Knoop Hardness on the (0001) Plane of 4H and 6H SiC Single Crystals Fabricated by Physical Vapor Transport

Abstract : The Knoop hardness of 4H and 6H single crystals of silicon carbide (SiC) was determined at room temperature. X-ray diffraction techniques confirmed the crystal structure and orientation of each polytype verifying that both discs had the six-fold symmetry expected for a hexagonal crystal and that the c-axis was oriented approximately perpendicular to disc faces. This symmetry was confirmed by the Knoop hardness values on the (0001) plane of the 4H crystal, but the symmetry was not as apparent in the 6H crystal, which may indicate that the c-axis was not as nearly aligned to the faces of the 6H as it was in the 4H crystal. The Knoop hardness was determined at 15 increments around the c-axis using 0.98 and 2.94 N indentation loads. The average Knoop hardness on the (0001) plane at 0.98 N was approximately 30 GPa for both crystals with the average dropping to around 24 GPa for the 6H crystal and 23 GPa for the 4H when the indentation load was increased to 2.94 N. The difference between the maximum and minimum hardness values on the (0001) plane of both crystals at the 0.98 N indentation load was approximately 2 GPa but the difference was significantly less at 2.94 N.