Clustering process of interstitial atoms in gallium phosphide studied by transmission electron microscopy

Growth of Frank-type dislocation loops of interstitial type in GaP crystal has been systematically examined by in situ transmission electron microscopy to understand the migration of point defects in the crystal. The loops were formed by annealing following 200-keV electron irradiation. Most of the loops were nucleated in the early stage of annealing and the number density of loops remained constant after nucleation. The radius of each loop increased with annealing time and then reached a certain final value. The number density of interstitials aggregated in loops therefore reached a maximum value when the growth of all loops stopped. The maximum density did not depend on annealing temperature but on irradiation conditions (electron dose and irradiation temperature) and it increased quadratically with electron dose. These results were well explained by a proposed model that the loops were formed through the thermal migration of (Formula presented)-(Formula presented) pairs that were introduced during electron irradiation. From the analysis, the migration energy for the interstitial pairs was estimated as 0.9±0.03 eV.