Modulation of bandgap in bilayer armchair graphene ribbons by tuning vertical and transverse electric fields

TL;DR

This study explores how vertical and transverse electric fields influence the electronic properties of bilayer armchair graphene nano-ribbons, revealing field-specific effects on bandgap modulation with potential applications in nano-electronic devices.

Contribution

It provides new insights into the differential impact of electric fields on bilayer armchair graphene nano-ribbons, highlighting anomalous bandgap enlargement under vertical bias.

Findings

Vertical fields open larger bandgaps in semi-metallic structures.

Vertical fields can enlarge bandgap in semiconducting structures.

Combined electric fields can rapidly reduce the bandgap.

Abstract

We investigate the effects of external electric fields on the electronic properties of bilayer armchair graphene nano-ribbons. Using atomistic simulations with Tight Binding calculations and the Non-equilibrium Green function formalism, we demonstrate that (i) in semi-metallic structures, vertical fields impact more effectively than transverse fields in terms of opening larger bandgap, showing a contrary phenomenon compared to that demonstrated in previous studies in bilayer zigzag graphene nano-ribbons; (ii) in some semiconducting structures, if transverse fields just show usual effects as in single layer armchair graphene nano-ribbons where the bandgap is suppressed when varying the applied potential, vertical fields exhibit an anomalous phenomenon that the bandgap can be enlarged, i.e., for a structure of width of 16 dimer lines, the bandgap increases from 0.255 eV to the maximum value of 0.40 eV when a vertical bias equates 0.96 V applied. Although the combined effect of two fields does not enlarge the bandgap as found in bilayer zigzag graphene nano-ribbons, it shows that the mutual effect can be useful to reduce faster the bandgap in semiconducting bilayer armchair graphene nano-ribbons. These results are important to fully understand the effects of electric fields on bilayer graphene nano-ribbons (AB stacking) and also suggest appropriate uses of electric gates with different edge orientations.