Effect of annealing process in tuning of defects in ZnO nanorods and their application in UV photodetectors

Abstract

ZnO nanorod (NR) arrays were grown by a simple two-step chemical bath deposition method. The as-deposited NRs were then annealed at different temperatures (300, 400 and 500°C) for two time durations (1 and 5 h). The NRs were studied by scanning electron microscopy, photoluminescence spectroscopy, X-ray diffraction and two-point electrical test. Finally, ultraviolet (UV) detection properties of samples as an active layer in UV photodetector devices were evaluated. The structural results showed that the sample annealed at 400°C had the best crystallinity. Furthermore, it was seen that the optical transparency and band gap of NRs increased with increase of the annealing temperature up to 400°C and then decreased at 500°C. The electrical resistance decreases with increment of the annealing temperature due to intensive desorption of oxygen molecules from the surface of ZnO NRs. The UV detection results proved a meaningful relevance of UV detection properties with the density of defects (O-vacancy and Zn-interstitial) and quantity of oxygen molecules absorbed on the surface. ZnO NRs annealed at 300°C for 1 h had the highest photosensitivity of 307 and photoresponsivity of 2.067 A/W which can be even competitive for the practical applications.