Effect of heat and plasma treatments on the photoluminescence of zinc-oxide films

The structure and electrical properties of ZnO films and the effect of annealing in a hydrogen-plasma atmosphere on the photoluminescence spectra of the films are studied. Short-term plasma treatment in a hydrogen atmosphere improves the electrical properties and brings about the appearance of an intense near-band-edge photoluminescence band. The heavy dependence of the intensity and spectral shape of nearband- edge photoluminescence on the conditions of preliminary annealing is observed. It is shown that the photoluminescence spectrum consists of several contributions. The effect of an ultraviolet-radiation-induced increase in the photoluminescence intensity is observed. The effect is reversible: the photoluminescence signal is intensified after exposure to ultraviolet radiation and reduced to the initial intensity upon keeping the samples in the dark. The nature of experimentally observed metastable shallow donors is discussed.