Investigation of the metal-to-insulator transition of N-doped VO2(M1) thin films

This work reports the effect of nitrogen doping on the electrical and optical properties of VO2 thin films. An innovative method based on a VN target and an O-2 ambient gas was used to synthesize N:VO2 films on quartz substrates using reactive pulsed laser deposition (RPLD). The doping percentage was determined by elastic recoil distribution (ERD) measurements, while temperature-dependent Raman spectroscopy as well as electrical resistivity and infrared reflectance measurements were performed to investigate the effect of N-doping on the insulator monoclinic-to-metallic tetragonal phase transition (IMT) of VO2. A small doping percentage around 0.7 at.% was achieved, inducing a decrease of the transition temperature TIMT from 68 degrees C to 50 degrees C, with slightly reduced electrical contrast Delta R and optical contrast Delta A. By comparing the volume fraction of monoclinic phase, obtained from Raman data to the volume fraction of metallic phase deduced concurrently from both electrical and optical measurements, the IMT in our nitrogen-doped VO2 films occurs through a percolation process.