Layered post-transition-metal dichalcogenide SnGe 2 N 4 as a promising photoelectric material: a DFT study.

First-principles calculations were performed to study a novel layered SnGe 2 N 4 compound, which was found to be dynamically and thermally stable in the 2H phase, with the space group P 6̄ m 2 and lattice constant a = 3.143 Å. Due to its hexagonal structure, SnGe 2 N 4 exhibits isotropic mechanical properties on the x-y plane, where the Young's modulus is 335.49 N m -1 and the Poisson's ratio is 0.862. The layered 2H SnGe 2 N 4 is a semiconductor with a direct band gap of 1.832 eV, allowing the absorption of infrared and visible light at a rate of about 10 4 cm -1 . The DOS is characterized by multiple high peaks in the valence and conduction bands, making it possible for this semiconductor to absorb light in the ultraviolet region with an even higher rate of 10 5 cm -1 . The band structure, with a strongly concave downward conduction band and rather flat valence band, leads to a high electron mobility of 1061.66 cm 2 V -1 s -1 , which is substantially greater than the hole mobility of 28.35 cm 2 V -1 s -1 . This difference in mobility is favorable for electron-hole separation. These advantages make layered 2H SnGe 2 N 4 a very promising photoelectric material. Furthermore, the electronic structure of 2H SnGe 2 N 4 responds well to strain and an external electric field due to the specificity of the p-d hybridization, which predominantly constructs the valence bands. As a result, strain and external electric fields can efficiently tune the band gap value of 2H SnGe 2 N 4 , where compressive strain widens the band gap, meanwhile tensile strain and external electric fields cause band gap reduction. In particular, the band gap is decreased by about 0.25 eV when the electric field strength increases by 0.1 V Å -1 , making a semiconductor-metal transition possible for the layered SnGe 2 N 4 .