Program

O.8 -- Oral, NCTP-41

Date: Monday, 1 August 2016

Time: 15h00 - 15h20

Modulation of bandgap in armchair bilayer graphene ribbons: a comparison between vertical and transverse fields

Vu Thanh Tra (1), Nguyen Thi Kim Quyen (2) , Tran Van Truong (3)

(1) Department of Physics, School of Education, Can Tho University, Can Tho, Vietnam (2) School of Graduate, College of Natural Sciences, Can Tho University, Can Tho, Vietnam. (3) IEF, Université Paris-sud, CNRS, UMR 8622, Bât 220, 91405 Orsay, France.

The electronic bandgap is an intrinsic property of semiconductors and insulators that largely determines their electrical and optical properties. As such, it has a central role in modern device physics and technology, and governs the operation of semiconductor devices such as p–n junctions, transistors, photodiodes and lasers. A tunable bandgap would be highly desirable because it would allow greater flexibility in design and optimization of such devices, in particular, if it could be tuned by applying variable external electric fields. Here we theoretically investigate the effects 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 armchair bilayer graphene ribbons (Bernal stacking). Using atomistic Tight Binding calculations and Green’s function formalism, we demonstrate that bandgap is opened when either field is applied and even enlarged under simultaneous influences of the two fields. The results also illustrated that armchair bilayer graphene ribbons always exhibits three classes such as 3p, 3p+1, 3p+2 in which the gap decreases as the ribbon width increases and eventually approaches metallicity like an infinite Graphene. Interestingly, although vertical electric fields are widely used to control band gap in bilayer graphene, here we also show that vertical fields exhibit more positive effects in terms of modulating a larger band gap and these results are totally different from the ones we obtained for zigzag bilayer graphene ribbons. These results may motivate new device designs made of bilayer graphene ribbons using electric gates. Combined with the remarkable electrical transport properties of such systems, this electrostatic bandgap control suggests novel nanoelectronic and nanophotonic device applications based on graphene. This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.01-2015.98

Presenter: Vu Thanh Tra