Recent advances in the growth of epitaxial oxide thin films have fostered a steady increase of research on perovskite oxide heterojunctions, which are now produced with unprecedented quality. The applications of these interfaces in the field of electronics, photon harvesting, photovoltaics and photocatalysis strongly rely on the capability to master band gap engineering at the nanoscale; in fact, the junction functional properties are crucially dependent on the energy bands alignment at the interface, corresponding to the conduction band offset and the valence band offset (VBO) between the two materials.
The VBO study provides important information about the current transport, potential distribution and quantum carrier confinement at the junction, since it determines the height of the barrier for hole and electron transfer through the interface. However, several factors may define the band junction properties, such as strain, orientation, oxygen vacancies, interdiffusion or stoichiometry. It is usually a difficult task to give an accurate theoretical description for all these effects (which may occur simultaneously); in fact, theoretical calculations are often performed on the ideal heterostructure. For this reasons, the experimental determination of the VBO offset is a critical task.
The most reliable methods to experimentally track the band alignment at the interface are based on photoelectron spectroscopy analysis of core level or valence band structures; such analysis can be performed with standard X-ray sources (XPS) or can also exploit synchrotron based techniques, such as resonant photoemission spectroscopy.
In this work we show the band gap alignment, obtained with photoelectron spectroscopy techniques, from several all-oxide perovskite interfaces grown on SrTiO3; in this context, we also show a detailed survey of band junction results in literature, theoretical and experimental. Both perovskite-SrTiO3 and non-perovskite – SrTiO3 junction are considered.