## 3 Results and Discussion
### Structure of ZnTe Electrodeposited on ITO  
Figure 2 shows the effect of the post-annealing process on the surface appearance of electrodeposited zinc telluride thin films. The as-electrodeposited samples (a) were post-annealed at 653 K (b), 663 K (c), 673 K (d), and 683 K (e) for 5 h. As shown in Figure 2a, the as-deposited zinc telluride thin film exhibited a black tilt, whereas the samples with the annealing treatment (Figure 2b-e) exhibited a reddish-brown tilt, a typical surface appearance of a single-phase zinc telluride. Figure 2: Effect of annealing temperature on the surface appearance of electrodeposited ZnTe thin films onto ITO glass substrates. As-deposited samples (**a**) were annealed at 653 K (**b**), 663 K (**c**), 673 K (**d**), and 683 K (**e**) for 5 h.  
Figure 3 shows the SEM images of the as-deposited zinc telluride thin films (a) as well as samples annealed at 683 K for 5 h (b). The samples were electrochemically synthesized at a potential of \(-\)0.8 V. Based on the SEM images, the samples consisted of small nodules with a diameter of approximately 1 \(\upmu\)m. We could not improve the micro-scale morphology of the electrodeposition, even though the citric acid bath was employed. The effect of annealing on the morphology of the electrodeposited zinc telluride thin films was not so obvious according to the SEM images. [PERSON] et al. also revealed that electrochemically synthesized zinc telluride thin films consisted of small nodules with a diameter ranging from 300 nm to 600 nm [30]. Their results gave good agreement with the present study. Considering Equation (2), the surface morphological appearance of electrochemically synthesized zinc telluride thin films will be affected by the morphology of electrodeposited Te. The solubility of Te complex ions is quite small in comparison with that of Zn(Cit)\({}^{2-}\) ions because the saturated concentration of Te complex ions is approximately \(10^{-3}\) mol L\({}^{-1}\). Hence, the electrochemical deposition current of the Te complex ions at \(-\)0.8 V seemed to reach the diffusion limitation, as described in Figure 1a. The crystal nucleation density of electrodeposited metals increases with an increase in the overpotential. Therefore, the surface morphology of crystals that are electrochemically synthesized at a high current density over the diffusion limit should be transformed to that of fine particles with powder-like nodules. Consequently, the small nodules of deposited zinc telluride obtained in our study seemed to be formed by the characteristic electrodeposition behavior of Te complex ions with a significant overpotential. Figure 4 shows the effect of the post-annealing temperature on the XRD profiles of the zinc telluride thin films. The as-deposited sample (a) was annealed at 653 K (b), 663 K (c), 673 K (d), and 683 K (e) for 5 h. As shown in Figure 4a, the as-deposited sample was composed of an amorphous-like phase, whereas the samples annealed at 653-673 K consisted of crystalline binary phases with ZnTe and Te, as shown in Figure 4b-d. By contrast, the sample annealed at 683 K was composed of crystalline single-phase ZnTe (Figure 4e). The melting points of pure Zn and pure Te are 693 K and 723 K, respectively, while that of the ZnTe compound is 1563 K. Usually, the recrystallization temperature \(T_{\text{R}}\) of metallic materials with the melting point \(T_{\text{M}}\) ranges from \(T_{\text{M}}\)/3 to \(T_{\text{M}}\)/2. Hence, the \(T_{\text{R}}\) of pure Zn, pure Te, and ZnTe compounds are assumed to be approximately 231-347 K, 241-362 K, and 521-782 K. Considering the annealing temperature range (653-683 K) in the present work, the pure Zn phase and pure Te phase would have been recrystallized preferentially rather than forming the compound phase ZnTe. Therefore, the pure Te phase seemed to be observed in the samples annealed at 653-673 K. [PERSON] et al.