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

Abstract

ac-conductivity measurements have been made on the ${\mathrm{Se}}_{80\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$${\mathrm{Te}}_{20}$ (0\ensuremath{\le}x\ensuremath{\le}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 ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{ac}}$(\ensuremath{\omega}) is proportional to ${\mathrm{\ensuremath{\omega}}}^{\mathit{s}}$. In the ${\mathrm{Se}}_{80}$${\mathrm{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), ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{ac}}$(\ensuremath{\omega}) 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 ${\mathrm{Sb}}^{(0,+)}$ 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.