It was found that Frank loops of interstitial type formed uniformly within the irradiated area of crystals upon annealing at temperatures above 700K, after 200keV electron irradiation. The results of  in situ  transmission electron microscopy showed that the loops grew with annealing time, and attained a specific radius. On the other hand, the number density of loops was almost independent of the annealing time, since most loop embryos were created uniformly in the early stages of annealing. As the annealing temperature was increased, the loop radius increased while the number density of loops decreased. The total number density of aggregated interstitial atoms, contained in all of the loops, was independent of the annealing temperature. The total number density depended only upon the irradiation conditions, and increased quadratically with increasing electron dose. In order to explain the results, it was proposed that the loops were formed by the migration and clustering of pairs (Ga-P) of interstitial atoms which were created during irradiation. The migration energy of such pairs was estimated to be 0.88eV.

Clustering Process of Point Defects in GaP Studied by Transmission Electron Microscopy. Y.Ohno, S.Takeda, M.Hirata: Materials Science Forum, 1995, 196-201, 1279-84