Papers by Author: Myong Chuel Chun

Abstract: We investigated the relation between the nucleation of dislocations and the lattice misfits by nitrogen concentration difference between seed and grown crystal during the initial stage of growth. 4H-SiC single crystals were grown with various nitrogen gas flow rates introduced into the crystal growing chamber under the same temperature and pressure to minimize the effect of thermal stress on the nucleation of dislocations. The nitrogen atomic concentrations of grown crystals depended on the introduced nitrogen gas ratios and they highly increased at the very early stage of growth. The generation of new threading dislocations at the interface also was affected by the nitrogen atomic concentrations differences between seed and grown crystals. Very few generated threading dislocations were observed in low nitrogen atomic concentration samples, however nucleation of threading dislocations at the interface were found in high nitrogen atomic concentrations samples. At initial stages of PVT growth process, the generation of threading dislocations induced by lattice misfits originated from nitrogen concentration difference between seed and grown crystals were investigated and found the appropriate nitrogen gas flow rates and profile at the heating and depressurized stage.

Abstract: The present research is focused to investigate a role of the porous graphite (PG) plate that could improve the quality of 4H-SiC crystal. The grown crystal in porous graphite inserted crucible showed the lower intensity of Al, B and Ti impurity concentration than SiC crystal grown in conventional crucible. The porous graphite plate before and after the growth process has been investigated by a Raman spectroscopy and a photoluminescence spectrum (PL). According to the analysis result, it was confirmed that the porous graphite plate had the effect of suppressing impurities supplied to SiC single crystal during the growth process.

Abstract: The present research was focused to extensively investigate the effect of TaC-coated crucible on the SiC crystal growth and then compare the difference of various properties between SiC crystals grown in conventional graphite crucible and TaC-coated crucible. The bulk growth was conducted around 2200°C of the growth temperature and 40 mbar of an argon atmosphere for the growth pressure. The better crystalline quality was obtained from the crystal grown in TaC-coated crucible. The SiC crystal grown in the TaC-coated crucible exhibited superior characteristics than SiC crystal grown in the conventional crucible in terms of the crystal quality and defect density. Furthermore, nitrogen incorporation in SiC crystal grown in the TaC-coated crucible was definitely decreased.

Abstract: SiC crystal ingots were grown on 6H-SiC dual-seed crystal with different surface properties by a PVT (Physical Vapor Transport) technique. And then SiC crystal wafers sliced from the SiC ingots were systematically investigated in order to find out the dependence of surface properties for seed on the polytype formation. While n-type SiC crystals exhibiting the 4H polytype were grown on seed crystal having high root-mean-square (rms) value, 6H-SiC crystals were grown on seed having lower rms value. However, 6H polytype was maintained on on-axis and off-axis seeds during the entire growth period. The crystal quality of 6H-SiC single crystals grown on on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on off-axis seed.

Abstract: The present research was focused to investigate the effect of internal crucible design that influenced the 4H-SiC crystal growth onto a 6H-SiC seed by PVT method. The crucible design was modified to produce a uniform radial temperature gradient in the growth cell. The seed attachment was also modified with a use of polycrystalline SiC plate. The crystal quality of 4H-SiC single crystals grown in modified crucible and grown with modified seed attachment was revealed to be better than that of crystal grown in conventional crucible. The full width at half maximum (FWHM) values of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 285 arcsec, 134 arcsec and 128 arcsec, respectively. The micropipe density (MPD) of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 101ea/cm^2, 81ea/cm^2 and 42ea/cm^2, respectively.

Abstract: The single crystal ingots by using a sublimation technique were grown on 6H-SiC dual-seed crystals with opposite face polarities and then SiC crystal wafers sliced from the SiC ingot were systematically investigated to find out the polarity dependence of the crystal quality. The growth rate of the SiC crystal grown in this study was about 0.2mm/hr. N-type 2’’ SiC crystals exhibiting the 4H- and 6H-SiC polytype were successfully fabricated on C-face and Si-face, respectively. The incorporation of nitrogen donors in the SiC crystals grown on the C-face seed crystal was exhibited to be higher than in SiC crystals grown on a Si-face crystal. When the SiC crystal ingot proceeded to grow, the SiC crystal region grown on the C-face seed crystal was enlarged compared to the SiC crystal region on the Si-face seed crystal.

Abstract: Extensive study of various process parameters to influence on the growth of 4H-SiC crystal has been carried out using the transformation of the 6H-SiC seed by a PVT method. The axial temperature gradients were increased throughout increasing the crucible length along growth direction in order to enhance the growth rate and transformed crystal yield. The N2/Ar gas ratio used during the crystal growth related with carrier concentration/mobility of grown crystal. In the initial stage of growth, foreign polytypes such as 6H/15R were observed on 6H-SiC seed crystal but 4H crystals were entirely grown after the process optimization. While the typical absorption spectrum of SiC seed crystal indicated that the SiC polytype was the 6H-SiC with fundamental absorption energy of about 3.02eV, absorption spectrum of grown SiC crystal exhibited 4H-SiC with fundamental absorption energy of about 3.26eV. The entirely transformed SiC region exhibited lower micropipe density than 6H/4H transition region.