Extremely Stable, High Performance Gd and Li Alloyed ZnO Thin Film Transistor by Spray Pyrolysis

The simultaneous doping effect of Gadolinium (Gd) and Lithium (Li) on zinc oxide (ZnO) thin-film transistor (TFT) by spray pyrolysis using a ZrOx gate insulator is reported. Li doping in ZnO increases mobility significantly, whereas the presence of Gd improves the stability of the device. The Gd ratio in ZnO is varied from 0% to 20% and the Li ratio from 0% to 10%. The optimized ZnO TFT with codoping of 5% Li and 10% Gd exhibits the linear mobility of 25.87 cm(2) V-1 s(-1), the subthreshold swing of 204 mV dec(-1), on/off current ratio of approximate to 10(8), and zero hysteresis voltage. The enhancement of both mobility and stability is due to an increase in grain size by Li incorporation and decrease of defect states by Gd doping. The negligible threshold voltage shift ( increment V-TH) under gate bias and zero hysteresis are due to the reduced defects in an oxide semiconductor and decreased traps at the LiGdZnO/ZrOx interface. Li doping can balance the reduction of the carrier concentration by Gd doping, which improves the mobility and stability of the ZnO TFT. Therefore, LiGdZnO TFT shows excellent electrical performance with high stability.