Interlayer and intralayer excitons in MoS2/WS2 and MoSe2/WSe2 heterobilayers

• Published in: Physical review. B 2018-06, Vol.97 (24)
• Main Authors: Torun, Engin, Miranda, Henrique P C, Molina-Sánchez, Alejandro, Wirtz, Ludger
• Format: Article
• Language: English
• Subjects: Absorption spectra; Bethe-Salpeter equation; Binding energy; Constituents; Current carriers; Eigenvalues; Electronic structure; Excitons; First principles; Interlayers; Mathematical analysis; Molybdenum disulfide; Multilayers; Oscillator strengths; Transition metal compounds
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.97.245427

Accurately described excitonic properties of transition metal dichalcogenide heterobilayers (HBLs) are crucial to comprehend the optical response and the charge carrier dynamics of them. Excitons in multilayer systems possess an inter- or intralayer character whose spectral positions depend on their binding energy and the band alignment of the constituent single layers. In this paper, we report the electronic structure and the absorption spectra of MoS2/WS2 and MoSe2/WSe2 HBLs from first-principles calculations. We explore the spectral positions, binding energies, and the origins of inter- and intralayer excitons and compare our results with experimental observations. The absorption spectra of the systems are obtained by solving the Bethe-Salpeter equation on top of a G0W0 calculation, which corrects the independent-particle eigenvalues obtained from density-functional theory. Our calculations reveal that the lowest energy exciton in both HBLs possess an interlayer character which is decisive regarding their possible device applications. Due to the spatially separated nature of the charge carriers, the binding energy of interlayer excitons might be expected to be considerably smaller than that of intralayer ones. However, according to our calculations, the binding energy of lowest energy interlayer excitons is only ∼20% lower due to the weaker screening of the Coulomb interaction between layers of the HBLs. Therefore, it can be deduced that the spectral positions of the interlayer excitons with respect to intralayer ones are mostly determined by the band offset of the constituent single layers. By comparing oscillator strengths and thermal occupation factors, we show that in luminescence at low temperature, the interlayer exciton peak becomes dominant, while in absorption it is almost invisible.