It was noted that highly mobile interstitial Fe and group-III impurities (B, Al, Ga, In) formed Fe-acceptor pairs. On the basis of the migration kinetics, and assuming the host to be a dielectric medium, simulations were made of the pairing process in a static lattice. Contrary to the usual point-charge ionic model, the present phenomenological calculations included a correction that took account of a valence electron cloud polarization which added a short-range attractive interaction to Fe-acceptor pair bonding. The calculations also took account of a lattice relaxation which was due to atomic size differences that produced local strain fields. This model qualitatively explained trends in the Fe-acceptor pairs, such as an increase in the electronic state hole emission energy with increasing principal quantum number of the acceptor and decreasing pair separation distance. It also explained the stable and metastable sites and configurational symmetries of Fe-acceptor pairs.

S.Zhao, L.V.C.Assali, L.C.Kimerling: Materials Science Forum, 1995, 196-201, 1333-8