Effect of pre-annealing process on semiconductor-to-metal transition properties of vanadium oxide thin films

Vanadium oxide (VOX) thin films were fabricated on the (0001) sapphire substrates by pre-annealing process and subsequent rapid thermal annealing (RTA). The XRD results showed that the intensity of VO2 peak was enhanced and the V2O5 peak was not much changed when pre-annealing process was added before RTA. In addition, the pre-annealing process lowered the roughness of thin film and made film surface smooth and uniform. After pre-annealing process and subsequent RTA, the semiconductor-to-metal transition (SMT) amplitude increased from 21.8 to 160 and the phase transition temperature (T-C) of the film reduced to the minimum of 50 degrees C. Moreover, the increase rate of solar modulation ability reached 61%. This study demonstrates that the pre-annealing enhanced the SMT amplitude and solar modulation ability, and decreased the T-C of VOX thin films simultaneously. Therefore, it is a promising way to fabricate thermochromic VOX thin films for smart windows.