Electric gating induced bandgaps and enhanced Seebeck effect in zigzag bilayer graphene ribbons

TL;DR

This paper theoretically shows that applying transverse and vertical electric fields to zigzag bilayer graphene ribbons can open and enlarge bandgaps, significantly enhance the Seebeck effect, and inform new device designs.

Contribution

It demonstrates that transverse electric fields are more effective than vertical fields in modulating bandgaps and conductance, and reveals a 13-fold enhancement of the Seebeck effect.

Findings

Bandgap opens with either electric field applied.

Simultaneous fields enlarge the bandgap.

Seebeck effect is enhanced by about 13 times.

Abstract

We theoretically investigate effect of a transverse electric field generated by side gates and a vertical electric field generated by top, back gates on energy bands and transport properties of zigzag bilayer graphene ribbons (Bernal stacking). Using atomistic Tight Binding calculations and Green function formalism we demonstrate that bandgap is opened when either field is applied and even enlarged under simultaneous influence of the two fields. Interestingly, although vertical electric fields are widely used to control bandgap in bilayer graphene, here we show that transverse fields exhibit more positive effect in terms of modulating a larger range of bandgap and retaining good electrical conductance. Seebeck effect is also demonstrated to be enhanced strongly about 13 times for a zigzag bilayer graphene ribbons with 16 chain lines. These results may motivate new designs of devices made of bilayer graphene ribbons using electric gates.