Terahertz conductivities of VO2 thin films grown under different sputtering gas pressures

The terahertz (THz) conductivities in the metal-insulator transition process of VO2 thin films on quartz substrates were investigated by using terahertz time-domain spectroscopy. It was found that the THz absorption and conductivity of the thin films are sensitive to the sputtering gas pressure, and the maximum THz amplitude modulation can reach as high as 75.9%. The complex THz conductivity in metallic state of the thin films can be well-fitted by the Drude-Smith model, and the temperature-dependent metallic domain fractions can be extracted by effective medium theory simulation. Based on these results, the metal-insulator transition of the VO2 thin films can be characterized. The mechanisms of the THz transmission and conductivity were analyzed and discussed.