SiC a case study in stacking faults

Silicon carbide is an important wide-energy-gap semiconductor used for high power switching devices and as a substrate for some optical devices. It is stable, easily created and the elements from which it is formed are inexpensive and common. 

The various structures are stable enough to be possible to create individually but are not separate phases. Therefore, a separate name was needed to describe them. The different faulted structures are known as polytypes. The stacking fault energy in SiC is low, which allows the mixture of stacking sequences present in the various 

The differences in lattice plane stacking have a direct effect on the electronic properties of SiC. For example, the energy gaps for the various polytypes are 3.33, 3.26, 3.02, and 2.39 eV for the 2H, 4H, 6H, and 3C respectively. [14] All four polytypes are indirect gap materials with a corresponding direct gap in excess of 4 eV. 

The changes in electronic structure of the various SiC polytypes have a corresponding effect on the electron and hole efieetive masses. Typical values are, for example, 1.1 mo in the 3C poly type and 1.75 mo and 0.66 mo in the 4H structure. The two latter values are for conduction in and perpendicular to the basal plane of the hexagonal strueture, respectively. [Egilsson et al. in Reference 15] The values for the 6H structure are similar to those of the 4H strueture but somewhat lower. Note that the effective mass in the 3C structure is roughly intermediate between the values 

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