Tunable Localized Charge Transfer Excitons in a Mixed Dimensional van der Waals Heterostructure

TL;DR

This paper demonstrates the formation and tunability of localized charge-transfer excitons in mixed dimensional van der Waals heterostructures, combining 2D materials and quantum confined nanostructures, with potential applications in tunable photonic devices.

Contribution

It introduces a method to localize and tune charge-transfer excitons in mixed dimensional heterostructures using 2D materials and nanoplates, overcoming delocalization issues.

Findings

Charge-transfer excitons are observed at the heterointerface using TEPL.

Exciton resonance energy can be tuned by up to 120 meV.

The approach enables highly tunable MDH-based photonic devices.

Abstract

Observation of interlayer, charge-transfer (CT) excitons in van der Waals heterostructures (vdWHs) based on 2D-2D systems has been well investigated. While conceptually interesting, these charge transfer excitons are highly delocalized and spatially localizing them requires twisting layers at very specific angles. This issue of localizing the CT excitons can be overcome via making mixed dimensional vdWHs (MDHs) where one of the components is a spatially quantum confined medium. Here, we demonstrate the formation of CT excitons in a 2D/quasi-2D system comprising MoSe2 and WSe2 monolayers and CdSe/CdS based core/shell nanoplates (NPLs). Spectral signatures of CT excitons in our MDHs were resolved locally at the 2D/single-NPL heterointerface using tip-enhanced photoluminescence (TEPL) at room temperature. By varying both the 2D material, the shell thickness of the NPLs, and applying out-of-plane electric field, the exciton resonance energy was tuned by up to 120 meV. Our finding is a significant step towards the realization of highly tunable MDH-based next generation photonic devices.