Band offsets and density of Ti~(3+) states probed by x-ray photoemission on LaAlO_3/SrTiO_3 heterointerfaces and their LaAlO_3 and SrTiO_3 bulk precursors

摘要

A set of LaAlO_3/SrTiO_3 (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 Ti~(+3) states, respectively. It is shown that the dominant effects on the local electronic properties are determined by the O_2 partial pressure during the growth. In particular, a low P_(O_2) yields Ti~(+3) states with higher density and lower binding energy compared to the sample grown at high P_(O_2) 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, which displays the largest Ti 2p and Sr 3d peak widths.