Hybrid Alkali Salt Catalysts-Promoted CVD Growth of 2D MoSe₂–WSe₂ and WSe₂–MoSe₂ Lateral Heterostructures

A scalable growth of atomically-thin 2D transition metal dichalcogenides (TMDs) with defect-free large-area surfaces is crucial for developing high-performing optoelectronic devices. Herein, a method to grow large-area, high-quality MoSe₂ monolayers, MoSe₂–WSe₂, and WSe₂–MoSe₂ lateral heterostructures using molten salt-based chemical vapor deposition (CVD) is systematically reported. First, effects of isolated inorganic (sodium chloride (NaCl) and sodium nitrate (NaNO₃)), organic (Perylene–3,4,9,10–tetracarboxylic acid tetrapotassium salt (PTAS), mixed inorganic (NaCl/NaNO₃), and hybrid organic–inorganic (PTAS/NaCl/NaNO₃) salt catalysts on the CVD growth and optoelectronic quality of MoSe₂ monolayers and their lateral heterostructures with WSe₂ in MoSe₂–WSe₂ and WSe₂–MoSe₂ assemblies are investigated. Results show that molten salt catalysts (NaCl/NaNO₃ and PTAS/NaCl/NaNO₃) support high-quality, large-area growth of MoSe₂ monolayers with low defect density. The mixed inorganic salt supports growth of MoSe₂–WSe₂ lateral heterostructures but not their counterpart. Meanwhile, WSe₂–MoSe₂ lateral heterostructures are optimally grown, supported by the hybrid organic–inorganic salt. These results are ascribed to the difference in the associated kinetic and thermodynamic mechanisms for the growths of MoSe₂ and WSe₂ as starting materials. Last, it is confirmed that optoelectronic quality of realized heterostructures and monolayers is improved compared to their mechanically exfoliated counterparts. The obtained high-quality, large-area 2D TMD heterostructures can be useful for various optoelectronic applications.