  The use of a foreign metallic cold source (CS) has recently been proposed as
a promising approach toward the steep-slope field-effect-transistor (FET). In
addition to the selection of source material with desired density of
states-energy relation (D(E)), engineering the source: channel interface for
gate-tunable channel-barrier is crucial to a CS-FET. However, conventional
metal: semiconductor (MS)-interfaces generally suffer from strong
Fermi-level-pinning due to the inevitable chemical disorder and defect-induced
gap states, precluding the gate-tunability of the barriers. By comprehensive
materials and device modeling at the atomic-scale, we report that the
two-dimensional (2D)-van der Waals (vdW)-MS-interfaces, with their atomic
sharpness and cleanness, can be considered as general ingredients for CS-FETs.
As test cases, InSe-based n-type FETs are studied. It is found that graphene
can be spontaneously p-type doped along with slightly opened bandgap around the
Dirac-point by interfacing with InSe, resulting in super-exponentially decaying
hot carrier density with increasing n-type channel-barrier. Moreover, the D(E)
relations suggest that 2D-transition-metal-dichalcogenides and
2D-transition-metal-carbides are rich libraries of CS materials. Both graphene
and H-TaTe2 CSs lead to subthreshold swing below 60 mV/decade. This work
broadens the application potentials of 2D-vdW-MS-heterostructures and serves as
a springboard for more studies on low-power electronics based on 2D materials.
