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

Abstract

The transport phenomena in (Zn,Fe)Se were studied. In order to obtain iron centers in Fe 3 + charge state the crystals were doped by Ag what produces acceptors compensating Fee+ donors. The results are explained in terms of thermally activated jumping of charges between Fe 3+ and Fee + 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 3 + ions resulting from the electrostatic interactions between them at high temperatures.PACS numbers: 71.55.Gs, 72.80.Ey More than 20 years ago studies on transport phenomena in phosphate glasses containing transition metal (TM) ions were carried out [1,2,3]. The thermally activated hopping of charges between TM ions in various charge states was proposed as the mechanism of conductivity.One may expect that a similar type of hopping could be observed in the II-VI semimagnetic semiconductors in which the levels of TM ions lie deep in the energy gap. We investigated the transport phenomena in the (Cd,Fe)Se crystals, where the Fe2+/3+ donor level lies about 600 meV above the top of the valence band. The results were interpreted in terms of "holes" (Fe in Fe3+ charge state) jumping to the nearest Fee+ centers [4]. A certain number of Fe 3 + ions is believed to result from the compensation caused by unidentified acception present in the crystals.Now we report the results of the studies of transport phenomena in (Zn,Fe)Se mixed crystals. In this material the Fe2 +/3 + donor level lies about 700 meV above the top of the valence band [5,6]. The as-grown crystals with iron content 0.6 at.% are semiinsulating. Their conductivity at 293 K is lower than 10 -1 0 S/cm. To produce Fe3+ centers necessary for hopping conductivity one has to dope the crystals with acceptors compensating iron donors. The Ag was chosen (749)