Manipulating Behaviors from Heavy Tungsten Doping on Interband Electronic Transition and Orbital Structure Variation of Vanadium Dioxide Films.

Abstract

Vanadium dioxide (VO2) with a metal-insulator transition (MIT) has been supposed as a candidate for optoelectronic devices. However, the MIT temperature ( TMIT) above room temperature limits its application scope. Here, high-quality V1- xW xO2 films have been prepared by pulsed laser deposition. On the basis of temperature-dependent transmittance and Raman spectra, it was found that TMIT increases from 241 to 279 K, when increasing the doping concentration in the range of 0.16 ≤ x ≤ 0.20. The interband electronic transitions and orbital structures of V1- xW xO2 films have been investigated via fitting transmittance spectra. Moreover, with the aid of first-principles calculations, an effective orbital theory has been proposed to explain the unique phenomenon. When the W doping concentration increases, the π* and dII orbitals shift toward the π orbital. Meanwhile, the energy gap between the π* and dII orbitals decreases at the insulator state. It indicates that the bandwidth is narrowed, which impedes MIT. In addition, the overlap of the π* and dII orbitals increases at the metal state, and more doping electrons occupy the π* orbital induced by increasing W doping concentration. It manifests that the Mott insulating state becomes more stable, which further improves TMIT. The present work provides a feasible approach to tune TMIT via orbital variation and can be helpful in developing the potential VO2-based optoelectronic devices.