Thickness dependent ultraviolet photoconductivity studies on sol-gel derived zinc oxide (ZnO) films

ZnO films of varying thicknesses (77-231 nm) were deposited using the sol-gel method for ultraviolet (UV) photodetection applications. The dependence of the photoconductivity parameters of the photodetector on the thickness of the ZnO films has been investigated for UV radiation having 365 nm wavelength and intensity of 24 mu W/cm2. The deposited ZnO films exhibited poly-crystallinity with significant surface roughness (30-92 nm) and oxygen-related defects (Oi, Ozn, Vo), which were found beneficial for obtaining enhanced UV photosensitivity. The photoconducting mechanism has been studied in detail using the statistical interpretation of defects observed from the deconvolution of photoluminescence spectra. The 221 nm thick ZnO film showed improved photoconducting parameters (photoconductive gain, current responsivity, rise time and fall time) which are attributed to the increased density of all the defects under deep-level emission.