Electric field and strain tunable band gap and band alignments of MoSi2N4/MSe (M = In, Ga) van der Waals heterostructures†

Using van der Waals heterostructures (VDWHs) to engineer novel electronic properties of two-dimensional (2D) material systems has proven to be a viable strategy in recent years. Given the excellent mechanical and electronic properties of air-stable MoSi₂N₄ and the high electron mobility of air-sensitive wide band gap 2D monolayers of GaSe and InSe, we investigate the interaction of these materials using first-principles calculations. We find that the VDWHs have narrow type-II direct band gaps. We apply either vertical electric field, vertical strain or biaxial strain to MoSi₂N₄/GaSe and MoSi₂N₄/InSe for band gap modulation. We find that the band structure of MoSi₂N₄/GaSe and MoSi₂N₄/InSe is highly tunable, exhibiting a variety of behaviours such as type-II-to-type-H band alignment, large band gap changes and direct-to-indirect band gap transitions. Interestingly, we also find that both heterostructures have a large band gap modulation of 1.4 to 2.3 eV under 8% biaxial strain. We also find that we can reverse the direction of the electron transfer between the monolayers under external stimuli. These findings therefore reveal another viable path towards InSe and GaSe based electronics and optoelectronics by using MoSi₂N₄-based VDWHs.