Thin films of Se_80-xTe₂₀Pb_x (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 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^-9 to 10^-5 (Ohm-m)^-l 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.

Date Published: 13 November 2002
PDF: 6 pages
Proc. SPIE 4934, Smart Materials II, (13 November 2002); doi: 10.1117/12.481297

Published in SPIE Proceedings Vol. 4934:
Smart Materials II
Alan R. Wilson, Editor(s)