Influence of annealing on optical properties and photoluminescence of 6H-SiC crystal

Using the double beam spectrophotometer, transmission and reflection spectra of 6H-SiC crystal were analyzed before and after high temperature annealing. It is found that both kinds of the SiC crystals in the ultraviolet region existed a strong absorption, whereas in the visible and near infrared region, the non-doped SiC sample had a high transmittance. After annealing, the transmittance of two samples improved significantly. Fluorescence spectrophotometer analysis, excited at the 390 nm line of a Xe lamp, showed that a blue double-peak(417 and 436 nm) photoluminescence was presented in both samples. The 417 nm emission was due to C cluster and the 436 nm emission was attributed to the radiation of carrier recombination. These carriers were excited from the core of the SiC crystal particles to the photoluminescent centers of the surface of the SiC crystal particles. Furthermore, nitrogen-doped SiC showed a peak at 575 nm, which was the light-emitting of amorphous SiC caused by nitrogen doping. Another PL peak at 525 nm may occur under the 325 nm line excitation of the Xe lamp, whose light-emitting mechanism remains to be further studied.