Continuous tuning of W-doped VO₂ optical properties for terahertz analog applications

Vanadium dioxide (VO₂), with its characteristic metal-insulator phase transition, is a prospective active candidate to realize tunable optical devices operating at terahertz (THz) frequencies. However, the abrupt phase transition restricts its practical use in analog-like continuous applications. Incorporation of tungsten is a feasible approach to alter the phase transition properties of thin VO₂ films. We show that amplitude THz modulation depth of ∼65%, characteristic phase transition temperature of ∼40°C, and tuning range larger than 35°C can be achieved with W-doped VO₂ films grown on sapphire substrates. W-doped VO₂ films can also be used to suppress Fabry-Perot resonances at THz frequencies but at temperatures much lower than that observed for undoped VO₂ films. The gradual phase transition temperature window allows for precise control of the W-doped VO₂ optical properties for future analog based THz devices.