  \ce{MoS_2} is a two dimensional material with a band gap depending on the
number of layers and tunable by an external electric field. The experimentally
observed intralayer band-to-band tunneling and interlayer band-to-band
tunneling in this material present an opportunity for new electronic
applications in tunnel field effect transistors. However, such a widely
accepted concept has never been supported up by theoretical investigations
based on first principles. In this work, using density functional theory, in
conjunction with non-equilibrilibrium Green's function techniques and our
electric field gating method, enabled by a large-scale computational approach,
we study the relation between band alignment and transmission in planar and
side-stack \ce{MoS_2} $p$-$i$-$n$ junction configurations. We demonstrate the
presence of negative differential resistance for both in-plane and interlayer
current, a staple characteristic of tunnel diode junctions, and analyze the
physical origin of such an effect. Electrostatic potentials, the van der Waals
barrier, and complex band analysis are also examined for a thorough
understanding of Esaki Diodes.
