Representative tin sulfide compounds, tin monosulfide (SnS) and tin disulfide (SnS) are strong candidates for future nanoelectronic devices, based on non-toxicity, low cost, unique structures and optoelectronic properties. However, it is insufficient for synthesizing of tin sulfide thin films using vapor phase deposition method which is capable of fabricating reproducible device and securing high quality films, and their device characteristics. In this study, we obtained highly crystalline SnS thin films by atomic layer deposition and obtained highly crystalline SnS thin films by phase transition of the SnS thin films. The SnS thin film was transformed into SnS thin film by annealing at 450 °C for 1 h in HS atmosphere. This phase transition was confirmed by x-ray diffractometer and x-ray photoelectron spectroscopy, and we studied the cause of the phase transition. We then compared the film characteristics of these two tin sulfide thin films and their switching device characteristics. SnS and SnS thin films had optical bandgaps of 1.35 and 2.70 eV, and absorption coefficients of about 10 and 10 cm in the visible region, respectively. In addition, SnS and SnS thin films exhibited p-type and n-type semiconductor characteristics. In the images of high resolution-transmission electron microscopy, SnS and SnS directly showed a highly crystalline orthorhombic and hexagonal layered structure. The field effect transistors of SnS and SnS thin films exhibited on-off drain current ratios of 8.8 and 2.1 × 10 and mobilities of 0.21 and 0.014 cm V s, respectively. This difference in switching device characteristics mainly depends on the carrier concentration because it contributes to off-state conductance and mobility. The major carrier concentrations of the SnS and SnS thin films were 6.0 × 10 and 8.7 × 10 cm, respectively, in this experiment.

In this work, we report on the layered deposition of few-layer tin disulfide (SnS 2 ) using atomic layer deposition (ALD). By varying the ALD cycles it was possible to deposit poly-crystalline SnS 2 with small variation in layer numbers. Based on the ALD technique, we developed the process technology growing few-layer crystalline SnS 2 film (3-6 layers) and we investigated their electrical properties by fabricating bottom-gated thin film transistors using the ALD SnS 2 as the transport channel. SnS 2 devices showed typical n-type characteristic with on/off current ratio of ∼8.32×10 6 , threshold voltage of ∼2 V, and a subthreshold swing value of 830 mV decade −1 for the 6 layers SnS 2 . The developed SnS 2 ALD technique may aid the realization of two-dimensional SnS 2 based flexible and wearable devices.

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Tin monosulfide (SnS) is a promising p-type semiconductor material for energy devices. To realize the device application of SnS, studies on process improvement and film characteristics of SnS is needed. Thus, we developed a new film process using atomic layer deposition (ALD) to produce SnS films with high quality and various film characteristics. First, a process for obtaining a thick SnS film was studied. An amorphous SnS2 (a-SnS2) film with a high growth rate was deposited by ALD, and a thick SnS film was obtained using phase transition of a-SnS2 film by vacuum annealing. Subsequently, we investigated the effect of seed layer on formation of SnS film to verify the applicability of SnS to various devices. Separately deposited crystalline SnS and SnS2 thin films were used as seed layer. The SnS film with a SnS seed showed small grain size and high film density from the low surface energy of the SnS seed. In the case of the SnS film using a SnS2 seed, volume expansion occurred by vertically grown SnS grains due to a lattice mismatch with the SnS2 seed. The obtained SnS film using the SnS2 seed exhibited a large reactive site suitable for ion exchange.