Two major outstanding issues in the oxidation of InP and GaAs(110) surfaces are addressed: (1) single phase versus multiphase oxidation and (2) surface versus bulk oxidation. From the analysis of O 1s, In 4d, and P 2p core level spectra it is concluded that InP oxidizes predominantly in a single phase at room temperature. Its stoichiometry is enhanced upon annealing to give InPO4. There is no evidence for any other oxide phase for the coverage range investigated (to ∼1 monolayer of adsorbed oxygen). It appears that the oxidation is nucleated, but forms a fairly homogeneous oxide layer at the surface. GaAs(110), on the other hand, oxidizes from submonolayer oxygen coverages on into separate gallium and arsenic oxide phases. There is evidence for several oxidation states of the As. These do not consolidate upon annealing into a stoichiometric phase, but rather are reduced by the presence of GaAs to form additional gallium oxide. Reference spectra obtained from β-Ga2O3 crystals were used to confirm the absence of this oxide in the oxidized GaAs surfaces and to calibrate the oxygen uptake. The experimental results confirm the issue of subsurface oxidation prior to a monolayer uptake of oxygen.
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Hughes et al. (1986) studied this question.