A STUDY OF DISLOCATIONS, PRECIPITATES, AND DEEP-LEVEL EL2 IN LEC GAAS GROWN UNDER GA-RICH CONDITIONS

Dislocations, precipitates, and the deep level EL2 are studied in LEC GaAs grown under Ga-rich conditions but still with the As atomic fraction in the melt above 0.475. It is found that even such Ga-rich GaAs crystals can contain a high density of very large precipitates decorating dislocations and involving a high density of As interstitials. This suggests that As supersaturation also exists under Ga-rich conditions. The relatively low density of EL2, with respect to published data, and the very large size of the precipitates are explained by means of TTT diagrams which show that As precipitation at dislocations might occur at higher temperatures than EL2 formation, thus reducing the probability of EL2 production.