Epitaxial Interface-Driven Photoresponse Enhancement in Monolayer WS₂–MoS₂ Lateral Heterostructures

2D transition metal dichalcogenides heterostructures are driving advancements in next-generation optoelectronic technologies. Lateral 2D heterojunctions with atomically seamless interfaces play a vital role in modulating charge separation and carrier dynamics, yet underlying transport mechanisms remain inadequately understood, limiting practical deployment. Here, monolayer WS₂-MoS₂ lateral edge-epitaxial heterostructures synthesized via chemical vapor deposition (CVD), providing critical insights into heterointerface effects on charge distribution and photoresponse are reported. Photodetector fabricated from this heterostructures exhibit broadband spectral response from ultraviolet to near-infrared, achieving peak responsivity of 1850 mA W⁻¹ and detectivity of 4.36 × 10¹¹ Jones under 565 nm illumination. This represents ≈200% enhancement compared to individual monolayer MoS₂ or WS₂ devices, directly demonstrating the synergistic benefits of lateral heterostructure engineering. Spatially resolved surface potential mapping and second-harmonic generation imaging reveal that enhanced performance originates at the epitaxial interface, confirming the critical role of interfacial electric fields and nonlinear optical effects in charge carrier dynamics. The characterization provides direct experimental evidence linking atomically seamless interface properties to macroscopic device performance enhancements. These findings underscore the significant potential of CVD-grown WS₂-MoS₂ lateral heterostructures for high-performance photodetectors and establish interface engineering as a powerful strategy for advancing 2D semiconductor device technologies.