ABSTRACT
Silicon carbide (SiC) is the oldest semiconductor known as a luminescence material. This material shows polytypism arising from different stacking possibilities. In hexagonal close packing of the Si-C pair, the positions of the pair in the first and second layers are uniquely determined. In SiC crystals, there can exist various combinations of these two structures, which give different stacking orders called polytypes. Among the many polytypes, 3C-, 6H-, and 4H-SiC appear frequently. The spectra contain shoulder features related to phonon-assisted transitions, which are characteristics of indirect band structures. Since SiC has an indirect band structure, strong luminescence can be expected from the recombination of either bound excitons or donor-acceptor pairs. In SiC, N atoms belonging to the fifth column of the periodic table work as donors, and B, Al, and Ga in the third column work as acceptors.
