N/B掺杂石墨烯的光学与电学性质

Optical and electronic properties of N/B doped graphene

石墨烯因其独特的化学成键结构而拥有出色的化学、热学、机械、电学、光学特性.由于石墨烯为零带隙材料,限制了其在纳电子学领域的发展.因此,为了拓宽石墨烯的应用范围,研究打开石墨烯带隙的方法显得尤为重要.本文构建了本征石墨烯、N掺杂石墨烯、B掺杂石墨烯三种模型,研究了本征石墨烯和不同掺杂浓度下的N/B掺杂石墨烯的能带结构、电子态密度及光学与电学性质,包括吸收谱、反射谱、折射率、电导率和介电函数等.研究结果显示:1)本征石墨烯费米能级附近的电子态主要是由C-2p轨道形成,而N/B掺杂石墨烯费米能级附近的电子态主要是由C-2p和N-2p/B-2p轨道杂化形成;2)N/B掺杂可以引起石墨烯费米能级、光学与电学性质的改变,且使狄拉克锥消失,进而打开石墨烯带隙;3)N/B掺杂可以引起石墨烯光学和电学性质的变化,且对吸收谱、反射谱、折射率、介电函数影响较大,而对电导率影响较小.本文的结论可为石墨烯在光电子器件中的应用提供理论依据.

Since its discovery in 2004,the graphene has attracted great attention because of its unique chemical bonding structure,which has excellent chemical,thermal,mechanical,electrical and optical properties.Due to the graphene being a zero band gap material,it has a limited development in the field of nano electronics.Therefore,in order to broaden its application scope,it is very important to carry out a study on opening the band gap of graphene.In this paper,we construct three models,i.e.,the intrinsic graphene model,the N-doped graphene model,and the B-doped graphene model.We study the energy band structures and the electronic densities of states for the intrinsic graphene and the N/B doped graphenes with different doping concentrations.Furthermore,we study their optical and electronic properties including the absorption spectra,the reflection spectra,the refractive indexes,the conductivities,and the dielectric functions.The results are as follows.1） The electronic states in the vicinity of the Fermi level for the intrinsic graphene are mainly generated by the C-2p orbits,while the electronic states in the vicinity of the Fermi level for the N/B doped graphenes are mainly generated through the hybridization between C-2p and N-2p/B-2p orbits.N doped graphene is of n-type doping,while B doped graphene is of p-type doping.2） Compared with that of the intrinsic graphene,the Fermi level of N doped graphene moves up 5 e V.In the meantime,the band gap is opened,and the Dirac cone disappears.On the contrary,the Fermi level of B doped graphene moves down 3 e V compared with that of the intrinsic graphene.However,like the N doping,the band gap is also opened,and the Dirac cone disappears.Furthermore,the N doping is more effective than the B doping in opening the energy gap of the graphene for the same N/B doping concentration.3） The N/B doping can cause the optical and electronic properties of the graphene to change,and exert great influences on the absorption spectrum,reflection spectrum,the refractive index,and the dielectric function,however it has little influence on the conductivity.When the energy of the incident wave is larger than a certain value,the optical and electrical properties of the intrinsic graphene remain unchanged.Besides,for the above case,the corresponding energies for the N/B doped graphenes are smaller than that for the intrinsic graphene.In addition,the energy for the B doped graphene is smallest.The conclusions of this paper can provide a theoretical basis for the application of graphene in optoelectronic devices.