Effect of annealing temperature on the performance of photoconductive ultraviolet detectors based on ZnO thin films

ZnO films prepared by sol–gel method and the ultraviolet detectors based on this material have been investigated in this paper. X-ray diffraction (XRD) patterns showed ZnO films present hexagonal wurtzite structure with a preferential orientation of (002) plane, and the crystallite size of films gradually increased from 44.3 to 54.8 nm as the annealing temperature increased from 400 to 600 °C. Ultraviolet–visible (UV–Vis) spectra indicated that the optical band gap decreases gradually with the increase of annealing temperature, and the minimum band gap is 3.06 eV at 600 °C. Photoluminescence (PL) spectra revealed that increasing annealing temperature can significantly reduce the defects and improve the crystallinity. Finally, gold (Au) coplanar interdigital electrodes were deposited on ZnO film surface and used to fabricate the ultraviolet photodetectors. The response performance of the devices improved as the annealing temperature of ZnO films increased, and the fastest response speed with a rise time of 4.172 s and a fall time of 11.012 s was obtained.