Elemental alloying in monolayer, two-dimensional (2D) transition metal dichalcogenides (TMDs) promises unprecedented ability to modulate their electronic structure leading to unique optoelectronic properties. MoS2 monolayer based photodetectors typically exhibit a high photoresponsivity but suffer from a low response time. Here we develop a new approach for Sn alloying in MoS2 monolayers based on the synergy of the customized chemical vapor deposition (CVD) and the effects of common salt (NaCl) to produce high-quality and large-size Mo1–x Sn x S2 (x < 0.5) alloy monolayers. The composition difference results in different growth behaviors; Mo dominated alloys (x < 0.5) exhibit uniform and large size (up to 100 μm) triangular monolayers, while Sn-dominated alloys (x > 0.5) present multilayer grains. The Mo1–x Sn x S2 (x < 0.5) based photodetectors and phototransistors exhibit a maximum responsitivity of 12 mA/W and a minimum response time of 20 ms, which is faster than most reported MoS2-based photodetectors. This work offers new perspectives for precision 2D alloy engineering to improve the optoelectronic performance of TMD-based photodetectors.

Re‐based transition metal dichalcogenides (TMDs) and alloys have many unusual features such as in‐plane anisotropic optical, electrical, and phonon properties and thus receive increasing research interest. However, the distorted 1T structure and the weaker interlayer coupling easily cause anisotropic growth and out‐of‐plane growth, making it particularly challenging to produce Re‐based TMD and alloy monolayers on amorphous SiO2/Si substrates. Here, a reliable method is developed for the synthesis of high‐quality and large‐size ReS2(1−x)Se2x monolayer crystals on SiO2/Si substrates by NaCl‐assisted, confined‐space chemical vapor deposition. The synergy of salt assistance with the confined reaction space facilitates the formation of intermediate metal oxychlorides and creates a relatively stable growth environment, finally leading to the successful synthesis of ReS2(1−x)Se2x monolayer crystals on SiO2/Si substrates. The as‐grown ReS2(1−x)Se2x monolayer alloys exhibit continuously variable composition, high crystal quality, and uniform distribution of Re, S, and Se elements. Furthermore, the ReS2(1−x)Se2x based photodetectors display good photoresponse to visible and near‐infrared light with a fast response of less than 15 ms. The salt‐assisted, confined‐space chemical vapor deposition provides a reliable way for the synthesis of large‐scale low‐lattice symmetry 2D materials on amorphous SiO2/Si substrates and opens up new prospects for Re‐based TMDs and alloys in optoelectronic devices.

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