Bipolar photoresponse ultraviolet photodetectors based on ZnO nanowires

Abstract

A comparative study on the photoresponse of zinc oxide nanowires in direct-current (DC) and alternating-current (AC) domains is presented. Zinc oxide ultraviolet photodetectors exhibit positive photoconductivity in DC domain which means that the resistance decreases upon illumination. However, in the frequency domain, zinc oxide nanowires exhibit a solid frequency-modulated response to the ultraviolet illumination leading to a tunable photoconductivity. It is shown that in AC domain the photoresponse of zinc oxide nanowires can be finely adjusted from the positive photoconductivity (resistance decrement) to negative photoconductivity (resistance increment) simply by tuning the driving frequency. Frequency-modulated photoresponse of zinc oxide nanostructures provides an exclusive platform for the realization of dual-response or bipolar photoresponse ultraviolet photodetectors which could be of high technological importance. The zinc oxide nanowires exhibit a responsivity of +180 mA W-1 to the ultraviolet illumination in the DC mode. The nanowires show an almost equal but negative responsivity in the AC domain. Practical implication of the bipolar ultraviolet photodetectors based on ZnO nanowires is presented.