The Car-Parrinello method was used to study Zn-enhanced interdiffusion in superlattices. The energetics of several mechanisms for the diffusion of Zn were examined. It was found that a pair which consisted of a substitutional Zn acceptor and an interstitial group-III atom had a substantially lower formation energy than did an isolated interstitial. The low formation energy of this pair resulted in the interstitial kick-out mechanism having a much lower activation energy than those which involved vacancies or the dissociative  (Frank-Turnbull or Longini) mechanism. The lowest-energy path for the interchange of group-III atoms involved the kick-out of Zn by a group-III interstitial, followed by fast Zn interstitial diffusion and the subsequent ejection of another group-III atom into the interstitial channel. The activation energies for these processes, as determined by following the kick-out trajectories and including full relaxation of all of the atoms, were in good agreement with experimental data.

Q.M.Zhang, C.Wang, J.Bernholc: Materials Science Forum, 1992, 83-87, 1351-6