Polarized Edge Emission of SiC

The photoluminescence of some relatively pure hexagonal SiC crystals (polytype $6H$) includes a strongly polarized edge emission. Two distinct patterns of edge emission lines have been found, but never in the same crystal. In either type, the edge emission includes several narrow lines (half-width ~kT/4 at 77^∘{}K) and a number of wider bands spaced at regular energy intervals of 0.03 ev, suggestive of a vibrational interaction. Some lines, found in the 77^∘{}K edge emission spectrum, vanish at 4^∘{}K. Mechanisms for producing polarized light are discussed, and it is concluded that the most probable luminescence centers are donor-acceptor pairs. The two types of spectra may be attributed to two different pairs. Intrinsic recombination radiation was looked for but not found.