Composition dependence of photoconductivity in amorphous thin films of $Se_{.80-x}Te_{.20}Ge_x$

Özet

The present paper reports the dependence on composition of photoconductivity in vacuum evaporated thin films of amorphous $Se_{.80-x}Te_{.20}Ge_x$(x= .05, .10, .15 and .20). Temperature dependence of conductivity in dark as well as in presence of light show that conduction is through a thermally activated process in both cases. The activation energy is found to decrease with increase in light intensity, indicating shift of the Fermi level with intensity. A correlation between activation energy and the pre-exponential factor is observed in all the compositions, which could be fitted to the Meyer-Neldel rule. Measurements on the dependence of photoconductivity on intensity show that photoconductivity increases with intensity as a power law, where the power is found to be between 0.5 and 1.0. The photosensitivity $\sigma_{ph}/\sigma_d$ increases with Ge concentration. This is explained in terms of the decrease in the density of defect states with increase of Ge content in a-$Se_{.80-x}Te_{.20}Ge_x$. This is consistent with the conclusions reported in the literature by dielectric loss measurements.