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

摘要

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.