Green's-function theory of impurity vibrations due to defect complexes in elemental and compound semiconductors

Green's-function theory has been reported for studying the vibrations of impurity complexes with a maximum of three defect centers in zinc-blende-type crystals. By incorporating appropriate perturbation models and lattice phonons from an eleven-parameter rigid-ion model we have made numerical calculations for the localized vibrational modes of almost all the existing cases of pair defects with $C_s$ and $C_{3v}$ pointgroup symmetries. The results of force perturbation for isolated charged defects have assisted us to reasonably fit the various optical experiments and tentatively assign the movements of "donor-acceptor," "acceptor-donor," "donor-host-acceptor," and "donor-host-vacancy" complexes. The force perturbation correlation with bond ionicity noticed for isolated donor or acceptor impurities has also proved to be an important factor for studying the pair vibrations in elemental and compound semiconductors.