Electrical and optical properties of highly crystalline W-VO 2 nano-films prepared by thermal oxidation of V-WO 3 precursors

Highly-crystalline W doped VO 2 (W-VO 2 ) nanofilms were obtained through thermal oxidation of V-WO 3 precursors, with the electric and optical properties being studied. The W-VO 2 films are composed of rutile and monoclinic phases due to the decrease of the phase transition temperature. The results show that the W dopants lead to a great decrease in the cool-state resistances and their apparent activation energy as they form donor levels. The electric analysis also shows that the W-VO 2 films have a smooth metal-insulator transitions across wide temperature range due to the W ununiform distribution, and the transition temperature, temperature coefficient of resistances, and hysteresis width are greatly reduced. The metallic phase contents are estimated based on the temperature dependent transmittances, which increases with the W contents at ambient temperatures. Because of the rutile phase and the conductance increase, the IR transmittances of the cool-state W-VO 2 films and their solar modulation becomes lower. It is also seen that the optical bandgap is unchanged when W dopant level is low, but can be decreased when the W content increases.