Current-doubling, chemical etching and the mechanism of two-electron reduction reactions at GaAs: Part 2. A unified model

Abstract

A model is proposed to account for the cathodic reduction of certain strong two-electron oxidizing agents at GaAs. It is suggested that reduction does not occur via direct charge transfer between the solid and an electroactive species in solution. Instead, a surface state intermediate is formed by hole injection from the oxidizing agent into a surface bond. This acts as a common precursor both to electrochemical reduction and to chemical etching of the semiconductor in these solutions. The model can account for the excellent kinetics of the reduction reaction and for the competition between the reduction and chemical etching processes. It also resolves an apparent contradiction with regard to the role of the conduction and valence bands in the photocurrent-doubling mechanism.