The ultraviolet responses of ZnO-based thin-film transistor prepared by sol-gel method

Bottom-gate and top-contact thin-film transistors with ZnO film as a channel layer were fabricated by sol-gel method. The structural and optical properties of the deposited ZnO films were investigated through X-ray diffractometer, scanning electron microscopy and UV-Vis spectrophotometer. ZnO film has a high absorption in the ultraviolet region and c-axis orientation normal to the substrate. The on/off current ratio, channel mobility and threshold voltage of ZnObased thin-film transistors in dark are 10⁵, 0.02 cm²V^-1 s^-1 and 8.3 V, respectively. Under UV light illumination (λ = 365 nm) with an intensity of 2.4 μW/cm², the drain-source current I_DS of thin-film transistor dramatically increases and the photo-to-dark current ratio is greater than 10⁴. The transient response of the device to ultraviolet illumination is also discussed. The results may open the possibility of employing ZnO-thin-film transistors as UV photodetector.