AB-INITIO TOTAL-ENERGY CALCULATIONS OF IMPURITY PINNING IN SILICON

The 90-degrees partial dislocation is used as a model dislocation to study pinning by impurities in silicon. Several electrically active impurities (As, B, N, P) are examined reinforcing earlier work on P and extending it, including a realistic assessment of basis set effects. Strongest pinning (3 eV per impurity atom) is obtained by association of the impurity with a reconstruction defect (''soliton''), replacing the threefold coordinated silicon site. Nitrogen was by far the most effective pinning agent. In addition impurity pairing energies are found which are generally slightly greater in the dislocation core than in bulk, with As being exceptional. Finally a formation energy for the neutral soliton on the 90-degrees partial (1.2 eV) is calculated.