U.V. Light Induced Oxidation of GaAs

The effect of far-U.V. light intensity (at constant dose: 45 J/ cm2) on the oxidation rate and composition of the oxides formed on GaAs was studied using an excimer laser or a U.V. lamp. The oxidation rates were deduced both from the measurements of quantities of oxygen (using nuclear microanalysis) and of cations (using RBS in channeling geometry) present in the oxides. It was found that the amount of cations was practically independent of light intensity, but the amount of oxygen was higher for the oxides formed by lamp irradiation. Both cations and oxygen contents decreased drastically with an increase of wavelength from 193 to 308 nm. By combining XPS and nuclear microanalysis, it was found that the oxides formed by laser were non stoichiometric, whereas those formed by lamp were stoichiometric containing large quantity of As+5. The mechanism of GaAs oxidation induced by U.V. light was discussed.