Optical investigation on oxygen defect states in SrTiO₃ compounds

We investigated oxygen defect states in SrTiO₃ (STO) thin films by using the photoluminescence spectroscopy and spectroscopic ellipsometry. The oxygen-deficient STO thin films were thermally treated in various oxygen environments systematically. The visible emission and absorption increased simultaneously with the increase of the oxygen vacancy concentration in the STO thin films. On the basis of the absolute values of the optical constants, we discussed the origins of the visible absorption features in STO, in relation to the defect formation and related electronic reconstruction. We also investigated the STO single crystals in the similar experimental procedure, and compared the results with the case of the thin films.