1Physics Department, State Key Laboratory of Advanced Special Steel, Materials Genome Institute, Shanghai Key Laboratory of High Temperature Superconductors, International Center of Quantum and Molecular Structures, Shanghai University, Shanghai 200444, China 2Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials (Ministry of Education), Anhui University of Technology, Maanshan 243002, China 3State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China 4State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
Abstract：Van der Waals (vdW) layered two-dimensional (2D) materials, which may have high carrier mobility, valley polarization, excellent mechanical properties and air stability, have been widely investigated before. We explore the possibility of producing a spin-polarized two-dimensional electron gas (2DEG) in the heterojunction composed of insulators MoSi$_{2}$N$_{4}$ and VSi$_{2}$N$_{4}$ by using first-principles calculations. Due to the charge transfer effect, the 2DEG at the interface of the MoSi$_{2}$N$_{4}$/VSi$_{2}$N$_{4}$ heterojunction is found. Further, for different kinds of stacking of heterojunctions, lattice strain and electric fields can effectively tune the electronic structures and lead to metal-to-semiconductor transition. Under compressive strain or electric field parallel to $c$ axis, the 2DEG disappears and band gap opening occurs. On the contrary, interlayer electron transfer enforces the system to become metallic under the condition of tensile strain or electric field anti-parallel to $c$ axis. These changes are mainly attributed to electronic redistribution and orbitals' reconstruction. In addition, we reveal that MoSi$_{2}$N$_{4}$/VSi$_{2}$N$_{4}$ lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties, such as a large band gap semiconductor and a metallic state. Our findings provide insights into electronic band engineering of MoSi$_{2}$N$_{4}$/VSi$_{2}$N$_{4}$ heterojunctions and pave the way for future spintronics applications.
2022, Vol. 39 
