Twist-Angle Dependence of Moiré Excitons in MoSe₂/MoS₂ Twisted Heterobilayers

Twisted heterobilayers (hBLs) of transition metal dichalcogenides can form a moiré superlattice of periodically varying atomic registry between the two layers. The excitonic properties in twisted hBLs can be altered drastically by the formation of moiré minibands that depends sensitively on the moiré periodicity controlled by the twist angle. To study the twist-angle dependence, conventional methods based on mechanical exfoliation and transfer of individual crystals are tedious to fabricate many hBLs with various twist angles within 5°. Here we report on the study of moiré excitons in MoSe₂/MoS₂ hBLs fabricated by stacking a large MoSe₂ flake on an ensemble of highly-oriented MoS₂ flakes grown by chemical vapor deposition. The small angle variations in the MoS₂ flakes form a large number of hBLs with various small twist angles, enabling the study of twist-angle dependence of moiré excitons. We observed systematic energy shifts and fine structures in intralayer excitons with the twist angle, signifying the formation of moiré minibands. The polarization selection rules of moiré excitons were also investigated by photoluminescence excitation spectroscopy. Understanding the twist-angle dependent properties of moiré excitons provides insights for future developments of “twistronics”.