ELECTRODEPOSITION OF THIN-LAYERED CdTe SEMICONDUCTOR FROM BASIC AQUEOUS SOLUTIONS

摘要

Cadmium telluride (CdTe) semiconductor has been well investigated as a CdS/CdTe heterojunction solar cell material since its band gap is suitable for energy conversion from sunlight into electricity. In this paper a new electrochemical processing of thin-layered CdTe using basic aqueous electrolytes is reviewed from the standpoint of thermodynamics using a potential-pH diagram. The cathodic electrodeposition of the stoichiometric CdTe with a flat surface morphology took place at more positive potentials than that of the Nernst potential for the bulk-Cd deposition and at more negative potentials than that for the bulk-Te. In this potential region deviation from the stoichiometric composition of electrodeposited CdTe was controllable by the Cd(Ⅱ)/Te(Ⅳ) concentration ratio, pH, or concentration of complexing agent for Cd~(2+) ions of the electrolytes. The deposition behaviors for ammoniacal media were well accounted for by the potential-pH diagram of the Cd-Te-NH_3-H_2O system devised by a combination of those of the Cd-NH_3-H_2O and the Te-H_2O systems. Diagrams for other complexing agents, ethylenediamine and diethylenetriamine, were also constructed to investigate and discuss the electrodeposition conditions regarding the corresponding media.