Mapping the Spatial Distribution of Charge Carriers in LaAlO3/SrTiO3 Heterostructures

TL;DR

This study uses conducting-tip atomic force microscopy to directly map the charge carrier distribution in LaAlO3/SrTiO3 heterostructures, revealing that the spatial extent of the electron gas varies significantly with growth conditions.

Contribution

First direct measurement of carrier density profiles in LaAlO3/SrTiO3 interfaces, demonstrating variable spatial extension of the electron gas based on growth protocols.

Findings

Electron gas can extend from nanometers to hundreds of microns.

CT-AFM is effective for characterizing complex oxide interfaces.

Growth conditions influence the spatial distribution of charge carriers.

Abstract

At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO3/SrTiO3 system. While this state has been predicted and reported to be confined at the interface, some works indicate a much broader spatial extension, thereby questioning its origin. Here we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending upon specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of microns into SrTiO3 to a few nanometers next to the LaAlO3/SrTiO3 interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system.