Fast Response Ultra-violet Photodetectors Based on Sol Gel Derived Ga-doped ZnO

Ultraviolet photoconductivity in Gallium doped ZnO (GZO) thin film synthesized by sol-gel technique is investigated. Response characteristics of Pure ZnO thin film and GZO thin film UV photodetector biased at 5 V for UV radiation of λ = 365 nm and intensity = 24 μwatt/cm2 have been studied. GZO UV photodetector is found to exhibit a high photocoductive gain (K = 9.32×102) with fast rise and fall time (Tr = 3 s and Tf = 9 s) in comparison to pure ZnO thin film based photodetector with K = 4.9×101, Tr = 6 s and Tf = 18 s. Formation of some neutral atoms at the grain boundaries of GZO thin film due to heavy doping of Gallium in ZnO lattice is the key factor for lowering of dark current (Ioff ∼ 0.11 μA). Upon UV illumination, the release of trapped electrons from surface defects or adsorbed oxygen results in an enhanced photocurrent (Ion = 0.1 mA) and hence higher value of K is obtained for GZO thin film based photodetector.