Influence of the conditions of pulsed laser deposition on the structural, electrical, and optical properties of VO2 thin films

Abstract

The technique of pulse laser deposition with the separation of plume drops is used to produce VO2 thin films on sapphire(0001) and silicon(111) substrates. It is established that the energy density at the target and the oxygen pressure influence the structural and electrical properties of the films. All of the VO2 crystal films exhibit semiconductor-metal transitions with a substantial change in the resistance (by 2–5 orders of magnitude). The transmittance in the range 200–800 nm and reflectance in the range 400–700 nm are studied in the temperature range from 20 to 100°C. The transmittance of the films at wavelengths from 300 to 800 nm shows a jump and hysteresis upon heating and cooling. It is for the first time established that the changes in the transmittance of the film are different in character at different wavelengths and the shape of the temperature hysteresis loop for optical transmittance in the visible and near-ultraviolet regions does not in all areas replicate the shape of the hysteresis loop for the resistivity of the VO2 films. The difference in the behavior of the hysteresis curves for the transmittance and resistance is attributed to variations in the absorption of the films under variations in temperature.