Hypotaxy of wafer-scale single-crystal transition metal dichalcogenides

Two-dimensional (2D) semiconductors, particularly transition metal dichalcogenides (TMDs), are promising for advanced electronics beyond silicon^1-3. Traditionally, TMDs are epitaxially grown on crystalline substrates by chemical vapour deposition. However, this approach requires post-growth transfer to target substrates, which makes controlling thickness and scalability difficult. Here we introduce a method called hypotaxy ('hypo' meaning downward and 'taxy' meaning arrangement), which enables wafer-scale single-crystal TMD growth directly on various substrates, including amorphous and lattice-mismatched substrates, while preserving crystalline alignment with an overlying 2D template. By sulfurizing or selenizing a pre-deposited metal film under graphene, aligned TMD nuclei form, coalescing into a single-crystal film as graphene is removed. This method achieves precise MoS₂ thickness control from monolayer to hundreds of layers on diverse substrates, producing 4-inch single-crystal MoS₂ with high thermal conductivity (about 120 W m^-1 K^-1) and mobility (around 87 cm² V^-1 s^-1). Furthermore, nanopores created in graphene using oxygen plasma treatment allow MoS₂ growth at a lower temperature of 400 °C, compatible with back-end-of-line processes. This hypotaxy approach extends to other TMDs, such as MoSe₂, WS₂ and WSe₂, offering a solution to substrate limitations in conventional epitaxy and enabling wafer-scale TMDs for monolithic three-dimensional integration.