Influence of Ga Doping on Electrical Performance and Stability of ZnO Thin-Film Transistors Prepared by Atomic Layer Deposition

Ga-doped ZnO (GZO) thin-film transistors (TFTs) with different doping concentrations (n(Ga): n(Zn) = 0, 1:150, 1:75, 1:50) were successfully fabricated by atomic layer deposition. Among them, GZO TFTs with the doping concentration of 1:75 exhibited a high field-effect mobility of 16.2 cm(2) V-1 s(-1), a small subthreshold swing of 0.22 V dec(-1), a high ON-/OFF-current ratio of 107, and a proper threshold voltage of 6.0 V as well as a small threshold voltage shift of 0.14 V under positive bias stress. Compared to ZnO (ZO) TFTs, GZO TFTs exhibit excellent bias stability and electrical properties, which can be attributed to appropriate Ga doping concentration suppressing the oxygen vacancy defects, decreasing the trap density at the Al2O3/ZO interfaces, and broadening energy band of the ZO thin films.