Photoemission features associated with states deep in the band gap of n-SrTiO3(001) are found to be ubiquitous in bulk crystals and epitaxial films. These features are present even when there is little signal near the Fermi level. Analysis reveals that these states are deep-level traps associated with defects. The commonly investigated defects - O vacancies, Sr vacancies, and aliovalent impurity cations on the Ti sites - cannot account for these features. Rather, ab initio modeling points to these states resulting from interstitial oxygen and its interaction with donor electrons.
Bibliographical noteFunding Information:
The work was supported by the U.S. Department of Energy, Office of Science, Division of Materials Sciences and Engineering under Award No. 10122 and was performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at PNNL. M.J.W. and L.F.J.P. acknowledge support from the National Science Foundation under Grant No. DMR 1409912. We thank the Diamond Light Source for access to beamline I09 (NT16630) and Dr. Tien-Lin Lee for his assistance with the experiments. The BU work was supported by the Air Force Office of Scientific Research under Award No. FA9550-18-1-0024. The work at UMN was funded by the U.S. Department of Energy through the University of Minnesota Center for Quantum Materials, under Grant No. DE-SC-0016371. A.P. acknowledges the support from the UMN Doctoral Dissertation Fellowship. Electron microscopy was carried out at the SuperSTEM Laboratory, the U.K. National Research Facility for Advanced Electron Microscopy, which is supported by the Engineering and Physical Sciences Research Council.