Self-diffusion in alpha and beta silicon carbide

The self-diffusion coefficients of ¹⁴C and ³⁰Si have been measured for lattice transport in high purity and N-doped α-SiC single crystals and in high purity polycrystalline CVD β-SiC in the temperature range of 2123–2573 K. Grain boundary diffusion of ¹⁴C has also been determined in the β-SiC material. The results of these studies reveal a vacancy mechanism wherein ¹⁴C diffuses considerably faster than ³⁰Si in both materials. Furthermore, D_c^★ in the N-doped single crystals is smaller than for the undoped materials, while the opposite is true for the ³⁰Si transport in these crystals. Changes in the concentration of the charged C and Si vacancies are reasoned to be the underlying cause of this last phenomena. A discussion of the effect of Si evaporation and its effect upon the value of the diffusion coefficient is also presented.