A New Route to Deep-UV Light
Generating efficient light in the deep-ultraviolet range — wavelengths shorter than about 280 nanometers — has been one of the harder problems in semiconductor photonics. Deep-UV light has powerful applications in pathogen disinfection, water purification, semiconductor lithography, and quantum information processing, but the materials that can efficiently emit it are limited and difficult to work with. A study published in Science describes a significant advance: highly efficient deep-UV luminescence achieved in moire quantum wells formed from hexagonal boron nitride, a material better known as a flat, two-dimensional insulator.
The result is surprising. Hexagonal boron nitride, or hBN, is a wide-bandgap material that researchers have known can emit UV light, but achieving efficient, controllable emission has proven elusive. The innovation here is the use of a moire superlattice structure — created by stacking two slightly misaligned layers of hBN — to confine and manipulate the quantum states responsible for light emission in ways that are not possible in conventional bulk or single-layer material.
What Moire Engineering Does
When two atomically thin crystal layers are stacked with a small twist angle or lattice mismatch, the resulting interference pattern creates a moire superlattice: a periodic modulation of the atomic potential that extends over much larger length scales than the underlying atomic structure. This superlattice acts as an array of nanoscale quantum confinement sites — artificial quantum wells and quantum dots — without the need for the complex nanofabrication that would otherwise be required to create them.
Moire engineering emerged as a transformative technique in condensed matter physics after the 2018 discovery that twisted bilayer graphene could become superconducting at specific twist angles. Since then, researchers have applied the concept across a wide range of two-dimensional materials, discovering phenomena including correlated insulator states, ferromagnetism, and — now — dramatically enhanced light emission in hBN.
In the current study, the moire structure in hBN creates localized quantum well states that trap excitons — bound electron-hole pairs — at specific sites in the superlattice. These trapped excitons recombine radiatively with high efficiency, emitting deep-UV photons. The moire confinement both enhances the probability of radiative recombination and narrows the emission spectrum, producing brighter and more spectrally pure UV light than had previously been achieved in hBN.
Why Deep UV Is Worth Pursuing
The deep-UV spectral range — roughly 200 to 280 nanometers — overlaps with the absorption peaks of DNA and proteins, making it effective for sterilizing surfaces, water, and air without the chemical residues associated with conventional disinfection methods. The COVID-19 pandemic renewed commercial interest in UV disinfection technology, and demand for efficient, compact deep-UV light sources has grown accordingly.
Current deep-UV LED technology based on aluminum gallium nitride is functional but limited in efficiency and requires complex growth conditions. An hBN-based approach, if it can be scaled from laboratory demonstrations to manufacturable devices, could offer a more accessible path to efficient deep-UV sources. The two-dimensional nature of hBN also makes it compatible with flexible substrates and integration with silicon photonic platforms.
Quantum Photonics Applications
Beyond disinfection, single-photon emitters in the UV range are a sought-after resource for quantum cryptography and quantum networking. hBN has previously been identified as a host material for single-photon emitters operating at room temperature — a significant advantage over many other quantum emitter platforms that require cryogenic operation. The moire quantum well structures could provide a route to arrays of high-quality UV single-photon emitters valuable for building scalable quantum photonic systems. The research represents a convergence of moire physics and deep-UV photonics that opens hBN as a platform for light-emitting devices in spectral ranges where conventional semiconductors struggle.
This article is based on reporting by Science (AAAS). Read the original article.
