Ab initio calculations of point defects in silicon

We use the ab initio plane wave pseudopotential method and the density functional theory (DFT) to study the arsenic(bs)-vacancy interactions in silicon. The detailed lattice distortions surrounding the As-vacancy defect and the energetics of As-vacancy reaction around the six-fold ring are investigated. We find that the As displaces its neighboring silicon atoms outward while the vacancy attracts its neighboring atoms inward. The binding energy and the formation energy of an As-vacancy pair are 1.21 eV and 2.37 eV, respectively. Once the vacancy and As binds together, the highest migration barrier for the whole complex is 1.19 eV, which is in good agreement with the experimental measurement of 1.07 eV. The calculated activation energy for the vacancy mediated diffusion of the neutral As in silicon is 3.56 eV. The nature of the binding between As and vacancy is explained from the lattice distortions introduced by the As-vacancy complex.