First-principles study of electronic, magnetic and optical properties of N doping topological insulator Bi2Se3

In this paper, the manipulative effect of N doping on topological insulator Bi 2Se3 was investigated by using density functional theory (DFT). The computational results reveal that the van der Waals (vdW) correction is necessary when calculating the geometric structure of Bi2Se3. Taking into account the spin–orbit coupling(SOC), the electronic structure of Bi2Se3 can be accurately described, especially for the energy bands near the Fermi level. The N doping at anion sites can produce an impurity band which appeared at Fermi energy. Comparing with pure Bi2Se3, the electronic structure of N doping Bi2Se3 changed obviously at Fermi energy. The valence band and conduction band meet when N doped on Se1 sites, the insulating properties of Bi2Se3 system are damaged. The indirect gaps between the valence band and conduction band are 0.135 eV and 0.115 eV with N doping on Se2 sites with the doping levels 6.67% and 1.67%, respectively. On the other hand, the N doping at Se sites of Bi2Se3 can induce magnetic moments. The magnetic moments are related to the covalent bond length between N atom and Bi atom. Furthermore, the real and imaginary parts of dielectric functions have been computed. The static dielectric constant ε1(0) becomes significantly larger and the peaks in the imaginary part of dielectric constant ε2 (ω) spectra move toward low energy. The intensity of the peak is gradually enhanced and there is a small bump in Bi6Se8N2 at 0.38 eV. The N doping paves a prospective way to tune the topological properties and may find change to potential spintronic applications and electronic devices.