Metal-Dimer Atomic Reconstruction Leading to Deep Donor States of the Anion Vacancy in II-VI and Chalcopyrite Semiconductors

The nonsymmetric atomic relaxation patterns induced by the formation of stable metal-metal-dimer bonds were identified as the energetically favorable reconstruction of the neutral anion vacancy in ZnSe, ZnS, CuGaSe₂, and CuInSe₂. The atomic relaxation alter the energy of the defect orbitals, rendering the anion vacancy a deep defect. A local atomic reconstruction mode around anion vacancies in II-VI and a chalcopyrite compounts resulting from the formation of metal dimers are revealed by first-principles total-energy calculations. The neutral Se vacancy was found to have a low symmetry in ZnSe and CuGaSe₂.