Investigation of the Switching Mechanism of Dirac Source Field-Effect Transistors by Atomistic Simulations

Dirac source field-effect transistors (DSFETs) are emerging as promising candidates for low-power applications. However, the switching mechanism of DSFETs from 2-D graphene to 1-D semiconductor is still controversial. In this work, DSFETs based on 2-D graphene–1-D graphene nanoribbon (GNR) heterojunctions are analyzed through atomistic quantum transport simulations. The local density of states (LDOS) and wave-vector-dependent transmission reveal that sub-60-mV/decade switching arises from the low-pass filtering effect of the Dirac source. Significant mode coupling at the graphene-GNR interface, induced by atomistic scattering, substantially suppresses mode-selective transport from 2-D graphene to 1-D GNR. Performance enhancements are explored, showing that extending the graphene source under the gate to form an optimized overlap region further improves subthreshold swing (SS). Furthermore, a gapped source enables an SS as low as 20 mV/decade for 15-nm DSFETs at the ballistic limit. Comparisons with conventional FETs and tunneling FETs highlight DSFETs’ advantages though scaling studies show SS degradation over 60 mV/decade for gate lengths smaller than 7.5 nm. Additionally, electron-phonon (e–p) scattering is found to rethermalize cold electrons, increasing SS to 45 mV/decade in DSFETs with a gapped graphene source. Suppressing optical phonon (OP) scattering is essential for a substantial enhancement in the performance of GNR-based DSFETs.