Photoelectric Properties of La, Ce, Th Doped 2D SiC: A First Principle Study

The geometrical structure, energy band structure, density of states and optical properties of La, Ce and Th doped two-dimensional (2D) SiC are investigated by using the first-principle method. Geometrical structure results show that all of the doping atoms cause obvious distortion of the crystal lattice near the doping atoms, and the degree of distortion is related to the covalent radius of different doping atoms. The pure 2D SiC is a direct-gap semiconductor with a gap of 2.60 eV. Near the Fermi energy, the density of states is mainly composed of C-2p and Si-3p. When doping with La, Ce and Th, the band gap of 2D SiC decreased and all of them turn into quasi-direct band-gap semiconductors. The valence band of La and Th doped 2D SiC are mainly composed of C-2p, Si-3p, La-5d and Th-6d, respectively, while Ce-doped has little effect on the valence band of 2D SiC. The conduction band of La, Ce and Th doped 2D SiC are mainly composed of Si-3p, La-5d, Ce-4f and Th-6s6d5f, respectively. When Si atom is replaced by rare earth atom, the rare earth atoms lose their charges. The bond of rare earth atom and C atom has weak covalent, while ionic is stronger. Among all of the studied systems, La-doped 2D SiC has the biggest static dielectric constant 2.33, the biggest peak of ε2(ω) in the low energy region, the maximum refractive index n0 1.53. Ce-doped 2D SiC has the maximum absorption 6.88 × 104 cm-1 in the lower energy region. La or Ce doped 2D SiC can enhance the absorption in the lower energy region, while Th-doped will decrease the absorption of 2D SiC in the range of 0 ~ 15 eV. The research results will provide some theoretical guidance for the development and application of 2D SiC.