It was shown via state-of-the-art theoretical calculations that self-diffusion in diamond was dominated by vacancies, independent of the position of the Fermi level. This was very different from self-diffusion in silicon and germanium, where vacancies, interstitials, and direct-exchange mechanisms all have comparable activation energies. The dominance of the vacancy mechanism was due to the stiffness of diamond bonds, which precludes bond twisting and large relaxations, and to the high electronic density and the large band gap in diamond, which result in a strongly repulsive potential-energy surface for self-interstitials.

Mechanism of Self-Diffusion in Diamond. Bernholc, J., Antonelli, A., Del Sole, T.M., Bar-Yam, Y., Pantelides, S.T.: Physical Review Letters, 1988, 61[23], 2689-92