Effects of oxygen flow ratios and annealing temperatures on Raman and photoluminescence of titanium oxide thin films deposited by reactive magnetron sputtering

Abstract

Titanium oxide (TiOx) thin films were deposited on the Si(100) substrates by direct-current reactive magnetron sputtering at 3–15 % oxygen flow ratios (FO2%=FO2/(FO2+FAr)×100%), and then annealed by rapid thermal annealing (RTA) at 350–750°C for 2min in air. The phase, bonding and luminescence behaviors of the as-deposited and annealed TiOx thin films were analyzed by X-ray diffraction (XRD), Raman spectroscopy and photoluminescence (PL) spectroscopy, respectively. The as-deposited TiOx films were amorphous from XRD and showed weak Raman intensity. In contrast, the distinct crystalline peaks of anatase and rutile phases were detected after RTA at 550–750°C from both XRD and Raman spectra. A mixture of anatase and rutile phases was obtained by RTA at 3 FO2% and its amount increased with annealing temperature. Only the anatase phase was detected in the 6–15 FO2% specimens after RTA. The PL spectra of all post-annealed TiOx films showed a broad peak in visible light region. The PL peak of TiOx film at 3 FO2% at 750°C annealing can be fitted into two Gaussian peaks at ~486nm (2.55eV) and ~588nm (2.11eV) which were attributed to deep-level emissions of oxygen vacancies in the rutile and anatase phases, respectively. The peak around 550nm was observed at 6–15 FO2% which is attributed to electron–hole pair recombination from oxygen vacancy state in anatase phase to valence band. The variation of intensity of PL peaks is concerned with the formation of the rutile and anatase phases at different FO2% and annealing temperatures.