Optimum oxygen concentration for the optoelectronic properties of IR sensitive VOx thin films

Abstract VO x films were fabricated on thermally grown SiO 2 layers by reactive r.f. sputtering at room temperature. The working pressure was 5 mTorr, adjusted by changing Ar and O 2 flow from 1:1 to 10:1. Post annealing was performed at the temperatures of 200°C, 300°C, 400°C, 450°C, and 500°C. Electrical resistivities of VO x films were measured at various temperatures from 25°C to 80°C and the temperature coefficient of resistance (TCR) was calculated for each film. The resistivity decreases with the increase of the annealing temperature and shows two steps of critical drops at 300°C and 450°C, respectively. This is attributed to the phase transitions of the as-deposited VO x as characterized by X-ray diffraction (XRD). Considering both the TCR and resistivities, it is concluded that the optimum oxygen concentration, x in the VO x films approaches to 2.25 (V 4 O 9 ).