Fano-interference effect of Raman scattering in doped SiC

Low-frequency optical phonon modes in heavily doped n-type 4H- and 6H-SiC crystals interfere with broad electronic Raman bands to produce Fano-type asymmetric profiles. We have observed variations of their spectral line shape with the temperature and the carrier density in the range of n=10(18),10(19)cm(-3) in order to study the electronic excitation mechanisms. It is shown that in 4H-SiC single-particle excitations of free carriers give large contributions to the interference in contrast to 6H-SiC, in which excitations of bound electrons mainly take part in the interference. The Fano-profile parameters, i.e., the asymmetry parameter, the broadening and the frequency shift, have been deduced from the observed profiles in 4H-SiC, and their carrier-density dependence is shown.