Crossover of spectral reflectance lineshapes in Ge-doped VO2 thin films

Adjusting the insulator-to-metal transition (IMT) temperature of vanadium dioxide (VO2) thin films for use in optical applications can be achieved via doping with various elements. An important aspect, which was largely overlooked in the literature, is the change in the spectral reflectivity lineshapes upon dopant addition in order to control the critical temperature T-C of VO2. Here, we demonstrate that the T-C in VO2 can be varied effectively with Ge doping. Moreover, we observe that the spectral lineshapes of the Ge doped VO2 films reveal rather interesting characteristics, such as a distinct crossover in the high-reflection and low-reflection regions during the IMT that could allow frequency specific spectral functionalities.