Transport properties of amorphous Se80-xTe20Pbx(0<x<2) thin films

Thin films of Se80-xTe20Pbx (0 < x < 2) glassy semiconductors have been prepared by thermal evaporation of bulk material of the above composition prepared by melt quenching technique. The glass transition temperature 'T-g', the peak crystallization temperature "T-p' and the melting temperature 'T-m' of the bulk samples have been estimated from the Differential Scanning Calorimetry (DSC) data. The DSC studies were performed at a heating rate of 10 deg/min. It has been found that 'T-g' initially decreases with small addition of Pb (x = 0.6), however its value increases with further addition of Pb (x > 0.6). This indicates that the addition of Pb (x >0.6) cross-links the already existing Se-Te chains, which in turn increases the chain length and results in the increase of T-g. The do conductivity of the films has been measured as a function of temperature and is found to be activated in the entire temperature range. Its value increases from 10(-9) to 10(-5) (Ohm-m)(-1) with the addition of Pb to Se-Te system. The do activation energy has been found to decrease from 0.67-0.23 eV with increase in Pb content. The optical energy gap determined at room temperature is found to decrease from 1.67-1.34eV with the addition of lead to the Se-Te matrix. The results are explained on the basis of enhanced valence band tailing when Pb is incorporated into the Se-Te system.