Room Temperature Optical Constants and Band Gap Evolution of Phase Pure M 1-VO 2 Thin Films Deposited at Different Oxygen Partial Pressures by Reactive Magnetron Sputtering

Spectroscopic ellipsometry study was employed for phase pure VO2(M1) thin films grown at different oxygen partial pressures by reactive magnetron sputtering. The optical constants of the VO2(M1) thin films have been determined in a photon energy range between 0.73 and 5.05 eV. The near-infrared extinction coefficient and optical conductivity of VO2(M1) thin films rapidly increase with decreasing O2-Ar ratios. Moreover, two electronic transitions can be uniquely assigned. The energy gaps correlated with absorption edge ( E 1 ) at varied O2-Ar ratios are almost the same (~2.0 eV); consequently, the absorption edge is not significantly changed. However, the optical band gap corresponding to semiconductor-to-metal phase transition ( E 2 ) decreases from 0.53 to 0.18 eV with decreasing O2-Ar ratios.