Effect of compressive uniaxial stress on the binding energies ofD−centers in Si:P and Si:As

The binding energies of $D^{\mathrm{-}}$ states in P- and As-doped silicon crystals are calculated as functions of uniaxial compressive stress along the [100] direction within a variational scheme in the effective-mass approximation and with a Chandrasekhar-type variational function. A model Hamiltonian which takes into account valley-orbit corrections, electron-electron interaction, and stress effects is proposed. Our calculation shows that as the stress is applied, the outer electron orbital is driven readily into the two stress-deepened valleys, which leads to a strong decrease in the $D^{\mathrm{-}}$ binding energy. With further increase in stress, the inner electron orbital changes gradually from a function almost evenly distributed among the six conduction valleys into one in which the two stress-deepened valleys are dominant, and the $D^{\mathrm{-}}$ binding energy increases. Our results agree qualitatively with previous theoretical calculations and are in good agreement with far-infrared photoconductivity measurements in Si:P.