Conduction Band Influence on the Properties of Bistable Donors

A theoretical description of bistable donors in polar semiconductors is proposed. The donor states are described within the one-band approximation, which takes into account a finite width and nonparabolicity of the conduction band. The interaction between the defect and the crystal lattice is assumed in the Fröhlich form. For the bistable indium impurity in cadmium fluoride, a coexistence of strongly and weakly localized donor states has been obtained. The calculated energies for both the states and absorption band shape in the 3-eV range are in agreement with experiment.