Bending of basal-plane dislocations in VPE grown 4H-SiC epitaxial layers

The propagation of basal plane dislocations from off-axis 4H-SiC substrates into the homoepitaxial layers has been investigated using KOH etching, optical microscopy, and transmission electron microscopy (TEM). The etch pit densities of threading edge and basal plane dislocations changed dramatically across the substrate/epilayer interface, but the total dislocation density remained constant. We have observed transformation of basal plane dislocations in the substrates into threading edge dislocations in the layers by KOH etching and TEM experiments. TEM observation of the dislocations revealed that they are threading in the epilayers, inclined from the c-axis toward the down-step direction. The conversion is interpreted as a result of the image force in epilayers between the flowing steps and basal plane dislocations. It is argued that this mechanism can cause an increase of the threading edge dislocation density in physical vapor transport (PVT) grown bulk crystals, and can lead to an apparent structural quality improvement of epilayers.