Metal-insulator transition characteristics of Mo-and Mn-doped VO ₂ films fabricated by magnetron cosputtering technique

Mo-and Mn-doped VO₂ thin films have been grown on c-cut sapphire substrates by the magnetron co-sputtering technique. The effects of Mo and Mn doping on the structure and metal-insulator transition of the doped VO ₂ thin films were studied. An enlargement of the out-of-plane lattice constant of the film caused by Mo doping was observed. As expected, the transition temperature (T_MI) is reduced by Mo doping. However, the valence of the Mo ions doped in the VO₂ films is determined by X-ray photoelectron spectroscopy to be 6+ on the surface, but 4+ and 3+ in the bulk part of the films. The reduction in TMI observed in this study is attributed to the variation in the band structure resulting from the incorporation of Mo ⁴⁺ into the VO₂ lattice. The optical transmission is remarkably enhanced by low-concentration Mo doping and then monotonically decreases with increasing Mo content. On the other hand, the out-of-plane lattice constant and T_MI are not affected by Mn doping. The transmission is enhanced and then monotonically increases with increasing Mn concentration. The thermochromism of doped films is suppressed by Mo and Mn doping.