title: Thermodynamic Ground States of Complex Oxide Heterointerfaces.
abstract: The formation mechanism of 2-dimensional electron gases (2DEGs) at heterointerfaces between nominally insulating oxides is addressed with a thermodynamical approach. We provide a comprehensive analysis of the thermodynamic ground states of various 2DEG systems directly probed in high temperature equilibrium conductivity measurements. We unambiguously identify two distinct classes of oxide heterostructures: For epitaxial perovskite/perovskite heterointerfaces (LaAlO3/SrTiO3, NdGaO3/SrTiO3, and (La,Sr)(Al,Ta)O3/SrTiO3), we find the 2DEG formation being based on charge transfer into the interface, stabilized by the electric field in the space charge region. In contrast, for amorphous LaAlO3/SrTiO3and epitaxial γ-Al2O3/SrTiO3heterostructures, the 2DEG formation mainly relies on the formation and accumulation of oxygen vacancies. This class of 2DEG structures exhibits an unstable interface reconstruction associated with a quenched nonequilibrium state.
authors.affiliation: Institute of Electronic Materials, IWE2, RWTH Aachen University , 52056 Aachen, Germany.
authors.forename: F
authors.identifier: http://orcid.org/0000-0003-1178-9986
authors.initials: F
authors.lastname: Gunkel
authors.affiliation: Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Hoffmann-Eifert
authors.affiliation: Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany.
authors.forename: R A
authors.initials: RA
authors.lastname: Heinen
authors.affiliation: Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark.
authors.forename: D V
authors.initials: DV
authors.lastname: Christensen
authors.affiliation: Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark.
authors.forename: Y Z
authors.initials: YZ
authors.lastname: Chen
authors.affiliation: Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Pryds
authors.affiliation: Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Waser
authors.affiliation: Peter Gruenberg Institute and JARA-FIT, Forschungszentrum Juelich GmbH , 52425 Juelich, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Dittmann
keywords: 2DEG; defect-chemistry; interface chemistry; oxide heterointerfaces; thermodynamics