Correlation between the step–terrace structure and the nitrogen doping variation observed on the $(0001¯)$ facet of 4H-SiC crystals

The variation in nitrogen doping concentration on the $(0001¯)$ facet of 4H-SiC single crystals grown by the physical vapor transport (PVT) growth method was investigated using Raman scattering microscopy. The observed variation was well correlated with the terrace-width variation in the step–terrace structure on the facet; regions with unevenly distributed terrace-widths always showed a lower nitrogen concentration compared to those having evenly distributed terrace-widths. It was revealed by low-energy electron channeling contrast imaging that in lower nitrogen concentration regions, terraces with two dangling bonds per silicon atom at the step riser in the step-down direction always became wider. On the basis of these experimental results, the nitrogen incorporation kinetics during PVT growth of 4H-SiC crystals was discussed.