heterostructures

Novel two-dimensional electron systems at the interfaces of oxide heterostructures such as LaAlO₃ /SrTiO₃ recently have attracted much attention as they display intriguing properties which may be exploited in future electronic devices. A key requirement for such applications is the controllability of the electronic interface properties such as the valence band offset. We demonstrate that these properties can be effectively engineered in LaAlO₃ /SrTiO₃ by virtue of the oxygen vacancy concentration. By angle-dependent hard x-ray photoelectron spectroscopy, we derive a complete band diagram of the heterostructure dependent on the oxygen vacancy concentration which is adjusted during the photoemission experiments by means of synchrotron light irradiation and simultaneous oxygen dosing. The dielectric constant of the SrTiO₃ substrates and its strong non-linear dependence on the electric field prove to be essential for the band arrangement of the LaAlO₃/SrTiO₃ heterostructures. The comprehensive analysis of the band situation at the LaAlO₃/SrTiO₃ heterointerface as a function of the oxygen vacancy concentration can reconcile the contradicting results of previous photoemission studies.