Hypochlorite reduction at GaAs : a multifaceted reaction

It is shown that the reduction of hypochlorite at p-GaAs is not a simple valence band process, as expected for a strong oxidizing agent. In the dark, reduction indeed occurs via hole injection into the valence band but the reduction rate is low. Under illumination at a low light intensity hypochlorite acts as a current doubling agent, indicating that reduction occurs in two discrete steps. It is argued that in the first step, electron transfer occurs via surface states. This is followed by a hole injection step. At high light intensity, the reduction rate is controlled by mass transport of OCl-1 ions in solution. In this case, the valence band reaction is markedly increased due to a large displacement of the semiconductor band edges as a result of negative charging of the surface states. An unexpected feature of this system is that hypochlorite etches GaAs "chemically" in the dark.