SOME PHYSICAL-PROPERTIES OF THE BI-SB-SE SYSTEM

The electrical and thermal conductivities of Bi-10 Sb-x Se-90-x (x = 3 5, 40 and 45) films have been studied as a function df temperature in the range 291-373 K below the corresponding glass transition temperatu re T-g(T-g similar to 418 K). The effect of film thickness in the rang e 350-650 nm for Bi-10 Sb-35 Se-55 as a representative example has bee n investigated in the considered temperature range. It is found that t he conduction in all the samples takes place in the extended states vi a thermally activated tunnelling in the entire range of temperature 29 1-373 K. In the high temperature region the conduction mechanism remai ns the same while al lower temperature, the conduction is due to varia ble range hopping in the localized states near Fermi level. An increas e in the film thickness was found to result in the increase of the act ivation energy E(at), decrease of the room temperature electrical cond uctivity sigma(RT) and pre-exponential factor sigma(Ot) for the consid ered system. The coefficient of thermal conductivity X increases linea rly with temperature below T-g for the compositions investigated. The increase of Sb content in the chalcopyrite glass Bi-10 Sb-x Se-90-x (x = 35, 40 and 45) system leads to an increase in the room temperature electrical conductivity sigma(RT) and the thermal conductivity X(20), and decreases the activation energy E(sigma) and the pre-exponential f actor sigma(0). The observed compositional dependence of sigma and E(a ) has been correlated with the weak bonds and strong bonds in the stru cture of the compositions investigated with increasing Sb content. The decrease in sigma(0) and the increase in X have been correlated with the decrease in mobility and the increase in phonon velocity, respecti vely.