Surface morphology and step instability on the (0001̄)C facet of physical vapor transport-grown 4H-SiC single crystal boules

Surface morphologies on the (0001¯) C facet of 4H-SiC boules grown using the physical vapor transport method were examined in various scales (from millimeter to nanometer) using different types of microscopies such as differential interference contrast (DIC) optical microscopy and atomic force microscopy (AFM). DIC optical microscopic observation revealed that there are three distinct morphological regions at the growth front of the 4H-SiC boules: the facetted region, non-facetted region and intermediate region between them. The local inclination of the facet surface from the {0001} basal plane increases toward the edge of the facetted region and then decreases in the intermediate region. AFM observations revealed that characteristic step structures were established in these two regions and that nitrogen doping significantly influenced the stability of the step structures. Based on the results, the formation mechanism of surface morphologies on the (0001¯) C facet of 4H-SiC boules is discussed.