TRANSIENT AND STEADY STATE PHOTOCONDUCTIVITY STUDIES ON BULK GLASSES AND AMORPHOUS FILMS OF Ge-Te-Pb- COMPOSITION AND SPECTRAL DEPENDENCE

Transient photoconductivity studies have been undertaken on bulk Ge20Te80-x Pbx glasses with varied lead content (2 < x < 8); The composition dependence of normalized photoconductivity and photo-decay have been investigated upon white light incidence. The photoconductivity rise and its decay with time indicate that the process may best be understood in terms of the recombination within the localized states. Further, it has been found that the addition of lead results in an initial decrease in the photoconductivity, showing anomalous variations at compositions x = 5, 6.5 and 7.5. Steady state photoconductivity studies on amorphous Ge20Te80-xPbx thin films (2 < x < 8) have also been undertaken. The intensity dependence of steady state photoconductivity indicates the existence of continuous distribution of localized states in the mobility gap of this material. Further, the spectral dependence of photoconductivity has been studied using various interference filters. The composition dependence of steady state photoconductivity due to white light incidence, shows pronounced anomalies at x = 5, 6.5 and 7.5. Based on the present photoconductivity studies and other investigations, it has been proposed that the rigidity percolation occurs in Ge20Te80-x Pbx glasses, over an extended composition region with the composition x = 5 (xc1) and x = 6.5 (xc2) being the onset and completion of the rigidity percolation. The composition x = 7.5 corresponds to the chemical threshold of the system