Positron study of native vacancies in doped and undoped GaAs

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Abstract
Positron lifetime measurements are used to study various doped and undoped GaAs samples in the as-grown state. In undoped GaAs the authors detect vacancy defects, the concentration of which varies across the sample and is of the order of 1018 cm-3. During isochronal annealing the defects disappear at 500 degrees C. The nature of the vacancy defects is discussed and their behaviour is compared with those of non-stoichiometric defects and radiation defects. It is concluded that the defects observed to trap positrons in undoped GaAs are neutral As vacancies. Systematic trends of the doping effects on positron lifetime are observed. The lifetime values in n-type GaAs are 10-20 ps higher than in p-type GaAs. This effect is attributed to positron trapping by acceptor-type Ga-vacancy-dopant complexes.