Interlayer excitons in MoSe2/WSe2 heterostructures from first-principles
Abstract
Based on ab initio theoretical calculations of the optical spectra of vertical heterostructures of MoSe2 (or MoS2) and WSe2 sheets, we reveal two spin-orbit-split Rydberg series of excitonic states below the A excitons of MoSe2 and WSe2 with a significant binding energy on the order of 250\,meV for the first excitons in the series. At the same time, we predict crystalographically aligned MoSe2/WSe2 heterostructures to exhibit an indirect fundamental band gap. Due to the type-II nature of the MoSe2/WSe2 heterostructure, the indirect transition and the exciton Rydberg series corresponding to a direct transition exhibit a distinct interlayer nature with spatial charge separation of the coupled electrons and holes. The experimentally observed long-lived states in photoluminescence spectra of MoX2/WY2 heterostructure are attributed to such interlayer exciton states. Our calculations further suggest an effect of stacking order on the peak energy of the interlayer excitons and their oscillation strengths.
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