Atomic layer deposition of SnS2film on a precursor pre-treated substrate

Two-dimensional (2D) materials are attracting attention because of their outstanding physical, chemical, and electrical properties for applications of various future devices such as back-end-of-line field effect transistor (BEOL FET). Among many 2D materials, tin disulfide (SnS2) material is advantageous for low temperature process due to low melting point that can be used for flexible devices and back-end-of-line (BEOL) devices that require low processing temperature. However, low temperature synthesis method has a poor crystallinity for applying to various semiconductor industries. Hence, many studies of improving crystallinity of tin disulfide film are studied for enhancing the quality of film. In this work, we propose a precursor multi-dosing method before deposition of SnS2. This precursor pre-treatment was conducted by atomic layer deposition cycles for more adsorption of precursors to the substrate before deposition. The film quality was analyzed by x-ray diffraction, Raman, transmission electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. As a result, more adsorbates by precursor pre-treatment induce higher growth rate and better crystallinity of film.

The atomic layer deposition (ALD) synthesis of copper-tin sulfide thin films using low-cost precursors

In this work we demonstrated the process of co-deposition of copper-tin sulfide species by the atomic layer deposition (ALD) technique using all-low-cost precursors. For the deposition of tin species, the tin(IV) chloride SnCl₄was used successfully for the first time in the ALD process. Moreover, we showed that the successful deposition of the tin sulfide component was conditioned by the pre-deposition of CuS_xlayer. The co-deposition of copper and tin sulfides components at 150 °C resulted in the in-process formation of the film containing Cu₂SnS₃, Cu₃SnS₄andπ-SnS phases. The process involving only tin precursor and H₂S did not produce the SnS_xspecies. The spectroscopic characteristic of the obtained materials were confronted with the literature survey, allowing us to discuss the methodology of the determination of ternary and quaternary sulfides purity by Raman spectroscopy. Moreover, the material characterisation with respect to the morphology (SEM), phase composition (XRD), surface chemical states (XPS), optical properties (UV-vis-NIR spectroscopy) and electric (Hall measurements) properties were provided. Finally, the obtained material was used for the formation of the p-n junction revealing the rectifyingI-Vcharacteristics.

Hydrothermally synthesized nanocrystalline photoactive SnS2 thin films: effect of surface directing agents

In the present work, we have synthesized tin disulphide (SnS2) thin films via a facile, low cost, single-step hydrothermal route using various surface directing agents.

Atmospheric pressure chemical vapor deposition growth of vertically aligned SnS2 and SnSe2 nanosheets

Laminated metal dichalcogenides are candidates for different potential applications ranging from catalysis to nanoelectronics. However, efforts are still needed to optimize synthesis methods aiming to control the number of layers, morphology, and crystallinity, parameters that govern the properties of the synthesized materials. Another important parameter is the thickness and the length of the samples with the possibility of large-scale growth of target homogeneous materials. Here, we report a chemical vapor deposition method at atmospheric pressure to produce vertically aligned tin dichalcogenide based-materials. Tin disulfide (SnS2) and tin diselenide (SnSe2) vertically aligned nanosheets have been synthesized and characterized by different methods showing their crystallinity and purity. Homogenous crystalline 2H-phase SnS2 nanosheets with high purity were synthesized with vertical orientation on substrates; sulfur vacancies were observed at the edges of the sheets. Similarly, in the crystalline 2H phase SnSe2 nanosheets selenium vacancies were observed at the edges. Moreover, these nanosheets are larger than the SnS2 nanosheets, show lower nanosheet homogeneity on substrates and contamination with selenium atoms from the synthesis was observed. The synthesized nanomaterials are interesting in various applications where the edge accessibility and/or directionality of the nanosheets play a major role as for example in gas sensing or field emission.

Large-area growth of SnS2 nanosheets by chemical vapor deposition for high-performance photodetectors

Two-dimensional tin disulfide (SnS₂) is very popular in electronic, optoelectronic, energy storage, and conversion applications. However, the uncontrollable large-area growth of SnS₂ nanosheets and unsatisfactory performance of the photodetectors based on SnS₂ have hindered its applications. Here, we propose a chemical vapor deposition (CVD) method using SnCl₂ as a precursor to grow SnS₂ nanosheets. We found that the as-grown SnS₂ nanosheets were high-quality crystal structures. Then, photodetectors based on the as-grown SnS₂ were fabricated and, exhibited a high responsivity (1400 A W^-1), fast response rate (a response time of 7 ms and a recovery time of 6 ms), perfect external quantum efficiency (EQE) (2.6 × 10⁵%), and remarkable detectivity (D*) (3.1 × 10¹³ Jones). Our work provides a new CVD method to grow high-quality SnS₂ nanosheets.

