Measurements were made of the 1-dimensional angular correlation of the annihilation radiation. The numerical values of the characteristic lengths of the radius of the spherical volume occupied by an annihilating electron (rs’) differed significantly from the corresponding value (rs) calculated by using the conventional independent-particle model for an ideal Fermi-gas, with rs’(AlN) equal to about 1.28rs, where rs(AlN) was about 1.61au, rs’(GaN) was about 1.66rs and rs(GaN) was about 1.64au. The so-called electron-positron ion radii, which were reconstructed by the high-momentum components of a 1-dimensional angular correlation of the annihilation radiation for Al3+, Ga3+ cores as well as the numerical rs’ values, suggested that Ga and Al vacancies and their impurity complexes were effective centers of positron localization in AlN and GaN. It was assumed that these complexes included VGa, VAl, and N atoms (VGa-NGa in GaN and VAl-NAl in AlN); where the N atom was likely to be in the substitutional configuration (antisite), N+Ga and N+Al, respectively.

Positron Annihilation in AlN and GaN. N.Y.Arutyunov, V.V.Emtsev, A.V.Mikhailin, V.Y.Davidov: Physica B, 2001, 308-310, 110-3