Dynamic and static photoresponse of ultraviolet-detecting thin-film transistors based on transparent NiOx electrodes and an n-ZnO channel

We report on the fabrication of an ultraviolet (UV)-detecting thin-film transistor (TFT) using NiOx as source∕drain electrodes and n-ZnO as its channel layer deposited on a SiO2∕p-Si substrate. Rapid thermal annealing of the TFT was carried out in an O2 ambient at 350°C for 1min to increase the transparency of NiOx. In an accumulation mode with a gate bias of 40V, a drain current of only 2μA was obtained in the dark. However, under an illumination of UV light with wavelength 325nm, the drain current dramatically increased up to 13μA. Under UV photons with wavelength 254nm or energy of 4.9eV, much higher than 4.1eV, the energy gap of NiOx, the photocurrent slightly decreased to ∼10μA due to the absorption by NiOx. These photoelectric effects were more pronounced under a gate-bias condition for a depletion (off) mode. The UV-dynamic behavior of our TFTs was also investigated, yielding the UV response time of ∼300ms and UV-on∕off ratio of about 10.