The suitability of the positronhyphen;lifetime technique to the study of native vacancies in GaAs is demonstrated. Significant variations in positron lifetime among a variety of ashyphen;grown GaAs single crystals were observed. The longest positron lifetime was found in undoped samples. Annealing in vacuum at 300ndash;500thinsp;deg;C reduced the longhyphen;lifetime component. The results present strong evidence for the existence of Ga vacancies in the ashyphen;grown material.
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