Using the nonequilibrium Green's function method combined with density functional theory, we systematically study the ferroelectric, interfacial, oxidative, and doping effects on electron transport of BaTiO${}_3$-based ferroelectric tunnel junctions (Pt/BaTiO${}_3$/Pt). The ferroelectric effect reduces the tunneling conductance compared to nonferroelectric BaTiO${}_3$ due to the large decay rate of the $\Delta$5 ($p_y$ and $d_{yz}$) band. The TiO${}_2$-terminated interface shows a better tunneling conductance than the BaO-terminated interface since electrons mainly transport through the Ti${}_{3d}$-O${}_p$ bonding state. Interfacial oxidation strongly reduces the conductance due to trapping of electrons and interfacial charge localization by additional O ions, while Nb doping enhances the conductance due to the delocalized distribution of charges on orbitals of the transport channel. Our studies provide a useful guide to practical applications of tunnel junctions with ferroelectric barriers.

• Received 1 November 2011

DOI:https://doi.org/10.1103/PhysRevB.85.064105