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

Abstract

Electronic Raman scattering from nitrogen defect levels in SiC is seen to be significantly enhanced with excitation by red (633 nm, 1.98 eV) or near-IR (785 nm, 1.58 eV) laser light at room temperature. Four nitrogen peaks are 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 concentration. Raman spectra taken at low temperature in 6H–SiC reveal differences between wafers and Lely grown platelets by the appearance of several additional peaks. The origin of the resonant enhancement is the near-IR absorption band associated with the green color characteristic of n-type SiC. These results demonstrate that the laser wavelength is a key parameter in the characterization of SiC by Raman scattering.