ZnTe thin films were electrodeposited onto Au-coated Cu substrates from an electrolytic solution containing ZnSO4, TeO2, citric acid and sodium citrate, and the dependence of structure, composition and surface morphology on the solution's Zn concentration were investigated. Results of examinations for resistivity and optical absorption demonstrated, respectively, that as the Zn concentration in the electrolyte was reduced over the range of 5–50 mmol dm−3, the resistivity of the films obtained continuously decreased and their band gap increased. Quantative analysis of energy dispersive x-ray analysis and inductively coupled plasma results indicated that the composition ratio (Zn : Te) was approximately stoichiometric under all conditions in this study. X-ray diffraction results revealed that all the ZnTe thin films obtained showed a preferred (111) orientation with cubic structure. ZnTe thin films we transferred onto nonconductive epoxy resin also showed the same structure.
The cathodic electrodeposition of ZnTe film was studied using an aqueous citric acid bath ͑pH 4; temperature 368 K͒ in which Zn͑II͒ and Te͑IV͒ species were dissolved to form Zn(Cit) 2 4Ϫ and HTeO 2 ϩ ions, respectively. The deposition mechanism was studied based on cyclic voltammetry. The influence of the deposition potential on the morphology, composition, and structure of the deposited film was also investigated. A smooth, dense polycrystalline ZnTe film with nearly stoichiometric composition was deposited at a constant cathode potential, ranging from Ϫ0.80 to Ϫ0.60 V vs. Ag/AgCl, from a solution containing 20 mmol dm Ϫ3 Zn͑II͒, 0.16 mmol dm Ϫ3 Te͑IV͒, 0.25 mol dm Ϫ3 H 3 Cit, and 0.25 mol dm Ϫ3 Na 3 Cit (Cit ϭ C 6 H 5 O 7 ). Potentials in this range provided the deposited ZnTe film with high current efficiency ͑above 98%͒. During electrodeposition of the nearly stoichiometric crystalline ZnTe, the current density was approximately stationary.
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 ZnH 2 Cit þ , ZnHCit, ZnCit À , Zn(Cit) 2 4À and HTeO 2 þ , HTeO 3 À , 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.
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