First Principles Analysis on the Excitonic Properties of MoS₂/WS₂ and MoSe₂/WSe₂ Heterobilayers

By using the method of many body perturbation theory (MBPT), we investigate the optical absorption spectra and the excitonic properties of MoS2/WS2 and MoSe2/WSe2 heterobilayers. We first correct the independent particle band gap by performing GW calculation on top of ground state density functional theory (DFT) calculations and the optical spectra of the bilayers are calculated by solving Bethe-Salpeter equation (BSE). Two different types of excitons present in this type of heterobilayers; the inter-layer excitons (electron and hole locate in different layers) and the intra-layer ones (electron and hole locate in the same layer). Relative spectral position of inter- and intra-layer excitons w.r.t. each other is determined by the band alignment of the constituent layers and binding energy of the excitons. The spectral position of the inter-layer exciton w.r.t. intra-layer one is crucial for the low energy optical response and the charge carrier dynamics of the heterobilayers. In this work, we show a detail analysis on inter- and intra-layer excitons in MoS₂/ WS₂ and MoSe₂/WSe₂ heterobilayers. We investigate their binding energy and origin as well as possible scenarios which might lead to alter the character of the lowest excitonic peak in the optical spectra of the bilayers.