Work function tuning of MXenes for N-type semiconductors: mechanisms and van der Waals contact engineering.

N-type semiconductors occupy a core position in modern electronic devices, yet their performance is persistently bottlenecked by the inherent limitations of traditional metal electrodes, including severe energy level mismatch, Fermi level pinning (FLP), and process-induced interfacial damage. This review systematically investigates the revolutionary potential of two-dimensional transition metal carbides and nitrides (MXenes) in surmounting these contact barriers. Distinguished by their ultra-high electrical conductivity, solution processability, and uniquely tunable surface chemistry, MXenes offer an unprecedented work function tuning range (1.8-6.2 eV), enabling perfect band alignment with a diverse array of N-type channel materials, such as MoS2, a-IGZO, and organic semiconductors. We provide a comprehensive analysis of the physical and chemical mechanisms governing MXenes work function modulation, encompassing surface termination engineering, defect control, interlayer intercalation, organic molecular covalent/non-covalent functionalization, and UV-ozone oxidation. Furthermore, we deeply explore the theoretical foundations of van der Waals (vdW) contacts, elucidating how the physical gap effectively suppresses metal-induced gap states (MIGS) and de-pins the Fermi level to approximate the Schottky-Mott limit. Finally, we highlight the cutting-edge integration of MXene electrodes in high-performance N-type logic circuits, flexible electronics, memory devices, and neuromorphic computing interfaces, while outlining the critical challenges of scalability and environmental stability that must be addressed to realize their full commercial potential in the post-Moore era.