We present a computational study of the device performance of graphene nanoribbon tunneling field-effect transistors (TFETs) with a heterogeneous channel. By varying the length and the energy bandgap (EG) of the heterogeneous region, the ON- and OFF-state currents (ION and IOFF) can be effectively optimized independently. Both semiconducting and semimetallic heterogeneous regions are studied to understand the effects of EG engineering on device behaviors. In addition, the effect of gate coverage (GC) over the heterogeneous region is also investigated. We found that device performance is greatly affected by the positioning of the gate to modify the region where band-to-band tunneling occurs. For a given ION/IOFF of eight orders, our results show that, for the semiconducting heterojunction, a higher ION can be obtained by having the gate partially covering the heterogeneous region. This is due to a combination of a short tunneling length and resonant states, which leads to an increase in carrier concentration for the tunneling mechanism. On the other hand, for the semimetallic case, a similar ION/IOFF is only attainable when the heterogeneous region is not covered by the gate. A large IOFF is observed for even small GC due to the valence electrons from the source traveling to the conduction bands of the semimetallic region, enhancing the carrier transport toward the drain. Our study highlights the device design consideration required when optimizing the device performance of heterojunction TFETs.
