ANTIMONY-DOPING EFFECT ON THE AC CONDUCTIVITY OF THE AMORPHOUS SE-TE SYSTEM

ac-conductivity measurements have been made on the Se80-xSbxTe20 (0 less-than-or-equal-to x less-than-or-equal-to 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 sigma-ac(omega) is proportional to omega-s. In the Se80Te20 (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), sigma-ac(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 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.