Samples of 4H–SiC, doped with N at to about 3 x 1019/cm3, were annealed in Ar (1.5h, 1150C). Transmission electron microscopy revealed stacking faults at a density of approximately 80/µm, whereas faults were not found prior to annealing. All of the faults examined were double-layer Shockley faults which were formed by shear on 2 neighboring basal planes. The structural transformation was interpreted as being due to quantum-well action; a mechanism in which electrons in highly n-type 4H–SiC entered stacking fault-induced quantum-well states so as to lower the system energy. The net energy gain was calculated, as a function of the temperature and N-doping concentration, by solving the charge neutrality equation. Calculations showed that doping levels in excess of about 3 x 1019/cm3 should result in double-layer stacking faults forming spontaneously at device-processing temperatures; in agreement with observations. Single-layer faults were not expected to be stable in 4H–SiC at concentrations below 1020/cm3, but were expected to form at doping concentrations above about 2 x 1019/cm3 in 6H–SiC. Charge build-up in the stacking fault was shown to produce an electrostatic potential that exceeded 90% of the energy difference between the Fermi level position and the lowest energy state in the fault-related quantum well.

Spontaneous Formation of Stacking Faults in Highly Doped 4H–SiC during Annealing. T.A.Kuhr, J.Q.Liu, H.J.Chung, M.Skowronski, F.Szmulowicz: Journal of Applied Physics, 2002, 92[10], 5863-71