Pulsed laser deposition and e-beam evaporation of vanadium dioxide thin films for IR-photonics applications

Vanadium dioxide thin films were prepared on r-plane sapphire substrates by using in-situ pulsed laser deposition (PLD) and by post-annealing pure metallic vanadium films in synthetic air atmosphere by varying the annealing temperature and annealing time. As a result, vanadium oxide thin films with various compositions were produced. Thin films produced by using PLD contained also pure VO2 thin films, while post-annealed films had mixed phase structure of metallic vanadium and vanadium oxides or only different vanadium oxides. SPM surface analysis showed that pulsed laser deposited films were very smooth with R-q < 16.7 nm. The magnitude of metal-insulator transition (MIT) of the optical transmission measured from pulsed laser deposited VO2 thin films was around 50% at the wavelengths of 1.5 and 2.5 mu m. Surface roughness of the post-annealed films was high, R-q < 86.1 nm. Although the post-annealed films were non-homogenous phase mixtures containing very little VO2 phase in their structure, some of them showed very good optical responses at IR-wavelengths. At the wavelength of 2.5 mu m, optical transition between insulator and conductive states as large as 74% was measured.