Stoichiometry Dependence of Potential Screening at La$_{(1-{\delta})}$Al$_{(1+{\delta})}$O$_3$/SrTiO$_3$ Interfaces

TL;DR

This study investigates how stoichiometry variations in LaAlO3 films influence electronic properties and interface conductivity at LaAlO3/SrTiO3 interfaces using advanced spectroscopy techniques.

Contribution

It reveals the impact of La:Al ratio on compositional depth profiles and electronic structure, highlighting defect-driven electronic reconstruction mechanisms.

Findings

Al-rich films show little intermixing and broad valence band

La-rich and stoichiometric films exhibit La enrichment at the interface

Al-rich films display a broadening of the valence band indicating an electric field

Abstract

Hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy x-ray photoelectron spectroscopy (VKE-XPS) analyses have been performed on 10 unit cell La$_{(1-{\delta})}$Al$_{(1+{\delta})}$O$_3$ films, with La:Al ratios of 1.1, 1.0, and 0.9, deposited on SrTiO$_3$. Of the three films, only the Al-rich film was known to have a conductive interface. VKE-XPS, coupled with maximum entropy analysis, shows significant differences in the compositional depth profile between the Al-rich, the La-rich, and stoichiometric films; significant La enrichment at the interface is observed in the La-rich and stoichiometric films, while the Al-rich shows little to no intermixing. Additionally, the La-rich and stoichiometric films show a high concentration of Al at the surface, which is not observed in the Al-rich film. HAXPES valence band (VB) analysis shows a broadening of the VB for the Al-rich sample relative to the stoichiometric and La-rich samples, which have insulating interfaces. This broadening is consistent with an electric field across the Al-rich film. These results are consistent with a defect driven electronic reconstruction.