Robust Interlayer Exciton Interplay in Twisted van der Waals Heterotrilayer on a Broadband Bragg Reflector up to Room Temperature

TL;DR

This work addresses the challenge of achieving robust room-temperature interlayer excitons in van der Waals heterostructures by integrating a MoSe2/WSe2/WSe2 trilayer onto a broadband chirped distributed Bragg reflector, enabling enhanced and spectrally accessible emission from three stacking regions (HBL, HoBL, HTL). The authors demonstrate RT interlayer exciton emission across all regions, with the HTL showing a tenfold PL enhancement at cryogenic temperatures and a distinctive, band-hybridized emission profile that includes indirect momentum transitions. Temperature-dependent PL, polarization, and TRPL measurements reveal valley-selective dynamics and thermally driven population redistribution between singlet and triplet IX states, as well as room-temperature persistence of excitonic features in the HTL. The results establish a design strategy that combines stacking orientation and optical resonator engineering to control exciton states from 4 K to RT, paving the way for scalable excitonic optoelectronics and quantum photonics with TMD heterostructures.

Abstract

We report robust room temperature interlayer excitons in transition metal dichalcogenide heterostructures engineered via precise stacking orientation and twist-angle control. We integrate 2H-stacked MoSe$_{2}$/$^{1}$WSe$_{2}$/$^{2}$WSe$_{2}$ heterotrilayer onto a chirped distributed Bragg reflector that acts as a backside mirror. This way, we fabricate a platform that hosts distinct heterotrilayer, heterobilayer, and homobilayer regions with enhanced excitonic features at elevated temperatures. Although the heterobilayer supports temperature-tunable singlet and triplet interlayer excitons, it exhibits low emission yield at 4 K. In comparison, the heterotrilayer shows remarkable excitonic properties, including pronounced band modulation, intervalley interlayer exciton transitions, and a tenfold photoluminescence enhancement along with a sevenfold increase in exciton decay time at cryogenic temperatures compared to the heterobilayer system. Temperature-dependent studies reveal intriguing interlayer exciton dynamics in the heterotrilayer, including the emergence of valley-polarized interlayer excitons, and the ability to maintain optical stability up to room temperature. Our results establish a clear strategy for engineering excitonic states across multilayer van der Waals heterostructures from 4 K to room temperature, providing a versatile platform for excitonic optoelectronics, quantum photonics, and tunable long-lived interlayer exciton states in scalable TMD heterostructures.

Figures (5)

• Figure 1: Structural and optical overview of twisted VdWHSs at RT. a Schematic of the HTL layer design showing the stacking order of TMD monolayers and the substrate configuration along with IX formation between layers. b Optical microscope image highlighting the monolayers of MoSe2, 1WSe2, and 2WSe2 with light blue, red, and blue outline respectively, indicating also the HTL, HBL, and twisted HoBL regions in the image. c Calculated reflection spectrum of the cDBR showing a 600 nm wide stopband. The inset illustrates the layer design of the cDBR. (d-f) RT PL spectra of the d MoSe2/1WSe2 HBL region e Twisted 1WSe2/2WSe2 HoBL region, and f MoSe2/1WSe2/2WSe2 HTL region which excited by a continuous-wave (CW) laser with energy 1.87 eV (660 nm), revealing the distinct emission features associated with each stacking configuration.
• Figure 2: Excitonic emission, valley polarization, and decay dynamics of the twisted MoSe2/1WSe2 hBL. a Temperature-dependent PL spectra of IX emission from 4 K to RT showing the evolution of IX emission features with increasing temperature. b PL spectra of IX from HBL at 100 K (bottom panel), where the triplet IX and singlet IX peaks can be well resolved. The middle panel shows polarization-resolved PL spectra at 100 K with pulsed right-circularly polarized laser excitation. ($\sigma^{+}$). The top panel represents the respective DCP. c Schematic illustration of the HBL band structure with a 2H stacking order, where the solid and dashed arrows correspond to triplet IX and singlet IX emission, respectively. The red arrows represent the spin orientation of electrons and holes. d Normalized PL intensity decay trace of triplet IX (top panel) and singlet IX (bottom panel) in semi-logarithmic scale from 4 K to RT. e Extracted decay time components of both triplet (blue square) and singlet (red circle) IX as a function of temperature.
• Figure 3: Evolution of PL and TRPL of twisted $^{1}$WSe$_{2}$/$^{2}$WSe$_{2}$ HoBL. a PL spectra of the HoBL measured from 4 K to RT, showing the temperature-dependent evolution of X$_{1}$, X$_{2}$, and X$_{3}$ emission with X$_{3}$, X$_{4}$, and the intralayer exciton of WSe$_{2}$. b Semi-logarithmic plot of normalized PL intensity decay traces of four phonon-assisted intervalley excitons X$_1$ to X$_4$. The signals were measured at the characteristic peak temperatures: X$_{1}$ (black), X$_{2}$ (red) at 4 K, X$_{3}$ (blue) at 80 K, and X$_{4}$ (magenta) at 200 K. The characteristic decay times were extracted by linear fits. c Radiative decay time ($\tau_{1}$) of the HoBL obtained from linear fitting of the PL decay in the semi-logarithmic plot as a function of temperature.
• Figure 4: Emission propoerties and decay dynamics of the twisted MoSe2/1WSe2/2WSe2 heterotrilayer system. a PL spectra of HTL from 4 K to RT plotted with vertical stacking. b (bottom panel) Polarization resolved PL spectra under pulsed laser excitation of right circularly polarized light ($\sigma^{+}$) at 4 K. (top panel) Extracted degree of circularly polarization with respect to temperature of the HTL region. d Temperature-dependent TRPL decay traces in semi-logarithmic presentation. e) Extracted temperature-dependent fast ($\tau\textsubscript{1}$) and slow ($\tau\textsubscript{2}$) decay constants of HTL emission.
• Figure 5: Comparative study of optical and valleytronic properties of IX in twisted HBL and HTL. a PL spectra of both HBL (red trace) and HTL (black trace) highlighting the difference in emission features at 4 K. b Calculated DCP of both HBL and HTL obtained from right ($\sigma^{+}$) and left ($\sigma^{+}$) circular polarization upon the pulsed laser excitation with ($\sigma^{+}$) polarization at 80 K. Top panel: DCP of HTL region with the range from -0.2 to 0.2. Bottom panel: DCP of the HBL region. c Comparative column plot of the temperature-dependent PL intensity of HBL and HTL from 4 K to RT. d TRPL traces recorded over the same temperature range comparing the radiative decay times of the HBL and HTL systems.