Mass-ratio dependence and critical binding of exciton-ionized donor complex in polar crystals

Abstract

The dependence of the binding energy of an excition-ionized donor complex on the electron-to-hole mass ratio is investigated. Recently published forms of the electron-hole interaction potential including the interaction via the phonon field are used. The calculations are performed for a few typical sets of parameters characterizing the coupling of the charges with the phonon field. The results indicate that the highly accurate estimates of the critical mass ratio obtained for the Coulomb form of the electron-hole interaction potential are inapplicable for most typical crystals, suffering from an inherent error due to the neglect of the exponential screening due to polarization. For crystals where the electron-phonon interaction is strong, the mass-ratio dependence of the binding energy is found to differ from the Coulomb-like behavior even in the most general qualitative features.