Iron-related defect levels in SrTiO3 measured by photoelectron paramagnetic resonance spectroscopy

The optical absorption of defect centers in SrTiO3 substrates grown by the Vernuil method are investigated using photoinduced electron paramagnetic resonance (photo-EPR) at room temperature. As received samples revealed EPR signatures for Fe3+, Cr3+, Mn4+, and an iron-oxygen vacancy complex, Fe3+VO. An anneal in dry oxygen at 800 degrees C decreased the intensity of all of the centers except, Mn4+. More significantly, the anneal induced a new charge state of Fe, Fe5+. Photo-EPR data of the annealed samples were interpreted in terms of two defect levels, the 4+ to 5+ transition of Fe (Fe4+/5+) at 2.5 eV below the conduction band edge and the 3+ to 4+ transition of the iron-oxygen vacancy complex (Fe3+/4+VO) at 1.2 eV above the valence band edge. The former is consistent with reported defect levels and the latter provides a modified value based on measurements over a larger portion of the band gap than had been reported previously. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3372760]