Hexagonal boron nitride (hBN) has emerged as a critical material for deep-ultraviolet (DUV) photonics due to its unique optical and structural properties. With a wide bandgap exceeding 6 eV, hBN exhibits intrinsic DUV emission, making it suitable for applications in DUV light-emitting diodes (LEDs), photodetectors, and optical waveguides. Its layered van der Waals structure, high thermal conductivity, and chemical stability further enhance its potential for next-generation DUV optoelectronic devices.

One of the most notable characteristics of hBN is its ability to emit DUV light efficiently. The material displays strong near-band-edge emission in the 210–230 nm range, attributed to excitonic recombination. Unlike conventional DUV emitters such as AlGaN, hBN does not suffer from severe efficiency degradation at high temperatures due to its robust exciton binding energy, which exceeds 100 meV. This property ensures stable DUV emission even under elevated operational conditions, making hBN a promising candidate for high-performance DUV light sources.

Optical waveguiding in hBN is another key advantage for DUV photonics. The material exhibits low optical losses in the DUV spectrum, enabling efficient propagation of deep-ultraviolet light. Its anisotropic crystal structure allows for polarization-dependent light confinement, which can be exploited to design waveguides with tailored dispersion properties. Additionally, hBN’s atomic smoothness and absence of dangling bonds reduce scattering losses, a common issue in conventional DUV waveguide materials like AlN or SiO2. These properties make hBN an ideal platform for integrated DUV photonic circuits, where low-loss light propagation is essential.

In the context of DUV LEDs, hBN offers several advantages over traditional III-nitride semiconductors. The absence of alloy disorder and reduced defect-related non-radiative recombination contribute to higher internal quantum efficiency. However, challenges remain in achieving efficient electrical injection in hBN-based LEDs. The material’s insulating nature and difficulty in achieving stable p-type doping limit the development of homojunction devices. Current approaches rely on heterostructures combining hBN with other wide-bandgap materials or exploiting defect-assisted emission mechanisms. While these methods have demonstrated DUV electroluminescence, further improvements in carrier injection efficiency are necessary for practical applications.

DUV photodetectors based on hBN benefit from its high absorption coefficient in the deep-ultraviolet range. The material’s solar-blind response—minimal sensitivity to visible and infrared light—makes it ideal for flame detection, environmental monitoring, and secure communications. Photoconductive and photovoltaic detectors using hBN have shown responsivities comparable to those of AlGaN-based devices, with the added advantage of faster response times due to reduced carrier trapping. Nevertheless, achieving low dark currents remains a challenge, as defects and impurities in hBN can contribute to unwanted leakage pathways. Advances in material purification and defect passivation are critical for improving detector performance.

Despite its promising properties, hBN faces several limitations in DUV photonics. The most significant hurdle is the difficulty in achieving controlled doping, which restricts the development of efficient p-n junction devices. While n-type doping has been demonstrated using silicon or oxygen incorporation, p-type doping remains elusive due to the material’s high ionization energy for acceptors. Alternative strategies, such as electrostatic gating or hybrid device architectures, are being explored to circumvent this limitation. Another challenge is the scalability of high-quality hBN synthesis. Although chemical vapor deposition (CVD) can produce large-area films, achieving uniform DUV emission and low defect densities across wafer-scale substrates requires further optimization.

The thermal management capabilities of hBN also play a crucial role in DUV photonic applications. Its high thermal conductivity, exceeding 400 W/m·K in the in-plane direction, helps dissipate heat generated during device operation, reducing thermal degradation and improving reliability. This property is particularly beneficial for high-power DUV LEDs and lasers, where heat accumulation can severely impact performance.

Looking ahead, research efforts are focused on improving the efficiency and functionality of hBN-based DUV devices. Heterostructures combining hBN with other 2D materials, such as transition metal dichalcogenides or graphene, offer new possibilities for bandgap engineering and carrier injection. Additionally, advances in defect engineering and doping techniques could unlock the full potential of hBN for commercial DUV optoelectronics.

In summary, hexagonal boron nitride stands out as a versatile material for deep-ultraviolet photonics, offering intrinsic DUV emission, low-loss waveguiding, and robust thermal properties. While challenges such as doping limitations and material uniformity persist, ongoing research continues to address these issues, paving the way for hBN-based DUV technologies to complement or surpass existing solutions in applications ranging from sterilization to optical communications.