Transport Enhancement and In Situ Control of Electronic Correlation via Photoinduced Modulation Doping of van der Waals Heterostructures

Abstract: Modulation doping, a well-established technique for traditional semiconductor heterostructures, is a promising approach for tailoring carrier concentration in 2D materials devices. In this letter we report on photoinduced modulation doping in hBN-graphene-hBN-SiO2 heterostructures utilizing standard white light sources and no additional fabrication complexity. We establish the use of this technique to both dope the channel material and to photoanneal devices, providing control over electronic doping and disorder in the graphene channel. We analyze the transport properties by employing Drude and Landauer transport models, highlighting the ability to reversibly tune the mobility and mean scattering length of the graphene with a high degree of accuracy. This tunability allows us to switch our device between the diffusive and quasi-ballistic transport regimes in situ. We utilize the exceptional control our technique provides over local disorder to realize quantum Hall isospin ferromagnetic states in a device whose initial quality would otherwise leave such states unobservable. These results demonstrate precise manipulation of carrier density and charge disorder in van der Waals heterostructures, providing a highly accessible approach to creating high-quality devices capable of realizing correlated electronic states.

• The paper demonstrates that photoinduced modulation doping significantly enhances carrier mobility by enabling precise, reversible control of disorder and charge density.
• It employs illumination-induced charge trapping at the hBN-SiO₂ interface to switch transport regimes from diffusive to quasi-ballistic, with notable improvements in mobility and reduced residual carrier densities.
• The technique allows observation of quantum Hall isospin ferromagnetic states at lower magnetic fields, paving the way for advanced control in 2D electronic devices.

Photoinduced Modulation Doping in van der Waals Heterostructures: Control of Electronic Transport and Correlated States

Introduction

The paper "Transport Enhancement and In Situ Control of Electronic Correlation via Photoinduced Modulation Doping of van der Waals Heterostructures" (2605.22452) presents a comprehensive study of photodoping approaches in hBN/graphene/hBN/SiO₂ heterostructures, providing both precise carrier density control and electronic disorder management. The authors demonstrate the utility of photoinduced modulation doping, using standard white light sources, to dynamically modulate charge density and enable nonvolatile, reversible control of graphene-based device transport properties. This methodology allows in situ tuning between diffusive and quasi-ballistic transport regimes, and the realization of quantum Hall isospin ferromagnetic states that would be otherwise inaccessible in devices of moderate initial quality.

Methodology and Device Architecture

The work employs mechanically exfoliated hBN/graphene/hBN stacks on SiO₂/Si substrates, patterned into Hall bar geometries. Device quality is initially assessed via transfer curves and quantum Hall measurements. Photodoping is achieved by illuminating the device in the presence of a backgate voltage, causing photoexcited carriers to become trapped at the hBN-SiO₂ interface, thus modulating the local electrostatic environment of the graphene channel. The process also enables “photoannealing,” which reduces Coulomb disorder without introducing net charge to the system.

Transport characteristics are analyzed using both Drude and Landauer transport models, extracting mobility, residual carrier density, and mean elastic scattering length as a function of photodoping parameters. Magnetotransport measurements are performed at low temperatures (1.6 K) under fields up to 9 T to interrogate quantum Hall signatures and correlated states.

Transport Enhancement via Photodoping

The authors observe that photoannealing yields an immediate improvement in device quality, with:

• Carrier mobility tunable in situ between $2 \times 10^5$ and $3 \times 10^5$ cm²/V·s.
• Residual carrier density reduced by nearly a factor of two post-photoannealing, remaining as low as $10^{10}$ cm⁻² during n-doping cycles.

Precise control of the charge neutrality point over a 40 V backgate voltage range is achieved, corresponding to electron densities up to $3 \times 10^{12}$ cm⁻², with a one-to-one mapping between photodoping voltage and CNP shift.

Landauer transport analysis demonstrates tunability of the mean scattering length:

• Values ranging from 0.1 μm (diffusive) to ~1 μm (quasi-ballistic) at representative carrier densities.
• Device can be reversibly switched between diffusive and quasi-ballistic regimes.

Photoannealing and n-type photodoping minimize electronic disorder, sharply enhancing transport characteristics and enabling higher on-off ratios for device operation.

Mechanistic Insights

The primary mechanism is spatially localized charge trapping at the hBN-SiO₂ interface facilitated by photoexcitation and electric field. Filled trap states are posited to distribute charged impurities in a correlated manner due to Coulombic repulsion, thus smoothing electron-hole puddle-induced fluctuations in the graphene channel. Device discharge sequences and p-type photodoping attempts demonstrate reversible disorder modulation, with difficulty achieving p-doping attributed to the specifics of optical excitation (longer wavelengths).

In Situ Control of Electronic Correlation: Quantum Hall States

A key result is the ability to observe and reversibly control quantum Hall isospin ferromagnetic states:

• In high disorder regimes, only conventional 4-fold degenerate Landau level plateaus appear.
• After photoannealing, full lifting of Landau level degeneracy is observed at filling factors $ν = -1$ to $ν = -14$ on the hole side and up to $ν = -11$ in photodoped regimes.
• Degeneracy lifting occurs at fields as low as 4 T, significantly lower than typical requirements (≥9 T), indicating exceptional suppression of disorder-induced Landau level broadening.

Degeneracy lifting on both carrier sides and at low field reflects strongly reduced disorder, enabling spontaneous symmetry breaking in spin and valley degrees of freedom. The minimum magnetic energy for degeneracy lifting drops from >1 meV to ≈0.4 meV post-photoannealing.

Implications and Future Directions

The demonstrated approach addresses intrinsic and extrinsic disorder in 2D materials heterostructures, enabling deterministic fabrication, homogenization of device variability, and realization of fragile correlated electronic states. Practical applications extend to threshold voltage normalization in 2D transistors and potential stabilization of moiré-induced correlated phases.

Theoretical implications include the realization of strongly interacting electron systems in van der Waals materials and advancement of high-mobility quasi-ballistic channels without additional fabrication complexity. The technique's accessibility (utilizing broadband laboratory illumination) and nonvolatile operation further facilitates integration into broader device development protocols.

Future prospects involve exploration of short-wavelength excitation for reliable p-doping, application to complex Moiré heterostructures, and evaluative studies across a broader range of 2D materials systems and dielectric interfaces.

Conclusion

The paper rigorously demonstrates photoinduced modulation doping as a direct, reversible, and nonvolatile tool for controlling carrier density and disorder in 2D van der Waals heterostructures. The approach enables substantial enhancement of electronic transport parameters and observation of correlated quantum Hall phenomena, providing a crucial methodology for next-generation electronic and quantum devices based on atomically thin materials. The implications span both practical device engineering and fundamental studies of correlated low-dimensional physics.