First-principle analysis of photoelectric properties of silicon-carbon materials with graphene-like honeycomb structure

This study uses the first-principle pseudo-potential method based on density functional theory to investigate the structure stability, geometrical structure, electronic structure, deformation charge density, atomic orbital and bond population, and optical properties of graphene-like structures SixC1−x (x = 0.02, 0.08, 0.2, 0.4, 0.5). Geometrical structure results show that the substituted Si atoms induce the structural deformation along the directions on the graphene plane without any buckling. The cohesion energy calculation indicates that these substituted systems are absolutely stable. The pure graphene forms a zero-band gap semiconductor, and the densities of states near the Fermi energy are composed mainly of C-2p. With Si doping, a direct band gap appears at the K point in the Brillouin zone. The band gap increases from 0.15 eV to 2.60 eV with the increase in Si content. The densities of states of Si0.50C0.50 near the Fermi energy are composed mainly of C-2p and Si-3p. After substituting Si atoms for C atoms, charges transfer from Si atoms to C atoms, the covalent bond of CC weakens, and the symmetry of the covalent bond of graphene is destroyed, which is very important for the appearance of direct band gap at the K point. All curves of optical properties of SixC1−x (x = 0.02, 0.08, 0.2, 0.4, 0.5) move to the high energy with the increase in Si content. Among those of all the studied SixC1−x systems, Si0.50C0.50 obtains the lowest static dielectric constant of 1.60, the lowest refractive index of 1.26, the highest absorption coefficient of 6.79 × 104 cm−1. The results will give a guide for design and application of the single layer SiC in further experimental and the theoretical investigations.