Spontaneous formation of stacking faults in heavily N-doped 4H-polytype SiC crystals were observed by transmission electron microscopy . Faults were present in as-grown boules and additional faults were generated by annealing in Ar at 1150C. All faults had identical structure consisting of 6 layers stacked in a cubic sequence as determined by high-resolution transmission electron microscopy, and were interpreted as a result of two Shockley partial dislocations gliding on two neighboring basal planes of SiC. It was argued that the energy of faulted 4H-SiC was lower than the energy of perfect heavily doped (n > 1019/cm3) crystal at typical processing temperatures, thus providing a driving force for transformation.

Structural Instability of 4H–SiC Polytype Induced by n-Type Doping. J.Q.Liu, H.J.Chung, T.Kuhr, Q.Li, M.Skowronski: Applied Physics Letters, 2002, 80[12], 2111-3