Vacancy defects in low-temperature-grown GaAs observed by continuous and pulsed slow positrons

A systematic investigation of GaAs grown at low temperatures (LT-GaAs) was carried out. The vacancy defects in the as-grown material were identified to be mainly Ga vacancies by comparing the core-(W) and valence-(S) annihilation parameters to that of Ga vacancies in highly Si-doped GaAs. The vacancy concentration increases up to 10¹⁸ cm^-3. Isochronal annealing was done at various samples. The S parameter in the samples increases with annealing, suggesting the formation of new defects. By checking the correlation between S and W we estimated that the defects seen in annealed LT-GaAs are physically different from that in the as-grown state. The annealed samples showed nearly saturated trapping with a defect related positron lifetime of 345 ps, which can be attributed to vacancy clusters or the As precipitates found by correlated TEM measurements.