  Room-temperature Fermi-Dirac electron thermal excitation in conventional
three-dimensional (3D) or two-dimensional (2D) semiconductors generates hot
electrons with a relatively long thermal tail in energy distribution. These hot
electrons set a fundamental obstacle known as the "Boltzmann tyranny" that
limits the subthreshold swing (SS) and therefore the minimum power consumption
of 3D and 2D field-effect transistors (FETs). Here, we investigated a novel
graphene (Gr)-enabled cold electron injection where the Gr acts as the Dirac
source to provide the cold electrons with a localized electron density
distribution and a short thermal tail at room temperature. These cold electrons
correspond to an electronic cooling effect with the effective electron
temperature of ~145 K in the monolayer MoS2, which enable the transport factor
lowering and thus the steep-slope switching (across for 3 decades with a
minimum SS of 29 mV/decade at room temperature) for a monolayer MoS2 FET.
Especially, a record-high sub-60-mV/decade current density (over 1
{\mu}A/{\mu}m) can be achieved compared to conventional steep-slope
technologies such as tunneling FETs or negative capacitance FETs using 2D or 3D
channel materials. Our work demonstrates the great potential of 2D Dirac-source
cold electron transistor as an innovative steep-slope transistor concept, and
provides new opportunities for 2D materials toward future energy-efficient
nanoelectronics.
