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

Vanadium dioxide (VO₂) with a metal-insulator transition (MIT) has been supposed as a candidate for optoelectronic devices. However, the MIT temperature (T_MIT) above room temperature limits its application scope. Here, high-quality V_1-xW_xO₂ films have been prepared by pulsed laser deposition. On the basis of temperature-dependent transmittance and Raman spectra, it was found that T_MIT 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 V_1-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 d_II orbitals shift toward the π orbital. Meanwhile, the energy gap between the π∗ and d_II orbitals decreases at the insulator state. It indicates that the bandwidth is narrowed, which impedes MIT. In addition, the overlap of the π∗ and d_II 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 T_MIT. The present work provides a feasible approach to tune T_MIT via orbital variation and can be helpful in developing the potential VO₂-based optoelectronic devices.