Properties of Silicon Carbide Polytypes under High Pressure Influence Calculated Using DFT

Theoretical molecular dynamic simulations based on plane-wave and pseudopotential density functional theory (DFT) calculations with CASTEP code were employed to explore the pressure influence on the properties of silicon carbide polytypes. The changes in lattice and electronic structures of 2H-, 4H-, and 6H-SiC polytypes at room temperature were investigated when pressures from 10 GPa to 200 GPa were applied. It’s found that the applied pressures didn’t cause a change in the hexagonal structure of the crystals, however the structural and electronic properties clearly affected by the compression. The dependences of volume reduction (V/Vo) and lattice parameters (a and c) on pressure were obtained successfully. The lattice parameters of the polytypes and c/a ratio showed a same trend under the compression with a clear similarity between 4H and 6H. The total energy-volume and enthalpy-pressure relations were estimated. The calculated energy gaps showed a reduction in the band gap width of 4H and 6H with the pressure increase while 2H band gap increased gradually with pressure. The tendency toward decreasing the density of state (DOS) at the conduction band edge was similar among the polytypes.