A theoretical study on tuning band gaps of monolayer and bilayer SnS₂ and SnSe₂ under external stimuli

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Based on density functional theory, we systematically study the mechanical and electronic properties of monolayer and bilayer SnS<SUB>2</SUB> and SnSe<SUB>2</SUB>. The electronic properties of these layers can be significantly tuned by applying in-plane strains and electric fields perpendicular to the sheets. The band gaps of monolayer SnS<SUB>2</SUB> and SnSe<SUB>2</SUB> slightly increase with the in-plane tensile strains, and they start to decrease after critical strains (5% for monolayer SnS<SUB>2</SUB> and 7% for monolayer SnSe<SUB>2</SUB>). The band gaps of bilayer SnS<SUB>2</SUB> and SnSe<SUB>2</SUB> have a similar tendency to the monolayers with smaller critical strains (1% for bilayer SnS<SUB>2</SUB> and 2% for bilayer SnSe<SUB>2</SUB>), which enables a semiconductor-to-metal transition at 10% strain for bilayer SnSe<SUB>2</SUB>. We also find that an external electric field perpendicular to bilayer SnS<SUB>2</SUB> and SnSe<SUB>2</SUB> modulates their electronic band gaps. Semiconductor-to-metal transitions are achieved at the electric fields of 0.27 V/Å for bilayer SnS<SUB>2</SUB> and 0.13 V/Å for bilayer SnSe<SUB>2</SUB>.</P>