The fabrication and ultraviolet detecting properties of ZnMgO-based thin film transistor by laser molecular beam epitaxy

Bottom-gate thin film transistors (TFTs) with a ZnMgO film as the channel layer were fabricated on thermally oxidized p-type silicon substrates by laser molecular beam epitaxy. The devices exhibit good electrical properties in dark with the current on/off ratio, threshold voltage and channel mobility of 10 ⁵, 6 V and 0.04 cm² V^-1 s^-1, respectively. In an accumulation mode with a gate bias of 30 V, the drain current is on the order of 1 νA. However, when exposed to ultraviolet light (λ = 365 nm) with an intensity of 0.2 mW cm^-2, the drain current dramatically increased to 9.4 νA and it was also shown that the photocurrent increased with the increase of photo intensity. The photo-detecting property is more remarkable under a depletion mode of -20 V gate bias with the photo-to-dark current ratio more than 10⁴. The spectral and transient responses of the device to ultraviolet illumination were also discussed. These results may open the possibility of employing ZnMgO-based thin film transistors as UV sensors.