Nanocrystalline Bi2S3 thin films grown by thio-glycolic acid mediated successive ionic layer adsorption and reaction (SILAR) technique

Bismuth sulfide (Bi2S3) nanocrystalline thin films were deposited on glass substrate by a simple and low-cost thioglycolic-assisted successive ionic layer adsorption and reaction method, using bismuth acetate and thioacetamide as cationic and anionic precursors respectively. Influence of cationic concentration on the structural, optical and electrical properties of Bi2S3 thin films were investigated. X-ray diffraction pattern revealed that the prepared Bi2S3 thin films are polycrystalline with orthorhombic structure. The surface morphology of Bi2S3 thin films examined by atomic force microscopy showed cluster like morphology, and having small hillocks of fairly uniform distribution. Optical studies showed a direct band-to-band transition, and the estimated optical band gap decreases from 1.81 eV to 1.25 eV with the increase in cationic concentration from 0.01 M to 0.03 M. Electrical resistivity measurements by four probe technique revealed negative temperature coefficient of resistance, which confirms the semiconducting nature of Bi2S3 thin films. The activation energy of Bi2S3 thin films was found to decrease from 0.059 eV to 0.022 eV with the increase in cationic concentration from 0.01 M to 0.03 M, which is attributed to improved grain size and reduction in the defect levels.