Mechanism of Photoinduced Charge Transfer in Co(Li)-Doped ZnO Film

Abstract
A three-layer film consisting of In-doped ZnO, Co(Li)-doped ZnO and Li-doped NiO has been fabricated by means of a sputtering technique. The photocurrent spectrum of the Co(Li)-doped ZnO has been measured by applying a bias voltage between the In-doped ZnO and Li-doped NiO electrodes. A broad peak around 640 nm in the photocurrent spectrum is assigned to photothermal ionization of Co2+ ions. The time dependence of photocurrents indicates that the concentration of Co2+ ions is decreased by the irradiation of 500 nm and is recovered to the initial value by turning off the bias voltage.