AC conductivity and dielectric properties of Sb2Te3 thin films

Sb2Te3 films of different thicknesses, in the thickness range 300-620 nm, were prepared by thermal evaporation. X-ray analysis showed that the as-deposited Sb2Te3 films are amorphous while the source powder and annealed films showed a polycrystalline nature. The AC conductivity and dielectric properties of Sb2Te3 films have been investigated in the frequency range 0.4-100 kHz and temperature range 303-373 K. The AC conductivity sigma(AC)(omega) was found to obey the power law omega(s) where s <= 1 independent of film thickness. The temperature dependence of both AC conductivity and the exponent s can be reasonably well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant epsilon(1) and the dielectric loss epsilon(2) are frequency and temperature dependent and thickness independent. The maximum barrier height W-M calculated from dielectric measurements according to the Guintini equation agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The effect of annealing at different temperatures on the AC conductivity and dielectric properties was also investigated. Values of sigma(AC), epsilon(1) and epsilon(2) were found to increase with annealing treatment due to the increase of the degree of ordering of the investigated films. The Cole-Cole plots for the as-deposited and annealed Sb2Te3 films have been used to determined the molecular relaxation timer. The temperature dependence of tau indicates a thermally activated process. (c) 2005 Published by Elsevier Ltd.