k ‐ and E ‐Dependence of Current Across a Ferroelectric Tunnel Junction at Room Temperature

Charge transport across a ferroelectric tunnel junction (FTJ) is affected by various parameters of the ferroelectric‐based tunnel barrier, metallic contacts, and temperature. At room temperature, the structure of the current density is analyzed as a function of the wavevector k and energy E . Due to the variation of the effective mass across the device, the charge transport may occur obliquely to the layers of the FTJ. It turns out that the current flows mainly perpendicular to the layers as long as the leading transport mechanism is direct tunneling. However, whenever the transport is affected by resonance states both at the Fermi energy or above that energy, the charge current flow mostly obliquely in a nontrivial way. The large effective mass in the barrier enhances the role of resonance states by positioning them lower in energy and thus becoming accessible through thermal activation. In terms of energy dependence, the structure of the current is an interplay between direct tunneling and thermionic emission, depending on the position of the Fermi energy with respect to the top of the barrier. Thus, usually for barrier heights around 0.5 eV, the current is of thermionic origin. Barriers higher than 1 eV support mainly direct tunneling.