Intrinsic Control of Interlayer Exciton Generation in Van der Waals Materials via Janus Layers

Abstract

We demonstrate the possibility of engineering the optical properties of transition metal dichalcogenide heterobilayers when one of the constitutive layers has a Janus structure. We investigate different MoS2@Janus layer combinations using first-principles methods including excitons and exciton–phonon coupling. The direction of the intrinsic electric field from the Janus layer modifies the electronic band alignments and, consequently, the energy separation between dark interlayer exciton states and bright in-plane excitons. We find that in-plane lattice vibrations strongly couple the two states, so that exciton–phonon scattering may be a viable generation mechanism for interlayer excitons upon light absorption. In particular, in the case of MoS2@WSSe, the energy separation of the low-lying interlayer exciton from the in-plane exciton is resonant with the transverse optical phonon modes (40 meV). We thus identify this heterobilayer as a prime candidate for efficient generation of charge-separated electron–hole pairs.

Spin Mixing Control of Interlayer Excitons in ZrS2/ZrNCl Heterostructures

“…The primary factors that determine the distance between layers are the electronegativity and the atomic radii. The different interfaces result in effective electric fields of 0.123 V/Å (the distance from the topmost S to Cl is 7.875 Å) and 0.079 V/Å (the distance from the upper N to the lowest S is 8.553 Å) for 1-S/N and 2-S/Cl, respectively …”

“…Two-dimensional Janus TMDs have recently attracted a great deal of attention due to their appealing properties and potential applications in devices. − These materials, especially when stacked into heterostructures, are highly advantageous for the photoexcitation features of electron–hole pairs, or excitons, due to their intrinsic out-of-plane dipole moment and significant band shift. ,,, To align type-II bands to form interlayer excitons (IXs), single-layer composition and stacking sequence have been selected to construct van der Waals (vdW) heterostructures out of distinct 2D materials. ,, Meanwhile, when light is absorbed, the weak dielectric screening of two-dimensional semiconductors enables the creation of tightly bound excitons, − resulting in exceptional optical characteristics like layer-dependent exciton modulation and discrete excitonic peaks with significant photoluminescence response . The heterostructures, including Janus TMDs, maintain the original performance of a single-layer TMDC while adding an electric field, which significantly enhances the interaction of the photoexcited electron and hole.…”