MOCVD growth and characterization of vanadium dioxide films

High-quality vanadium dioxide (VO₂) films were synthesized on sapphire and silicon substrates by metal–organic chemical vapor deposition. Optimal growth conditions for obtaining abrupt and reversible semiconductor–metal phase transition of VO₂ were found. X-ray diffraction, Raman scattering spectroscopy, and scanning electron microscopy measurements suggested that grown VO₂ films have high crystal quality. It was shown that, at a fixed proportion between the rates of the oxygen and argon flows in the reactor and at a substrate temperature in the range of 440 ≤ T ≤ 470 °C, the monoclinic phase of VO₂ formed in the deposited films. The films grown on sapphire and silicon substrates were found to have an underlying conducting transition layer forming ohmic back contact to VO₂ film. The presence of such back contact layer has allowed us to form VO₂-based vertical devices. In such structures, VO₂ films have shown conductivity changes up to four orders of magnitude due to the phase transition. This demonstrates the high quality of grown films without post-deposition annealing.