ROLE PLAYED BY N AND N-N IMPURITIES IN TYPE-IV SEMICONDUCTORS

Ab initio all-electron Hartree-Fock calculations within the molecular-cluster model are performed to analyze the role of N impurities, both isolated and complex, in type-IV semiconductors. The results are used to investigate the structural and electronic properties. For isolated impurities the N atom distorts in the (111) direction towards a vacancy leading to a final local C-3 upsilon symmetry. The N atom forms sp(2) bonds with the host atoms and leaves an unoccupied N lone pair. For Nz both N atoms tend to form similar sp(2) bonds and move away from each other in the (111) direction without N-N bond formation. For the case of N-2(+), localized N-N hole states are obtained. A detailed picture at the orbital level is given. These achievements should also be important for amorphous hydrogenated semiconductors.