Photoconductive properties of amorphous Se85– x Te15Bi x thin films

Abstract

The optical and electrical properties of Se85– x Te15Bi x (where x = 0, 1, 2, 3, 4, 5) amorphous thin films prepared by vacuum evaporation have been measured at room temperature (303 K). Dark conductivity measurements in the temperature range 303–333 K show that for all compositions conduction occurs via an activated process with a single activation energy (ΔE d). The optical band gap (E g) as determined by the Tauc extrapolation method follows a similar trend to that of the dark activation energy, except for the sample with x = 1 at.%. The photoconductivity follows a power law with intensity σ Ph , where γ lies between 0.5 and 1.0, suggesting that the recombination process is bimolecular in nature. The variation in photocurrent with time reveals a persistent photocurrent which takes several hours to decay. The differential lifetime (τ d) is determined from the rise and decay of photocurrent with time and is found to increase with increasing Bi content. The dispersion parameter (α) and localized state distribution parameter (E 0 ) have also been determined from the decay curves and are reported for the studied compositions.