Angle-resolved XPS structural investigation of GaAs surfaces

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) analysis has been performed on GaAs (1 0 0) surfaces in different conditions as naturally oxidized, Ar+ ion sputtering (E=1–5 keV) and chemical etching in H2SO4/H2O2/H2O (3:1:1). The most sensitive angle to the surface compositional changes was the take-off angle (TOA): 25°. Native oxide phases on GaAs consist of a mixture of Ga2O3, As2O3 and As2O5. Ar+ ion sputtering procedure modifies the surface composition, in the altered layer where the concentration ratio CGa/CAs tends to 1.5–1.6. Wet chemical etching removes the oxide layer and the As-rich region from the surface. In the experiment combining chemical etching with Ar+ ion sputtering for cleaning purpose, the native oxides are removed from the surface and CGa/CAs tends to stoichiometry. The experiment on native oxide reconstruction after storage in high-vacuum conditions (p∼10−8 Torr) provides evidence of the high reactivity of GaAs (1 0 0) surfaces. We have observed the presence of an As oxide (BE=43 eV) within a concentration range of 2–3%.