It was shown how the nature of defects could be investigated by positron 2-dimensional angular correlation of annihilation radiation measurements. It was possible to identify a specific distribution for each defect. In the present material, it was possible to characterize negative ions (identified as antisites) as well as As and Ga vacancies in various charge states. It was found that each 2-dimensional angular correlation of annihilation radiation distribution was different, and therefore provided so-called 2-dimensional fingerprints of the defects which could then be used for the characterization of real materials. It was also shown that 2-dimensional angular correlation of annihilation radiation measurements provided information on atomic relaxations around vacancies. This revealed that VAs- had a smaller open volume than did VAs0. This was in agreement with the results of positron lifetime experiments and molecular dynamics calculations.

A.A.Manuel, R.Ambigapathy, K.Saarinen, P.Hautojärvi, C.Corbel: Applied Surface Science, 1995, 85, 301-4