Pulsed laser deposition of oriented VO2 thin films on R-cut sapphire substrates

We have deposited highly oriented VO2 thin films on R-cut sapphire substrates by the pulsed laser ablation technique. The stabilization of pure VO2 is complicated due to a large number of distinct phases in the vanadium oxide system. As many as 13 different phases ranging from oxygen stoichiometry of V4O to V2O5 can exist in this system. The deposition parameters for fabrication of phase pure, highly oriented VO2 thin films on R-cut sapphire substrates by the pulsed laser deposition technique are discussed. A KrF laser (wavelength λ=248 nm, pulse duration τ=15×10−9 s) was used to ablate a pure vanadium target in an atmosphere containing specific ratios of oxygen and argon. The partial pressure of oxygen in the chamber was critical in stabilizing the VO2 phase. X-ray diffraction and other microstructural characterization revealed that the films were single phase and strongly oriented with the (200) planes parallel to the sapphire substrate. Short transition widths of 2 K and resistivity changes of 3×104 have been observed, thus indicating the growth of highly oriented VO2 films.