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A new type of 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation has been developed. Multiple resistance heaters ensure uniform radial temperature distribution throughout a 150-mm-diameter wafer. Enhancement of the growth rates is realized by high-speed wafer rotation under a relatively high system pressure, and growth rates of 40–50 µm/h are achieved on 4° off 4H-SiC substrates, maintaining a low defect density and a smooth surface without macrostep bunching. Excellent thickness and doping uniformities are simultaneously obtained for a 150-mm-diameter wafer at a high growth rate of 50 µm/h.

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A threading dislocation (TD) in 4H-SiC, which was interpreted as a right-handed threading screw dislocation (TSD) by synchrotron monochromatic-beam X-ray topography (SMBXT) and molten KOH etching with Na2O2 additive (KN etching), was characterized by large-angle convergent-beam electron diffraction (LACBED) and weak-beam dark-field methods. It was found that this TD was a so-called c+a dislocation with Burgers vector of b=[0001]+(1/3)[2110], which is often misinterpreted as TSD (c-dislocation) by SMBXT and KN etching. The rotation direction of the screw component within the c+a TD determined by LACBED agreed with the SMBXT observation.

GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.