Substitutional Impurities in Si: Impurity-Host Bond Lengths and Spring Constants

Trends for impurity-Si bond lengths and spring constants of 19 substitutional impurities in Si are determined using ab initio calculations. We find periodic behaviors in both properties across the periodic table. These structural trends correlate with the known variation in character of the defect electronic states ranging from substitutionlike to vacancylike. Both are accounted for by a dominance of covalent interactions. The common usage of covalent radii to predict impurity bond lengths is shown to be qualitatively incorrect.