Threading Screw Dislocations in 4H-SiC Wafer Observed 
by the Weak-Beam Method in Bragg-Case X-ray Topography
Dislocations in 4H-SiC have been observed by x-ray topography in the Bragg-case (reflection) geometry by means of a weak-beam technique. Using an x-ray beam with an angular divergence of 0.87 μrad, collimated by an asymmetric Si 331 reflection, a nearly intrinsic rocking curve of the SiC 0008 reflection was obtained. High-resolution contrast of threading screw dislocations by kinematical diffraction was observed under diffraction conditions that deviated from the rocking curve peak by 24 μrad. Threading screw dislocations running inside the wafer were projected onto the topograph. In addition, the sense of each screw dislocation was determined directly from the weak-beam image in consideration of lattice displacement around the dislocation.