Challenges and opportunities in 2D heterostructures for electronic and optoelectronic devices

Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and their heterojunctions are prospective materials for future electronics, optoelectronics, and quantum techno! ogles. Assembling different 2D layers offers unique ways to control optical, electrical, thermal, mas.,etic, and topological phenomena. Controlled fabrications of electronic grade 'R heterojunctions are of paramount importance. Here, we enlist novel and scalable strat egies to fabricate 2D vertical and lateral heterojunctions, consisting of semiconductors, metals, and/or semimetals. CH' :cal issues that need to be addressed are the device-to-device variations, reliability, stability, and performances of 2D heterostructures in electronic and optoelectronic applications. Also, stacking orderdependent formation of moire excitons in 2D heterostructures are emerging with exotic physics and new opportunities. Furthermore, the realization of 2D heterojunction-based novel devices, including excitonic and valleytronic transistors, demands more extensive research efforts for real-world applications. We also outline emergent phenomena in 2D heterojunctions central to nanoelectronics, optoelectronics, spintronics, and energy applications.