Improved responsivity performance of ZnO film ultraviolet photodetectors by vertical arrays ZnO nanowires with light trapping effect

The light trapping effect of zinc oxide (ZnO) ultraviolet photodetectors (UV PDs) has been established as a promising way to optimize the performance of optoelectronic devices. In this paper, we report a light trapping fabricated metal-semiconductor-metal structure, consisting of a ZnO nanowire array as a top layer light absorber supported by a ZnO film. The ZnO film is bridged between two interdigitated metal electrodes for collecting photo-generated carriers. In this connection, high-dense ZnO nanowires can be used as a light trapping unit and to transmit the photogenerated carriers towards the ZnO film. The photogenerated carriers diffuse along the longitudinal direction of the ZnO nanowire and then to the ZnO film and are collected by the applied bias electrode. Compared to present ZnO thin film UV PDs, our device has an effective light trapping effect and the enhancement of photo-generated carriers at the top interface by a ZnO nanowire array structure are highly beneficial to UV light detection as they can provide a long optical path and more surface area. In addition, when the device was connected with nanowires, a 10 times augment of responsivity appeared accompanied by a giant photo-to-dark current ratio (1.6 x 10(3)). This novel work not only enhanced fundamental improvement of nanowires to ZnO film UV PDs, but also provided a distinct contrast between light trapping UV PDs and ZnO film UV PDs.