Naohiro Sugiyama

Step structures and dislocations of SiC single crystals grown by modified Lely method

Step structures on the {0 0 0 1} facet of SiC single crystals grown by the modified Lely method were examined through an optical microscopy and an atomic force microscopy to discuss the dependence on the polytype and the polarity. The results were compared with those of CVD method. Step structures around micropipes were quite different for the different polarity of a growing surface. No micropipes were detected at the center of spirals with a step height of 1.5 nm for 6H-SiC. Quantitative morphological features could be corresponded to the variety of etch pits by chemical etching on the growing surface. The dislocations and their motions during the growth were also characterized through etching and polishing the grown crystal from the surface to the inside successively. The screw dislocations shifted outwards from the center of a giant spiral as the growth proceeded. In contrast, the edge dislocations glided in any directions. Discussion was carried out on these results.

The photoelastic constant and internal stress around micropipe defects of 6H-SiC single crystal

Abstract Hexagonal silicon carbide (6H-SiC) single crystals made by a modified Lely method contain a ‘micropipe’ which is one kind of serious defects degrading device performance. The micropipe accompanies strong internal stress around itself. We determined the photoelastic constant in the plane of (00·1) 6H-SiC and then estimated the magnitude of the internal stress around the micropipes. The photoelastic constant was 2.73 brewster at λ =546 nm. The internal stress around the micropipe was estimated to be 113∼166 MPa.

Phase relations between Y- α′ - and β′ -Sialons in Si3N4—AlN—Y2O3 system

This paper discusses the phase relations between Y-α′-and β′-Sialon in Si3N4−AlN-Y2O3 system. The total amount of AlN and Y2O3 varied from 5 to 11 wt%, and the molar ratio of AlN/Y2O3 was 0 to 11. Specimens were prepared by hot-pressing, and were then heat treated for 50 hr. Compounds including SiO2 were formed in the region of small amounts of AlN. The phases formed by hot pressing changed during the heat treatment. The fraction of α′-Sialon was decreased by the heat treatment. The solubility of α′-Sialon, changing with the composition before the heat treatment, converged to a constant after the heat treatment. On the other hand, that of β′-Sialon showed little change due to the heat treatment.