Characterization of Polytype Distributions in Nitrogen-doped 6H-SiC Single Crystal by Raman Mapping

Nitrogen-doped 6H-SiC crystal with the diameter of 2-inch was grown along (0001) direction by physical vapor transport method. The spatial distribution of different polytypes such as 6H-SiC, 4H-SiC and 15R-SiC was characterized by mapping Raman spectra. The formation and evolution of different polytypes were investigated during the growth progress. 15R-SiC and 4H-SiC were observed in the as-grown 6H-SiC single crystal. Two different polytype regions are observed from the spatial distribution of different polytypes. One region originates from the growth interface of different polytypes. This region has higher nitrogen doping level and carrier concentration, and the area can become large during the growth process. The other region is dominated by 15R-SiC which appears in the main 6H-SiC due to the perturbation in growth temperature, pressure, etc. This region has less effect on the crystal quality, which could be inhibited by increasing the growth temperature.