The interaction of unexcited oxygen with vacuum-cleaved GaAs(110) surfaces has been studied by XPS (hν=1253 eV) and UPS (hν=21.2, 40.8, and 48.4 eV) over the exposure range 105 to 1014L. The corresponding coverage range is estimated as ϑ∠0.2 to ϑ∠0.8 monolayers (where ϑ=1 corresponds to an oxygen atom for each surface atom). From the UPS and O 1s XPS results it is concluded that the adsorption is dissociative over this entire range. From a study of the Ga and As 3d core levels; and the Ga and As L3MM x-ray-induced Auger lines it is shown that chemical shifts associated with both As and Ga levels occur over the entire adsorption range. These shifts are appropriate to those for Ga2O3 and As2O3, as is the stoichiometry of the reacted layer. There is no direct evidence for a stable chemisorption state preceeding oxidation in the 105 to 1015 L exposure regime. It is suggested that reaction with molecular oxygen takes place by dissociation at defect sites leading to growth of Ga and As oxides.
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Brundle et al. (1979) studied this question.