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

TL;DR

This study uses X-ray photoemission spectroscopy to analyze how growth conditions affect the electronic properties of LaAlO3/SrTiO3 heterointerfaces, focusing on band offsets and Ti3+ state density.

Contribution

It provides detailed insights into how oxygen partial pressure during growth influences Ti3+ states and band offsets in LAO-STO heterostructures, advancing understanding of their electronic behavior.

Findings

Lower P(O2) increases Ti3+ density and reduces binding energy.

Band offsets are below 0.7 eV and affect peak widths.

Conducting samples show the largest valence band offsets.

Abstract

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.