Ferroelectric Control of Interlayer Excitons in 3R-MoS$_{2}$ / MoSe$_{2}$ Heterostructures

TL;DR

This work demonstrates ferroelectric-domain–dependent control of interlayer excitons in $3R$-MoS$_2$/MoSe$_2$ heterostructures. By combining low-temperature μ-PL, PLE, TRPL, SHG, and first-principles GW/BSE calculations, the authors show that ILX energies redshift with MoS$_2$ layer count and vary with ferroelectric domain polarity, enabling local, non-volatile tuning of excitonic states. DFT/BSE reveals type-II band alignment and domain-dependent interfacial dipoles, while gate-induced domain-wall motion enables electrically driven reconfiguration of the ILX landscape. The results establish a foundation for ferroelectric optoelectronic devices in van der Waals heterostructures, where local ferroelectric order serves as a tunable, non-volatile control parameter for excitonic properties.

Abstract

We investigate the interaction between interlayer excitons and ferroelectric domains in hBN-encapsulated 3R-MoS$_2$/MoSe$_2$ heterostructures, combining photoluminescence experiments with density functional theory and many-body Green's function calculations. Low-temperature photoluminescence spectroscopy reveals a strong redshift of the interlayer exciton energy with increasing MoS$_2$ layer thickness, attributed to band renormalization and dielectric effects. We observe local variations in exciton energy that correlate with local ferroelectric domain polarization of the 3R-MoS$_2$ layer, showcasing distinct domain-dependent interlayer exciton transition energies. Gate voltage experiments demonstrate that the interlayer exciton energy can be tuned by electrically induced domain switching. These results highlight the potential for interlayer exciton control by local ferroelectric order and establish a foundation for future ferroelectric optoelectronic devices based on van der Waals heterostructures.

Figures (11)

• Figure 1: (a) Optical image of an hBN-encapsulated nL-MoS$_{2}$/MoSe$_{2}$ heterostructures on gold contacts. The heterostructure is divided into a region with 3L-MoS$_{2}$ (I) and a region with 4L-MoS$_{2}$ (II), indicated by the orange lines. The black scale bar corresponds to 10 µm. (b) Schematic of the hBN-encapsulated 3L-MoS$_{2}$/MoSe$_{2}$ heterostructure, highlighting the 3R stacking of MoS$_2$. (c) PL signals of different MoS$_{2}$/MoSe$_{2}$ heterostructures with 2L/3L/4L-MoS$_{2}$ from top to bottom. The green and blue areas indicate the intralayer excitons of MoSe$_{2}$ and MoS$_{2}$, respectively. The salmon-colored area shows the ILX signal of the heterostructures. While the 2L and 3L spectra were recorded using a Si CCD, the 4L spectrum was measured using an InGaAs photodiode array. (d) Power dependence of the PL signal in region I of panel (a). The grey arrow indicates a blueshift in the signal with increasing power. (e) Exemplary PL and PLE spectra of an hBN-encapsulated 2L-MoS$_{2}$/MoSe$_{2}$ heterostructure. (f) Time-resolved PL of the ILX feature in the 2L-MoS$_{2}$/MoSe$_{2}$ heterostructure. The pink line is a double exponential fit to the data, yielding the decay times displayed in the figure.
• Figure 2: (a) ILX PL heatmap from a 2L-MoS$_{2}$/MoSe$_{2}$ heterostructure. (b) Corresponding spatial map of the ILX peak energy in the heterostructure. The white scale bar corresponds to 4 µm. (c) Representative PL spectra from (a), showing the energy difference between AB and BA domains of the underlying 3R-2L-MoS$_{2}$. (d) Illustration of the sample highlighting the ferroelectric effect on the ILX. AB and BA refer to distinct domain configurations with opposite polarizations, and DW denotes the domain wall separating them. A detailed description can be seen in Fig. \ref{['fig:theo1']}.
• Figure 3: (a,b) Side views of the ABA and BAA stackings, respectively. The two parallel black lines denote the unit cell. (c,d) Side and top views of the charge density difference isosurfaces for ABA and BAA stackings, respectively, highlighting interfacial dipoles and polarization reversal; red and green isosurfaces represent charge depletion (holes) and accumulation (electrons), respectively, at an isovalue of 0.001 e/Å$^{3}$. (e,f) In-plane averaged charge density difference profiles along the $z$-axis for ABA and BAA stackings, respectively, with the 2L-MoS$_2$ (AB) in ABA exhibiting a Max$\to$Min sequence (Max $\approx$ +0.005 e/Å$^{3}$, Min $\approx$ -0.0065 e/Å$^{3}$) and BA is showing an inverted ordering.
• Figure 4: (a, b) Band structures of 2L-MoS$_{2}$/MoSe$_{2}$ for the ABA and BAA stacking configurations. A top view of the stacking geometry, which is identical for both configurations, is included as an inset in panel (b) for reference. (c,d) Exciton charge density distributions of the CBM and VBM states for ABA and BAA stackings as indicated.
• Figure 5: (a-e) Gated PL false color maps of the ILX peak energy in a 3L-MoS$_{2}$/MoSe$_{2}$ heterostructure. The purple dashed line is a guideline to highlight the boundary edge between two domains in the different false color maps. The white scale bar corresponds to 2 µm. (f-i) PL spectra corresponding to the positions highlighted by the coloured dots in panel (c). The pink dotted lines show the spectral centroid range of the spectra, which is also written next to the lines in eV. While the change in the spectral centroid is smaller on the extreme positions (red and blue dots) of the false color map ($\approx$ 5-7 meV), the spectra in the middle of the false color maps (yellow and green dots) show more substantial change ($\approx$ 12-16 meV).