Electrical conductivity and dielectric properties of Se₈₅Te _15-x Sb_x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) thin films

The alternating-current (ac) conductivity and dielectric properties of Se₈₅Te_15-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 σ_ac (ω) and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of σ_ac (ω) 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 Δ E (ω) was found to decrease with increasing frequency. The dielectric constant ε₁ and dielectric loss ε₂ 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 ε₂ 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.