The growth of Frank-type dislocation loops of interstitial type was systematically studied, by means of  in situ  transmission electron microscopy, in order to investigate the migration of point defects in the crystals. The loops were produced by annealing after 200keV electron irradiation. It was found that most of the loops nucleated in the early stages of annealing, and that the number density of loops remained constant after nucleation. The radius of each loop increased with annealing time, and then reached a limiting value. The number density of the interstitials which aggregated into loops therefore reached a maximum value when the growth of all loops stopped. The maximum density did not depend upon the annealing temperature but upon the irradiation conditions (dose, temperature). It increased quadratically with the electron dose. These results were explained by a model in which the loops were supposed to form via the thermal migration of Gai-Pi pairs that were introduced during irradiation. On the basis of this model, the migration energy of interstitial pairs was estimated to be 0.9eV.

Clustering Process of Interstitial Atoms in Gallium Phosphide Studied by Transmission Electron Microscopy. Y.Ohno, S.Takeda, M.Hirata: Physical Review B, 1996, 54[7], 4642-9