Junction Geometry-Dependent Nonlinear Optical Responses and Diode Effects of MoSe₂-WSe₂ Heterostructures Synthesized...

Two-dimensional (2D) heterostructures composed of transition metal dichalcogenides (TMDCs) are promising materials for next-generation electronics and optoelectronics due to their unique electronic and optical properties. Although 2D TMDC heterostructures with coexisting vertical and lateral junctions are highly desirable for both fundamental research and technological applications, they have rarely been explored. Here, we report for the first time the synthesis of 2D heterostructures with coexisting vertical and lateral junctions composed of MoSe₂ and WSe₂. Monolayer MoSe₂ is first synthesized on a substrate due to its lower thermodynamic formation energy followed by the growth of monolayer WSe₂ on both the basal plane and edges of MoSe₂, thereby forming MoSe₂-WSe₂ heterostructures with coexisting vertical and lateral junctions. These heterostructures are characterized using various analytical techniques. We investigated nonlinear optical (NLO) properties using harmonic generation measurements to determine the crystal orientation of star-shaped MoSe₂-WSe₂ heterostructures. In addition, we investigated the junction geometry-dependent NLO responses of the vertical and lateral heterojunctions over a broad spectral range to demonstrate their resonant features and interlayer coupling effects. Furthermore, we fabricated electronic devices using these heterostructures and compared the diode characteristics of the vertical and lateral p-n junctions. These MoSe₂-WSe₂ heterostructures with coexisting vertical and lateral junctions are advanced materials for 2D electronics, optoelectronics, and nonlinear optical applications.