Investigation of vacancy-type complexes in GaN and AlN using positron annihilation

The momentum distribution of electron-positron pairs in GaN and AlN has been investigated for the first time by measuring the one-dimensional angular correlation of the annihilation radiation (1D-ACAR). The characteristic parameter of the electron density rs′ (the radius of the sphere occupied by an electron) estimated from the experimental data differs noticeably from rs calculated in terms of a standard model of noninteracting particles: rs′ (AlN)≈1.28rs, and rs′(GaN)≈1.66rs, where rs(AlN)≈1.6091 au, and rs(GaN)≈1.6568 au. The chemical nature of atoms in the environment of the annihilating positron in AlN and GaN was identified from the electron-positron ionic radius of Al3+, Ga3+, and N5+ cores, which were determined from the characteristics of the high-momentum component of 1D-ACAR curves. The analysis was based on a comparison of the electron-positron ionic radii with those considered standard for Al and Ga metals and the related compounds GaP, GaAs, and GaSb. A conclusion is made that positron annihilation dominates in the regions of vacancy-type “nitrogen antisite”-“vacancy” complexes, [NGa+VGa] and [NAl+VAl], in GaN and AlN, respectively.