Performance of sol-gel deposited Zn_{1 - x}Mg_xO films used as active channel layer for thin-film transistors

ZnO thin-film transistors (TFTs) have attracted considerable R&D interest due to their high transparency and low photosensitivity compared with typical a-Si:H TFTs. The electrical characteristics of ZnO thin films may be controlled by doping with ternary element, for instance Al, Ga, In, Mg, Zr, etc. In this study, Zn_{1 - x}Mg_xO (x = 0 to 0.36) thin films were deposited on glass substrates by spin coating. The as-deposited films were baked at 300 °C for 10 min and then annealed at 500 °C for 1 h in air. The results show that, addition of Mg-species in ZnO films markedly enhanced the uniformity of film thickness and improved optical properties. The Zn_0.8Mg_0.2O film exhibited the best transparency of 92%, an increase of ∼ 15% over a pure ZnO film, and the rms roughness value decreased to 1.63. The Zn_{1 - x}Mg_xO TFTs were demonstrated to have n-type enhancement behavior. The optimum device with Zn_0.8Mg_0.2O channel layer had a field-effect mobility of 0.1 cm²/V s, a threshold voltage of 6.0 V, and an on/off ratio more than 10⁷.