Formation of alternative surface oxide phases on GaAs by adsorption of O2 or H2O: A UPS, XPS, and SIMS study

Adsorption of O2 and H2O on GaAs exhibits a sharp contrast in behavior: O2 bonds to As sites almost exclusively while H2O predominantly bonds to Ga sites. The formation of Ga–OH bonds due to dissociative adsorption of H2O preceded by a molecular adsorption step is inferred from UPS data. Corroboration of these findings is provided by SIMS data for positive Ga and negative As ions. The role of hydrogen is discussed in the formation of stable oxides on the GaAs surface.