Equibiaxial strain: tunable electronic structure and optical properties of bulk and monolayer MoSe2

Using ab initio calculations based on density functional theory, we have studied the equibiaxial strain effect on the electronic and optical properties of bulk and monolayer MoSe2. Very low value of the elastic constants of monolayer MoSe2 compared to bulk MoSe2 suggests that the tailoring of the electronic structure and optical properties of monolayer MoSe2 may easily be achieved by strain. We find that the band gap (E-g) of MoSe2 undergoes a transition from indirect to direct upon reducing the thickness of the monolayer which is associated with an enhancement of E-g and is further tunable by strain engineering. We noticed that the splitting of the bands that generally determines the luminescence property of MoSe2 can be modified by strain. Strain effect on bond ionicity, dielectric property (real and imaginary component) of bulk and monolayer MoSe2 has also been briefly discussed. We noticed that the plasma oscillation, found in bulk MoSe2, is absent in MoSe2 monolayer.