The ac conduction mechanism and dielectric relaxation behavior of amorphous Te81Ge15Bi4 chalcogenide glass thin films

Abstract

Various chalcogenide amorphous films of Te81Ge15Bi4 in the range (143–721 nm) were synthesized using the thermal evaporation technique. The ac electrical conductivity {sigma }_{ac}left(omega right) and dielectric measurements were examined for the studied films over the temperature and frequency ranges of (303–393 K) and (100 Hz–1 MHz), respectively. The obtained results of ac conductivity {sigma }_{ac}left(omega right) are temperature dependent and follow the relation {sigma }_{ac}left(omega right)propto {omega }^{s}, where the frequency exponent s decrements with temperature through the examined range. These results of {sigma }_{ac}left(omega right) and s are explained based on the correlated barrier hopping CBH model. Values of ac activation energy Delta {E}_{sigma }left(omega right) show thickness independence and decrease from 0.270 to 0.144 eV as the frequency increases. The estimated maximum barrier height {W}_{M} values decrement with temperature in the considered frequency range. The density of localized states near the Fermi level Nleft({E}_{F}right) increases with increasing temperature and frequency. The dielectric constant {varepsilon }_{1}(omega ) and loss {varepsilon }_{2}(omega ) were found to increment with temperature and decrement with frequency. The obtained results indicate that {sigma }_{ac}left(omega right), Nleft({E}_{F}right), {varepsilon }_{1}left(omega right) and {varepsilon }_{2}left(omega right) are enhanced by decreasing the thickness of the film sample in the investigated ranges of temperature and frequency. The real {M}_{1}(omega ) and imaginary {M}_{2}(omega ) parts of the electric modulus were studied for the films under test, and the value of the activation energy for relaxation Delta {E}_{r} (0.143 ± 0.002 eV) is thickness independent in the investigated range.