A model for the direct-to-indirect band-gap transition in monolayer MoSe2 under strain

A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, within ab-initio electronic structure calculations, that a modest biaxial tensile strain of 3% can drive it into an indirect band-gap semiconductor with the valence band maximum (VBM) shifting from K point to Γ point. An analysis of the charge density reveals that while Mo–Mo interactions contribute to the VBM at 0% strain, Mo–Se interactions contribute to the highest occupied band at Γ point. A scaling of the hopping interaction strengths within an appropriate tight binding model can capture the transition.