Phase transition analysis of thermochromic VO2 thin films by temperature-dependent Raman scattering and ellipsometry

Vanadium dioxide (VO2) has a fantastic phase transition behavior from insulator to metal which could be used for numerous areas. Research on the optical constant and fine structure of VO2 at various temperatures is favorable to investigate the mechanism of phase transition, and benefits the design and fabrication of vanadium dioxide integrated devices or applications. So the micro structure variation and evolution process during the transformation of VO2 thin film which deposited via DC reactive magnetron sputtering method was characterized by temperature-dependent spectroscopic ellipsometry and Raman spectroscopy, along with X-ray diffraction. It could be observed that the Raman scattering peaks decreased corresponded with temperature, as well as the blue shift and red shift occurred in V-V vibration (@192 cm−1) and V-O vibration (@613 cm−1), respectively. The result revealed the M1 phase to R phase transform process of VO2 film. The refraction index determined by ellipsometry keep almost stable in ultraviolet and visible wavelength at various temperatures, but show abrupt decline at MIT temperature in near-infrared wave band. Moreover, the tendency of temperature-dependent refraction index at 990 nm match well with the sheet resistance which could be described by Boltzmann model.