacement of an As dimer atom at trough site or row site As dimer atoms, an As–As bond is broken. Mid gap states are produced leading to the Fermi level pining due to the unsaturated As dangling bonds.