The UD-3 photoluminescence spectrum was observed in highly-resistive or semi-insulating bulk 4H, 6H and 15R SiC. It consisted of one no-phonon line in 4H and 6H SiC and of 2 no-phonon lines in 15R SiC. The line positions were at 1.3555eV in 4H SiC, at 1.3440eV in 6H SiC and at 1.3474eV (UD-3L) and 1.3510eV (UD-3H) in 15R SiC. In photoluminescence excitation experiments, an additional set of 4 lines (UD-3I to UD-3IV) was observed in all 3 polytypes. The symmetries of the ground state and of the excited states involved in these transitions were deduced from Zeeman and polarization data. The no-phonon line was accompanied by a broad phonon-assisted side-band. In addition, 3 sharp transitions (UD-3a, UD-3b, UD-3c) and 3 broader features were observed. These were attributed to local phonons.

UD-3 Defect in 4H, 6H, and 15R SiC - Electronic Structure and Phonon Coupling. M.Wagner, B.Magnusson, W.M.Chen, E.Janzén: Physical Review B, 2002, 66[11], 115204 (9pp)