CLUSTERING PROCESS OF INTERSTITIAL ATOMS IN GALLIUM-PHOSPHIDE STUDIEDBY TRANSMISSION ELECTRON-MICROSCOPY

Growth of Frank-type dislocation loops of interstitial type in GaP cry stal has been systematically examined by in situ transmission electron microscopy to understand the migration of point defects in the crysta l. The loops were formed by annealing following 200-keV electron irrad iation, Most of the loops were nucleated in the early stage of anneali ng and the number density of loops remained constant after nucleation, The radius of each loop increased with annealing time and then reache d a certain final value. The number density of interstitials aggregate d in loops therefore reached a maximum value when the growth of all lo ops stopped. The maximum density did not depend on annealing temperatu re but on irradiation conditions (electron dose and irradiation temper ature) and it increased quadratically with electron dose. These result s were well explained by a proposed model that the loops were formed t hrough the thermal migration of Ga-i-P-i pairs that were introduced du ring electron irradiation. From the analysis, the migration energy for the interstitial pairs was estimated as 0.9+/-0.03 eV.