Origin of charge density at LaAlO3-on-SrTiO3 hetero-interfaces; possibility of intrinsic doping

TL;DR

This paper investigates the origin of high charge density at LaAlO3/SrTiO3 interfaces, concluding that oxygen vacancies from fabrication processes are the main source, and proposes a model for high mobility based on dielectric effects.

Contribution

It provides evidence that oxygen vacancies cause the high charge density and introduces a model explaining the high mobility through dielectric constant variations.

Findings

Oxygen vacancies are the primary source of large carrier densities.

Annealing limits the carrier density at the interface.

High mobility is explained by carrier redistribution related to dielectric properties.

Abstract

As discovered by Ohtomo et al., a large sheet charge density with high mobility exists at the interface between SrTiO3 and LaAlO3. Based on transport, spectroscopic and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also present a model that explains the high mobility based on carrier redistribution due to an increased dielectric constant.