Synthesis of nanostructured CuxS thin films by chemical route at room temperature and investigation of their size dependent physical properties

Nanostructured semiconductors show very interesting physical properties than bulk crystal due to size effects that arises because of quantum confinement of the electronic states. Using cupric acetate and sodium thiosulphate as cationic and anionic precursor, nanostructured Cu2S thin films were successfully prepared at room temperature by chemical bath deposition technique. By varying the deposition time from 9 to 24 h, the Cu2S films of thickness 70-233 nm were prepared. The different characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption and electrical resistivity measurement techniques were used to investigate size dependent properties of Cu2S thin films. As thickness increases, the hexagonal covellite phase of CuS observed at thickness 70 nm gets converted to monoclinic chalcosite phase of Cu2S. The resistivity and activation energy is found to be thickness dependent. The optical band-gap energy increases from 2.48 to 2.90 eV as thickness decreases from 233 to 70 nm. The influence of film thickness on carrier concentration, mobility and thermo-emf is reported. (C) 2011 Elsevier B. V. All rights reserved.