GROWTH, LOCAL STRUCTURAL AND ELECTRONIC PROPERTIES, AND BAND ALIGNMENT AT SRTIO3-BASED ALL-OXIDE HETEROJUNCTIONS

Recent advances in the growth of epitaxial oxide thin films have fostered a steady increase of research on oxide heterojunctions, which are now produced with unprecedented quality. Applications of these systems in the field of electronics, photovoltaics and photocatalysis strongly rely on the capability to master band gap engineering on the atomic scale. Strontium titanate (SrTiO3) is the substrate of choice commonly used in the production of all-oxide heterostructures, as in many cases these systems display a two dimensional electron gas (2DEG) confined at the interface, such as in the LaAlO3/SrTiO3 junction. The band offsets at the interface determine on which of the constituent materials the 2DEG will be confined, and provide additional information on the degree of confinement as well, so the study of the band alignment in oxide-based heterostructures is of crucial importance. Novel properties and functionalities can be achieved upon substitution of LaAlO3 with other oxide materials, an example being the BiFeO3 perovskite. In fact, BiFeO3 is a multiferroic material, and a complete control of the BiFeO3/SrTiO3 heterostructure may allow the tuning of the 2DEG at the interface through the application of an external electric or magnetic field. A 2DEG is also observed in the Al2O3/SrTiO3 junction, which show electron mobilities greater than those previously measured in perovskite-based heterojunctions. Despite in many structures the 2DEG is not observed, different interesting applications can still be obtained, such as in the CuO/SrTiO3 heterostructure, which is a promising material for the production of solar cells and for photoelectrochemical water splitting applications. The main objective of this work is to demonstrate the growth of high quality BiFeO3/SrTiO3, Al2O3/SrTiO3 and CuO/SrTiO3 heterostructures by off-axis sputtering, and to provide a detailed analysis of the interface properties. The band alignment at the interface is thus measured and discussed for each of these materials.