DARK DISSOLUTION AND PHOTODISSOLUTION OF ZNO

Dissolution both in the dark and under illumination at 365 nm and the flat-band potential display a linear pH dependence which can be explained by a thermodynamic model. The photocurrent was studied potentiostatically and its potential dependence is interpreted using Gaertner's theory for illuminated metal-semiconductor contacts. The linear relation between photocurrent and the pH corresponds to a stationary state under constant illumination in which the current is equal to the hole oxidation rate of H//2O at pH 9. 2 and H//2O plus ZnO at pH less than 9. 2. The decomposition of the ZnO lattice is thermodynamically controlled by hole oxidation of desorbing OH** minus ions to OH radicals which are assumed to form H//2O//2 by combination.