Influence of oxygen assisted recombination on persistent photocurrent characteristics of ZnO polycrystalline thin films prepared by RF magnetron sputtering

Abstract

Decay characteristics in persistent photocurrent (PPC) of zinc oxide (ZnO) polycrystalline films highly aligned in the hexagonal c-axis direction (0002) deposited by radio frequency magnetron sputtering were investigated. Long-term decay of the photocurrent after turning off UV light illumination has been known as a PPC, which affected the performance of optical and electrical devices. Compared to the case of argon ambient, the decay characteristics were strongly influenced by the oxygen ambient. Our phenomenological model proposed could derive the recombination coefficient from an average waiting time that electrons/holes encounter the oxygen molecules attacking the surface of the ZnO polycrystalline films. The decay time response resulted is explained as a modified hyperbolics with the time constant τ and dispersion parameter β. Our experimental results are adapted to the theoretical equation. Using the average β value, τ dependence on the oxygen volume rate is in agreement with the theoretical one and presented a dispersive process on the surface reaction of oxygen gas. These investigations are useful for applications such as photoconductive sensors, gas sensors and a photocatalytic electrode.