  The availability of transistors capable of operating at low supply voltage is
essential to improve the key performance metric of computing circuits, i.e.,
the number of operations per unit energy. In this paper, we propose a new
device concept for energy-efficient, steep-slope transistors based on
heterojunctions of 2D materials. We show that by injecting electrons from an
isolated and weakly dispersive band into a strongly dispersive one,
subthermionic subthreshold swings can be obtained, as a result of a cold-source
effect and of a reduced thermalization of carriers. This mechanism is
implemented by integrating in a MOSFET architecture two different monolayer
materials coupled through a van der Waals heterojunction, combining the
subthermionic behavior of tunnel field-effect transistors (FETs) with the
robustness of a MOSFET architecture against performance-degrading factors, such
as traps, band tails and roughness. A further advantage with respect to tunnel
FETs is that only an n-type or p-type doping is required to fabricate the
device. In order to demonstrate the device concept and to discuss the
underlying physics and the design options, we study through abinitio and
full-quantum transport simulations a possible implementation that exploits two
recently reported 2D materials.
