High Quality Epitaxial V2O3 Thin Films: A Material for Infrared Switching Devices?

Abstract

ABSTRACTThe compound V20O13 undergoes a metal-insulator-transition (MIT) at T=150K with an optical gap in the insulating phase of ∼0.6eV. Therefore epitaxial films of V2O3 are of interest for infrared (IR) applications. We present the results of a systematic study of the growth conditions of such films utilizing electronic transport and infrared transmission measurements in addition to studies of crystal and microstructure.Epitaxial V2O3 thin films were grown in a reactive oxygen atmosphere on c-axis oriented sapphire substrates by electron beam evaporation. While V2O3 single crystals show a MIT in a narrow temperature range ΔT < 1K, the MIT broadened in epitaxial thin films due to defects and stress induced by the film-substrate interaction.In our study we defined the quality of the films by the width ΔT of the transition and the change of resistivity p and IR transmission at the MIT. We found the most important growth parameter to be the growth temperature. Only in a narrow region around 600°C the growth of high quality films was observed. The optical constants of such films were determined from IR transmission measurements in combination with an oscillator fit method. While the spectra in both the metallic and the insulting phase are dominated by d-d-transitions for photon energies above leV, in the IR region (λ > 2μm) a high transmission contrast between the two phases was almost independent of the wavelength. This behavior suggests e.g. applications as a non mechanical IR shutter or as switchable interference filter in the IR regime.