## 1 Introduction  
SnS is a tin compound with desirable qualities such as nontoxicity, low cost, and good hydrolytic stability [1; 2; 3]. SnS has been actively studied due to its p-type semiconductor characteristics and remarkable optoelectronic properties. Particularly, the low process temperature of the tin compound is a great advantage. The use of a low process temperature improves the process efficiency, prevents device degradation, and enables application on flexible substrates. Crystallographically, SnS has a double-layered orthorhombic structure under usual process conditions, as shown in Figure 1a. Atoms are covalently bonded in the planar layers, and individual layers are bonded by van der Waals forces. The orthorhombic structure has two carrier paths perpendicular to each other along the basal plane [4]. One path has zigzag shape, and the other is called the armchair direction. In the case of physical properties, SnS thin films generally have a carrier concentration of \(10^{15}\) to \(10^{17}\) cm\({}^{-3}\), carrier mobility greater than 15 cm\({}^{2}\)/Vs, a strong absorption coefficient greater than \(10^{4}\) cm\({}^{-1}\) in the visible region, and a bandgap of 1.4 eV [2; 5; 6; 7; 8; 9]. Some simulation studies have shown that SnS has an indirect bandgap of 1.1 eV, but most experimental results have shown a direct bandgap of 1.4 eV. Thus, the value of 1.4 eV is considered as a typical band gap of SnS. [10]. Additionally, SnS exhibits intrinsic p-type semiconductor characteristics due to tin vacancies [8; 11; 12]. SnS is a strong candidate material for various energy devices, such as solar cells, batteries, water splitting devices, and thermoelectrics, due to the excellent optoelectronic properties and stable p-type characteristics [13; 14; 15; 16; 17; 18; 19; 20; 21]. However, studies of SnS for energy device applications do not show good performance corresponding to the optoelectronic characteristics of SnS. At present, atomic layer deposition (ALD) is suitable for verifying the applicability of SnS to various device applications. This is due to the characteristics of ALD process suitable for high quality film deposition. However, target applications require a greater film thickness than the nanometer scale. The ALD method is known as a slow deposition method and is suitable for nanometer-scale thin-film processes. Specifically, the highest efficiency record of a SnS solar cell was based on the ALD method, but the SnS study using ALD is not active. In that research, the growth rate of the ALD SnS process was 0.9 A/cycle, and the deposition of a 500 nm thick SnS film required a long deposition time [2; 22]. Other ALD SnS studies have showed lower growth rates of 0.24 to 0.36 A/cycle [23; 24; 25; 26]. The growth rate of general films deposited with ALD is about 1 A/cycle, but the growth rates of ALD-deposited SnS films are lower than 1 A/cycle. Therefore, the development of SnS studies for energy devices requires a new process for a thicker, high-quality film. In addition, studies on crystal growth behaviors and film characteristics of SnS films are insufficient. Because SnS is formed as a crystalline film and has a two-dimensional structure, it is difficult to control the characteristics of the film in the process. Due to the planar growth characteristic of orthorhombic structure, the defects are more exacerbated at the grain boundaries compared with other polycrystalline films [27; 28]. Defects between planar grains cause shunt loss in solar cells and retard the carrier transport in the devices. Additionally, for electrochemical applications, films with vertically grown grains have advantages due to their large ion exchange area [29; 30]. However, the planar growth  
Figure 1: (**a**) Structure of the orthorhombic SnS crystal. X-ray diffraction (XRD) patterns of vacuum-annealed amorphous SnS\({}_{2}\) (a-SnS\({}_{2}\)) film (**b**) with various temperatures for 10 min and (**c**) various time conditions at 400 \({}^{\circ}\)C.  
trend of SnS film is different from this demand.