Te_{42}As_{36}Ge_{10}Si_{12} chalcogenide composition was prepared by conventional melt-quenching. The ac conductivity and the dielectric properties were carried out in the frequency range 0.5×10^{3}-4×10^{6} Hz and temperature range 300-423 K. The analysis of the experimental results of the frequency dependence of ac conductivity σ_{ac}(ω) indicates that σ_{ac}(ω) is proportional to ω^{s} where s> 1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier hopping model. The maximum barrier height W_{m} calculated from ac conductivity and the density of localized states were determined. Values of dielectric constant ε_{1} and dielectric loss ε_{2} were found to decrease with frequency and increase with temperature. The analysis of dielectric loss leads to determine the barrier height W_{m} and agrees with that proposed by the theory of hopping of charge carriers over potential barrier between charged defect states as suggested by Elliott in case of chalcogenide glasses.
Thermally evaporated As_{36}Te_{42}Ge_{10}Si_{12} amorphous chalcogenide films were prepared in a vacuum of 10^{-5} Torr on to glass substrates hold at about 300 K during the deposition process. Measurements of the optical properties have been made. The optical transmittance and reflectance spectra of films in the thickness range 155-395 nm were measured in the wavelength λ range 500-2500 nm. The refractive index n, the extinction coefficient k and the absorption coefficient α were calculated for the studied films. It is found that both n and k are independent on the film thickness. The refractive index n has anomalous behavior for the wavelength λ range 500-1500 nm, while it has normal dispersion for the wavelength greater than 1500 nm. The optical energy gap was estimated from absorption coefficient. The allowed optical transitions were found to be nondirect transitions with optical gap of 1.08 eV for the sample under test. The effect of annealing on the obtained optical parameters was also investigated.
The ac conductivity and dielectric properties of Ge_{15}Se_{60} X_{25} (X = As or Sn) thin films are reported in this paper. The thin films were deposited by thermal evaporation at 10^{-5} Torr pressure. The films were well characterized by X-ray diffraction, differential thermal analysis and energy dispersive X-ray spectroscopy. The ac conductivity was measured over temperature range 303-413 K and frequency range 10^2-10^5 Hz. The frequency dependence of the ac conductivity was found to be linear with slope which lies very close to unity and is independent of temperature. This behavior can be explained in terms of the correlated barrier hopping between centers forming intimate valence alternation pairs. Values of the dielectric constant ε_1 were found to decrease with frequency and increase with temperature. The maximum barrier height W_{m} for each sample, which was calculated from the dielectric measurements according to the Guinitin equation, agrees with the theory of hopping of charge carriers over potential barrier as suggested by Elliott in case of chalcogenide glasses. The density of localized state near the Fermi level was estimated for the studied films.
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