Excitonic response in TMD heterostructures from first-principles: impact of stacking, twisting, and interlayer distance

Van der Waals heterostructures of two-dimensional transition metal dichalcogenides provide a unique platform to engineer optoelectronic devices tuning their optical properties via stacking, twisting, or straining. Using ab initio Many-Body Perturbation Theory, we predict the electronic and optical (absorption and photoluminescence spectra) properties of MoS_2/WS_2 and MoSe_2/WSe_2 hetero-bilayers with different stacking and twisting. We analyse the valley splitting and optical transitions, and explain the enhancement or quenching of the inter- and intra-layer exciton states. Contrary to established models, that focus on transitions near the high-symmetry point K, our results include all possible transitions across the Brillouin Zone. This result, for a twisted Se-based heterostructures, in an interlayer exciton with significant electron density in both layers and a mixed intralayer exciton distributed over both MoSe_2 and WSe_2. We propose that it should be possible to produce an inverted order of the excitonic states in some MoSe_2/WSe_2 heterostructures, where the energy of the intralayer WSe_2 exciton is lower than that in MoSe_2. We predict the variability of the exciton peak positions (∼100 meV) and the exciton radiative lifetimes, from pico- to nano-seconds, and even micro-seconds in twisted bilayers. The control of exciton energies and lifetimes paves the way towards applications in quantum information technologies and optical sensing.