THE INFLUENCE OF CADMIUM SALT ANION ON THE GROWTH MECHANISM AND ON THE PHYSICAL PROPERTIES OF CdS THIN FILMS

Cadmium sulphide films were prepared by Chemical Bath Deposition (CBD) technique from CdCl2, CdSO4, Cd(CH3COO)2 respectively, as cadmium precursor salts, and thiourea in ammoniacal medium. In this paper we study the changes in the morphology and properties of the films prepared from different cadmium salts, although the starting reaction parameters as concentration of the reactants, pH (denoted as pHi), temperature, and time of reaction for all precursor cadmium salts are identical. It is proposed that, during the deposition process, depending upon the anion type of cadmium salt the pH of reaction mixture decrease with different rates. The pHi decreases in the deposition bath could allow the change of the layers growth mechanism and therefore the change in the morphology and properties of the films. Above a certain value of starting pH (pHi >12.5), the pH decrease did not affect the growth mechanism and properties of the layers. The structure and morphology of the films were investigated by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Xray diffraction (XRD). Also the optical, electrical and photoelectrical characteristics of the layers and their dependence on films morphology were presented. These studies have allowed us to establish the optimum conditions for fabrication of quality CdS films using CdCl2, CdSO4, or Cd(CH3COO)2 as cadmium precursor salts.