Band alignment of epitaxial SrTiO3 thin films with (LaAlO3)0.3-(Sr2AlTaO6)0.7 (001)

TL;DR

This study investigates the electronic band alignment at the interface of epitaxial SrTiO3 thin films and LSAT substrates, revealing how surface termination influences valence and conduction band offsets, which impacts electronic properties.

Contribution

It provides the first detailed measurement of band offsets at the STO/LSAT interface using x-ray photoelectron spectroscopy, highlighting the dependence on surface termination.

Findings

Valence band offset varies with surface termination (+0.2 eV to -0.2 eV).

Conduction band offset ranges from -2.4 eV to -2.8 eV.

LSAT does not act as an electron sink or trap.

Abstract

SrTiO$_{3}$ (STO) epitaxial thin films and heterostructures are of considerable interest due to the wide range of functionalities they exhibit. The alloy perovskite (LaAlO$_{3}$)$_{0.3}$-(Sr$_{2}$AlTaO$_{6}$)$_{0.7}$ (LSAT) is commonly used as a substrate for these material structures due to its structural compatibility with STO and the strain-induced ferroelectric response in STO films grown on LSAT. However, surprisingly little is known about the electronic properties of the STO/LSAT interface despite its potentially important role in affecting the overall electronic structure of system. We examine the band alignment of STO/LSAT heterostructures using x-ray photoelectron spectroscopy for epitaxial STO films deposited using two different molecular beam epitaxy approaches. We find that the valence band offset ranges from +0.2(1) eV to -0.2(1) eV depending on the film surface termination. From these results we extract a conduction band offset from -2.4(1) eV to -2.8(1) eV, indicating that the conduction band edge is more deeply bound in STO and that LSAT will not act as a sink or trap for electrons in the supported film or multilayer.