TRANSPORTPROPERTIESOFSOME CHALCOGENIDE ALLOYS BASED ON BISMUTH

Abstract

The cast alloy of the proposed ternary BiSnSe2 was prepared by the traditional melt quenching technique. The XRD diffraction analysis of the as-quenched powder proved the polycrystalline structure of the prepared ingot. The transport properties which were suggested were all measured using powder compact samples prepared by the cold pressing technique of the as-quenched alloy after being pulverized in the form of powder. Measurements were carried out on green as well as compacts sintered at 250 °C, 325 oc and 400 °C for different periods of time extended from 5 mins to 640 mins.

First of all, as for chalcogenide semiconductors, the current­ voltage characteristics were followed and were found to be non-linear, passing through different successive stages. The ohmic stage was the characteristic of the lowest range of the applied potential. This was followed by a field enhancement conductivity region which was terminated by a turn-over behaviour showing a tendency of switching on process to occur. Throughout the field enhancement region, the nature of the field dependence of the electrical conductivity was studied using the Marshall-Miller model. This gave the possibility of calculating both the zero-field conductivity and the characteristic length Both these parameters were found to obey temperature dependence power equations. Meanwhile, because of the thermal activation nature the temperature dependence of both parameters could be generalized in an Arrhenious form equations and the corresponding activation energies were calculated at different conditions of sintering.

As for many chalcogenides based on Bi and doped with Sn, Pb and Sb, the temperature dependence of resistivity showed the possibility of domination of whether semiconductor or semimetallic behaviours. This in addition to the possibility of semiconductor-semimetallic transition were found to be a matter of the conditions of sintering (both temperature and time) and the range of temperature at which the resistivity was measured.