Computational studies of positron states and annihilation parameters in semiconductors – vacancy-type defects in group-III nitrides –

We have computationally studied positron sates and annihilation parameters in semiconductors, especially in group-III nitrides. A random alloy system In0.5Ga0.5N was model with the special-quasirandom-structure scheme and distributions of annihilation parameters for cation monovacancies and divacancies were investigated. On GaN, we calculated annihilation parameters considering spin polarization for Ga vacancies with various charge sate and demonstrated how the positron annihilation technique is useful to study defect-induced or mediated magnetism in dilute magnetic semiconductors. We also made calculations based on the two-component density functional theory and compared their results with those obtained by the conventional scheme.