Tuning transport coefficients of monolayer MoSi2N4 with biaxial strain*

Experimentally synthesized MoSi2N4 (Science 369 670 (2020)) is a piezoelectric semiconductor. Here, we systematically study the large biaxial (isotropic) strain effects (0.90-1.10) on electronic structures and transport coefficients of monolayer MoSi2N4 by density functional theory (DFT). With a/a (0) from 0.90 to 1.10, the energy band gap firstly increases, and then decreases, which is due to transformation of conduction band minimum (CBM). Calculated results show that the MoSi2N4 monolayer is mechanically stable in the considered strain range. It is found that the spin-orbital coupling (SOC) effects on Seebeck coefficient depend on the strain. In unstrained MoSi2N4, the SOC has neglected influence on Seebeck coefficient. However, the SOC can produce important influence on Seebeck coefficient, when the strain is applied, for example, 0.96 strain. The compressive strain can change relative position and numbers of conduction band extrema (CBE), and then the strength of conduction bands convergence can be enhanced, to the benefit of n-type ZT (e). Only about 0.96 strain can effectively improve n-type ZT (e). Our works imply that strain can effectively tune the electronic structures and transport coefficients of monolayer MoSi2N4, and can motivate farther experimental exploration.

Automated summary

Experimentally synthesized MoSi2N4 is a piezoelectric semiconductor that can be effectively tuned by strain to modulate electronic structures and transport coefficients, with significant influence from spin-orbital coupling. A strain of about 0.96 can effectively enhance the n-type ZT (e) due to changes in conduction band extrema and strength.