Simulation of threading dislocation images in X-ray topographs of silicon carbide homo-epilayers

Three types of dislocation are seen in homo-epilayers of SiC grown on 4H-SiC wafers with an 8° surface offcut: axial screw dislocations, basal plane dislocations propagated into the epilayer at an 8° inclination and threading edge dislocations. These types may be imaged by monochromatic synchrotron X-ray topography in the grazing-incidence reflection geometry using the 118 reflection. Equations needed to apply the ray-tracing method of computer simulating X-ray topographic defect images in this experimental geometry were derived and used to simulate images of all three. Simulations for axial screw dislocations appear as white circles surrounded by narrow dark rings, and those for basal plane dislocations as linear white streaks, both consistent with experimental topographs. Simulations of the threading edge dislocations showed 4 µm wide white ovals with narrow arcs of dark contrast at their ends, inclined relative to the g vector of the topograph according to the sign of their Burgers vector. These images resembled the experimental topographs inasmuch as was possible at the maximum resolution of X-ray topographs.