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

Abstract

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. Characterization via Raman spectroscopy, photoluminescence (PL), and transmission electron microscopy (TEM) confirms atomically coherent and chemically abrupt interfaces. The resulting WS2-WSe2 heterostructure exhibits high-performance self-powered photodetection (high responsivity of 1.94 A/W, impressive detectivity of 1.58 × 1010 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.