Antimony-doping effect on the ac conductivity of the amorphous Se-Te system

ac-conductivity measurements have been made on the Se_80-x{Sb}ₓTe₂₀ (0{≤}x{≤}9) system at temperatures from 150 to 300 K in the frequency range from 0.5 to 10 kHz. In this frequency range the ac conductivity σac({ω}) is proportional to ωˢ. In the Se₈₀{Te}₂₀$ (x=0) sample the ac conductivity and the frequency exponent s show a weak temperature dependence, and the results are interpreted on the basis of the correlated-barrier-hopping (bipolaron-hopping) model for random distribution of defect centers. In samples containing Sb (x>0), σac({ω}) and s show a strong temperature dependence at higher temperatures. The low-temperature ac-conductivity results of these samples can be explained by the bipolaron hopping between the charged states. However, to account for the high-temperature data, it has been proposed that an addition of antimony in the Se-Te system introduces Sb(0,+) states near the Fermi level and single electron hopping between these antimony-related states is responsible for the observed behavior of ac conductivity at high temperatures. The values of density and energy of the charged states and the Sb-related centers have been estimated.