Highly tunable electronic properties in γ-XSe (X=Ge and Sn) bilayer with strain and electric field

Recent experimental synthesis of the monolayer γ-GeSe, which possesses a unique Mexican-hat band dispersion, has drawn much research interests. Nevertheless, there is still a lack of investigation of band gap engineering by strain and electric field. Here, we report that strain and electric field are effective avenues for the band gap engineering of bilayer γ-GeSe and γ-SnSe. It is found strain can tune the band gap and even lead to a indirect-direct band gap transition. It is also found that the band gap of bilayer γ-GeSe and γ-SnSe can be engineered by the electric field, which can even result in semiconductor to metal transition. Our results imply that the strain and electric field band gap engineering is an effective avenue to design bilayer γ-GeSe and γ-SnSe based nanoelectronic and optoelectronic devices.