Controlled Growth of Large-Area Bilayer Tungsten Diselenides with Lateral P–N Junctions

Bilayer two-dimensional (2D) van der Waals (vdW) materials are attracting increasing attention due to their predicted high quality electronic and optical properties. Here, we demonstrate dense, selective growth of WSe₂ bilayer flakes by chemical vapor deposition with the use of a 1:10 molar mixture of sodium cholate and sodium chloride as the growth promoter to control the local diffusion of W-containing species. A large fraction of the bilayer WSe₂ flakes showed a 0 (AB) and 60° (AA′) twist between the two layers, whereas Moiré 15 and 30° twist angles were also observed. Well-defined monolayer–bilayer junctions were formed in the as-grown bilayer WSe₂ flakes, and these interfaces exhibited p–n diode rectification and an ambipolar transport characteristic. This work provides an efficient method for the layer-controlled growth of 2D materials, in particular, 2D transition metal dichalcogenides, and promotes their applications in next-generation electronic and optoelectronic devices.