In the work, the numerical simulations highlighted the advantages of GNM lattices for designing NDC devices with a high peak-to-valley ratio (PVR). The group proposed typical devices based on a pn junction and a uniform n-doped structure. In the former device, the peak current is controlled by the interband tunnelling between the conduction band of the n-side and the valence band of the p-side while the valley current is governed by the bandgap in both sides. It gives rise to a high PVR of NDC, but at the expense of a strong sensitivity to the length of the transition region between p-doped and n-doped zones. In the uniformly n-doped structure, the PVR is smaller because of the enhanced valley current controlled by a small minigap. However, the peak current resulting from normal transmission is higher and not significantly influenced by the transition length.

Remarkably, the team demonstrated that when pristine graphene is introduced in the transition region of the pn junction, the NDC effect is improved significantly. In such a GNM/pristine graphene/GNM heterostructure, due to the gapless character of pristine graphene, the evanescent states do not appear in the transition region, which makes the peak current high and weakly dependent on the transition length while the valley current controlled by the large bandgap in both junction sides is maintained at a low value. This results in a high PVR of a few hundred at room temperature, even for a large transition length.

This work demonstrates the high potential of GNM lattices to introduce all the benefits of bandgap engineering in graphene devices.

The team presented its work in the journal Nanotechnology.