Fabrication of ZnO nanorods and ZnO/CdS core-shell nanorods for the ultraviolet photosensing application

The Zinc oxide nanorod arrays (ZnO NRAs) were prepared by hydrothermal method on sol-gel spin coated ZnO seed layers on glass substrates. The CdS shell layers were grown on these ZnO nanorods by SILAR technique to form ZnO/CdS core-shell nanorod arrays (ZnO/CdS NRAs). ZnO nanorods show hexagonal crystal structure with highly directional (00 2) c-axis orientational growth of the nanorod with a hexagonal shaped tip. CdS shell enhances the optical absorption of the ZnO nanorods, whereas it reduces the photoluminescence intensity in UV region. The MSM based ultraviolet (UV) photodetectors with ZnO and ZnO/CdS NRAs have been fabricated and characterized. The device performance was obtained at 0.01 V external bias with 365 nm and 410 nm ultraviolet light illumination. ZnO NRAs shows photosensitivity of 2.4 x 104 and 2.2 x 104, responsivity of 0.17 and 0.02 A/ W; corresponding to the 365 nm and 410 nm wavelengths, respectively. The surface modification of the ZnO nanorod by CdS capping decreases the surface states on the ZnO nanorod surface and hence increases the photocurrent. ZnO/CdS NRAs with CdS coating of 4 SILAR cycles show an increased responsivity of 2.6 and 0.23 A/W, corresponding to the 365 nm and 410 nm wavelengths.