Growth mechanism of pulse electrodeposited cadmium sulfide and zinc sulfide thin films with tartaric acid and glycerol as additives

Room temperature electrodeposition of thin films is beneficial, especially for cadmium sulfide (CdS) and zinc sulfide (ZnS), which are utilized in optoelectronic applications. The present study is unique, owing to its utilization of tartaric acid in the electrochemical deposition of these binary sulfides. This organic acid has been shown to play a vital role in mitigating the precipitation of sulfides and facilitating deposition. Also, the impact of this organic acid on the growth mechanism is evaluated by electroanalytical techniques including cyclic voltammetry and chronoamperometry. From the Randles-Sevcik plot, it is verified that the deposition is governed by a diffusion-controlled process. The elemental analyses unveil that the composition at deposition potentials of -1.1 V for cadmium sulfide and -1.4 V for zinc sulfide are near stoichiometric. The electrocrystallization of the films is interpreted employing Scharifker-Hills nucleation model and is observed to follow progressive nucleation for cadmium sulfide and instantaneous nucleation for zinc sulfide. The deposition process is characterized using impedance measurements that have affirmed the formation of cadmium sulfide and zinc sulfide via intermediate metal tartrate complex. The X-ray diffraction and Raman spectroscopy of as-deposited cadmium sulfide and zinc sulfide thin films confirm the hexagonal and cubic phases, respectively. The results show the adequacy of the method for the deposition of crystalline quality thin films at room temperature in the presence of tartaric acid.