MA₂Z₄ family heterostructures: Promises and prospects

Recent experimental synthesis of ambient-stable MoSi2N4 monolayer has garnered enormous research interest. The intercalation morphology of MoSi2N4-composed of a transition metal nitride (Mo-N) inner sub-monolayer sandwiched by two silicon nitride (Si-N) outer sub-monolayers-has motivated the computational discovery of an expansive family of synthetic MA(2)Z(4) monolayers with no bulk (3D) material counterpart (where M = transition metals or alkaline earth metals; A = Si, Ge; and N = N, P, As). MA(2)Z(4) monolayers exhibit interesting electronic, magnetic, optical, spintronic, valleytronic, and topological properties, making them a compelling material platform for next-generation device technologies. Furthermore, heterostructure engineering enormously expands the opportunities of MA(2)Z(4). In this review, we summarize the recent rapid progress in the computational design of MA(2)Z(4)-based heterostructures based on first-principle density functional theory (DFT) simulations-a central work horse widely used to understand the physics, chemistry, and general design rules for specific targeted functions. We systematically classify the MA(2)Z(4)-based heterostructures based on their contact types, and review their physical properties, with a focus on their performances in electronics, optoelectronics, and energy conversion applications. We review the performance and promises of MA(2)Z(4)-based heterostructures for device applications that include electrical contacts, transistors, spintronic devices, photodetectors, solar cells, and photocatalytic water splitting. We present several prospects for the computational design of MA(2)Z(4)-based heterostructures, which hold the potential to guide the next phase of exploration, moving beyond the initial "gold rush" of MA(2)Z(4) research. This review unveils the vast device application potential of MA(2)Z(4)-based heterostructures and paves a roadmap for the future development of MA(2)Z(4)-based functional heterostructures and devices.