Raman spectroscopic study of the electrical properties of 6H–SiC crystals grown by hydrogen-assisted physical vapor transport method

Raman spectroscopy has been used to determine the carrier concentration of 6H–SiC crystal so as to understand the effects of hydrogen on the electrical property of 6H–SiC crystal grown by hydrogen-assisted physical vapor transport method. The spatial distribution of the carrier concentration is determined in a longitudinally-cut sample grown by an on-off hydrogen supply based on the empirical relationship between the frequency of the LO-phonon-plasmon-coupled modes (LOPC modes) and carrier concentration. It is found that the carrier concentration dramatically drops when the supply of hydrogen turns on and decreases more quickly in the hydrogen-assisted region than that in the undoped region. It is proposed that the vapor phase shifts toward more C-rich condition in case of hydrogen-assisted growth. As a consequence, the N incorporation in 6H–SiC crystal is depressed and the inactive electrically center $Vc+H$ complexes are formed during hydrogen-assisted physical vapor transport SiC crystal growth.