In this work, we present a first-principles study of quantum transport in tunnel FETs based on van der Waals (vdW) heterostructures of transition metal dichalcogenides (TMDs). We focus on 1T-HfSe2 and 1T-SnS2 monolayers to construct a vertical heterostructure with a type-II band alignment. By including dissipative effects due to the electron-phonon interaction, we show that vdW tunnel FETs are highly sensible to the phonon coupling due to polar optical phonons present in TMDs which results in an increased sub-threshold swing (SS) and reduced ON-current. However, vdW TFETs are still able to provide high ON-current values due to the inversion of CB and VB at high V-GS and high inter-valley tunneling.
