Understanding the atomic structure of epitaxial SrTiO$_{3}$-GaAs (001) hetero-interfaces.

The combination of high-resolution Z-contrast imaging, electron energy-loss spectroscopy (EELS), and density functional theory (DFT) calculations was used to study the interfacial structure of ultra-thin SrTiO$_{3}$ films on GaAs(001). Z-contrast imaging suggests an atomically sharp hetero-interface with SrTiO$_{3}$ [110] in registry with As-terminated GaAs [100] with no visible reconstruction of either surface. Our initial DFT-calculations reveal that such a stoichiometric interface would have states in the band gap, while X-ray photoelectron spectroscopy (XPS) shows a clean band gap and a valence band offset more than twice of the calculated offset. Therefore, we will use atomic-column resolved EELS and further DFT-calculations to explore the role of oxygen vacancies at the interface in compensating for the As dangling bonds and search for the low-energy semi-conducting SrTiO$_{3}$/GaAs-system.