The phase identification of the H2SO4-etched GaAs by X-ray diffraction

The chemical compositions of the surface oxides formed on p-type GaAs (1 0 0), after etching in H2SO4/H2O and in H2SO4/H2O2/H2O solutions were analyzed using conventional wide angle diffraction (WAD) and glancing angle diffraction (GAD) methods. These oxides all showed different degrees of preferred orientation with respect to the substrate. Measurements of the GaAs dissolution rate in H2SO4/H2O2/H2O solutions increase dramatically with the adding of H2O2 concentration, and GaOOH compound was found on the oxidized surface. In contrast, the dissolution rate in H2SO4/H2O was severely restricted even in the most acidic solutions under illumination, about 3-order lower when comparing with H2SO4/H2O2/H2O solution and no GaOOH compound was formed on GaAs surface. The differences in their reactivities can be interpreted in terms of the differences in the stability of GaOH2+ intermediate in H2O2 and in H2O, which, in turn, determine whether or not is the formation of GaOOH on GaAs surface. It is postulated that the production of the GaOH2+ intermediate is thermodynamically favored so that the dissolution rate of GaAs in H2SO4 system is accelerated by H2O2.