Abstract
Thin films of Se<sub>80-x</sub>Te<sub>20</sub>Pb<sub>x</sub> (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<sub>g</sub>", the peak crystallization temperature "T<sub>p</sub>" and the melting temperature "T<sub>m</sub>" 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<sub>g</sub>" 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<sub>g</sub>. The dc 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<sup>-9</sup> to 10<sup>-5</sup> (Ohm-m)<sup>-l</sup> with the addition of Pb to Se-Te system. The dc 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.
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