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

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)x100%), and then annealed by rapid thermal annealing (RTA) at 350-750 degrees C for 2 min 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 degrees 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 degrees C annealing can be fitted into two Gaussian peaks at similar to 486 nm (2.55 eV) and similar to 588 nm (2.11 eV) which were attributed to deep-level emissions of oxygen vacancies in the rutile and anatase phases, respectively. The peak around 550 nm 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. (C) 2009 Elsevier B.V. All rights reserved.