Influence of inter-layer interactions in transition metal dichalcogenides MX₂ (M = Mo/W, X = S/Se) heterobilayers

In this work, we explore the electronic and optical properties for stable MX 2 (M = Mo/W, X = S/Se) transition metal dichalcogenide (TMD) heterobilayers for different system compositions and strains based on first-principles density functional theory calculations. From the calculated binding energies, we found that both AA ′ (2H type) and AB (3R type) stacked TMDs are the most energetically favorable structures. The bandgaps obtained for these stacking configurations typically range between 1.4 and 2.0 eV (1.2-1.31 eV) and are direct/indirect for different/same chalcogen atom systems and can often be induced through expansive/compressive biaxial strains of a few percent using the G 0 W 0 ( G 0 W 0 + SOC) calculations. Our studies strongly indicate the influence of interlayer interactions on electronic properties, and a direct-to-indirect gap transition is verified for heterobilayers upon the application of a minimal strain that weakens interlayer coupling. The large interlayer exciton binding energies of the order of ∼ 240-250 meV are estimated by solving the Bethe-Salpeter equation without spin-orbit corrections. These values are enriched as ∼ 270-290 with SOC corrections to optical absorption due to bandgap reduction, suggesting that these are amenable to be studied through infrared and Raman spectroscopy. These results have potential implications for the design of excitonic devices leveraging the distinctive interlayer coupling and recent moiré pattern effects in TMD heterobilayers.