Black and blue SiSe monolayers are new types of group IV–VI two-dimensional semiconductors. The structural, electrical, and optical characteristics of black and blue SiSe monolayers subjected to in-plane biaxial strain are examined using first-principles calculations. Both monolayers exhibit an indirect band gap that is sensitively dependent to the application of strain. The black and blue SiSe monolayers have band gaps of 1.11 eV (2.94 eV) and 0.62 eV (2.12 eV) computed by the Perdew–Burke–Ernzerhof (PBE) Heyd–Scuseria–Ernzerhof (HSE06) functional. The band gap (based on HSE06 method) reduces when compressive or tensile biaxial strain is applied to the blue SiSe monolayer. The electronic band gap of the black SiSe monolayer increases with the tensile biaxial strain and reduces in the presence of compressive biaxial strain. We found that the blue SiSe monolayer remains a semiconductor under biaxial strain from −6% to 6%, while the black SiSe monolayer experiences a transition from semiconductor to metal when subjected to compressive biaxial strain of about −4%. These results show very intriguing possibilities to modify the electrical and optical properties of SiSe sheet.
