WSe2/Graphene Heterostructures

• WSe2/Graphene heterostructures are vertically stacked van der Waals systems that combine graphene’s ultrahigh carrier mobility with WSe2’s semiconducting and spintronic properties.
• Advanced fabrication techniques such as mechanical transfer, CVD growth, and precise rotational alignment yield atomically sharp, strain-engineered interfaces critical for optimal performance.
• Emergent phenomena including proximity-induced spin splitting, tunable quantum spin Hall effects, and efficient interlayer charge transfer have been demonstrated through first-principles calculations and advanced spectroscopies.

WSe$_2$/Graphene heterostructures are vertically stacked van der Waals systems in which a layer of graphene is interfaced with monolayer or multilayer tungsten diselenide (WSe$_2$). These heterostructures combine the unique Dirac fermion physics and ultrahigh carrier mobility of graphene with the strong spin–orbit coupling, excitonic behavior, and semiconducting characteristics of WSe$_2$. The interplay at the interface leads to emergent phenomena not present in either material alone, including proximity-induced spin splitting, tunable quantum spin Hall effects, hybrid electronic and optoelectronic functionalities, and controllable interlayer charge transfer. The structure and properties of these systems are highly sensitive to twist angle, interfacial cleanliness, layer thickness, strain, and external fields. This entry details the structural, electronic, spintronic, and optical features of WSe$_2$/graphene heterostructures as revealed by first-principles calculations, advanced spectroscopy, and device measurements.

1. Structural and Interfacial Characteristics

High-quality WSe$_2$/graphene heterostructures can be fabricated via various techniques, including mechanical transfer, CVD growth, and wafer-scale electrodeposition. When a monolayer of graphene is placed in contact with WSe$_2$, the lattice mismatch is minimal (e.g., 4×4 graphene on 3×3 WSe$_2$ supercells with $d\approx3.42$ Å, preserving the C–C bond length at 1.42 Å and W–Se bond lengths near their intrinsic values) (Kaloni et al., 2014). Raman and AFM studies indicate compressive strain in the graphene due to differences in thermal expansion coefficients and growth-induced strain (Huang et al., 10 Sep 2025, Piccinini et al., 2019). Precise rotational alignment (rotational misfit within ±2.3°) has been routinely achieved using epitaxial graphene on SiC, yielding sets of preferentially oriented heterostructures with atomically sharp interfaces (Barrera et al., 2016).

The binding between graphene and WSe$_2$ is dominated by van der Waals interactions with a binding energy around 54 meV per carbon atom (Kaloni et al., 2014). Strain and interface stoichiometry, such as oxygen loss from SiO$_2$ during CVD growth, can further induce significant chemical doping and alter the electronic structure of the component layers (Piccinini et al., 2019). Commensurate stacking and minimized disorder at the interface are key for achieving the proximity effects discussed below.

2. Band Structure Engineering and Topological Phases

Graphene exhibits very weak intrinsic spin–orbit coupling (SOC) and a zero bandgap. When interfaced with WSe$_2$0, proximity effects lead to significant band modifications (Kaloni et al., 2014, Yu et al., 2024). First-principles and effective Hamiltonian studies show that:

• Without SOC, weak hybridization at the interface opens a small gap (~3.6 meV).
• When SOC is included, pronounced spin splittings emerge at the K and K′ points: $_2$1 meV (valence), $_2$2 meV (conduction), with a small but finite gap (~0.9 meV). This is captured in the Hamiltonian

$_2$3

where $_2$4 (K/K′ valley), $_2$5 is spin, and $_2$6 is the enhanced SOC (Kaloni et al., 2014).

• The band inversion near the Dirac points leads to a quantum spin Hall (QSH) phase. Time-reversal symmetry is preserved, making the system a topological insulator with edge states supporting dissipationless spin currents.
• In sandwich structures (graphene between two WSe$_2$7 layers), the SOC and associated band splittings are further enhanced (splittings $_2$8–153 meV), tunable by stacking geometry (Kaloni et al., 2014).

