Strain-induced semiconductor to metal transition in MA2Z4 bilayers (M = Ti, Cr, Mo; A = Si; Z = N, P)

Very recently, a new type of two-dimensional layered material, MoSi2N4, was fabricated that is semiconducting with weak interlayer interaction, high strength, and excellent stability. We systematically investigate the effect of vertical strain on the electronic structure of MA(2)Z(4) (M = Ti/Cr/Mo, A = Si, Z = N/P) bilayers. Taking bilayer MoSi2N4 as an example, our first-principles calculations show that its indirect band gap decreases monotonically as the vertical compressive strain increases. Under a critical strain around 22%, it undergoes a transition from semiconductor to metal. We attribute this to the opposite energy shift of states in different layers, which originates from the built-in electric field induced by the asymmetric charge transfer between two inner sublayers near the interface. Similar semiconductor to metal transitions are observed in other strained MA(2)Z(4) bilayers, and the estimated critical pressures to realize such transitions are within the same order as semiconducting transition metal dichalcogenides. The semiconductor to metal transitions in the family of MA(2)Z(4) bilayers present interesting possibilities for strain-induced engineering of their electronic properties.

Automated summary

This study systematically investigates the effect of vertical strain on the electronic structure of bilayer materials, and reveals that under a certain compressive strain, semiconductor materials can transition to metallic materials due to energy shifts of electronic states. Similar transitions are observed in other strained bilayers, showing potential for strain-induced engineering of electronic properties.