Twin formation in As precipitates in low-temperature GaAs during high-temperature annealing

High-resolution electron microscopy was employed to study the atomic structure of As precipitates formed in low-temperature GaAs during high-temperature annealing. Almost all the precipitates after annealing at 850 and 950 °C were found to be twinned with a {1̄104} crystallographic twin plane. Twinning is associated with the crystallization of amorphous or liquidlike As precipitates during cooling. Nucleation of rhombohedral As appears to be most favorable on the short facet that is parallel to the {111}B plane of GaAs. Twin formation usually initiates on the long facet bounded by the {111}A plane. The crystallization usually terminated with a void because of the shrinkage of the As volume during solidification.