In the present letter, we report the structural, electronic and optical properties of hexagonal buckled GeS and SiS monolayers under in-plane biaxial strain. The hybrid functional was adopted to calculate more accurate band gaps. The calculated electronic structures using Heyd–Scuseria–Ernzerhof (Perdew-Burke-Ernzerhof) methods show that both GeS and SiS monolayers display indirect band gap of 3.30 and3.03 eV (2.49 and 2.19 eV), respectively. We show that the buckling height, electronic structure and optical absorption of hexagonal buckled GeS and SiS monolayers can be tuned by applying in-plane biaxial strain. The band gap of SiS monolayer decreases by applying the tensile or compressive strain. The band gap of GeS monolayer reaches its maximum value under -2% strain and it decreases when the structure is more compressed or stretched. Both GeS and SiS monolayers exhibit optical absorption with energy covering ultraviolet light and partial visible light. By increasing the biaxial tensile strain, the absorption in visible region is expanded and enhanced due to the red shift of absorption edge.
