Intrinsic asymmetric ferroelectricity induced giant electroresistance in ZnO/BaTiO superlattice.

Here, we combine the piezoelectric wurtzite ZnO and the ferroelectric (111) BaTiO as a hexagonal closed-packed structure and report a systematic theoretical study on the ferroelectric behavior induced by the interface of ZnO/BaTiO films and the transport properties between the SrRuO electrodes. The parallel and antiparallel polarizations of ZnO and BaTiO can lead to intrinsic asymmetric ferroelectricity in the ZnO/BaTiO superlattice. Using first-principles calculations we demonstrate four different configurations for the ZnO/BaTiO/ZnO superlattice with respective terminations and find one most favorable for the stable existence of asymmetric ferroelectricity in thin films with thickness less than 4 nm. Combining density functional theory calculations with non equilibrium Green's function formalism, we investigate the electron transport properties of SrRuO/ZnO/BaTiO/ZnO/SrRuO FTJ and SrRuO/ZnO/BaTiO/SrRuO FTJ, and reveal a high TER effect of 581% and 112% respectively. These findings provide an important insight into the understanding of how the interface affects the polarization in the ZnO/BaTiO superlattice and may suggest a controllable and unambiguous way to build ferroelectric and multiferroic tunnel junctions.