Modulation of Energy Bandgap in Graphene Nanoribbons Using KWANT

Graphene, the wonder material, consists of a single-atom thick layer of SP²-hybridized carbon atoms arranged in a hexagonal honeycomb structure. It became popular mainly due to its ideally zero band gap and ultra high electron mobility. To make graphene more functional in the domain of device design, it is essential to create a certain amount of band gap, which can be realized by following different techniques like width modulation, chemical doping, field gating, etc. In this chapter, we adopt some existing techniques to study modulation of bandgap in two-dimensional and one-dimensional nanoribbon (GNRs) form with its arm chair and zigzag ribbon edges (known as AGNR and ZNRs). The band energy has been calculated numerically employing tight-binding model. Moreover, band gaps of GNRs are studied for different sets of ribbon width, and energy bands are obtained using an open-source python-based simulation tool “KWANT”. For AGNR, a decrease in width enhances the band gap, while for ZNR, it is pinned at zero, for all width configurations. The study also includes the behavior of the energy diagram of GNRs for different biasing voltages. Shifting of energy levels to higher and lower values with the application of positive and negative voltage is observed, by maintaining the same band gap.