ZnO nanorod-based UV photodetection and the role of persistent photoconductivity

We report on the substantial persistent photoconductivity (PPC) response exhibited by the zinc oxide (ZnO) nanorod-based ultraviolet (UV) photodetection system. An increase in photocurrent and, hence, rise in PPC was observed for larger UV exposure times at regular intervals. Triggered by quantum efficiency, the increment in sustained conduction band electrons is proposed as the main reason behind the increased photocurrent response. In contrast, the trap centers located below the conduction band are expected to slow down the recombination rate, which accounts for the rise in PPC. The lowering of PPC upon annealing suggests the surface dependent nature of the PPC. The growth and decay mechanism of PPC has a direct relevance while assessing figure of merit of prototype nanostructure-based optical sensor and UV photodetectors.