Electronic structure of graphene nanoribbons under external electric field by density functional tight binding

Abstract

<sec> In recent years, the rapid development of electronic information technology has brought tremendous convenience to people’s lives, and the devices used have become increasingly miniaturized. However, due to the constraints of the process and the material itself, as the size of the devices made of silicon materials is further reduced, obvious short channel effects and dielectric tunneling effects will appear, which will affect the normal operations of these devices. In order to overcome this development bottleneck, it is urgent to find new materials for the devices that can replace silicon. Carbon has the same outer valence electron structure as silicon. Since 2004, Geim [Novoselov K S, Geim A K, Morozov S V, et al. 2005 <i>Nature</i> <b>438</b> 197] prepared two-dimensional graphene with a honeycomb-like planar structure formed by sp<sup>2</sup> hybridization, graphene has received extensive attention from researchers and industrial circles for its excellent electronic and mechanical properties. However, graphene is not a true semiconductor, and it has no band gap in its natural state. The energy gap can be opened by preparing graphene nanoribbons. On this basis, the electronic structure of the nanoribbons can be further controlled by using an external electric field to destroy the symmetric structure of the nanoribbons. </sec><sec>In this paper, the tight-binding method based on density functional theory is used to calculate and study the influence of external transverse electric field on the electronic structure and electron population of un-hydrogenated/hydrogenated armchair graphene nanoribbons. The calculation results show that whether there is hydrogen on the edge of the graphene nanoribbons or not, the energy gap changed at the Г point shows a three-group periodic oscillation decreasing law, and as N increases, the energy gap will disappear. Under the external electric field, the band structure and the density of states of the nanoribbons will change greatly. For un-hydrogenated nanoribbons with semiconducting properties, as the intensity of the external electric field increases, a semiconductor-metal transition occurs. At the same time, the electric field will also have a significant influence on the energy level distribution, resulting in significant changes in the peak height and peak position of the density of states. The external electric field causes the electron population distribution on the atoms in the nanoribbons to break its symmetry. The greater the electric field strength, the more obvious the population asymmetry is. The edge hydrogenation passivation can significantly change the population distribution of atoms in nanoribbons.</sec>