Papers by Author: Nobuyoshi Yashiro

Abstract: In this study, we have investigated the rate-limiting process of 4H-SiC solution growth using Si-Cr based melt, and have tried high-speed growth. It is revealed that the rate-limiting process of SiC growth under our experimental condition is interface kinetics, which can be controlled by such factors as temperature and supersaturation of carbon. By enhancing the interface kinetics, SiC crystal has been grown at a high rate of 2 mm/h. The FWHM values of X-ray rocking curves and threading dislocation density of the grown crystals are almost the same as those of seed crystal. Possibility of high-speed and high-quality growth of 4H-SiC has been indicated.

Abstract: We attempted the traveling solvent method (TSM) growth of SiC on 6H-SiC(0001) substrates using Si and Si-M (M=Ti, Cr and Dy) solvents at growth temperatures of 1500-1800°C. It was confirmed that 4H-SiC polytype was extremely stabilized in the highly carbon dissolved liquid phase. 4H-SiC growth on 6H-SiC, i.e. hetropolytype epitaxial growth, was observed only from Si-Dy solvent. The Dy content above 60at% was necessary to obtain 100% 4H-SiC polytype.

Abstract: The stable long time growth with the use of Si -C-Ti ternary solution was realized　by improving the thermal condition during the growth. We have succeeded in obtaining a maximum 10 mm thick bulk 6H-SiC crystal, which is the largest bulk crystal ever obtained by the solution growth technique. The obtained crystal was free of cracks and exhibited a homogeneous light green color. The crystallinity of the grown crystal was characterized by X-ray rocking curve measurements using (0006) reflection and by the molten KOH etching. The mapping of the full width at half maximum (FWHM) revealed the average FWHM around 30 arc seconds and the minimal FWHM under 16 arc seconds. The etch pit density (EPD) was typically in the range between 104 and 105 cm-2, which was comparable to that of the crystal seed.

Abstract: LPE (liquid phase epitaxy) growth of low nitrogen unintentionally doped SiC epitaxial layer on on-axis 4H-SiC substrate using nitrogen getter Si based solution was investigated to realize basal plane dislocation (BPD) free epitaxial layer. A significant reduction in BPD was demonstrated.

Abstract: We performed liquid phase epitaxial growth of SiC layers on on-axis 4H-SiC substrates using Si solvent. It was found that the polytype controllability of the epilayer significantly depends on the growth process conditions. By optimizing them, polytype mixing in the epilayers can be completely suppressed. It is shown that the density of basal plane dislocations in the epilayers is much less than in the substrates due to on-axis growth. SIMS analysis showed that the concentrations of trace impurity elements (B,Al,Ti,V,Cr,Fe,Ni,P) in the epilayers are under lower detection limit. The only impurity is nitrogen resulting in an n-type layer. Carrier concentrations Nd-Na ranging from high 1016 to low 1017cm-3 are achievable.

Abstract: We have successfully grown 3C-SiC(111) single crystals 10mm x 10mm in dimension on 6H-SiC(0001) substrate by the solution growth method using cold crucible technique. The growth rate of 60μm/hr was achieved. The use of Si-Ti-C ternary solution as well as the electromagnetic stirring are responsible for the relatively high growth rate in solution method. The threading dislocation density is low and the etch pit density amounts to 105-106 /cm2 at the lowest region. Polytype of the grown layer has changed from 3C to 6H with an increase in the dip depth of substrate. A mathematical model was applied to get better understanding of what happened in the crucible.

Abstract: Top seeded solution growth of SiC on on-axis 6H-SiC was performed using Si solvent at growth temperature as high as 1645-1870°C. It was found that different polytypes of SiC layers were grown on 6H-SiC depending on gas species during growth. The growth under He atmosphere produced 6H-SiC homoepitaxial layers. On the other hand, the growth under N2-He atmosphere led to 3C-SiC epitaxial layers. It was obvious that the nitrogen dissolved in solvent strongly favoured the 3C-SiC polytype formation on 6H-SiC. We also conducted characterization of 3C-SiC layers grown on 6H-SiC (0001)Si by TEM, molten KOH etching and precise XRD measurement.

Abstract: We carried out the characterization of the crystallinity of the solution growth self-standing silicon carbide (SiC) crystals, which were grown from Si-C-Ti ternary solution with Accelerated Crucible Rotation Technique (ACRT). The self-standing crystal exhibited homogeneous green color without cracks and inclusions. The crystallinity of the self-standing crystal was characterized by various precise XRD diffraction measurements, such as の-scan rocking curve measurement, X-ray topography and reciprocal lattice mapping. The Full Width at Half Maximum (FWHM) of the の-scan rocking curves was about 20 arcsec. The X-ray topography showed a large area with a homogeneous orientation. The reciprocal lattice mapping exhibited a sharp single peak indicating the excellent crystallinity. Finally we confirmed rather high crystallinity of the self-standing crystals by etch pits measurement using molten KOH etching.

Abstract: Solution growth of 6H-SiC single crystal from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT) was performed. The SiC growth rate exceeding 200 μm/hr was achieved in several ACRT conditions. Such a high growth rate can be ascribed to the enhancement of the carbon transport from the graphite crucible to the growth interface due to the use of the ACRT. The incorporation of inclusions of Si-Ti solvent in the grown SiC crystal was also significantly suppressed by using the ACRT. The intensive convection near the growth interface induced by the ACRT resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth could be accomplished in the SiC solution growth using the ACRT. The obtained SiC self-standing crystal exhibited homogeneous green colour without cracks and inclusions. We investigated the crystalline quality of the grown SiC crystal by means of X-ray diffraction. The, ω-scan rocking curves of (0006) reflection measured by X-ray diffraction provided the FWHM of 15-20 arc-second showing the excellent crystallinity of the solution grown 6H-SiC single crystal.

Abstract: We performed solution growth of SiC single crystals from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT). It was confirmed that the growth rate exceeding 200 μm/hr was achievable by several ACRT conditions. This high growth rate might be due to the enhancement of the carbon transport from the graphite crucible to the growth interface using the ACRT. Moreover, the incorporation of inclusions of the Si-Ti solvent in the grown crystal was significantly suppressed by using the ACRT. It was thought that the intensive convection near the growth interface resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth can be accomplished in the SiC solution growth using the ACRT.