First- and second-order Raman scattering from semi-insulating 4H-SiC

We have measured the first- and second-order Raman spectra from semi-insula ting 4H-SiC at room temperature under nonresonant excitation. The results a re compared with Raman spectra of n-type doped 4H- and 6H-SiC. The second-o rder spectra for both 4H- and 6H-SiC contain an acoustic branch and an opti cal branch, which is clearly dependent on SiC polytype. The measured two-ph onon spectra are assigned by comparison with theoretical calculations. [S01 63-1829(99)03211-7].