Photoconductivity studies in a-Se75In25-xPbx thin films

The present paper reports the steady state and transient photoconductivity measurements in vacuum evaporated thin films of amorphous Se(75)ln(25-x)Pb(x) (x = 0, 4, 6 & 10). The behaviour of photoconductivity is found to be same in all the compositions except that the photoconductive parameters show a discontinuity at a Pb concentration of 4 at %. This is explained in terms of mechanically stabilized structure at a particular average coordination number following the theory of Phillips and Thorpe for the topological model in case of chalcogenide glasses. Transient photoconductivity measurements at different temperatures indicate that a persistent photoconductivity occurs in these glasses, which increases at higher temperatures. This is attributed to light induced effects in these materials. Even after subtracting the persistent photoconductivity the decay of the resulting photoconductivity is quite slow which is found to be non - exponential in the present case indicating the presence of continuous distribution of defect states.