Growth and characterization of epitaxial films of tungsten-doped vanadium oxides on sapphire (110) by reactive magnetron sputtering

Epitaxial films of W-doped vanadium oxides including W-V2O3, W-VO2 and W-V2O5 were deposited on sapphire (110) by reactive magnetron sputtering of a V-W (1.6 at. % W) alloy target in a range of oxygen partial flows. The deposited films were characterized by x-ray diffraction (XRD), Rutherford backscattering spectrometry, atomic force microscopy and resistance-temperature measurement. The W-to-V ratio in the oxide films showed values higher than that in the target, and the ratio increased with increasing oxygen flows. With precise control of the oxygen partial, flow, not only the W-V2O3, W-VO2 and W-V2O5, but also a series of epitaxial films with lattice parameters varying between those of W-V2O3 and W-VO2 were formed. It was found from an XRD pole figure study that the W-VO2 exhibited a triple-domain structure with the three domains correlated by 120 degrees in the in-plane orientation. The W-VO2 epitaxial films clearly showed a semiconductor-to-metal phase transition with a reduced T-c by 23 degrees C/at. % W, whereas the phase transition of W-V2O3 seemed to be suppressed due, presumably, to the W-doping effect. (C) 1999 American Vacuum Society.