Acceptor-bound phonons in cubic semiconductors.

Abstract

The theory of impurity-electron--LO-phonon binding considered by Dean, Manchon, and Hopfield, among others, is reformulated and generalized. When there are several impurity electronic states having excitation energies comparable with the LO-phonon energy, the impurity-phonon binding energies can essentially be obtained by diagonalizing the exchange integrals among electronic ground and relevant excited states. The theory is then applied to the LO phonons bound to acceptors in cubic semiconductors, whereby the effect of valence-band degeneracy is taken into account in the spherical approximation of Baldereschi and Lipari. Compared with the coupling to the hydrogenlike impurity, binding becomes deeper because of the shrinkage of acceptor wave functions and the bound phonon states acquire fine structures which are classified according to the total momentum change in excitation. Detailed numerical calculations are carried out for ZnS, ZnSe, ZnTe, and CdTe, and compared with available experimental data on ZnTe.