Investigation of uniaxial and biaxial strains on the band gap modifications of monolayer MoS_2 with tight-binding method

摘要

In this article a tight-binding model is used to study the changes in crystal structure, hopping parameters, and electronic band gap of semiconductor monolayer MoS2 under uniaxial strain in zigzag (x-) and armchair (y-) directions, and biaxial strain in xy-direction. The change in crystal structure modifies the reciprocal lattice structure, the hopping parameters, and the Hamiltonian matrix elements. So, by determining the nearest neighbor atoms and orbital analyzing, we have calculated the modified hopping parameters and the Hamiltonian matrix elements under various types of strains, up to first-order of corrections due to the changes in the interatomic bond lengths. Our calculations show that by applying the x-direction (y-direction) strain up to 4% (up to 3%) the direct band gap of monolayer MoS2 increases. With further increasing the strain, the direct band gap changes into an indirect band gap and starts to decrease. On the other hand, by applying the biaxial strain, the direct band gap decreases and after a 5% strain the direct band gap changes to an indirect band gap. In this paper, we also demonstrate the shift of the position of the minimum of conduction and the maximum of valence bands due to both uniaxial and biaxial strains.