Cation mixing, band offsets and electric fields at LaAlO3/SrTiO3(001) heterojunctions with variable La:Al atom ratio

Interfacial intermixing and electronic structure were investigated at thin (3–5 unit cells.), epitaxial La1 − xAl1 + xO3/SrTiO3(001) heterojunctions for x = 0 and ± 0.05. Angle-resolved X-ray photoelectron spectroscopy reveals rather extensive cation intermixing for all films, independent of composition. The valence band offset for the nominally stoichiometric (x = 0) film is 0.16 ± 0.10 eV, with the valence band maximum of SrTiO3 being deeper in binding energy than that of LaAlO3. Similar values are obtained for x = ± 0.05. There is no measurable band bending in either the LaAlO3 or the SrTiO3 near the interface. These results are at odds with first principles theoretical predictions based on perfect stoichiometry and an abrupt interface model. However, inclusion of intermixing in the compositional description of the interface results in successful prediction of the valence band offset and absence of band bending.