Oxygen-vacancy enhanced tunnel electroresistance in LaNiO3/BaTiO3/LaNiO3 ferroelectric tunnel junctions

Oxygen vacancies (OVs) usually exist in perovskite oxides in ferroelectric tunnel junctions (FTJs), which significantly influence electron transport properties of FTJ. However, the role of OVs is currently not well understood since the OVs concentration is difficult to detect in experiments or to simulate using traditional first-principles methods. Here, using the density functional theory combined with nonequilibrium Green's function and coherent potential approximation (NECPA-DFT), we investigate electron transport properties of the LaNiO3/BaTiO3/LaNiO3 FTJ, which has a low concentration OVs in the left LaNiO3/BaTiO3 interface. The tunnel barrier height monotonously decreases with the increase in the OVs concentration for the rightward polarization in BaTiO3, leading to an increased electron tunneling coefficient. In contrast, for a leftward polarization, the barrier height only slightly decreases with the increasing OVs concentration, leading to a nearly invariant electron tunneling coefficient. The tunnel electroresistance ratio, therefore, increases monotonously with the OVs concentration and reaches to 5898% for a OVs concentration of 9%. Our results show that OVs play a critical role in determining electron transport properties of an FTJ as well as provide an alternative avenue to realize a natural asymmetric FTJ to improve its performance.

Automated summary

In this study, the electron transport properties of the LaNiO3/BaTiO3/LaNiO3 FTJ with a low concentration of OVs were investigated using NECPA-DFT, revealing that OVs play a critical role in determining the electron transport properties of an FTJ. The tunnel electroresistance ratio monotonously increases with the OVs concentration, reaching 5898% for a 9% OVs concentration.