Extended $_2$9 modeling incorporating Rashba and valley-Zeeman SOC captures the emergence of Dirac-Rashba fermions and the possibility for a quantum valley Hall state with nonzero valley Chern number ($_2$0 for a canonical choice of model parameters), where edge states are protected at the boundaries (Yu et al., 2024).

3. Spin-Orbit Coupling, Magnetotransport, and Spintronics

Proximity-induced SOC in graphene dramatically alters its spin physics and magnetotransport response:

• Enhanced SOC is directly evidenced by the emergence of weak antilocalization (WAL) in low-field magnetoconductance. In diffusive graphene/WSe$_2$1/SiO$_2$2 devices (mobility $_2$3 cm$_2$4/Vs), WAL manifests as a pronounced peak (with extracted $_2$5 ps, over two orders of magnitude shorter than in pristine graphene) (Völkl et al., 2017).
• Encapsulating graphene between WSe$_2$6 and hBN boosts mobility to $_2$7 cm$_2$8/Vs, suppresses WAL, and results in full lifting of spin and valley degeneracies in Shubnikov–de Haas oscillations, revealing a transition from diffusive to quasiballistic transport at the boundary between WAL and size-effect resistance regimes (Völkl et al., 2017).
• Gate-tunable SOC in bilayer graphene/WSe$_2$9 (BLG/WSe$_2$0) heterostructures is evidenced by nonmonotonic WAL visibility with respect to vertical displacement field. The WAL visibility maximizes at zero displacement due to the interplay between Rashba (in-plane) and valley–Zeeman (out-of-plane) SOC contributions, as confirmed by an $_2$1 Hamiltonian analysis (Amann et al., 2020).
• Hydrostatic pressure is a powerful tuning parameter for SOC strength. In BLG/WSe$_2$2, weak localization gives way to WAL as pressure is increased, indicating enhanced orbital overlap and stronger proximity-induced SOC (Rashba parameter $_2$3 rising from $_2$4meV to $_2$5meV at $_2$6GPa) (Fülöp et al., 2021). At $_2$7GPa, the Ising SOC parameter increases from $_2$8 meV to $_2$9 meV, and Rashba SOC from $_2$0 meV to $_2$1 meV (Szentpéteri et al., 2024).
• These phenomena underpin proposals for spin field-effect transistors, reconfigurable spin logic, and topological edge-state engineering.

4. Interlayer Charge Transfer and Interfacial Coupling

WSe$_2$2/graphene heterostructures exhibit efficient charge transfer and strong interfacial coupling:

• Raman and PL spectroscopy show that, as WSe$_2$3 thickness increases, graphene's G and 2D bands blue-shift and are attenuated—signatures of p-doping in graphene and n-doping in WSe$_2$4 due to electron transfer across the interface. This is driven by the work function disparity:

$_2$5

with $_2$6 eV (graphene/SiC) and $_2$7 eV (Huang et al., 10 Sep 2025).

• Enhanced interlayer vibrational modes (blue-shifted shear and breathing phonons, emergence of higher-order breathing modes) are observed only on graphene substrates, not on SiO$_2$8, indicating that graphene actively modulates interlayer mechanical coupling (Huang et al., 10 Sep 2025).
• PL in monolayer WSe$_2$9 on graphene is almost completely quenched, attributed to ultrafast interlayer charge transfer (sub-picosecond) and highly efficient Forster resonance energy transfer (FRET, with $_2$0 dependence). In contrast, multilayer WSe$_2$1 shows partial PL recovery (Huang et al., 10 Sep 2025).
• Exciton energies (A- and B-excitons) remain nearly pinned as a function of WSe$_2$2 thickness on graphene—starkly contrasting with the rapid red shift seen on inert substrates. This is due to the combined effect of graphene's dielectric screening and screening by free carriers accumulated via charge transfer (Huang et al., 10 Sep 2025).

