Photovoltaic Response of Transparent Schottky Ultraviolet Detectors Based on Graphene-on-ZnO Hexagonal Rod Arrays

Abstract

Herein, we report the ultraviolet (UV) photoresponse characteristics of vertically grown ZnO rod arrays and graphene hybrid detectors. Graphene serves as a UV transparent electrode for efficient light absorption and as a Schottky electrode for promoting the separation of charge carriers photogenerated in ZnO. In particular, when the ZnO rods were passivated by polymer encapsulation, the proposed device (device I) exhibited improved Schottky junction characteristics and photovoltaic response to UV light when compared to the device based on bare ZnO rods (device II). These improvements, which originated from the reduced photodesorption effect, enable device I to operate in a zero-bias condition, producing a substantial photovoltaic output current with a photoresponsivity of 5.14 × 10–4 A/W, which is not achievable using device II. More importantly, compared to the photoconductive response of device II operating in bias conditions, the photovoltaic response of device I yields a higher on/off ratio of ∼280 an...