Resonant band engineering of ferroelectric tunnel junctions
Jing Su, Xingwen Zheng, Zheng Wen, Tao Li, Shijie Xie, Karin M. Rabe, Xiaohui Liu, Evgeny Y. Tsymbal
Abstract
We propose energy band engineering to enhance tunneling electroresistance (TER) in ferroelectric tunnel junctions (FTJs). We predict that an ultrathin dielectric layer with a smaller band gap, embedded into a ferroelectric barrier layer, acts as a switch controlling high- and low-conductance states of an FTJ depending on polarization orientation. Using first-principles modeling based on density functional theory, we investigate this phenomenon for a prototypical $\mathrm{SrRu}{\mathrm{O}}_{3}\text{/}\mathrm{BaTi}{\mathrm{O}}_{3}\text{/}\mathrm{SrRu}{\mathrm{O}}_{3}$ FTJ with a $\mathrm{BaSn}{\mathrm{O}}_{3}$ monolayer embedded in the $\mathrm{BaTi}{\mathrm{O}}_{3}$ barrier. We show that in such a composite-barrier FTJ, ferroelectric polarization of $\mathrm{BaTi}{\mathrm{O}}_{3}$ shifts the conduction-band minimum of the $\mathrm{BaSn}{\mathrm{O}}_{3}$ monolayer above or below the Fermi energy depending on polarization orientation. The resulting switching between direct and resonant tunneling leads to a TER effect with a giant ON/OFF conductance ratio. The proposed resonant band engineering of FTJs can serve as a viable tool to enhance their performance, useful for device applications.