**Abstract**

The successful isolation of graphene in 2004 has attracted great interest to search for potential applications of this unique material and other newborn members of the two-dimensional (2-D) family in electronics, optoelectronics, spintronics and other fields. Compared to graphene, the 2-D transition metal dichalcogenides (TMDs) have the advantage of being semiconductors, which would allow their use for logic devices. In the past decade, significant developments have been made in this area, where opportunities and challenges co-exist. Stacking different 2-D materials significantly increases the already considerable design space, especially when a type-II band alignment is obtained. This chapter will describe the recent progresses in the tunnel field-effect transistors based on 2-D TMD van-der-Waals heterostructure, which is one of the promising candidates for increasingly important low-power mobile computation applications. Due to their small size, such devices are intrinsically dominated by quantum effects. This requires the adoption of a fairly general theory of transport, such as the nonequilibrium Green's functions (NEGF) formalism, which is a method having been more-and-more used for the simulation of electron transport in nanostructures in recent years.

**Keywords:** two-dimensional material, van-der-Waals heterostructure, tunnel field-effect transistor, steep-slope switch, subthreshold swing
