Nitrogen doping concentration dependence of nitrogen incorporation kinetics during physical vapor transport growth of 4H–SiC crystals

Uniform nitrogen doping in SiC crystals is crucial for high-yield production of SiC power devices. This paper tries to provide clues to implementing uniformly nitrogen-doped 4H–SiC crystals by considering the nitrogen doping kinetics during physical vapor transport (PVT) growth of 4H–SiC crystals. We measured the doping uniformity in PVT-grown 4H–SiC crystal using Raman scattering microscopy, finding that the doping uniformity improved as the nitrogen doping concentration increased. Using data from doping variations in PVT-grown SiC crystals, we deduced the step-flow velocity dependence of nitrogen incorporation at the growth front of three variable nitrogen-doped (mid-1017 to more than 1019 cm−3) PVT-grown 4H–SiC crystals, where the step-flow velocity was estimated from the local inclination angle of the growth front surface from the (0001¯) plane. The results were analyzed using the two-site exchange model for surface segregation of impurity atoms on the growing crystal surface. The model reproduced the experimental results of nitrogen incorporation well. This analysis provides two critical physical parameters for the surface segregation of nitrogen on growing 4H–SiC crystal surfaces: the Gibbs energy and kinetic barrier height for surface segregation, which were extracted from the experimental data. The Gibbs energy and the kinetic barrier height for surface segregation of nitrogen atoms decreased for greater nitrogen doping concentrations. These results are discussed with the improved mechanism of nitrogen doping uniformity in 4H–SiC crystals at greater nitrogen doping concentrations.