Behavior of p-type GaAs in an aerated boric acid solution at the open-circuit potential. Influence of the presence of Co(II) ions

The electroless dissolution of p-GaAs in aerated 0.5 M boric acid solutions , in the absence and in the presence of Co(II) ions in the solution, is rep orted. At the pH of these solutions, the anodic dissolution of GaAs occurs in oxide-forming conditions. The oxide film formed during GaAs dissolution is composed of Ga2O3. The evolutions of the morphology and of the thickness of the oxide layer are followed using scanning electron microscopy (SEM), energy-dispersive X-ray analyses (EDX), and X-ray photoelectron spectroscop y (XPS). All of the results show that the oxidation rate of p-GaAs in an ae rated boric acid solution is enhanced in the presence of Co(II) in the solu tion; the increase is larger for higher Co(II) concentration. This leads to an increase of the oxide layer thickness. From the position of the redox p otentials of the various species present in the electrolyte, with respect t o the GaAs valence bandedge, it appears that dioxygen is responsible for th e GaAs anodic dissolution. At the GaAs/solution interface, O-2 reduction oc curs, leading to GaAs oxidation. The mechanism of O-2 reduction at the GaAs surface is discussed regarding the energetic situation at the interface. T he influence of the Co(II) on the kinetics of O-2 reduction is discussed, t aking into account the results of the literature.