A first-principles study was made of energetics, complex formation and Al diffusion Al in crystalline Si. First considered was the interaction of Al with self-interstitials Sii. In contrast to B and In, the complex formed by substitutional AlSi and a self-interstitial Sii was metastable and transformed into interstitial Ali in the tetrahedral site. Therefore, in the presence of excess self-interstitials Sii, the Al went off-site and ceased to be an acceptor. The Ali could then bind to AlSi; forming a trigonal complex (also not an acceptor) compatible with the properties of the Si-G19 center. A further sizable energy gain was obtained by forming the deep-donor Al-Al-self-interstitial complex. It was therefore predicted that a sufficiently high externally generated Sii population would cause deactivation, and presumably clustering and disordering, of the Al acceptor in Si. With regard to Al-vacancy interaction: AlSi and a first-neighbor Si vacancy spontaneously formed a divacancy-interstitial complex, similarly to the case of In. The activation energy for diffusion was evaluated for the various mechanisms investigated, and was found to be predominantly interstitial-assisted. The calculated activation energies were in good general agreement with experiment.

Complexes, Clustering and Native-Defect-Assisted Diffusion of Aluminum in Silicon. P.Schirra, G.M.Lopez, V.Fiorentini: Physical Review B, 2004, 70[24], 245201 (7pp)