Bandgap engineering of MoS2/MX2 (MX2 = WS2, MoSe2 and WSe2) heterobilayers subjected to biaxial strain and normal compressive strain

Using first-principles calculations, we studied the electronic properties of quasi-2D MoS2/MX2 (MX2 = WS2, MoSe2 and WSe2) heterobilayers, focusing on engineering the band gap via application of in-plane biaxial strain and out-of-plane normal compressive strain (NCS). All heterobilayers show semiconducting characteristics with an indirect band gap except for the MoS2/WSe2 system which exhibits direct band gap character. The band gaps can all be widely tuned through strain and semiconductor-metal transitions can occur. In particular the direct band gap can be tuned and an appropriate compressive strain can tune the direct band gap of MoS2/WSe2 and MoS2/MoSe2, but MoS2/WS2 does not exhibit a direct band gap under any circumstances.