Influence of doping in thermochromic V1−xWxO2 and V1−xAlxO2 thin films: Twice improved doping efficiency in V1−xWxO2

The parameters of thermal evaporation and magnetron sputtering deposition were optimized for fabrication of vanadium dioxide thin films. The O2 partial pressure during film deposition is critical for obtaining a pure VO2 phase. Thermochromic V1−xWxO2 (x =  0.16 at.%) thin films were synthesized by thermal evaporation, while thermochromic VO2, V1−xWxO2 (x =  0.04 at.%, 0.12 at.%, 0.35 at.%) and V1−xAlxO2 thin films were synthesized by magnetron sputtering. The structural properties of the deposited films were analyzed by X-Ray Diffraction (XRD), while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-probe technique. Contamination from the crucible was shown by chemical analysis of the V1−xWxO2 film deposited by thermal evaporation. Subsequent analyses of the films by Rutherford Backscattering Spectrometry (RBS), yielded doping efficiency of −49 ± 5°C/at.% and of −55 ±  7°C/at.% is respectively reported for films deposited by thermal evaporation and for films deposited by magnetron sputtering. These results suggest that the doping efficiency observed in the present study is twice as effective as previously reported in literature. X-ray diffraction analyses showed a progressive amorphization of the V1−xAlxO2 films with increasing aluminum doping.