Amorphous-crystalline transformation and conductivity enhancement in annealed bismuth sulphide thin films

Post-deposition vacuum annealing of chemically deposited Bi 2 S 3 thin films has been found to enhance the dark conductivity of the films from approximately=10 -7 Omega cm -1 to approximately=10 2 Omega -1 cm -1 and the photoconductivity from approximately 10 -5 Omega cm -1 to approximately=10 2 Omega cm -1 . Such increase is attributed to (i) an amorphous-to-crystalline transformation of the setting in at approximately=175 degrees C, confirmed by X-ray diffraction studies and (ii) loss of sulphur from the film during vacuum annealing at temperatures >200 degrees C, confirmed by the absence of this effect in air/nitrogen annealing. In the case of annealing in air, the competing effect of mobility enhancement by amorphous-crystalline transformation and mobility depreciation by oxygen chemisorption at the intergrain region is seen to contribute to a dark conductivity and photoconductivity maxima at an annealing temperature of approximately=200 degrees C.