STUDIES OF THE CATHODIC ELECTRODEPOSITION OF CDS FROM AQUEOUS-SOLUTION

The cathodic electrodeposition of CdS from aqueous solutions of Cd2+ a nd S2O32- a 90-degrees-C has been investigated using a combination of voltammetric and galvanostatic techniques. It was found that the overa ll deposition is an EC-type mechanism, where the initial, electrochemi cal step is the reduction of Cd2+. This is followed by the reaction of S2O32- with the reduced Cd species, which is the rate-determining ste p. The presence in the electrolyte of both Cd2+ and S2O32- at 90-degre es-C results in the spontaneous formation of finely-divided CdS and a decrease in solution pH. The lower pH increases the rate of the chemic al reaction of the EC process, shown by the increase in CdS film thick ness as pH decrease. Lower pH also promotes a low potential process wh ich interferes with both controlled-potential and controlled-current C dS growth.