Transition metal dichalcogenides (TMDC) have become an emerging platform for optoelectronic, spintronic, and valleytronic devices due to their unique properties. The band offset of hetero-stacks is the crucial parameter for designing improved electronic/photonic devices. To this end, here we present a dispersion-corrected density functional theory study to investigate the band-alignment induced interlayer excitons and the impact of spin-orbital coupling on valleytronics of WS2/MoSe2 hetero-bilayers. We have performed an intensive search for moirépatterns with the different relative angle between the two atomic layers using 1o intervals. By considering the calculated binding energies and the size of vertically stacked moiré superlattices, we have down selected a few candidates for further study. The band structures of 12o, 16o, 20o and 30o rotated layers were studied. Calculations indicate that the band alignment due to interlayer electronic coupling in WS2/MoSe2 hetero-bilayers lead to an indirect band gap. The valence-band maximum state is from the Γ point is strongly localized in the MoSe2 layer. The conduction band minimum state which is at K point is localized to WS2 layer. Valance-band localization can have major impacts on the carrier mobility and other electronic and optical properties. Splitting of the conduction band minimum is an evidence of strong spin orbital coupling. The higher spin orbital coupling is due to the lattice mismatch of these twisted hetero bilayers. Splitting of these bands increase the valley-degree of freedom by creating electron holes that then bind to electrons, forming excitons. The results demonstrate profound band alignment and enhanced valleytronics owing to interlayer excitons strongly associated with spin-orbital interactions in the TMDC hetero-stacks.

Band alignment, interlayer excitons, and enhanced valleytronics in hetero-stacks of transition-metal dichalcogenides

2019 Spring National Meeting

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