Gate- versus defect-induced voltage drop and negative differential resistance in vertical graphene heterostructures

To enable the computer-aided design of vertically stacked two-dimensional (2D) van der Waals (vdW) heterostructure devices, we here introduce a non-equilibrium first-principles simulation method based on the multi-space constrained-search density functional formalism. Applying it to graphene/few-layer hBN/graphene field-effect transistors, we show that the negative differential resistance (NDR) characteristics can be produced not only from the gating-induced mismatch between two graphene Dirac cones in energy-momentum space but from the bias-dependent energetic shift of defect levels. Specifically, for a carbon atom substituted for a nitrogen atom (C-N) within inner hBN layers, the increase of bias voltage is found to induce a self-consistent electron filling of in-gap C-N states, which in turn changes voltage drop profiles and produces symmetric NDR characteristics. With the C-N placed on outer hBN layers, however, the pinning of C-N states to nearby graphene significantly modifies device characteristics, demonstrating the critical impact of atomic details for 2D vdW devices.

Automated summary

In this study, a non-equilibrium first-principles simulation method based on the multi-space constrained-search density functional formalism is introduced for the computer-aided design of vertically stacked 2D van der Waals heterostructure devices. The research shows that the negative differential resistance (NDR) characteristics can be produced through the gating-induced mismatch between two graphene Dirac cones in energy-momentum space and the bias-dependent energetic shift of defect levels. Furthermore, the placement of carbon atoms substituted for nitrogen atoms on different layers of hBN significantly affects the device characteristics, emphasizing the importance of atomic details for 2D vdW devices.