Hexagonal Silicon Carbide (2H-, 4H-, and 6H-SiC)

Abstract

Of all the poly types, 6H is by far the most commonly occurring modification in commercial SiC. The next most common polytypes are 15R and 4H, respectively. SiC also crystallizes in the wurtzite structure (2H-SiC). Assuming that the 3C and 2H structures are extremes in the parameter describing the percentage of hexagonal close packing (often called hexagonality) with 0 and 100%, respectively, we get the hexagonal nature of 33% for 6H structure, 40% for 15R structure, and 50% for 4H structure. The hexagonal and rhombohedral polytypes have a sixhold symmetry axis along the stacking direction (c axis), and thus these crystals present an anisotropic (uniaxial) behavior of phySiCal properties.