A guide for achieving multiple VO2/Si heterostructures for thermally tunable near- and mid-infrared optics and electronics

Abstract

This work reports on the thermochemical reaction in air of layers between 110 and 285 nm of vanadium zigzag oblique columns on silicon. A gradual oxygen diffusion results in different linear velocity growth of the formed VO2-based overlayers depending on the initial V thickness. The study can be used as a practical operational guide for choice since it reveals a reference chart of multiple thermochromism, microstructure, composition, thickness and color features for many products achieved in different situations of reactivity evolution, that can be technologically attractive at one or another stage. For the conditions allowing larger VO2 yields, outstanding optical responses for films up to 500 nm (over 95 % of relative MIR and NIR transmittance modulation with temperature) are achieved, which is relevant for IR filtering or shuttering applications. However, the wavelengths for which this near-absolute optical blockage works, vary and can expand to a wide spectral window of 2 to 9 μm for a thickness of about 250 nm even tolerating the presence of incipient V2O5. For every thickness series, depending on the oxidation extent till V is consumed, the maximum NIR-MIR transmittances and the ranges of resistivities of the electric hysteresis can be adjusted with temperature, from more transparent to more opaque, and from more similar to a metal to more similar to an insulator, respectively, that may be useful in thermo-optic and thermo-resistive tunable applications.