Facile synthesis of various epitaxial and textured polymorphs of vanadium oxide thin films on the (0006)-surface of sapphire substrates

Extensive attention has been paid to vanadium oxide polymorphs because of their potential to be used in applications in information and optoelectronic devices, as well as in energy harvesting technologies. However, vanadium oxides always form a very complex phase diagram; in particular, it is still challenging to synthesize pure vanadium oxide epitaxial polymorphs on low-cost, transparent and wafer-scale substrates. Here, we demonstrate the growth of epitaxial polymorphs of vanadium oxide (VO2 (R, M1 and their mixed phase), and V2O3) and (001)-textured VO2 (B) thin films on the (0006) surface of sapphire without selecting specific substrate orientations. This is achieved by controlling the vanadium arrival rate via sputtering power and oxidation of vanadium atoms through the partial pressure of oxygen using magnetron sputtering techniques, which enables wafer-scale production of the vanadium oxide thin films on the sapphire substrates. Growth phase diagrams of the various polymorphs are also developed for guiding device design based on the vanadium oxide thin films. This work paves a way towards practical applications of vanadium oxide thin films on chemically stable, transparent and low-cost sapphire substrates.