Ferroelectric dead layer driven by a polar interface

Abstract

Based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As a representative model, we consider a TiO 2 -terminated BaTiO 3 film with LaO monolayers at the two interfaces that serve as doping layers. We find that the polar interfaces create an intrinsic electric field that is screened by the electron charge leaking into the BaTiO 3 layer. The amount of the leaking charge is controlled by the boundary conditions which are different for three heterostructures considered, namely, vacuum/LaO/ BaTiO 3 / LaO, LaO/ BaTiO 3 , and SrRuO 3 / LaO/ BaTiO 3 / LaO. The intrinsic electric field forces ionic displacements in BaTiO 3 to produce the electric polarization directed into the interior of the BaTiO 3 layer. This creates a ferroelectric dead layer near the interfaces that is nonswitchable and thus detrimental to ferroelectricity. Our first-principles and model calculations demonstrate that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces.

Interface dipole effect on thin film ferroelectric stability: First-principles and phenomenological modeling

“…34,10 We note however that this dipole forms due to fixed interface displacements and hence has a different origin compared to the charge mismatch effect 37 or the effect of a polar interface. 39 The question remains as to what role, if any, this built-in dipole affects the polarization stability. First, we note that the two polarization states in the n = 8 structure differ in energy by…”

Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

“…This mechanism is akin to the proposed 2DEG confinement at polar interfaces created by ferroelectrics. 36,37 In this paper, we use first-principles calculations based on hybrid Hartree-Fock (HF) and DFT calculations to elucidate the origin and properties of 2DEG at the interfaces of wurtzite ZnO/Zn(Mg)O heterostructures. We calculate the charge distribution, band profile, and band alignment in the heterostructure to test that the interface charge and the electric fields in the slabs are consistent with the polarization discontinuity hypothesis.…”

La-doped BaTiO3 heterostructures: Compensating the polarization discontinuity

“…22 In contrast, we observe a zero polarization at the nominal (LaO) + /BTO interface with a polarization enhancement at the BTO surface which is in contact with a top metal electrode. The charge density and polarization profile observed in our BTO film is self-consistent with the presence of a uniform distribution of La in the BTO.…”