In-gap electronic structure of LaAlO3-SrTiO3 heterointerfaces investigated by soft x-ray spectroscopy

We investigated LaAlO3-SrTiO3 heterointerfaces grown either in oxygen-rich or -poor atmosphere by soft x-ray spectroscopy. Resonant photoemission across the Ti L-2,L-3 absorption edge of the valence band and Ti 2p core-level spectroscopy directly monitor the impact of oxygen treatment upon the electronic structure. Two types of Ti3+ related charge carriers are identified. One is located at the Fermi energy and related to the filling of the SrTiO3 conduction band. It appears for low oxygen pressure only. The other one is centered at E-B approximate to 1 eV and independent of the oxygen pressure during growth. It is probably due to defects. The magnitude of both excitations is comparable. It is shown that low oxygen pressure is detrimental for the Ti-O bonding. Our results shed light on the nature of the charge carriers in the vicinity of the LaAlO3-SrTiO3 interface.