Photoconductive properties of amorphous Se_85–xTe₁₅Bi_x thin films

Abstract

The optical and electrical properties of Se_{85– 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.

Keywords:

• chalcogenide glasses
• dark conductivity
• defect states
• transient photoconductivity