Interaction of oxygen with cleaved GaAs: influence of the cleavage defects

Abstract

The interaction of oxygen with the clean cleaved (110) face of GaAs (n=3*10¹⁶ cm^-3) has been studied by Auger electron spectroscopy up to exposures of 10⁷ Langmuir. The first stage of oxidation, characterised by an initial sticking coefficient ranging from 10^-3 to 10^-2, is very much cleavage dependent; it is shown that the better the cleavage the lower the reactivity. Then, between roughly 10⁴ and 10⁵ Langmuir, a reproducible saturation is observed which corresponds to an absolute coverage of about half a monolayer. The kinetics governing this stage of oxidation corresponds either to an immobile oxygen layer and a non-activated process, or to a mobile layer and a thermally activated adsorption with an activation energy of approximately 0.17 eV independent of coverage. Oxidation proceeds beyond half a monolayer and the coverage dependence of the sticking coefficient is then described by an Elovich equation.