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

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