A Study of the Microstructural Effects on Optical Parameters and Quantum Efficiency in VO₂ Thin Films on TiO₂ and TiO₂:Nb

The project goal is to optimize the photosensitivity of VO₂ thin films in the near-UV and UV regions; following the recent demonstration that VO₂ grown on niobium doped TiO₂ (TiO₂:Nb) substrates can push the photoconductive response into the visible spectrum. By controlling the microstructure of the films via deposition parameters and substrate doping, we optimize the VO₂ growth for TiO₂ and TiO₂:Nb substrates. In doping the substrates, we strain the monoclinic structure in the insulating VO₂ phase toward the tetragonal structure in the metallic phase. Using X-ray diffraction, we determine that films grown on TiO₂:Nb structurally exhibit a ~.25^o shift in peak location compared to the undoped films. Under a 405 nm laser, the VO₂ on TiO₂:Nb exhibits sharp and comparatively large optical responses, through the thermally induced insulator to metal transition, to those seen with VO₂ on TiO₂. The films exhibit a photocurrent, upon 405 nm illumination, for both the doped and undoped films with a greater quantum efficiency associated with the optimized doped films. Suggesting that the optimized doping enhances the near-UV optical response and quantum efficiency of the film.