CORRELATION BETWEEN ATOMIC-STRUCTURE AND LOCALIZED GAP STATES IN SILICON GRAIN-BOUNDARIES

Tight-binding molecular-dynamics simulations of a typical high-energy grain boundary in silicon show that its equilibrium atomic structure i s similar to that of bulk amorphous silicon and contains coordination defects. The corresponding electronic structure is also amorphouslike, displaying gap states mainly localized around the coordination defect s, where large changes in the bond-hybridization character are observe d. It is proposed that such coordination defects in disordered high-en ergy grain boundaries are responsible for the experimentally observed gap states in polycrystalline Si.