Improvement in the Stability of Cation (Si)/Anion (F or N) Codoped ZnO Thin-Film Transistors Formed via Atomic Layer Deposition

The characteristics of cation (Si) and anion (F or N) codoped ZnO thin films formed via atomic layer deposition and corresponding device properties were investigated for different anion doping concentrations with a fixed Si doping amount. All films exhibited the (100) primary diffraction peak, indicating a hexagonal wurtzite structure. All codoped ZnO films exhibited the same effect of oxygen vacancy passivation, i.e., reduced oxygen vacancy. However, the electrical and optical characteristics of the films exhibited contrasting tendencies depending on the type of anion element. The optimized device properties, i.e., the subthreshold swing, field-effect mobility, threshold voltage, and bias stability were 6.62E-01 V/dec, 5.10 cm2/V·s, -11.16 V, and 6.32 V in the Si/F-19 condition and 5.98E-01 V/dec, 16.60 cm2/V·s, 1.07 V, and 0.14 V in the Si/N-19 condition, respectively. These characteristics were attributable to the correlation effects of the reduced interfacial trap density from Si doping and oxygen vacancy passivation from anion doping. Notably, the behavior of each anion was different in terms of the charge carrier concentration. First-principles calculations based on the density functional theory using the Vienna ab initio simulation package (VASP) code were performed to obtain valuable insights into the energy band structure in terms of the performance of the codoped ZnO films.