Heterostructures combining boron nitride (BN) and two-dimensional (2D) materials have emerged as a promising platform for engineering electronic properties with precision. The unique properties of hexagonal boron nitride (hBN), such as its atomically smooth surface, absence of dangling bonds, and insulating nature, make it an ideal substrate or encapsulation layer for 2D materials like graphene, transition metal dichalcogenides (TMDCs), and black phosphorus. By carefully designing these heterostructures, researchers can manipulate electronic behavior, enhance device performance, and unlock new functionalities in nanoelectronics and optoelectronics.

The interface between hBN and 2D materials plays a critical role in determining the electronic properties of the resulting heterostructure. When graphene is placed on hBN, the lattice mismatch of approximately 1.7% induces a moiré superlattice, which modulates the electronic band structure. This moiré potential can lead to the formation of secondary Dirac points and Hofstadter butterfly spectra under high magnetic fields. The quality of the interface is paramount; impurities or trapped charges can introduce scattering centers that degrade carrier mobility. Studies have shown that graphene devices on hBN substrates can achieve mobilities exceeding 100,000 cm²/Vs at room temperature, significantly higher than those on conventional SiO₂ substrates.

Interface engineering extends beyond simple stacking. Techniques such as dry transfer, polymer-assisted pick-up, and van der Waals assembly enable the creation of clean, atomically sharp interfaces. The alignment angle between the crystallographic axes of hBN and graphene also influences electronic properties. For instance, a zero-degree alignment can enhance the moiré superlattice effect, while a random orientation may suppress it. Recent work has demonstrated that twisting the layers at specific angles can induce correlated insulating states and superconductivity in graphene/hBN heterostructures, opening avenues for exploring quantum phenomena.

Beyond graphene, hBN has been integrated with TMDCs like MoS₂ and WSe₂ to improve device performance. The absence of dangling bonds on hBN reduces charge trapping and Coulomb scattering, leading to sharper photoluminescence peaks and higher exciton binding energies in TMDCs. For example, monolayer MoS₂ on hBN exhibits photoluminescence intensities up to two orders of magnitude higher than on SiO₂. The dielectric environment provided by hBN also screens defects and enhances valley polarization, which is crucial for valleytronics applications. In field-effect transistors (FETs) based on TMDCs, hBN encapsulation has been shown to increase carrier mobility by reducing interfacial roughness scattering.

Black phosphorus (BP) is another material that benefits from hBN integration. BP is highly sensitive to environmental degradation, but encapsulating it with hBN layers preserves its electronic properties. The anisotropic nature of BP, combined with hBN’s dielectric screening, allows for the tuning of effective masses and bandgaps. Studies have reported hole mobilities in excess of 1,000 cm²/Vs in hBN-encapsulated BP FETs, along with improved on/off ratios and stability. The heterostructure also mitigates the formation of charged impurities, which are known to degrade BP’s performance over time.

Device performance in hBN/2D heterostructures is further enhanced by optimizing contact engineering. Traditional metal contacts often introduce Fermi-level pinning and high contact resistances. However, edge contacts or the use of graphene as an intermediate layer between the metal and the 2D material can reduce these effects. For example, graphene edge contacts to MoS₂ have achieved contact resistances as low as 200 Ω·µm, enabling high-performance transistors with subthreshold swings approaching the thermionic limit. The combination of hBN encapsulation and optimized contacts has led to FETs with near-ideal subthreshold characteristics and high current densities.

Optoelectronic devices also benefit from hBN/2D heterostructures. In photodetectors, hBN acts as a protective layer that minimizes surface recombination and dark current. Graphene/hBN/graphene vertical heterostructures have demonstrated photoresponsivities exceeding 0.1 A/W, with response times in the picosecond range. Similarly, TMDC-based light-emitting diodes (LEDs) with hBN tunneling barriers exhibit enhanced electroluminescence efficiency due to improved charge injection and reduced non-radiative recombination. The ability to stack multiple hBN and 2D layers enables the design of resonant tunneling diodes and other quantum devices with tailored transport properties.

Thermal management is another critical aspect of these heterostructures. hBN’s high thermal conductivity, around 600 W/mK in the basal plane, helps dissipate heat generated in 2D devices. This property is particularly important for high-power applications, where localized heating can degrade performance. Measurements have shown that hBN-encapsulated graphene devices maintain lower operating temperatures compared to those on other substrates, leading to improved reliability and longevity.

Challenges remain in scaling up the production of hBN/2D heterostructures with uniform properties. Variations in layer thickness, alignment angles, and interfacial cleanliness can lead to device-to-device variability. Advanced characterization techniques, such as scanning tunneling microscopy (STM) and transmission electron microscopy (TEM), are essential for probing these interfaces at the atomic scale. Additionally, developing scalable transfer and assembly methods will be crucial for integrating these heterostructures into commercial applications.

The potential applications of hBN/2D heterostructures span a wide range of fields. In flexible electronics, the mechanical robustness of hBN enables the fabrication of bendable and stretchable devices without performance degradation. For quantum computing, the clean interfaces and tunable moiré potentials provide a platform for hosting and manipulating qubits. In sensors, the combination of hBN’s chemical inertness and 2D materials’ sensitivity allows for highly selective and stable detection of gases, biomolecules, and other analytes.

Future research will likely focus on exploring new combinations of hBN with emerging 2D materials, such as Janus monolayers and twisted multilayers. The role of defects, strain, and electrostatic gating in modulating heterostructure properties also warrants further investigation. As the understanding of these systems deepens, the design of hBN/2D heterostructures will become increasingly precise, enabling the realization of novel electronic and optoelectronic devices with tailored functionalities.

In summary, hBN/2D material heterostructures represent a versatile platform for engineering electronic properties through meticulous interface control. By leveraging the unique attributes of hBN and the diverse characteristics of 2D materials, researchers can achieve unprecedented device performance and explore new physical phenomena. The continued refinement of fabrication and characterization techniques will be key to unlocking the full potential of these heterostructures in next-generation technologies.