The positron-electron auto-correlation function was calculated for neutral and negatively charged In vacancies and for perfect InP. The ab initio calculations were performed for the electron wave functions in density functional theory, with the local density approximation for the exchange potential of electrons. The positron wave function was calculated by directly diagonalizing the single-particle Hamiltonian of the positron in the local density approximation, with a density-gradient correction. It was found that the auto-correlation function was suitable for identifying the charge states of the In vacancies. Neutral In vacancies greatly diminished the nearest peaks and dips of the auto-correlation function which were located after the nearest-neighbor lattice points in the case of perfect material. Negatively charged In vacancies nearly eliminated those peaks and dips, together with the next-nearest peaks that were located at the next-nearest neighbor lattice points. Therefore, the diminution of the nearest peaks and dips could be taken to be an indication of the formation of neutral In vacancies. Diminution of the next-nearest peak could be taken to be an indication of the formation of negatively charged In vacancies. However, the 3 negative charge states of the In vacancies (VIn-, VIn2-, VIn3-) were still difficult to distinguish from each other by using the auto-correlation function method.

Identification of charge states of indium vacancies in InP using the positron-electron auto-correlation function W.LiMing, S.Fung, C.D.Beling, M.Fuchs, A.P.Seitsonen: Journal of Physics - Condensed Matter, 1998, 10[41], 9263-71