Control of composition and conduction type of CdTe film electrodeposited from ammonia alkaline aqueous solutions

Potentiostatic cathodic electrodeposition of CdFe films was studied using aqueous ammonia-alkaline electrolytic baths in which Cd(II)- and Te(IV)-species were dissolving to form Cd(NH3)(4)(2+) and TeO32- ions, respectively. Deposition of three kinds of films, i.e., Te-rich amorphous, Te-rich polycrystalline CdTe, and Cd-rich polycrystalline CdTe films, can be controlled by changing the pH (pH 10.5-12.2) and Cd(II)/Te(IV) concentration ratio of the baths. All the films deposited at -0.70 V vs. the standard hydrogen electrode (SHE) had a flat and smooth morphology. Deposition current density and efficiency were reduced with increasing Cd content of the film. The deposition behavior was interpreted with a potential-pH diagram of the Cd-Te-NH3-H2O system. Based on the results, the mechanism of the CdTe electrodeposition was presumed to be (i) deposition of tellurium atoms followed by (ii) an immediate adsorption of Cd(II) ions on the surface tellurium atoms, and (iii) an underpotential deposition of Cd on the surface Te. Conduction types of the Te-rich and Cd-rich CdTe films after heat-treatment were p- and n-type, respectively, whereas untreated CdTe film was n-type. (C) 1999 The Electrochemical Society. S0013-4651(99)06-036-X. All rights reserved.