Facile zinc oxide nanowire growth on graphene via a hydrothermal floating method: towards Debye length radius nanowires for ultraviolet photodetection

Vertically aligned zinc oxide nanowires on graphene (ZnO-NW/graphene) heterojunction nanohybrids combine the superior sensitivity of crystalline ZnO-NWs with high charge mobility of graphene to provide an ideal platform for high-performance detectors and sensors. Controlling the ZnO-NW microstructure and ZnO-NW/graphene interface is of primary importance for the device performance. This work explores floating hydrothermal growth of ZnO-NWs on seedless and ZnO seeded graphene, and investigates the effects of the microstructure and interface on the performance of ZnO-NW/graphene ultraviolet (UV) detectors. It has been found that the ZnO seed layer facilitates the growth of a dense ZnO-NW array with a NW radius approaching the Debye length. In contrast, the seedless process results in a lower NW areal density and a larger NW diameter on the order of sub-to-few micrometers. Consequently, higher UV responsivity up to 728 A W-1 was obtained in the former. However, a strong charge trapping effect was also observed, which is attributed to the poorer crystallinity of the ZnO-NWs originating from the ZnO seed layer. These results shed light on the importance of controlling the microstructure and interface towards high-performance ZnO-NW/graphene nanohybrid optoelectronics.