Effects of Ti–W codoping on the optical and electrical switching of vanadium dioxide thin films grown by a reactive pulsed laser deposition

Thin films of thermochromic VO₂, V_1-xW_xO₂ and V_1-x-yW_xTi_yO₂ (x=0.014, and y=0.12) were synthesized onto quartz substrates using a reactive pulsed laser deposition technique. The films were then characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The W and Ti dopant effects on the semiconductor-to-metal phase transition of VO₂ were investigated by measuring the temperature dependence of their electrical resistivity and their infrared transmittance. Remarkably strong effects of Ti–W codoping were observed on both the optical and electrical properties of V_1-x-yW_xTi_yO₂ films. The IR transmittance was improved, while the transition temperature could be varied from 36°C for W-doped VO₂ film to 60°C for Ti–W codoped VO₂ film. In addition, at room temperature, a higher temperature coefficient of resistance of 5.12%/°C is achieved. Finally, both optical and electrical hysteresis are completely suppressed by Ti–W codoping the VO₂ films.