Electric field driven abnormal increase in conductivity of tungsten-doped VO₂ nanofilms

Ion doping is an effective way in tuning the metal-insulator transition (MIT) and physical properties of vanadium dioxide (VO₂). However, the mechanism of ion doping effect is not quite clear up to now. The first principle calculations in our last paper indicated that W dopants injected localized d-electrons in rutile VO₂ (VO₂(R)). Herein, we prepared a group of V_1-xW_xO₂ (0 ≤ x ≤ 2.7%) films, and applied external electric field to drive the MIT transition of W-doped VO₂. The variation of electrical conductivity of W-doped VO₂ was investigated with different W concentrations and applied voltages. Without external electric field, the conductivity of W-doped VO₂(R) is lower than that of undoped VO₂(R), and decreases with increasing the W concentration. Upon loading electric field, the conductivity of W-doped VO₂(R) is increased by applied voltages and reaches a saturation value which is higher than that of undoped VO₂(R) and increases with the W concentration, while the conductivity of undoped VO₂(R) is independent of applied voltage. The experimental results suggest external electric field drives the excitation of the localized d electrons injected by W dopants. This work presents useful information for understanding the ion doping effect in VO₂, and demonstrates the existence of conduction multiplets in W-doped VO₂, proposing potential application of W-doped VO₂ in multi-field effect devices such as for high-density storage.