New 5-6-6-5 (fourfold) and 5-9-6 defect Configurations in g-SiC (graphene-like hexagonal monolayer silicon carbide)

Computational studies using the density functional theory (DFT) were employed to analyze defect configurations in g-SiC. The SiC supercells containing 72 atoms were used for simulation. We simulate C-vacancy (VC) and Si-vacancy (VSi). We relaxed all atoms so that the atomic force tolerance is 1.0 × 10-4 Ha/Bohr. The unrelaxed defective configurations have the same symmetry as the perfect configuration, which is a D3h symmetry. During relaxation, atoms neighboring the vacancy were displaced to reach a ground state condition. In the case of VC, a Si atom at the center of the defect has four bonds, resulting in a new 5-6-6-5 fourfold configuration with a C2v symmetry. In the case of VSi, a C atom forms bonds with two other C atoms, resulting in a new configuration, namely a 5-9-6 configuration. We identified that this configuration also has a C2v symmetry. Thus, symmetry breaking (lowering) occurs from D3h to C2v. We calculated the formation energy, which is 3.28 eV for the 5-6-6-5 fourfold and 3.92 eV for the 5-9-6 configuration. We also calculated the Density of States (DOS), and the results show that both configurations have semiconductor material properties suitable for promising optoelectronic devices with an infrared spectrum for future applications.