KINETICS AND MECHANISMS OF PHOTOELECTROCHEMICAL REACTIONS AT SEMICONDUCTOR ELECTRODES

Some kinetic aspects of the photocurrent response of semi-conductor electrodes are considered. Particular attention is given to surface recombination, which reduces the photocurrent conversion efficiency, and to photocurrent multiplication, which leads to quantum efficiencies greater than unity. The advantages of non steady-state photocurrent measurements are considered, and it is shown that the coupling of electron and hole fluxes via the surface leads to a characteristic time or frequency dependence of the photocurrent conversion efficiency. The principle of intensity modulated photocurrent spectroscopy (IMPS) is described, and its application is illustrated with several examples, including the reduction of oxygen at p-GaAs and the photooxidation of Si in NH4F. It is shown that frequency response analysis offers unique insights into complex photoelectrode processes of this kind.