Microstructural Engineering of the UV/Near-UV Photocurrent Production in VO₂ Thin Film Based Detectors

We sought to optimize the photosensitivity of VO₂ thin films in the near-UV (NUV) and UV regions after recent reports demonstrating it is possible to push the typical IR photoresponse of VO₂ into the visible spectrum via thin film growth on TiO₂:Nb substrates. By controlling the microstructure of the films via deposition parameters and substrate doping, we optimize VO₂ growth for TiO₂ and TiO₂:Nb substrates and compare their photocurrent response using 405 nm (NUV) and 254 nm (UV) light. We found that the VO₂ on TiO₂:Nb heterostructure demonstrates greater photocurrent response. By measuring the external quantum efficiency (EQE), we found a dramatic photosensitivity improvement for the VO₂ on TiO₂:Nb compared to undoped TiO₂ substrates. Notably, we demonstrated greater than 100% EQE for VO₂ on TiO₂:Nb for both wavelengths and an improvement in the EQE using UV in comparison to the NUV. Finally, we additionally propose a mechanism for this photoresponse which potentially allows for greater than 100% EQE.