Gallium nitride on silicon carbide

From an optical viewpoint, on the other hand, the difference between semiconductors and insulators lies in the value of Eg. The admitted boundary is usually set at 3 eV (see Appendix A for the energy units) and materials with Eg below this value are categorized as semiconductors, but crystals considered as semiconductors like the wurtzite forms of silicon carbide and gallium nitride have band gaps larger than 3 eV, and this value is somewhat arbitrary. The translation into the electrical resistivity domain depends on the value of Eg, and also on the effective mass of the electrons and holes, and on their mobilities. The solution is not unique moreover, the boundary is not clearly defined. Semi-insulating silicon carbide 4H polytype samples with reported room temperature resistivities of the order of 1010flcm could constitute the... 

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