Non-toxic growth of CuxS thin films in alkaline medium by ammonia free chemical bath deposition

CuxS thin films were deposited on commercial glass substrates at different temperatures by an ammonia-free chemical bath deposition process. The deposition process is based in a copper chloride- sodium citrate- thiourea system. The pH value in the reactive solution was adjusted at 10 by addition of KOH and buffer solution. In order to investigate the effect of the deposition temperature and time, four reaction baths were prepared and set at temperatures 25, 40, 55 and 70 °C. The deposited films were studied by X-ray diffraction, Raman spectroscopy, 3D optical microscopy, energy dispersive X-ray spectroscopy, electron probe X-ray microanalysis, UV-vis spectroscopy and two-points probe electrical measurements. The chemically deposited CuxS films showed good adherence to the substrate, homogeneity, metallic luster and light reddish-brown appearance. The thickness of the films varied in the range of 40-80 nm, depending on the deposition conditions. The X-ray diffraction revealed that the films present amorphous nature, excepting those deposited at the highest temperature, which had CuS covellite crystalline structure. The chemical composition of the films exhibited the presence of the covellite phase with excess of sulphur atoms in all cases. The electrical analysis showed a strong decrease in the resistivity with increasing the deposition temperature with values in the range from 106 to 10−2 Ωcm.