Room Temperature Optical Constants and Band Gap Evolution of Phase Pure M₁‐VO₂ Thin Films Deposited at Different Oxygen Partial Pressures by Reactive Magnetron Sputtering

Abstract

Spectroscopic ellipsometry study was employed for phase pure VO 2 (M 1 ) thin films grown at different oxygen partial pressures by reactive magnetron sputtering. The optical constants of the VO 2 (M 1 ) 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 VO 2 (M 1 ) thin films rapidly increase with decreasing O 2 ‐Ar ratios. Moreover, two electronic transitions can be uniquely assigned. The energy gaps correlated with absorption edge ( E 1 ) at varied O 2 ‐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 O 2 ‐Ar ratios.