Synchrotron white-beam topographic studies of 2H-SiC crystals

Synchrotron white beam X-ray topography (SWBXT) has been used to characterize 2H-silicon carbide crystals grown by the chemical reduction of methyltrichlorosilane at 1400°C. The crystals studied had the form of tapered needles around 1 mm long with hexagonal cross-sections 0.4 mm in diameter. SWBXT images recorded from two different crystals showed their excellent quality, as evidenced by the presence of Pendellösung fringes. Topographs recorded with various diffraction vectors revealed no evidence of the axial screw dislocations reported in 2H-SiC by Setaka and Ejiri, based on their observations of spiral growth steps. Neither were there any dislocations with Burgers vectors lying in the crystals' basal planes. The absence of axial screw dislocations indicates that the growth was not screw dislocation assisted, but occurred by diffusion-controlled growth; and some other influence such as thermodynamics, initial nucleation, and/or impurity assisted growth, was responsible for the isolation of the 2H polytype.