Effect of free carrier screening on the binding energy of D− centers in polar semiconductors

A calculation of the binding energy of a D^? center, defined as the energy required to remove one of the two electrons from the D^? center to infinity, in the presence of other free carriers is reported in polar crystals. It is assumed that the effective interaction between each of the two electrons and the positive ion is described by Thomas-Fermi potential. The effective interaction between the two electrons in polar crystals is, however, described by two recently proposed potentials. The binding energy of a D^? ion is calculated variationally in several polar crystals as a function of the screening parameter δ and the value of δ at which the binding energy goes to zero (D^? Mott transition) is determined. A possible experimental situations where this system may be studied is discussed.