EXPERIMENTAL AND THEORETICAL STUDY OF CdS DEPOSITION BY CHEMICAL BATH

Abstract

In this work experimental data from a chemical bath deposition process for CdS growth were compared against simulated data of the evolution of the concentration curves of Cd2+, S2-, and cadmium complexes (CdnOHm, Cdn(NH4)m2+, CdClm), obtained with HySS speciation software. We considered equilibrium reactions of complexes from atmospheric CO2 hydrolysis like HCO3- and CO32- on CdS formation mechanism. Series of CdS thin films were prepared in a bath containing 0.02M CdCl2, 0.5M KOH, 1.5M NH4NO3, 0.2M SC(NH2)2 at 65 ºC, compared with another growth with only CdCl2 + KOH + NH4NO3 to compare CdCO3 formation non related with thiourea hydrolysis. The model was initially feed with experimental data from the chemical bath, i.e. [NO3-] was determined by Raman spectroscopy, pH, pCd2+ and pS2- from potentiometric data. The pH evolution was reproduced almost exactly with the proposed model. Films were characterized by XRD and UV-Vis spectroscopy, Film thickness was calculated by using SCOUT software from transmittance data. CdCO3 was identified by XRD confirming the influence of atmospheric CO2 and also the data indicate an important role of the nitrate complexes in the film growth kinetics.