The optical absorption of 4H-,6H-and 15R-SiC single crystals has been measured at room temperature. The band gaps were calculated,and the reasons for band gap shrinking were discussed. Influence of free carrier concentration was considered. The first-and second-order Raman spectra of 4H-,6H- and 15R-SiC samples were analyzed. Raman spectra of disorder structure in 6H-SiC grown by Lely method were given and simulated. The low wave-number Raman spectrum is a reliable method to distinguish the SiC polytypes. We analyzed the similarity of the second-order Raman spectra of all polytypes.
