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

摘要

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.