Quantum-Confined States and Band Shifts Arising from Moiré Patterns in MoS₂-WSe₂ Heterojunctions

Using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS), the electronic states of heterojunctions formed by a monolayer of MoS₂ on WSe_2, grown on epitaxial graphene, have been investigated. A 4% lattice mismatch between the MoS₂ and the WSe₂ results in a moiré pattern with period 8.5 nm and corrugation height 0.1 nm. The band gap was found to form between the valence band (VB) of the WSe₂ and the conduction band (CB) of the MoS₂. Band edge shifts of 0.1-0.2 eV are observed depending on the location within the moiré unit cell. Furthermore, quantum-confined states at both the VB and CB edges were found to form near the minimum of the corrugation. Hybridization of orbitals was found to explain these features for the VB of the WSe₂, however, intrinsic charge transfer between layers must also be considered for the features in the CB of the MoS₂. We find that this electrostatic model results in band edge shifts and confined states that are consistent with the experiments.