Resonance enhancement of electronic Raman scattering from nitrogen defect levels in silicon carbide

Electronic Raman scattering from nitrogen defect levels in SiC is seen to b e significantly enhanced with excitation by red (633 nm, 1.98 eV) or near-I R (785 nm, 1.58 eV) laser light at room temperature. Four nitrogen peaks ar e observed in 6H-SiC (380, 430, 510, and 638 cm(-1)) and three peaks in 4H- SiC (about 400, 530, and 570 cm(-1)). The peaks in the 4H-SiC spectrum are seen to shift to lower frequency with increasing nominal doping concentrati on. Raman spectra taken at low temperature in 6H-SiC reveal differences bet ween wafers and Lely grown platelets by the appearance of several additiona l peaks. The origin of the resonant enhancement is the near-IR absorption b and associated with the green color characteristic of n-type SiC. These res ults demonstrate that the laser wavelength is a key parameter in the charac terization of SiC by Raman scattering. (C) 1999 American Institute of Physi cs. [S0021-8979(99)03016-9].