The precipitation of excess As on dislocations in semi-insulating crystals of liquid-encapsulated Czochralski-type material was investigated during heat treatment at temperatures of between 800 and 1000C. It was found that the precipitate size increased with the duration of the heat-treatment, and saturated. The growth rate was strongly affected by the heat-treatment temperature, and by the amount of excess As in the crystal. The rate was also different, depending upon the location of the dislocations. Thus, precipitates on dislocations in cell walls grew larger than those on isolated dislocations. The EL2 concentration, which reflected that of the dissolved excess As, decreased at large precipitate sizes and became the same in all of the samples after heat treatment for 36h; when the growth of precipitates saturated. The excess As was in a state of undersaturation at temperatures above 810C; according to the Ga-As phase diagram. The existence of dislocations broke the symmetry of the under-saturated state and caused precipitation.

Y.Otoki, M.Sahara, M.Shibata, S.Kuma, M.Kashiwa: Materials Science Forum, 1995, 196-201, 1431-6