Effects of pH value on the characteristics of CBD-CdS films

CdS films were prepared by chemical bath deposition (CBD) method at different pH values. The influences of the pH value, measured at reaction temperature, on the surface morphology, structure, thickness and optical properties of CdS films were studied by analysising the films with SEM, XRD, step profiler and UV spectrophotometer. The results showed that films with compact grains, no pinholes and cubic crystal structure were obtained in the whole range of the pH values studied. With the decrease of pH value from 10.09 to 8.43, the crystals tends to grow along the orientation of (111) face, the size of the clusters decreases from more than 200 nm to 80 nm while the size of the crystal grains increases from 15.5-27.0 nm, the thickness of the films decreases from 340-80 nm, the transmittance of the films increases, the absorption edge shifts to the blue side and the band gap value of film increases from 2.36-2.44 eV.