## 3 Results and Discussion
### Process to Control the Film Characteristics of SnS Film Using Seed Layer  
This section shows the changes in grain growth behavior in SnS film by crystalline SnS and SnS\({}_{2}\) seed layers. The first reason to use SnS and SnS\({}_{2}\) thin films as seed layers is that they can be deposited by the ALD process using the same precursor and reactants as a-SnS\({}_{2}\). Thus, all the processes can be performed continuously in the same chamber. Second, as the vacuum annealing process results of SnS and SnS\({}_{2}\) are both SnS phase, there is no discontinuity in the finally formed SnS film. In the case of studies using other seed layers, the seed layer remains in the SnS film. The remaining seed layer can finally affect the operation of devices. In this study, three SnS films were prepared by the method shown in Figure 5a. The samples were the nonseeded SnS film (sample A) obtained previously, SnS film using a crystalline ALD SnS seed layer (sample B), and SnS film using a crystalline ALD SnS\({}_{2}\) seed layer (sample C). The seed layer and a-SnS\({}_{2}\) films were continuously deposited by changing the substrate temperature and annealed at 400 \({}^{\circ}\)C for 10 min in a vacuum atmosphere. The thickness of the deposited seed layer was 50 nm, and the total thickness of a-SnS\({}_{2}\) with the seed layer was 500 nm. First, formation of the SnS phase was identified when only seed layers were annealed at 400 \({}^{\circ}\)C for 10 min in a vacuum atmosphere. Figure 5b shows the XRD results before and after vacuum annealing of the 50 nm ALD SnS and SnS\({}_{2}\) seed layers. SnS and SnS\({}_{2}\) seed layers showed the (111) SnS peak at a Bragg angle of 31.53\({}^{\circ}\) and the (001) SnS\({}_{2}\) peak at a Bragg angle of 15.03\({}^{\circ}\), respectively. The seed tin sulfide films were highly oriented along the direction of the main peak. In addition, SnS and SnS\({}_{2}\) seed layers exhibited a main peak of SnS at 31.53\({}^{\circ}\) after vacuum annealing. The crystallinity of the seed SnS thin film increased with sharpening of the (111) SnS peak. The seed SnS\({}_{2}\) thin film was transformed into crystalline SnS phase after vacuum annealing and showed the (111) peak at 31.53\({}^{\circ}\). Figure 5c shows the XRD analysis of the three SnS films using the seed layer. The SnS film using SnS seed layer (sample B), exhibited a very sharp and intensive (111) peak of SnS at 31.53\({}^{\circ}\). Other SnS peaks appeared very small. Based on the XRD results, it can be estimated that the SnS seed transformed  
Figure 4: (a) Schematic image of a showerhead-type atomic layer deposition (ALD) chamber used in this study. (b) SEM images of 16 points on four-inch scale wafer for uniformity testing of the SnS film process. a-SnS film into a very highly crystalline SnS film, but the SEM images show that this interpretation is incorrect. Figure 5d-f is the SEM images of the three SnS films using various seed layers. In the top view of the SEM images, sample B showed very small and densely packed grains compared to the nonseeded SnS film (sample A). Therefore, the sharp SnS main peak of sample B shown in Figure 5c is mainly due to the peak of the SnS seed layer shown in Figure 5b. The grain size reduction and increased packing density of the SnS film are due to the surface energy of the SnS seed layer. Figure 6a exhibits the result of the water contact angle test to compare the surface energies of the SiO\({}_{2}\) substrate and SnS and SnS\({}_{2}\) seed layers. The contact angle of the SiO\({}_{2}\) substrate and SnS seed layer were 41.4\({}^{\circ}\) and 77.1\({}^{\circ}\), respectively. The high contact angle of the SnS seed layer indicates that the SnS seed had a lower surface energy than the SiO\({}_{2}\) substrate. As the surface energy of the SnS seed layer was much smaller than that of the SiO\({}_{2}\) substrate, grains of the SnS film formed on the SnS seed were also smaller than grains of the SnS formed on SiO\({}_{2}\).