Theoretical study of migration processes in bulk diamond

A large number of complex defects are seen in natural and synthetic diamonds, but it is not known whether they form during growth or as a result of later processes. An understanding of diffusion profiles of the dopant impurities is crucial for design of electronic devices. We present here theoretical work on migration processes for several complexes including N, H and vacancies in diamond, to find out how they form. First-principles density functional calculations have been performed to study structural properties and the activation energies for migration of these defects. Migration paths were derived by constructing a set of several intermediate structures between two energy minima by linear interpolation. The effect of temperature on calculated barriers is described by including vibrational energy and entropy. It was found that the energy barrier for migration of interstitial hydrogen between two bond-centred positions is 2.8 eV. Also, hydrogen is readily trapped by both vacancies and by the N–V complex. Energies liberated in these reactions are 5.5 eV and 5.8 eV respectively.