Metalorganic chemical vapor deposition of highly oriented thin film composites of V₂O₅ and V₆O₁₃: Suppression of the metal–semiconductor transition in V₆O₁₃

Abstract

Thin films of vanadium oxides were grown on fused quartz by metalorganic chemical vapor deposition using vanadyl acetylacetonate as the precursor. Growth at temperatures ≥560 °Cresults in composites of strongly (00l)-oriented V₂O₅ and V₆O₁₃. The dominant phase of the film changes from V₂O₅ to V₆O₁₃, and back to V₂O₅, as the growth temperature is raused from 560 to 570 °C, then to 580 °C, as evidenced by x-ray diffraction and Rutherfor d backscattering analyses. This reentrant-type growth trend was interpreted on the basis of the small difference in the free energy of formation of V₂O₅ and V₆O₁₃ and the presence of metal–oxygen bonds in the precursor. In contrast with single-crystalline V₆O₁₃, the film predominantly composed of highly oriented single-crystalline platelets of V₆O₁₃ did not undergo the semiconductor–metal transition at -123° K, despite the connectivity being well above the percolation threshold. Instead, a semiconductor-to-semiconductor transition was observed in this film, which is explauned in terms of the observedrelaxation of the edges of all the platelets of metallic V₆O₁₃ to semiconducting V₂O₅.