Single crystals of 4H-SiC and 6H-SiC were implanted at room temperature with 3MeV 3He ions to a fluence of 1016/cm2. Analysis of helium migration was carried out using the 3He(d, p)4He nuclear reaction. No clear thermally-activated migration in the end-of-range region was found below 1100C, meaning that helium was strongly trapped probably in helium-vacancy clusters. At 1100C and above, a fraction of 3He atoms remained trapped in the clusters, but a significant fraction was de-trapped into a broad distribution, which was slightly shifted towards the sample surface. Helium de-trapping from the end-of-range region increased with increasing annealing time and temperature. Moreover, the helium content was not conserved, since a significant fraction of 3He atoms was released out of the sample. Helium out-gassing actually increased with increasing annealing time and temperature, up to about 40% at 1150C. No clear difference was found between the 4H-SiC and 6H-SiC polytypes.

Nuclear Reaction Analysis of Helium Migration in Silicon Carbide. S.Miro, J.M.Costantini, J.Haussy, L.Beck, S.Vaubaillon, S.Pellegrino, C.Meis, J.J.Grob, Y.Zhang, W.J.Weber: Journal of Nuclear Materials, 2011, 415[1], 5-12