Influence of the charge compensation effect on the metal–insulator transition of Mg-W co-doped VO2

Abstract

Cation co-doping was proved an effective approach to reduce the metal–insulator transition (MIT) temperature (θc) of vanadium dioxide (VO2) for realizing excellent optical switching properties near room temperature, but its mechanism is remaining a great challenge. Herein, the Mg-W co-doped VO2 films are fabricated through hydrothermal growth. By changing the Mg content with maintaining 1 at% W doping level, it is observed that Mg dopants raise the θc of co-doped VO2 at a rate of ∼ 22 ℃ per at% Mg as the Mg content is less than ∼ 1 at%, but loses efficacy more than 1 at% Mg. The resistance of the co-doped VO2 films show the similar variation trend. The valence-band XPS spectra indicate that the Mg dopants counteract the VBE uplifting of VO2 caused by W dopants, consequently enlarging the optical band gap of W-doped VO2, which would partially explain the improvement of the visible light transmittance of W-doped VO2 induced by Mg dopants. The results clearly evidence that the charge compensation takes effect in the co-doped VO2, demonstrating the co-doping of high- and low-valent cations is unfavorable for effectively decreasing θc of VO2, and reveal the electron doping plays a key role in reducing θc.