Effect of pH on the Electrodeposition of ZnTe Film from a Citric Acid Solution

Potentiostatic cathodic electrodeposition of ZnTe was investigated from the viewpoint of the effect of pH on the deposits' composition and crystallinity using citric acidic electrolytic baths, in which Zn(II) and Te(IV) species were dissolved to form ZnH₂Cit⁺, ZnHCit, ZnCit^-, Zn(Cit)₂^4- and HTeO₂⁺, HTeO ₃^-, respectively (Cit: citrate) at various pH. The complex equilibrium calculation was carried out to examine the most predominant complex ion for Zn-Cit system at different pH. Deposition of three kinds of deposits, i.e., polycrystalline ZnTe with closely stoichiometric composition, crystalline Te, and the mixed crystal due to Te and ZnTe, can be controlled by changing the pH and [Zn(II)]/[Te(IV)] concentration ratio of the baths. All the deposits obtained at pH 4.0 were well crystallized with a ZnTe cubic preferential orientation along the (111) plane without any post-treatment. The difference of the electrodeposition behavior at various pH was also discussed.