Optical Properties of Vanadium Dioxide Film during Semiconductive–Metallic Phase Transition

The optical constants of vanadium dioxide (VO 2 ) films were determined at visible and near-infrared wavelengths at various temperatures during a semiconductive–metallic phase transition by ellipsometric analysis with Lorentz-oscillator formulae. The reversible changes in optical constants against temperature due to thermochromism were observed at around 70 °C. The wavelength dispersions of the optical constants were well expressed by the sum of three oscillators and their oscillating energies were attributed to photon-excited transitions. The variation in band structure during the phase transition was monitored, and the relationship between the band structure and optical properties was discussed.