Multilayer oxidation of AlAs by thermal and electron beam induced decomposition of H₂O in ultrahigh vacuum

The oxidation of AlAs by the decomposition of water has been investigated in ultrahigh vacuum using high-resolution electron energy loss spectroscopy, Auger electron spectroscopy, and temperature-programmed desorption. Significant oxidation of the AlAs near-surface region was observed after a single adsorption/anneal cycle in which multilayers (>10 monolayers) of water, adsorbed at 100 K, were annealed to above room temperature. Sputter profiling shows that repeated cycles of multilayer water exposure at 100 K followed by annealing results in a surface oxide that is at least 20-30 Å thick. The extent of surface oxidation, as measured by Auger electron spectroscopy, is not affected by annealing to 700 K. However, at temperatures in excess of 800 K, diffusion of subsurface AlAs to the oxide surface was observed. Moreover, it was found that irradiating a partially oxidized AlAs surface with a 3 keV electron beam for sufficiently long times would significantly increase the extent of surface oxidation.