Controlling the density of the 2DEG at the SrTiO3/LaAlO3 interface

TL;DR

This paper investigates the factors limiting the electron density at the SrTiO3/LaAlO3 interface, revealing that structural asymmetry and surface passivation issues prevent reaching the theoretically predicted density.

Contribution

It combines first-principles and Schrodinger-Poisson simulations to identify structural asymmetry as the key factor affecting electron density at oxide interfaces.

Findings

Asymmetry prevents achieving full 2DEG density

Full density observed in symmetric GdTiO3/SrTiO3 interfaces

Insights applicable to general oxide interface design

Abstract

The polar discontinuity at the SrTiO3/LaAlO3 interface (STO/LAO) can in principle sustain an electron density of 3.3E14 cm-2 (0.5 electrons per unit cell). However, experimentally observed densities are more than an order of magnitude lower. Using a combination of first-principles and Schrodinger-Poisson simulations we show that the problem lies in the asymmetric nature of the structure, i.e., the inability to form a second LAO/STO interface that is a mirror image of the first, or to fully passivate the LAO surface. Our insights apply to oxide interfaces in general, explaining for instance why the SrTiO3/GdTiO3 interface has been found to exhibit the full density of 3.3E14 cm-2.