The sonochemical synthesis of vertically aligned ZnO nanorods and their UV photodetection properties: Effect of ZnO buffer layer

Abstract

Vertically aligned Zinc oxide nanorods (ZnO NRs) were successfully synthesized in this study using the sonochemical method to improve the intrinsic properties of UV photodetector (PD). Three different thin films: Ti/Zn, Ti/ZnO, and Ti/ZnO/Zn, with the thicknesses of 10 nm/55 nm, 10 nm/85 nm, and 10 nm/85 nm/55 nm respectively, were deposited on glass substrates using the RF-sputtering technique. The synthesized ZnO NRs were investigated using XRD, FESEM and Raman spectroscopy to determine the effect of Zn and ZnO as seed layers, and ZnO as a buffer layer on the surface morphology, crystal structure, optical properties of ZnO NRs. The ZnO NRs grown on Zn/Ti, ZnO/Ti, and Zn/ZnO/Ti are characterized by hexagonal crystal structure with preferential growth in the c-axis direction. The ZnO NRs grown on Zn/ZnO/Ti displayed the highest density, uniform size distribution, vertically aligned rods and aspect ratio. The UV device fabricated from the ZnO NRs grown on Zn /ZnO/Ti also showed the highest photocurrent (360 µA) and responsivity of (878 mA/W). ZnO NRs grown on Zn/ZnO/Ti were also observed to be highly stable and exhibited a relatively rapid response and recovery times for different time intervals when exposed to the UV light of 365 nm wavelength. Thus, the inclusion of the ZnO as a buffer layer (Zn as a seed layer/ZnO as buffer layer/Ti as a buffer layer) improve the properties of the ZnO NRs. In addition, the current gain of ZnO NRs grown on Zn (55 nm)/ZnO (85 nm)/Ti (10 nm) – based ultraviolet (UV) photodetector (PD) is about two times higher than that of conventional Zn (55 nm)/ZnO (85 nm)/Ti (10 nm) thin-films UV PD, which is due to the higher surface-to-volume ratio of ZnO nanorods (NRs) compared with their thin films. This study confirms the possibility of sonochemically fabricating vertically aligned ZnO nanorods as well as its applicability as a viable UV photodetector.