Effect of Impurity Core Squeezing on Donor Energy Levels in Silicon

Using first principle Pseudo Impurity Theory (PIT) and variational method, the binding energies of group V shallow donors in silicon are estimated incorporating the effect of core squeezing of the substitutional impurity atoms, with an empirical squeezing scheme of the core orbitals. Scaling factors are defined for various core states of the impurity atom to take explicit account of the varying degree of rigidity on squeezing. From the extent of squeezing required to reproduce the experimental binding energies of the donors, the local relaxation due to the size difference between the host and donor atoms is deduced and compared with experimental results and theoretical predictions available in literature. It is demonstrated that the squeezing scheme of the present work combined with the first principle pseudo impurity theory could deduce information about a purely local phenomenon such as lattice distortion reasonably well from the binding energy of the donor impurity.