Hole Injection and Electroluminescence of n ‐ GaAs in the Presence of Aqueous Redox Electrolytes

The process of hole injection into the valence band of n ‐ GaAs from the oxidized component of redox couples in aqueous solution has been studied by means of the rotating ring‐disk system and by luminescence measurements as a function of electrode potential, mass transport, and electrolyte p H. It has been found that in all cases in which hole injection takes place, a luminescence signal is observed as a consequence of electron‐hole recombination. The intensity of this signal depends on the electron density at the interface (therefore on potential) and on the chemical composition of the electrode surface. The luminescence signal at cathodic bias demonstrates that electron transfer from the valence band is still dominating if the electronic energy levels of the redox species match the energy levels of the valence band, although electron transfer from the conduction band is energetically more favorable.