Reflectance anisotropy studies of the oxidation of (001) GaAs surfaces in an MOCVD reactor

We have employed reflectance anisotropy spectroscopy (RAS) and dynamic reflectance anisotropy (RA) operating at 2.6 eV to monitor the influence of air on a freshly cleaned (001) GaAs surface prepared via heating under H₂ and AsH₃ in an MOCVD reactor. RA transients have been obtained which correspond to the removal of surface dimers as a result of surface oxidation. It is demonstrated that the rate of change of the RA response is strongly dependent upon the rate of introduction of the air and show that the reaction proceeds, at least initially, by a pseudo-first order process. Experiments performed over a range of temperatures for fixed rate of gas introduction allow us to estimate the activation energy for the oxidation process. The value obtained, ca. 21 kJmol^-1, is representative of a facile process, which we speculate to arise from the reaction of surface Ga-As bonds exposed on the surface under the c(4×4)/d(4×4) surface reconstruction that is believed to form under the conditions employed.