SEMICONDUCTOR ELECTRODES .16. CHARACTERIZATION AND PHOTOELECTROCHEMICAL BEHAVIOR OF NORMAL AND PARA-GAAS ELECTRODES IN ACETONITRILE SOLUTIONS

The photoelectrochemical behavior of n-type and p-type GaAs is investigated in acetonitrile solutions containing various redox couples. The cyclic voltammograms of the semiconductor electrodes in the dark and illuminated with red light are compared to the Nernstian behavior at a Pt disk electrode. The photodissolution of the semiconductors was surpressed and did not occur until potentials well positive of the flatband potential. An underpotential (negative overpotential) was developed on the photoassisted oxidation (n-type semiconductor) and reduction (p-type material) of solution species. Intermediate levels or surface states are shown to be capable of mediating electron transfer and limiting the magnitude of the underpotential produced. It is also shown that the production of surface films at potentials negative of the conduction bandedge can produce a photovoltaic effect with the GaAs assisting in electron transfer. Thus, photoassisted electron transfer with electroactive solution species is observed spanning a potential range greater than 2.5V utilizing a 1.35 eV photon. © 1979, The Electrochemical Society, Inc. All rights reserved.