Hopping Conductivity in (Zn,Fe)Se Intentionally Doped with Ag

The transport phenomena in (Zn,Fe)Se were studied. In order to obtain iron centers in Fe$\text{}^{3+}$ charge state the crystals were doped by Ag what produces acceptors compensating Fe$\text{}^{2+}$ donors. The results are explained in terms of thermally activated jumping of charges between Fe$\text{}^{3+}$ and Fe$\text{}^{2+}$ centers. The nature of activation energy is discussed. The polaron model seems to be not valid in our case. The Coulomb interaction between charged acceptors and "holes" on iron centers is considered as the origin of thermal activation of jumps. We suggest the deviation from random and mutually independent distributions of charged Ag acceptors and Fe$\text{}^{3+}$ ions resulting from the electrostatic interactions between them at high temperatures.