Band offsets and density of Ti3+ states probed by X-ray photoemission on LaAlO3/SrTiO3 heterointerfaces and their LaAlO3 and SrTiO3 bulk precursors

A set of LaAlO3/SrTiO3 (LAO-STO) interfaces has been probed by X-ray photoemission spectroscopy in order to contrast and compare the effects of LAO overlayer thickness and of the growth conditions on the electronic properties of these heterostructures. These effects are tracked by considering the band-offset and the density of Ti3+ states, respectively. It is shown that the dominant effects on the local electronic properties are determined by the O2 partial pressure during the growth. In particular, a low P(O2) yields Ti3+ states with higher density and lower binding energy as compared to the sample grown at high P(O2) or to the bare STO reference sample. Band offset effects are all below about 0.7 eV, but a careful analysis of Ti 2p and Sr 3d peaks shows that valence band offsets can be at the origin of the observed peak width. In particular, the largest offset is shown by the conducting sample, that displays the largest Ti 2p and Sr 3d peak widths.
Comment: Submitted to Physical Review B, revised version