Continuous modulation of VO2 film’s phase transition threshold and transmittance via n-AZO/n-VO2 heterojunction

Abstract

To solve the irreconcilable contradiction between the phase transition threshold and the optical property of VO2 film, an n-AZO/n-VO2 heterojunction, in which AZO is Al-doped ZnO, was constructed with the radio frequency (RF) magnetron sputtering and the post annealing. The effects of annealing on the composition and properties of vanadium oxide films have been investigated, as well as the effects of annealing and AZO layer thickness on the phase transition performance of the n-AZO/n-VO2 heterojunction. The results indicate that the V2O5 film will gradually transform into VO2 (M) through V6O13 and VO2 (B) during the reduction annealing at 500 °C. The phase transition temperature (Tc) of VO2 (M) film increases with the annealing temperature. In the heterojunction formed by the ohmic contact between AZO and VO2 layers, the free electrons will be injected into the VO2 layer from AZO layer, which reduces the heterojunction’s Tc from 69.2 to 41.5 °C. The first-principles calculations were performed with the Vienna Ab initio Simulation Package (VASP) to assist in the influence mechanism explanation. In addition to modulating Tc, the AZO layer in the heterojunction also plays an antireflection role, increasing the maximum visible transmittance of VO2 film by ∼ 10 %.