Infrared and Terahertz Spectra of Sn-Doped Vanadium Dioxide Films

This work reports the effect of tin (Sn) doping on the infrared (IR) and terahertz (THz) properties of vanadium dioxide (VO2) films. The films were grown by hydrothermal synthesis with a post-annealing process and then fully characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and temperature-controlled electrical resistivity as well as IR and THz spectroscopy techniques. Utilizing (NH4)2SnF6 as a Sn precursor allows the preparation of homogeneous Sn-doped VO2 films. Doping of VO2 films with Sn led to an increase in the thermal hysteresis width while conserving the high modulation depth in the mid-IR regime, which would be beneficial for the applications of VO2 films in IR memory devices. A further analysis shows that Sn doping of VO2 films significantly affects the temperature-dependent THz optical properties, in particular leading to the suppression of the temperature-driven THz transmission modulation. These results indicate Sn-doped VO2 films as a promising material for the development of switchable IR/THz dichroic components.