Oxygen adsorption on the GaAs(110) surface

The adsorption of nonexcited molecular oxygen on cleaved GaAs(110) surfaces at room temperature has been studied using photoemission techniques. Detailed analysis of the oxygen-induced structure in the valence-band region revealed two different forms of adsorbed oxygen. Adsorption in the first form saturates at a very low coverage (approx.0.01 monolayer) and is probably associated with defect sites. Adsorption in the second form occurs at normal surface sites and produces measurable chemical shifts in Ga-3d and As-3d core levels. The nature of the second form of oxygen has been further investigated with core level studies of surfaces oxidized at room temperature and subsequently heated to a high temperature. Annealing to moderately high temperature (approx.3700C) causes transfer of oxygen from As--O bonds to form additional Ga--O bonds. Fast heating to high temperature (4300--4500C) leads to desorption of roughly half of the oxygen atoms and all of the chemically affected As atoms, while little change in the Ga-3d core level is observed. Several previously proposed oxidation models are compared based on the present data