Modification in the chemical bath deposition apparatus, growth and characterization of CdS semiconducting thin films for photovoltaic applications

In this paper, growth and characterization of CdS thin films by Chemical Ba th Deposition (CBD) technique using the reaction between CdCl2, (NH2)(2)CS and NH3 in an aqueous solution has been reported. The parameters actively i nvolved in the process of deposition have been identified. A commonly avail able CBD system has been sucessfully modified to obtain the precious contro l over the pH of the solution at 90 degrees C during the deposition and stu dies have been made to understand the fundamental parameters like concentra tions of the solution, pH and temperature of the solution involved in the c hemical bath deposition of CdS. It is confirmed that the pH of the solution plays a vital role in the quality of the CBD-CdS films. Structural, optica l and electrical properties have been analysed for the as-deposited and ann ealed films. XRD studies on the CBD-CdS films reveal that the change in Cad mium ion concentration in the bath results in the change in crystallization from cubic phase with (1 1 1) predominant orientation to a hexagonal phase with (0 0 2) predominant orientation. The structural changes due to varyin g cadmium ion concentration in the bath affects the optical and electrical properties. Optimum electrical resistivity, band gap and refractive index v alue are observed for the annealed films deposited from 0.8 M cadmium ion c oncentration. The films are suitable for solar cell fabrication. Further on , annealing the samples at 350 degrees C in H-2 for 30 min resulted in an i ncreased diffraction intensity as well as shifts in the peak towards lower scattering angles due to enlarged CdS unit cell, This in turn brought about an increase in the lattice parameters and narrowing in the band-gap values . The results are compared with the analysis of previous work. (C) 2000 Els evier Science B.V. All rights reserved.