Recent Advances in van der Waals Heterojunctions Based on Semiconducting Transition Metal Dichalcogenides

Due to the direct bandgap with coupled spin–valley physics, semiconducting MX (M = Mo, W; X = S, Se) materials have attracted considerable attention and have numerous proposed applications. With the development of 2D materials research, many 2D materials have been discovered, such as insulators, semiconductors, ferromagnetic semiconductors, topological insulators, metals, and ferromagnetic metals. van der Waals heterojunctions (vdWHs), based on MX and other 2D materials, have attracted increasing attention because of their various potential applications, such as field effect transistors, solar cells, photodetectors, light emitting diodes, and lasers. Based on the functionality of 2D materials, vdWHs are classified into six classes: MX/semiconductors, MX/insulators, MX/topological insulators, MX/ferromagnetic semiconductors, MX/metals, and MX/ferromagnetic metals. For each class of vdWHs, the structural, electronic, and optical properties, as well as potential applications in electronics and optoelectronics, are reviewed. Finally, an overview of perspectives and challenges regarding vdWHs based on MX materials is presented.