Simulation of a Steep-Slope p- and n-Type HfS₂/MoTe₂ Field-Effect Transistor with the Hybrid Transport Mechanism

The use of a two-dimensional (2D) van der Waals (vdW) metal-semiconductor (MS) heterojunction as an efficient cold source (CS) has recently been proposed as a promising approach in the development of steep-slope field-effect transistors (FETs). In addition to the selection of source materials with linearly decreasing density-of-states-energy relations (D(E)s), in this study, we further verified, by means of a computer simulation, that a 2D semiconductor-semiconductor combination could also be used as an efficient CS. As a test case, a HfS2/MoTe2 FET was studied. It was found that MoTe2 can be spontaneously p-type-doped by interfacing with n-doped HfS2, resulting in a truncated decaying hot-carrier density with an increasing p-type channel barrier. Compared to the conventional MoTe2 FET, the subthreshold swing (SS) of the HfS2/MoTe2 FET can be significantly reduced to below 60 mV/decade, and the on-state current can be greatly enhanced by more than two orders of magnitude. It was found that there exists a hybrid transport mechanism involving the cold injection and the tunneling effect in such a p- and n-type HfS2/MoTe2 FET, which provides a new design insight into future low-power and high-performance 2D electronics from a physical point of view