Dielectric properties of thin films of chalcogenide glasses

Abstract

The temperature-frequency dependences of the conductivity (σ), capacitance (C), and dielectric-loss coefficient (ε″) have been measured for metalglass film (composition As₃₀Ge₁₀Si₁₂Te₄₈)-metal structures in an alternating electric field. The glass film was obtained by the method of radiofrequency sputtering in an argon atmosphere, and the top and bottom molybdenum electrodes by thermal evaporation in vacuum. The measurements were made in the frequency range 4·10²−2·10⁴ Hz at temperatures 209–299°K. The relaxation component σ_r=σ_∼−σ₋ of the conductivity for T < 240°K and high frequencies does not depend on the temperature (T) and is proportional to ω^0.8. At higher temperatures, σ_r(ω) is described by a complicated curve, which has at low frequencies the behavior ≈ω² and goes over to saturation at large values of ω. In this range of frequencies and for positive temperatures σ_r ≈ exp(ΔE/ϰT), where ΔE ≈ 0.45 eV. The frequency-temperature dependences of σ_r, C, and ε′' are interpreted on the basis of Fröhlich's model. The calculated and experimental curves are compared. It is assumed that the loss of relaxation type is due to two processes, one of which is governed by carrier hops between localized states near the Fermi level and is predominant at low temperatures. The other is determined by carrier hops between the same states through the valence band and is predominant at positive temperatures.