Thermoelectric power of the bulk amorphous GexSe1-xsystem

DC conductivity and thermoelectric power of bulk amorphous samples of GexSe1-x (0.1<x<0.4) have been studied as functions of temperature (77-350 K) and composition. The thermoelectric power was found to be positive. The thermo-electric power exhibits a less steep temperature dependence compared with that of the conductivity data. This discrepancy has been explained on the basis of the small polaron model, the chaotic band model and the two-channel model. It was observed that the discrepancy cannot be reconciled with the small polaron model and chaotic band model predictions but the data are best fitted to a parallel current path model, in extended and localised states at the band edges as proposed by Nagels et al. (1985). The present analysis also provides evidence for the existence of a small tail of localised states at the valence band edge.