First-principles study on the structural properties of 2D MXene SnSiGeN 4 and its electronic properties under the effects of strain and an external electric field.

The MXene SnSiGeN 4 monolayer as a new member of the MoSi 2 N 4 family was proposed for the first time, and its structural and electronic properties were explored by applying first-principles calculations with both PBE and hybrid HSE06 approaches. The layered hexagonal honeycomb structure of SnSiGeN 4 was determined to be stable under dynamical effects or at room temperature of 300 K, with a rather high cohesive energy of 7.0 eV. The layered SnSiGeN 4 has a Young's modulus of 365.699 N m -1 and a Poisson's ratio of 0.295. The HSE06 approach predicted an indirect band gap of around 2.4 eV for the layered SnSiGeN 4 . While the major donation from the N-p orbitals to the band structure makes SnSiGeN 4 's band gap close to those of similar 2D MXenes, the smaller distributions from the other orbitals of Sn, Si, and Ge slightly vary this band gap. The work functions of the GeN and SiN surfaces are 6.367 eV and 5.903 eV, respectively. The band gap of the layered SnSiGeN 4 can be easily tuned by strain and an external electric field. A semiconductor-metal transition can occur at certain values of strain, and with an electric field higher than 5 V nm -1 . The electron mobility of the layered SnSiGeN 4 can reach up to 677.4 cm 2 V -1 s -1 , which is much higher than the hole mobility of about 52 cm 2 V -1 s -1 . The mentioned characteristics make the layered SnSiGeN 4 a very promising material for use in electronic and photoelectronic devices, and for solar energy conversion.