Ternary cadmium and zinc sulfides: composition,morphology and photoelectrochemistry.

Morphology, structure and electronic properties of CdS, ZnS and the mixed ternary compounds of formula CdxZn1-xS deposited on Ag(1 1 1) by electrochemical atomic layer epitaxy (ECALE) have been characterized as a function of the composition. The number of the attainable x values is limited by the necessity of using well-defined ZnS/CdS deposition sequences. However, the quantitative analysis carried out with different techniques indicates that the ECALE method has a good control on composition. The morphological analysis, performed on the basis of the roughness and clusters’ size evaluation, indicates both two-dimensional and three-dimensional growth. Photoelectrochemical measurements, carried out at the film electrodes in liquid junction with an alkaline (poly)sulfide electrolyte, show in all cases photospectra shapes typical of a direct transition. The bandgap of CdxZn1-xS is roughly linear with composition parameter x, a behavior consistent with the formation of solid solutions in a system without miscibility gap. Despite the limits and deviations from an ideal epitaxial process, the ECALE method provides mixed ternary compounds with predictable composition and related electronic properties (e.g. the bandgap).