Two-dimensional electron gas in MoSi₂N₄/VSi₂N₄ heterojunction from first principles

Abstract The van der Waals (vdW) layered two-dimensional (2D) materials, which might have high carrier mobility, valley polarization, excellent mechanical properties and air stability, have been widely investigated for years. In this work, we explored the possibility of producing spin-polarized two-dimensional electron gas (2DEG) in the heterojunction composed of insulators MoSi2N4 and VSi2N4 by using first-principles calculations. Due to the charge transfer effect, a 2DEG at the interface of the MoSi2N4/VSi2N4 heterojunction is found. Further, for different stacking of heterojunctions, lattice strain and electric fields can effectively tune the electronic structures and lead to the transition of metal-to-semiconductor. Under compressive strain or electric field parallel to c axis, 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 the electronic redistribution and orbitals’ reconstruction. In addition, we reveal that MoSi2N4/VSi2N4 lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties, such as a large band gap semiconductor and a metallic state, respectively. Our findings provide insights into the electronic band engineering of MoSi2N4/VSi2N4 heterojunctions and pave the way for the future spintronics applications.