Valley-optical absorption in planar transition metal dichalcogenide superlattices

Abstract

In this study, we investigate the optical absorption of a planar superlattice comprising alternatively arranged two-dimensional Transition Metal DiChalcogenide semiconductors. Within a semi-classical model and using the Dirac-like equation in the presence of light interaction as a perturbation, we obtained the governing Hamiltonian. Using this Hamiltonian, we derived a fully analytical relationship for the absorption coefficient of the structure. By calculating the effective mass for different bands and using the Drude-Lorentz model, our approach is able to determine the oscillator strength and the effective refractive index of the structure. We found that the spin–orbit coupling has important effect on the absorption coefficient and energy bands where it reduces the absorption coefficient of the structure from typical value of 11.54 ({10}^{5}{mathrm{cm}}^{-1})–5.937({10}^{5}{mathrm{cm}}^{-1}), also the valence band experiences a significant blue shift, while the conduction band shows minor changes due to spin orbit coupling. Moreover, the role of incident light angle and light polarization were studied in details at different valleys of K and {K}^{^{prime}}. The most important finding is that by changing the polarization of incident light, it is possible to increase the absorption coefficients of K and {K}^{^{prime}} valleys by up to 30 times. For light propagation direction close to perpendicular to the plane of the superlattice, the right-circular polarization is absorbed only by K valley in contrast to the left-circular polarization, which is absorbed by the {K}^{^{prime}} valley. Our model might be used to design newly developed 2D optovalleytronic devices.