The diffusion of 13C and 30Si was studied by using isotopically enriched 4H-28Si12C/natSiC heterostructures which were grown by chemical vapour phase epitaxy. After diffusion annealing (2000 to 2200C), the 30Si and 13C profiles were measured by means of secondary ion mass spectrometry. It was found that the Si and C diffusivity was of the same order of magnitude (figure 29) but was several orders of magnitude lower than reported data. Both the Si and C tracer diffusion coefficients were in satisfactory agreement with the native point defect contribution to self-diffusion, deduced from B diffusion in SiC. This revealed that the native defect which mediated B diffusion also controlled self-diffusion. Its contribution could be described by:

D (cm2/s) = 4.8 x 100 exp[-7.6(eV)/kT]

Assuming that the B atoms within the extended tail region of B profiles were mainly dissolved on C sites, it was proposed that B diffused via a kick-out mechanism involving C interstitials. Accordingly, C diffusion should proceed mainly via C interstitials. The mechanism of Si diffusion remained unsolved, but Si was suggested to diffuse via both Si vacancies and interstitials; with the preference depending upon the doping level.

Self-Diffusion in Isotopically Enriched Silicon Carbide and its Correlation with Dopant Diffusion. K.Rüschenschmidt, H.Bracht, N.A.Stolwijk, M.Laube, G.Pensl, G.R.Brandes: Journal of Applied Physics, 2004, 96[3], 1458-63

Figure 29

Diffusivity of C and Si in SiC