Epitaxial integration of improper ferroelectric hexagonal YMnO3 thin films in heterostructures

Abstract

We report on multiple fundamental qualitative improvements in the growth of improper ferroelectric hexagonal YMnO3 (YMO) thin films and heterostructures by pulsed laser deposition (PLD). By a combination of pre-growth substrate annealing and low-energy-fluence PLD, we obtain a two-dimensional growth mode of the YMO films on yttria-stabilized zirconia (YSZ) with ultralow roughness and devoid of misoriented nanocrystalline inclusions. By inserting a hexagonal manganite buffer layer capped with conducting indium-tin oxide between the substrate and the final film, the latter is grown in a fully lattice-relaxed mode and, thus, without any misfit dislocations while maintaining the extraordinary flatness of the films grown directly on pre-annealed YSZ. This provides a template for the fabrication of heterostructures based on hexagonal manganites as a promising class of multiferroics with improper room-temperature ferroelectricity and the implementation of these into technologically relevant epitaxial metal ferroelectric-type multilayers.