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 σAC(ω) was found to obey the power law ωs 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 ε1 and the dielectric loss ε2 are frequency and temperature dependent and thickness independent. The maximum barrier height WM 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 σAC, ε1 and ε2 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 time τ. The temperature dependence of τ indicates a thermally activated process.