Determination of free carrier density in the low doping regime of 4H-SiC by Raman scattering

The free carrier concentration of n-4H-SiC was deduced by Raman spectroscopy using LO phonon plasmon coupled (LOPC) modes as a monitor band. We could determine the free carrier concentration from the reading of the peak frequency of the LOPC mode in the concentration range from 1019 down to 1016cm−3. The damping of LO phonons was evaluated as a function of the carrier concentration. Line shape analysis of the LOPC mode revealed that the damping of the LO phonon deduced from this analysis is sensitive to charged defects including ionized impurities.