The electronic structure and spectroscopic properties of 3C, 2H, 4H, 6H, 15R and 21R polymorphs of SiC

The electronic structure, bonding, and optical properties of six polymorphs of SiC: 3C, 2H, 4H, 6H, 15R, and 21R were studied by the density functional-based first-principles OLCAO method. The results were compared with other existing calculations as well as experimental data. It is shown that the different stacking sequences of the Si–C bi-layers in these polymorphs result in minute but recognizable differences in the partial density of states, Mulliken effective charges, and bond order values, indicating the importance of the intermediate range ordering in these crystals. The optical properties calculation for these polymorphs also shows some marked differences among them and can be explained, at least partially, by the LDA-based electronic band structures. Also presented is the calculated X-ray absorption near edge spectroscopy (XANES) of the Si-K, Si-L3 and N-K edges in 3C-SiC.