Intrinsic origin of interface states and band-offset profiling of nanostructured LaAlO3/SrTiO3 heterojunctions probed by element-specific resonant spectroscopies

The origin of electronic states at the basis of the 2DEG found in conducting LaAlO3/SrTiO3 interfaces (5 u.c. LaAlO3) is investigated by resonant photoemission experiments at the Ti L-2,L-3 and La M-4,M-5 edges. As shown by the resonant enhancement at the Ti L-2,L-3 edge, electronic states at E-F receive a dominant contribution from Ti 3d states. Both Ti and La resonance effects in the valence-band region are used to estimate the valence-band maxima at the two sides of the junction. Through a comparison with the valence-band states of the LaAlO3 and SrTiO3 parent compounds, we reconstruct the band diagram of the heterojunction, which is revealed to be type I (straddling gap), with a large notch of the band profile at the interface as compared with the reference insulating (3 u.c. LaAlO3) interface.