Photoenhanced oxidation of gallium arsenide

Abstract

Auger electron spectroscopy has been used to observe the influence of low-intensity visible/near-ultraviolet radiation on the oxidation of n- and p-type GaAs (110). Irradiation increases the rate of formation of the first monolayer by factors of 5–10 for p-type and 10–20 for n-type material. Kelvin-probe measurements of the change in work function with O2 exposure have also been carried out. The results suggest a model in which defects present on the clean surface pin the Fermi level at midgap, bending the bands sufficiently to allow stabilization of photogenerated broken Ga–As bonds. Similar experiments for physisorbed CO and H2O gave no photoeffect. This indicates that chemisorption (as in the case of O2) is necessary to weaken (or break) the intramolecular bond. Subsequent oxidation of GaAs is then accelerated by photoenhanced breaking of Ga–As bonds. Experiments with NO indicate a smaller sticking coefficient and a much smaller photoeffect than for O2.