Electrical Conductivity and Dielectric Properties of Se85Te15−x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films

Abstract

The alternating-current (ac) conductivity and dielectric properties of Se85Te15−x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10−5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 102 Hz to 105 Hz. The experimental results indicate that the ac conductivity \( \sigma_{\rm{ac}} (\omega ) \) and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of \( \sigma_{\rm{ac}} (\omega ) \) was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N(E F) at the Fermi level is estimated. The activation energy \( \Updelta E(\omega ) \) was found to decrease with increasing frequency. The dielectric constant e 1 and dielectric loss e 2 were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W m for the studied films was calculated from an analysis of the dielectric loss e 2 according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.