Layer-dependent band to band tunneling in WSe 2 -ReS 2 van der Waals heterojunction

Van der Waals (vdW) heterostructure is promising for building tunneling Field-effect transistor (TFET) owing to an inherent narrow vdW gap between two stacked materials induced by the dangling bond free surface. However, the band to band tunneling (BTBT) of such vdW heterostructure TFET strongly depends on the layer-dependent band structure variation at the interface. Here, we report a first principle simulation on the BTBT transition of the monolayer ReS2 based heterostructures with monolayer and bilayer WSe2. An obvious decrease of the turn-on gate voltage from 36V to 12V was achieved by adding a layer of WSe2 due to the band gap narrowing and momentum conservative Γ-Γ tunneling. Under the gate voltage of 20 V with bias of 0.27 V, the upper limit of BTBT saturate current density in bilayer WSe2 vdW heterojunction can reach 990 μA/μm. These results show the bilayer WSe2 heterojunction could be ideal candidate for lower power and high operating speed TFET