Transport in vertically stacked hetero-structures from 2D materials

TL;DR

This paper investigates the transport properties of a MoS2-WTe2 hetero-structure TFET using atomistic quantum transport simulations, revealing energy filtering as the switching mechanism and demonstrating high on-current potential for low-power applications.

Contribution

It introduces a novel atomistic simulation approach for MoS2-WTe2 hetero-structure TFETs and demonstrates their promising high on-current capabilities.

Findings

Energy filtering is the switching mechanism.

Extension region length is critical for device turn-off.

Achieves a large on-current of 1000 μA/μm at 0.3V.

Abstract

In this work, the transport of tunnel field-effect transistor (TFET) based on vertically stacked hereto-structures from 2D transition metal dichalcogenide (TMD) materials is investigated by atomistic quantum transport simulations. WTe2-MoS2 combination was chosen due to the formation of a broken gap hetero-junction which is desirable for TFETs. There are two assumptions behind the MoS2-WTe2 hetero-junction tight binding (TB) model: 1) lattice registry. 2) The $S-Te$ parameters being the average of the $S-S$ and $Te-Te$ parameters of bilayer MoS2 and WTe2. The computed TB bandstructure of the hetero-junction agrees well with the bandstructure obtained from density functional theory (DFT) in the energy range of interest for transport. NEGF (Non-Equilibrium Green$'$s Function) equations within the tight binding description is then utilized for device transfer characteristic calculation. Results show 1) energy filtering is the switching mechanism; 2) the length of the extension region is critical for device to turn off; 3) MoS2-WTe2 interlayer TFET can achieve a large on-current of $1000 \mu A/\mu m$ with $V_{DD} = 0.3V$, which suggests interlayer TFET can solve the low ON current problem of TFETs and can be a promising candidate for low power applications.