Intrinsic asymmetric ferroelectricity induced giant electroresistance in ZnO/BaTiO3 superlattice

Here, we combine the piezoelectric wurtzite ZnO and the ferroelectric (111) BaTiO3 as a hexagonal closed-packed structure and report a systematic theoretical study on the ferroelectric behavior induced by the interface of ZnO/BaTiO3 films and the transport properties between the SrRuO3 electrodes. The parallel and antiparallel polarizations of ZnO and BaTiO3 can lead to intrinsic asymmetric ferroelectricity in the ZnO/BaTiO3 superlattice. Using first-principles calculations we demonstrate four different configurations for the ZnO/BaTiO3/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 SrRuO3/ZnO/BaTiO3/ZnO/SrRuO3 FTJ and SrRuO3/ZnO/BaTiO3/SrRuO3 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/BaTiO3 superlattice and may suggest a controllable and unambiguous way to build ferroelectric and multiferroic tunnel junctions.