Band alignment in LaAlO3/SrTiO3oxide heterostructures inferred from hard x-ray photoelectron spectroscopy

Abstract

We present a detailed study of the electronic structure and band alignment in LaAlO 3 /SrTiO 3 oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for the strong potential gradient within the polar LaAlO 3 film predicted by band theory. Due to the high interface sensitivity of the method, we are further able to determine the valence band offset between the LaAlO 3 film and the SrTiO 3 substrate, which is found to be independent of the number of LAO overlayers. Finally, we discuss several explanations for the apparent absence of the built-in field in ex situ prepared LaAlO 3 /SrTiO 3 heterostructures.

Band bending and alignment at the spinel/perovskiteγ−Al2O3/SrTiO3heterointerface

“…Similar findings have been reported for LAO/STO heterostructures [23,29,30,43]. Different scenarios have been introduced to account for these observations, of which photoinduced carriers, oxygen vacancies, and antisite defects will be discussed in the following.…”

“…Furthermore, due to its large band gap (≈7.9 eV) [20], the CBM of GAO is above that of STO. Accordingly, in contrast to LAO/STO [15,28,30,40], the heterointerface between GAO and STO is found to be of type I.…”

“…Similar observations have been made for other polar oxide heterostructures. In particular, the related heterostructure LAO/STO does not show a potential gradient as inferred from HAXPES [5,23,[27][28][29][30].…”

“…Furthermore, the positive sign of E VB means that the VBM of STO is above that of GAO, corresponding to an interface of type I. This distinguishes GAO/STO from the case of LAO/STO, where the interface is found to be of type II [5,28,30,40].…”

Influence of oxygen vacancies on two-dimensional electron systems at SrTiO3-based interfaces and surfaces

“…The electronic reconstruction scenario, however, was also seriously cast into doubt by X-ray photoemission measurements providing a fairly sensitive probe for binding energy shifts -e.g., due to an internal electric field in the LaAlO 3 film -but being unable to reveal such traces of a finite potential gradient in the data [83][84][85]. Likewise, angle-resolved photoemission measurements using soft X-rays failed to observe O 2p-derived hole pockets due to the LaAlO 3 valence band Fermi level crossing as expected and predicted in an electronic reconstruction scenario [86].…”