We report on an electronic structure study of SrTiO3 under ultraviolet illumination. Photoemission measurements at 20K under ultraviolet illumination show that the illumination induces electronic states within the band gap. The photo-induced in-gap states show the power-law energy distribution with exponent of 3.4- 3.7 and weakly depends on the strength of illumination. The photo-induced in-gap states indicate that most of the photo-excited electrons are trapped by local lattice distortions with various size scale. We argue that the free carriers in the Ti 3d band and the localized Ti 3d electrons and O 2p holes within the band gap contribute to the photoconductivity and the ferroelectricity under the ultraviolet illumination, respectively.
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