5. Twist Angle, Spin Texture, and Spin–Charge Interconversion

Twist angle between WSe$_2$3 and graphene introduces moiré periodicity and enables manipulation of spin texture, with profound implications for spintronic functionality:

• First-principles calculations show proximity-induced Dirac Hamiltonians modified by twist-dependent Rashba and valley–Zeeman terms. The continuum Hamiltonian reads:

$_2$4

where the Rashba angle $_2$5 is twist-dependent (Lee et al., 2022).

• Experimental Hanle precession and nonlocal transport measurements reveal both conventional (tangential) and unconventional (radial) spin textures. For specific twist angles, a radial component of the spin emerges and can even be reversed, with the total spin polarization parameterized by the Rashba angle $_2$6 (Yang et al., 2023).
• The charge-to-spin conversion (CSC) efficiency, quantifying processes such as the spin Hall effect (SHE) and Rashba–Edelstein effect (REE), is maximized near 30° twist. In clean systems, REE dominates; increased disorder favors SHE. Breaking mirror symmetry via twisting enables unconventional REE with induced spins collinear to the applied field, unlike the purely transverse response in untwisted structures (Lee et al., 2022).
• Twist-tunable spin texture ("spin twistronics") enables engineering of spin-charge interconversion for reconfigurable devices, memory, or logic applications (Yang et al., 2023).

6. Ultrafast Exciton Diffusion and Screening Effects

WSe$_2$7/graphene heterostructures support exceptional exciton mobility and dynamic optical tunability:

• Heterodyne transient grating spectroscopy reveals that the ambipolar exciton diffusion coefficient in WSe$_2$8/graphene is $_2$9cm$_2$0/s (early times), far exceeding the $_2$1cm$_2$2/s in isolated WSe$_2$3 (Rieland et al., 2024).
• Photoexcitation in graphene leads to rapid (picosecond-scale) modulation of screening. The resulting transient, highly doped graphene layer dynamically screens impurities, traps, and defects at the WSe$_2$4 interface, substantially enhancing exciton diffusion (Rieland et al., 2024).
• The nature of exciton dynamics—early ultrafast mode and later slower mode—depends on excitation fluence, indicating strong coupling between graphene carrier dynamics and WSe$_2$5 transport properties (Rieland et al., 2024).

7. Applications and Device Implications

These heterostructures offer a platform for a range of functional quantum, electronic, and optoelectronic devices:

• Quantum Spin Hall insulator devices with robust edge conduction channels for dissipationless spin transport, feasible at zero magnetic field (Kaloni et al., 2014).
• High-mobility transistors and high-frequency components; mobilities reach $_2$6 cm$_2$7/Vs at room temperature in WSe$_2$8/graphene/hBN stacks, with weak temperature-dependent resistivity due to modified acoustic phonon dispersion (gapped with $_2$9) (Banszerus et al., 2019).
• Spintronic elements such as tunable spin filters, spin inverters, and logic architectures, where spin injection and relaxation are electrically controllable via interface resistance, bias, gating, or pressure (Omar et al., 2016, Mrenca-Kolasinska et al., 2018, Fülöp et al., 2021, Szentpéteri et al., 2024).
• Optoelectronic devices including vertically integrated, cavity-enhanced electroluminescent sources; monolithic microcavity devices incorporating WSe$d\approx3.42$0/graphene show intensity enhancements by up to two orders of magnitude and emission wavelength tuning exceeding 35 nm by varying collection angle (Pozo-Zamudio et al., 2019).
• Ultrafast photodetectors or optical switches based on exciton diffusion modulation, and memory devices leveraging dynamic charge transfer and screening (Rieland et al., 2024).
• Engineering and stabilization of quantum Hall phases by tailoring Landau level gaps and screening with WSe$d\approx3.42$1 as an interfacial layer, enabling control of correlated or symmetry-broken ground states (Chuang et al., 2019).

These functionalities depend critically on the ability to control interfacial mechanics, charge transfer, twist angle, and external fields, and leverage the interplay of proximity-induced SOC, dielectric screening, and charge transfer in the heterostructure stack.