Microscopic Description of the Mechanism of Transition between the 2H and 4H Polytypes of Silicon Carbide

The mechanism of displacement of one close-packed SiC layer from one minimum position to another on the example of SiC polytype transition 2H → 4H has been studied by ab initio methods. It has been shown that the intermediate state with monoclinic symmetry Cm greatly facilitates this displacement breaking it into two stages. Initially, the Si atom chiefly moves, only then—mainly the C atom. In this case, the Si–C bond is significantly tilted in comparison with the initial position, which allows the reducing of the compression of the SiC bonds in the ( $$11\bar {2}0$$ ) plane. Two transition states of this process, which also possess the Cm symmetry, have been computed. It has been found that the height of the activation barrier of the process of moving the close-packed layer of SiC from one position to another is equal to 1.8 eV. The energy profile of this movement has been calculated.