Unravelling the Origin of Ultra‐Low Conductivity in SrTiO ₃ Thin Films: Sr Vacancies and Ti on A‐Sites Cause Fermi Level Pinning

Different SrTiO3 thin films are investigated to unravel the nature of ultra-low conductivities recently found in prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic for a broad range different dopants (Fe, Al, Ni) and partly high dopant concentrations up several percent. Using inductively-coupled plasma optical emission reciprocal space mapping, severe Sr deficiency is positron annihilation lifetime revealed vacancies as predominant point defects. From synchrotron-based X-ray standing wave absorption measurements, change site occupation deduced Fe-doped films, accompanied type. Based on these experiments, model deduced, which explains almost ubiquitous conductivity films. suggested key driver introducing causing changes (FeSr TiSr) accommodate nonstoichiometry. act mid-gap acceptor states, pinning Fermi level, provided that additional donor states (most probably Ti • \[{\rm{Ti}}_{{\rm{Sr}}}^{ \bullet }\] ) present. Defect chemical modeling such level also causes self-limitation leads very robust situation, irrespective Sr/Ti ratios doping.