First-Principle Calculation Of SiC Polytype

As the representative of the third generation of semiconductor, SiC has been concerned proverbially because of its wide band-gap, high hardness and high conductivity. With the development of theoretical study and experimental technology, more researchers are interested in the field of the atomic and electronic structure of SiC by theoretical and experimental methods.In this paper, the first principles calculation technique based on the plane-wave pseudo-potential was employed to study the atomic and electronic structures and phonon density of states of the 3C-, 2H-, 4H-, 6H-SiC polytypes. The systematic calculations were performed using CASTEP code.We investigated systematically the crystal structure, electronic and mechanical properties of the 3C-, 2H-, 4H- and 6H-SiC by means of plane wave pseudopotential method with generation gradient approximation (GGA) and local density approximation (LDA) based on density function theory. The calculated parameters of equilibrium unit cells are excellently consistent with those of experimental values. Semiconducting character and gaps were observed both with the band structure and density of states of all the SiC polytypes. We got that 3C-SiC had direct band gap, and 2H-, 4H-and 6H-SiC had indirect band gap. The hardness values for the SiC polytypes were calculated according to the intrinsic hardness calculation theory of covalent crystal based on the Mulliken overlap population. And the results are consistent with the experimental values, which indicates that these phases are superhard materials.Furthermore, the phonon structures and phonon density of states of the 3C-, 2H-, 4H- and 6H-SiC were calculated by using the CASTEP program based on density function theory with local density approximation. With some related theories, we got the relationships between the thermodynamical functions of SiC in vacuum. And we derived the change of some thermodynamic properties , such as heat capacity and Debye temperature, following temperature increasing. Results show that the Debye temperature of those forms is from 1200 K to 1500 K.