Comparative study of GaAs corrosion in H2SO4 and NH3·H2O solutions by electrochemical methods and surface analysis

Abstract

Corrosion of GaAs can readily happen in acidic and alkaline aqueous electrolytes. The instability of GaAs is a major difficulty in implementing GaAs-based photoelectrochemical solar energy-conversion systems. In this paper, the corrosion behavior was investigated by electrochemical methods and surface-analysis approaches, in both H2SO4 and NH3·H2O solutions. Open-circuit testing showed that the GaAs surface was very sensitive to water/air although the process to build a stable interface between GaAs and electrolyte is slow. Comparison of the impedance data for n- and p-GaAs showed that an inductive loop only appeared at a high corrosion rate. This induction loop was due to the Faradaic adsorption process being the rate-determining step. This can only be explained by a mechanism in which a reaction intermediate, instead of holes, after capture of the first hole is the oxidant for further decomposition steps in combination with a chemical reaction with water. The results suggest that the same corrosion/decomposition mechanism occurred on both n- and p-GaAs and also in the two solutions. When the surface hole concentration was low, the hole injection or generation process was the rate-determining step. At large reverse bias on n-GaAs, with high hole concentration or forward biasing of p-GaAs, the corrosion rate was limited by a Faradaic adsorption process, involving an adsorbed intermediate. The different surface compositions after corrosion in the two solutions can be explained by the dissolution of As(0). It is pointed out that the further oxidation of As(0) to As(III) in NH3·H2O solution is still slow, as suggested from X-ray photoelectron spectroscopy (XPS) analysis.