First-principles study on the structural, mechanical and optoelectronic properties of the hydrogenated and fluorinated dumbbell silicene monolayers and their vertical heterostructures

Using first-principles calculations, we systematically investigate the structural, mechanical, and optoelectronic properties of hydrogenated and fluorinated dumbbell silicene (DB-SiH and DB-SiF) monolayers, as well as their vertical heterostructures. Ab initio molecular dynamics (AIMD) calculations demonstrate that both the DB-SiH and DB-SiF monolayers, along with their heterostructures, exhibit excellent structural and thermal stability. Furthermore, hydrogenation and fluorination can increase the band gap of dumbbell silicene, resulting in a direct band gap of 1.99 eV and an indirect band gap of 1.55 eV, respectively. The work function of dumbbell silicene can be effectively tuned by the chemical functionalization. The DB-SiH/DB-SiF heterostructures display direct band gap characteristics and a typical type-II band alignment. Notably, the significant charge transfer from DB-SiH to DB-SiF induces a built-in electric field at the interface of the heterostructures, which facilitates the separation of electrons and holes. Additionally, the DB-SiH/DB-SiF heterostructures exhibit enhanced visible light absorption coefficients compared to those of the individual monolayers. The interesting findings suggest that these novel structures hold valuable potential for applications in optoelectronics.