Competitive surface effects of oxygen and water on UV photoresponse of ZnO nanowires

UV photoresponse of ZnO nanowires is measured in air under different humidity conditions to study the competitive surface effects of oxygen and water vapor. During UV illumination, it was found that the current decreases gradually under high humidity, whereas the current increases under low humidity. In the recovery phase, a change of two to three orders of magnitude in the decay time is observed by varying the humidity. A model that takes into account the solid-state process of photocarrier generation/recombination and the competitive surface effects of oxygen/water is proposed to explain the observed variations in photoresponse under different humidity conditions.