Photodetecting properties of ZnO-based thin-film transistors

We report on the photodetecting properties of a ZnO-based thin-film transistor (TFT) that has been fabricated on a SiO2/p-Si substrate by rf magnetron sputtering at room temperature. Our ZnO-based TFT exhibited a saturation current level of about 6.5 μA under a gate bias of 40 V, decent electron mobility of 0.1 cm2/V s, and on/off current ratio of ∼106 in the dark. Illuminated by ultraviolet (λ=340 nm), blue (λ=450 nm), and green (λ=540 nm) light with intensity of 0.7 mW/cm2, our TFT displays high photocurrent gain of 50, 32, and 15 μA, respectively, under a gate bias of 40 V. In the channel depletion state with gate bias of −30 V, the photodetecting sensitivity becomes much higher than in the accumulation state. It is thus concluded that our ZnO-based TFT can be a good UV photodetecting device as well as an electronic device.