Instability, intermixing and electronic structure at the epitaxial LaAlO3/SrTiO3(001) heterojunction

Abstract

The question of stability against diffusional mixing at the prototypical LaAlO3/SrTiO3(001) Interface is explored using a multi-faceted experimental and theoretical approach We combine analytical methods with a range of sensitivities to elemental concentrations and spatial separations to investigate interfaces grown using on-axis pulsed laser deposition We also employ computational modeling based on the density function theory as well as classical force fields to explore the energetic stability of a wide variety of intermixed atomic configurations relative to the idealized atomically abrupt model Statistical analysis of the calculated energies for the various configurations is used to elucidate the relative thermodynamic stability of intermixed and abrupt configurations We find that on both experimental and theoretical fronts the tendency toward intermixing is very strong We have also measured and calculated key electronic properties such as potential energy gradients and valence band discontinuity at the Interface We find no measurable electric field in either the LaAlO3 or SrTiO3 and that the valence band offset is near zero partitioning the band discontinuity almost entirely to the conduction band edge Significantly we find it is not possible to account for these electronic properties theoretically without including extensive intermixing in our physical model of the Interface The atomic configurations which give the greatest electrostatic stability are those that eliminate the interface dipole by intermixing calling Into question the conventional explanation for conductivity at this interface-electronic reconstruction Rather evidence is presented for La indiffusion and doping of the SrTiO3 below the interface as being the cause of the observed conductivity (C) 2010 Elsevier B V All rights reserved