Theoretical studies on the structures and properties of doped graphenes with and without an external electrical field

To expand the applications of graphene in optoelectronic devices, B, Al, Si, Ge, As, and Sb doped graphenes (marked as B-G, Al-G, Si-G, Ge-G, As-G, and Sb-G, respectively) were synthesised. The geometric structures, population analyses, and also electronic and optical properties of these doped graphene materials were investigated employing the density functional theory (DFT) method. It was shown that the band gaps of doped graphenes were opened and their absorption spectra were red-shifted by the addition of doping atoms, and their dielectric functions and refractive indexes of low frequency were decreased compared with those of pure graphene. Moreover, the electronic and optical properties of doped graphenes under an external electrical field ranging from -0.4 to 1.2 eV Å^-1 have been explored. It was found that the band gaps of As-G and Sb-G were increased to 0.864 and 1.841 eV under a 1.2 eV Å^-1 external electrical field, respectively. On the contrary, the band gaps of B-G, Al-G, Si-G, and Ge-G were decreased with the increase of the external electrical field intensity. Additionally, the absorption peaks of B-G, Al-G, Si-G, and Ge-G were red-shifted upon applying the external electrical field. Correspondingly, their dielectric functions and refractive indexes of low frequency were increased. Surprisingly, the absorption spectra, dielectric functions, and refractive indexes of As-G and Sb-G have no significant changes.