Accelerated temperature and humidity testing of 2D SnS2 thin films made via four-inch-wafer-scale atomic layer deposition

Tin disulfide (SnS₂) has emerged as a promising two-dimensional (2D) material due to its excellent electrical and optical properties. However, research into 2D SnS₂ has mainly focused on its synthesis procedures and applications; its stability to humidity and temperature has yet to be studied. In this work, 2D SnS₂ thin films were grown by atomic layer deposition (ALD) and characterized by various tools, such as x-ray diffraction, Raman analysis, and transmission electron spectroscopy. Characterization reveals that ALD-grown SnS₂ thin films are a high-quality 2D material. After characterization, a four-inch-wafer-scale uniformity test was performed by Raman analysis. Owing to the quality, large-area growth enabled by the ALD process, 98.72% uniformity was obtained. Finally, we calculated the thermodynamic equations for possible reactions between SnS₂ and H₂O to theoretically presurmise the oxidation of SnS₂ during accelerated humidity and temperature testing. After the accelerated humidity and temperature test, x-ray diffraction, Raman analysis, and Auger electron spectroscopy were performed to check whether SnS₂ was oxidized or not. Our data revealed that 2D SnS₂ thin films were stable at humid conditions.

Wafer-Scale, Conformal, and Low-Temperature Synthesis of Layered Tin Disulfides for Emerging Nonplanar and Flexible Electronics

Two-dimensional (2D) metal dichalcogenides have drawn considerable interest because they offer possibilities for the implementation of emerging electronics. The emerging electronics are moving toward two major directions: vertical expansion of device space and flexibility. However, the development of a synthesis method for 2D metal dichalcogenides that meets all the requirements remains a significant challenge. Here, we propose a promising method for wafer-scale, conformal, and low-temperature (≤240 °C) synthesis of single-phase SnS₂ via the atomic layer deposition technique. There is a trade-off relationship between the crystallinity and orientation preference of SnS₂, which is efficiently eliminated by the two-step growth occurring at different temperatures. Consequently, the van der Waals layers of the highly crystalline SnS₂ are parallel to the substrate. Thin-film transistors (TFTs) comprising the SnS₂ layer show reasonable electrical performances (field-effect mobility: ∼0.8 cm² V^-1 s^-1 and on/off ratio: ∼10⁶), which are comparable to that of a single-crystal SnS₂ flake. Moreover, we demonstrate nonplanar and flexible TFTs to identify the feasibility of the implementation of future electronics. Both the diagonal-structured TFT and flexible TFT fabricated without a transfer process show electrical performances comparable to those of rigid and planar TFTs. Particularly, the flexible TFT does not exhibit substantial degradation even after 2000 bending cycles. Our work would provide decisive opportunities for the implementation of future electronic devices utilizing 2D metal chalcogenides.

Layered deposition of SnS2 grown by atomic layer deposition and its transport properties

In this work, we report on the layered deposition of few-layer tin disulfide (SnS₂) using atomic layer deposition (ALD). By varying the ALD cycles it was possible to deposit poly-crystalline SnS₂ with small variation in layer numbers. Based on the ALD technique, we developed the process technology growing few-layer crystalline SnS₂ film (3-6 layers) and we investigated their electrical properties by fabricating bottom-gated thin film transistors using the ALD SnS₂ as the transport channel. SnS₂ devices showed typical n-type characteristic with on/off current ratio of ∼8.32 × 10⁶, threshold voltage of ∼2 V, and a subthreshold swing value of 830 mV decade^-1 for the 6 layers SnS₂. The developed SnS₂ ALD technique may aid the realization of two-dimensional SnS₂ based flexible and wearable devices.

Two-Dimensional Hybrid Composites of SnS2 Nanosheets Array Film with Graphene for Enhanced Photoelectric Performance

Two-dimensional (2D) metal dichalcogenides have attracted considerable attention for use in photoelectric devices due to their unique layer structure and strong light-matter interaction. In this paper, vertically grown SnS₂ nanosheets array film was synthesized by a facile chemical bath deposition (CBD). The effects of deposition time and annealing temperature on the quality of SnS₂ films was investigated in detail. By optimizing the preparation conditions, the SnS₂ array film exhibited efficient photoelectric detection performance under sunlight. Furthermore, in order to improve the performance of the photodetector based on SnS₂ nanosheets film, a transparent graphene film was introduced as the hole-transport layer by wet-chemical method directly transferring techniques. Graphene/SnS₂ nanosheets array film heterojunction photodetectors exhibit enhanced photoresponsivity. The light on/off ratio of the photodetector based on graphene/SnS₂ was 1.53, about 1.4 times higher than that of the pristine SnS₂ array films. The improved photoresponse performance suggested that the effective heterojunction between vertical SnS₂ nanosheets array film and graphene suppresses the recombination of photogenerated carriers. The results indicate that the graphene/SnS₂ heterojunction photodetectors have great potential in photodetection devices.

