Photoluminescence of Radiation Defects in Ion-Implanted $6H$ SiC

Radiation defects were introduced into $6H$ SiC by ion implantation and by electron bombardment. The defects produce a new low-temperature luminescence that is independent of the implanted ion, and one portion, the $D_1$ spectrum, persists after a 1700°C anneal. A comparison of the $D_1$ spectrum in ion- and electron-bombarded samples shows that its intensity is strongly dependent on defect concentration, suggesting that the luminescence center is a pure-defect complex, possibly a divacancy. The $D_1$ spectrum, which was previously observed in cubic SiC, has a strong vibronic structure with localized and resonant modes. In $6H$ SiC it is repeated three times, due to the three inequivalent sites in this polytype. $D_1$ has an unusual temperature dependence, the low-temperature (1.4°K) spectrum being extinguished as the high-temperature (77°K) form is activated. The abrupt change of spectrum is attributed to a lattice distortion at the low temperature. The changes in luminescence on annealing are correlated with changes in electrical properties observed in ion-implanted samples by Marsh and Dunlap.