Optical properties of vanadium dioxide film during semiconductive-metallic phase transition

The optical constants of vanadium dioxide (VO2) 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 degrees 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.