Tuning electronic and optical properties of free-standing Sn2Bi monolayer stabilized by hydrogenation

In this study, we systematically investigated the structural, mechanical, electronic, and optical properties of the Sn2Bi monolayer, a sheet experimentally synthesized recently [Gou et al., Phys. Rev. Lett. 121, 126801 (2018)], which has been hydrogenated (Sn2BiH2) to stabilize free-standing form using density functional theory. For tuning the electronic properties, the mechanical strain and the electric field are used. Our investigations show that in this free-standing form, there are electron flatbands and free hole bands like the deposited sample on the silicon substrate, which provide the possibility of having strongly localized electrons and free holes. Also, the bandgap of the Sn2BiH2 monolayer has experienced a growth of 80% compared with the experimental sample. The strain-related results suggest that the bandgap can be properly manipulated within a range from 0.2 to 1.6 eV by biaxial strain (−13% to +21%). It should be mentioned that the stability and flexibility of the corresponding monolayer under tensile and compressive strain are due to the strong σ bonds between atoms. We also realized that the strain can cause indirect-direct transition in the bandgap. Furthermore, our optical findings indicate that the Sn2BiH2 monolayer has almost metallic properties in a specific range of the UV spectrum and it is transparent in the IR and visible spectra of electromagnetic radiation. All these tunable properties and nontrivial features portend that the Sn2BiH2 monolayer has great potential in applications as near-infrared detectors, thermoelectric devices, field-effect transistors, sensors, photocatalysis, energy harvesting, and optoelectronics.