Tunable bilayer WS₂-WSe₂ and WS₂-MoS₂ lateral heterostructures for self-powered photodetectors

Two-dimensional lateral heterostructures based on transition metal dichalcogenides (TMDs) are promising for optoelectronics due to their layer thickness-dependent properties. Bilayer structures, in particular, offer advantages like enhanced electron mobility and improved stability. However, precisely controlling layer growth in these heterostructures remains a challenge. We report a simple two-step chemical vapor deposition (CVD) method for growing bilayer WS₂-WSe₂ and WS₂-MoS₂ lateral heterostructures. By strategically positioning a bilayer WS₂ template to create temperature gradients, we manipulate the supersaturation of the second material, enabling precise control over the epitaxial width ratio on layer growth. Raman spectroscopy, photoluminescence (PL), and transmission electron microscopy (TEM) confirm coherent lattice continuity and chemically abrupt interfaces. The resulting WS₂-WSe₂ heterostructure exhibits high-performance self-powered photodetection (responsivity of 30.31 mA W^-1, detectivity of 2.42 × 10⁸ Jones and fast response time <20 ms under 638 nm laser illumination, respectively). This performance is attributed to the type-II band alignment-induced built-in electric field and the high-quality interface. This work provides novel perspectives on the growth mechanism of bilayer lateral heterostructures and highlights their potential for advanced optoelectronic applications.