Control of 4H polytype of SiC crystals by moving up the crucible to adjust the temperature field of the growth interface
It is difficult to control the stability of the 4H polytype in the growth of SiC single crystals by the PVT method. When the crucible was immovable, it was found that the temperature and the temperature gradient of the growth interface gradually increased and were almost unchanged with the crystal growth by the simulation. This resulted in the segregation of the gas composition and a variable Si/C ratio of the growth interface, due to which polytype inclusions and defects were easily formed. In this paper, we proposed a new method for stabilizing the 4H polytype of the SiC crystals by controlling the temperature field of the growth interface and gradually moving up the graphite crucible during crystal growth. The simulation results showed that the method could simultaneously reduce the range of the temperature rise and drop the temperature gradient at the growth interface. Thus, the gas phase composition was stable during the growth process, which will be useful for the stability of the 4H polytype. Finally, 4 inch SiC single crystals with 4H polytype stability and low defects were successfully obtained though this new method. Also, the quality of the as-grown SiC crystals was characterized by X-ray diffraction, Raman spectroscopy and Candela optical surface analysis. The results show that the method of slowly moving up the crucible during crystal growth is very effective in controlling the 4H polytype and improving the quality of SiC single crystals.