Optical properties of semiconducting VO2 films

The reflectivity of a thick sputtered film of VO₂ has been measured in the energy range 0.5-11.0 eV at room temperature. The complex dielectric constant (ε₁,ε₂) and the complex index of refraction (n,k) have been obtained from the reflectivity measurements using the Kramers-Kronig relations. We have also measured the transverse electroabsorption spectrum of a thin sputtered film of VO₂ at liquid-nitrogen temperature. Comparison of the electroabsorption spectrum with theoretical predictions identifies the edge at 2.011 eV as corresponding to a direct transition at an M₀ edge. In spite of the lack of a band-structure calculation for VO₂, the singularities in ε₂ at 0.6, 1.04, 1.32, 1.82, 2.64, 3.6, 5.89, and 9.6 eV are assigned to specific interband transitions.