AC conductivity and dielectric behaviour of chalcogenide Bi 30Se (70−x)Te x thin films

Abstract

Thin chalcogenide films of Bi30 Se(70−x) Te x (x=35, 40, and 45 at%), with a thickness of about 200 nm, have been prepared by the thermal evaporation technique. The physical properties that have been studied are: the density (d), the heat of atomisation (Hs), the average coordination number (Z), and the number of lone pair bonds. The AC conductivity (σac or σω) has been measured in the frequency range of 0.1–20 kHz over the temperature range 303–373 K. All samples exhibit a common pattern, where ln(σac) or ln(σω) is a linear function of ln(ω ), and the frequency exponent (s) was found to be less than unity. It was found that there were two conduction mechanisms in all samples. At low temperature, small polaron-tunneling is the dominant mechanism. On the other hand, at high temperature, correlated barrier hopping is the mechanism involved. The dependence of the complex dielectric function ϵ’ and the loss factor (tanδ) on both frequency and temperature has been also studied.