Damage annealing behavior of Se implanted GaAs

High resolution Rutherford backscattering-channeling (RBS-C) and transmission electron microscopy (TEM) have been used to investigate the annealing behavior of Se implanted Cr-doped GaAs layers. Two distinct annealing stages were observed; one at 250°C which is associated with amorphous zone annihilation and/or onset of solid phase epitaxial growth and the other at about 400–500°C, depending on the dose, that can be related to the dissociation of microtwins. Above 500°C, the residual defects are primarily dislocation loops and precipitates. The calculated number of atoms associated with the precipitates has been found to correspond closely to the number of implanted atoms, implying 100% precipitation for the cases studied in this work. This could explain the poor or nonexistent electrical activation of Se after low temperature annealing (6̃00°C), even though good regrowth of the amorphous layer has taken place. Experiments with high purity GaAs produced the same result, as far as the observed residual damage was concerned, thus eliminating speculation about the involvement of Cr in the nucleation of microtwins. Transmission electron microscopy investigations of the amorphous-crystalline interface in the as-implanted samples failed to reveal any extended defects. In the present paper, we discuss various mechanisms that could be responsible for the formation of twins in low temperature annealed GaAs.