The enhancement of the infrared switching efficiency and laser protection performance of VO2 film with Ta gradient doping

A low phase transition threshold (Tc) and high infrared switching efficiency (r) are essential for the practical application of VO2 film in laser protection field. A Ta gradient-doped VO2 film with low Tc and high r was fabricated successfully. The effect of the gradient doping method on the phase transition performance of VO2 film was investigated. The film's Tc decreases to 34.6 degrees C as the Ta uniform doping concentration increases, but its r also decreases to 45.1 %. Fortunately, the gradient doping can restore the r, increasing it from 45.1 % to 56.2 %, while maintaining a low Tc of 37.2 degrees C. The total density of state and the band structure of the Ta doped VO2 film were calculated with the first principles, and the action mechanism of the gradient doping to optimize the phase transition performance was investigated. The overall laser protection performance of the Ta gradient-doped film was superior to that of the uniform-doped film and the pure VO2 film. Both an IMT quality factor and a laser protection quality factor were proposed for the comprehensive evaluation of the VO2 film's phase transition performance.