Enhancement in Photoelectrochemical Performance of Optimized Amorphous SnS2 Thin Film Fabricated through Atomic Layer Deposition

Two-dimensional (2D) nanomaterials have distinct optical and electrical properties owing to their unique structures. In this study, smooth 2D amorphous tin disulfide (SnS₂) films were fabricated by atomic layer deposition (ALD), and applied for the first time to photoelectrochemical water splitting. The optimal stable photocurrent density of the 50-nm-thick amorphous SnS₂ film fabricated at 140 °C was 51.5 µA/cm² at an oxygen evolution reaction (0.8 V vs. saturated calomel electrode (SCE)). This value is better than those of most polycrystalline SnS₂ films reported in recent years. These results are attributed mainly to adjustable optical band gap in the range of 2.80 to 2.52 eV, precise control of the film thickness at the nanoscale, and the close contact between the prepared SnS₂ film and substrate. Subsequently, the photoelectron separation mechanisms of the amorphous, monocrystalline, and polycrystalline SnS₂ films are discussed. Considering above advantages, the ALD amorphous SnS₂ film can be designed and fabricated according to the application requirements.

Nanostructured SnS2 Thin Films from Laser Ablated Nanocolloids: Structure, Morphology, Optoelectronic and Electrochemical Properties

Tin disulfide (SnS₂ ) is a binary chalcogenide semiconductor having applications in solar cells, energy storage, and optoelectronics. SnS₂ thin films were deposited by spraying the nanocolloids synthesized by pulsed laser ablation in liquid. The structure, morphology, and optoelectronic properties were studied for films obtained from two liquid media (ethanol and isopropanol) and after heat treatments at various temperatures. X-ray diffraction analysis confirmed the hexagonal crystal structure of the films, whereas the 2-H polytype structure was identified by micro-Raman spectroscopy. Oxidation states of Sn (4+) and S (2-) identified from high resolution X-ray photoelectron spectra confirmed the composition and chemical states of the films. The SnS₂ thin films exhibited distinct porous surface morphologies as the liquid medium in laser ablation was varied. All as-prepared and annealed films showed photoluminescence with a high intensity peak at 485 nm and a low intensity peak at 545 nm. Thin films annealed at 300 °C showed improved electrochemical properties upon illumination using a blue LED light source. Current-voltage curves recorded in dark and light as well as the photoresponse measurements showed their suitability for utilization in optoelectronic devices. The results of this study may trigger further research towards fabrication of nanostructured thin films in large area for optoelectronic and photoelectrochemical applications in an environment friendly and cost-effective way.

Thickness-Dependently Enhanced Photodetection Performance of Vertically Grown SnS2 Nanoflakes with Large Size and High Production

Photodetection based on two-dimensional (2D) SnS₂ has attracted growing interest due to its superiority in response rate and responsivity, but high-quality growth and high performance photodetection of 2D SnS₂ still face great challenges. Here, high-quality SnS₂ nanoflakes with large-size and high-production are vertically grown on an Si substrate by a modified CVD method, having an average size of 30 μm with different thicknesses. Then a single SnS₂ nanoflake-based phototransistor was fabricated to obtain a high current on/off ratio of 10⁷ and excellent performance in photodetection, including fast response rates, low dark current, and high responsivity and detectivity. Specifically, the SnS₂ nanoflakes show thickness-dependent photodetection capability, and a highest responsivity of 354.4 A W^-1 is obtained at the average thickness of 100.5 nm. A sensitized process using an HfO₂ nanolayer can further enhance the responsivity up to 1922 A W^-1. Our work provides an efficient path to select SnS₂ crystal samples with the optimal thickness as promising candidates for high-performance optoelectronic applications.

Low-Temperature Wafer-Scale Deposition of Continuous 2D SnS2 Films

Semiconducting 2D materials, such as SnS₂ , hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS₂ films has remained a great challenge. Herein, continuous wafer-scale 2D SnS₂ films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 °C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS₂ films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS₂ films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.