Growth structure of chemisorbed oxygen on GaAs(110) and InP(110) surfaces

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Abstract
A study of oxygen chemisorption on GaAs(110) surfaces with both high-resolution synchrotron-photoemission spectroscopy and x-ray-photoemission spectroscopy of the oxygen 1s core level is presented in light of what can be learned about the atomic-scale structure during the growth of the first layers of oxide. Additional results for oxygen chemisorption on InP(110) are included for comparison with GaAs(110). Curve fitting of the synchrotron-photoemission data indicates that the spectra contain peaks due to direct oxygen bonding to semiconductor atoms, inducing large binding-energy shifts, as well as peaks arising from second-order charge transfer and structural relaxation, with smaller binding-energy shifts. These peak identifications are supported by the correlation between semiconductor and oxygen core-level intensities, the behavior of peak areas as a function of oxygen exposure, and the peak binding-energy spacings. The changes in intensity of the oxide peaks show that both Ga and As atoms are involved to an equal extent in the bonding with oxygen at coverages from 0.1 monolayers (ML) to at least 1.5 ML. Comparisons of the oxide peak areas for spectra taken with different surface sensitivity also demonstrate that oxygen chemisorption for InP and GaAs proceeds layer by layer, with large kinetic barriers to oxidation beyond the first two monolayers. The dominance of surface oxidation is confirmed by oxygen core-level spectroscopy and by calibration of the experimental surface sensitivity with surface-shifted peaks on the clean surface.