DFT study on the electronic structure and optical properties of N, Al, and N-Al doped graphene

The electronic structures and optical properties of pure, N-doped, Al-doped, and N-Al co-doped graphenes were studied by the first-principle calculation. The pure graphene is a zero bandgap semiconductor. The energy gaps were opened after N, Al, and N-Al doping. The gap value of N-Al co-doped graphene is the largest, 0.47 eV, then Al-doped graphene, 0.40 eV, and N-doped graphene, 0.21 eV. For N-doped graphene, carbon atom loses electrons, nitrogen atom gains electrons, while carbon gains electrons, aluminum atom loses electrons for Al-doped graphene. For N-Al co-doped graphene, aluminum atom loses a bit more electrons (2.31 e) than that in Al-doped graphene (2.27 e), while nitrogen atom gains a lot more electrons (- 0.76 e) than that in N-doped graphene (- 0.27 e). After N, Al, N-Al doping, the absorption peaks of graphene become weak, especially low frequency peaks of N and Al doping. The absorption curve of N-Al doped graphene is similar with that of pure graphene. However, the absorption peak of low frequency for N-Al doped graphene shifts to low energy relative to pure graphene, showing that it is easier for the transitions between pi and pi*, and lead to the opened gap.