Formation, Identification, and Regulation Mechanisms of Interlayer Excitons in TMD Heterostructures

Interlayer excitons (IXs), formed in type-II van der Waals (vdW) heterostructures where electrons and holes reside in adjacent monolayers, have attracted increasing interest due to their spatially indirect nature, long lifetimes, strong Coulomb binding, and unique out-of-plane dipole moments. These features render IXs a promising platform for exploring many-body physics and enabling next-generation excitonic devices. This review systematically presents the formation mechanisms, identification methods, and external modulation strategies of interlayer excitons in twodimensional materials.We begin by analyzing the prerequisites for IX formation, emphasizing the role of band alignment, interlayer charge transfer, and momentum mismatch. Recent studies also reveal direct interlayer absorption as an alternative IX generation pathway. For identification, we summarize multiple optical techniques—including photoluminescence (PL), photoluminescence excitation (PLE), transient absorption (TA), and electro-absorption (EA)—that probe IX energy positions, binding energies, and recombination pathways. However, distinguishing between interlayer and defect-bound or momentum-indirect excitons remains experimentally challenging due to spectral overlap and measurement-dependent interpretations.In the core part, we review five primary external modulation methods: electric field, strain, magnetic field, twist angle, and optical cavities. Electric fields enable fast, reversible tuning of exciton energy levels, especially for excitons with large dipole moments. Strain offers nanoscale spatial control and can reshape local potential landscapes. Magnetic fields affect spin-valley configurations and allow access to exciton polarization dynamics. Moiré engineering via twist angles introduces periodic potential landscapes, yielding moiré-trapped IXs and novel hybrid exciton– polaritons. Optical cavities enhance exciton radiative recombination via light–matter coupling and open up possibilities for strong coupling regimes. We further discuss additional strategies such as substrate-induced screening, dielectric environment, probe-induced local stress, and ferroelectric gating, all of which enrich the modulation toolbox.To facilitate cross-comparison, we present a comprehensive summary table comparing different modulation approaches in terms of tuning targets, dimensionality, efficiency, dynamic responsiveness, and implementation complexity.Finally, we discuss emerging applications of IXs in optoelectronic and quantum devices. Their tunable emission and long-lived nature make them suitable for exciton-based memory, logic, lasers, and reconfigurable photonic circuits. With advances in material synthesis, interface engineering, and hybrid integration, interlayer excitons are evolving from fundamental quasiparticles toward programmable excitonic elements in chip-scale photonics and quantum information technologies.