Substitutional nth-neighbor P-P and As-As impurity pairs in zincblende-structured material, where n was between 1 and 6, were investigated by using self-consistent plane-wave pseudopotential and empirical pseudopotential methods. A single impurity introduced a deep gap level. It was shown that interaction between the orbitals of the impurity pairs led to an interesting pattern of single-particle level splitting which was largest for the first (n = 1) and fourth (n = 4) neighbor pairs. The total energy of the nth-order pair, relative to isolated impurities, indicated a pairing tendency for n = 1 and n = 2, while n = 4 pairs were unstable. The behavior was explained as being a consequence of an interplay between an elastic contribution which represented the interaction between the elastic strain fields of the 2 impurities, and an electronic contribution which described interactions of the defect orbitals of the 2 impurity atoms. The binding energies of the impurity-pair bound excitons were calculated for the n = 1, As-As and P-P pairs, and were found to be significantly higher than those for the corresponding isolated impurities.

P-P and As-As Isovalent Impurity Pairs in GaN. T.Mattila, A.Zunger: Physical Review B, 1999, 59[15], 9943-53