Continuously tuning the impedance matching at the broadband terahertz frequency range in VO 2 thin film

We experimentally investigated the terahertz (THz) reflection modulation property of tungsten-(W-) doped vanadium dioxide (V1-xWxO2) thin film enabled by impedance matching at the interface, which behaves as a giant modulation within a broadband THz frequency range during insulator-to-metal transition. A systematical theoretical model for impedance matching is also established, which includes three factors: sheet conductivity of V1-xWxO2 thin film, incidence angle of THz wave, and refractive index of substrate. With the modeling, we demonstrated a method to continuously tune the impedance matching at the interface of substrate-V1-xWxO2 thin films-air. Four different conductivities of V1-xWxO2 thin films realized by tuning W-doping densities (x = 0, 0.35%, 0.51%, and 1.06%), three incident angles (35°, 45°, 60°), and three substrates (SiO2, Al2O3, and Si,) with refractive indices of 1.95, 2.7, 3.4 were used in our experiments to validate our proposed model. These results provide a promising route for continuously tuning broadband THz wave modulation with the impedance matching effect at the thin film interface.