Monolayer-Scale AlGaN/AlN Multiple Quantum Wells as Active Media for Efficient Cathodoluminescent UVC Emitters

Ultraviolet light sources are essential for disinfection, water purification and biomedical applications, where compact, efficient, mercury-free emitters are needed. We report on the growth and optical characterization of ultrathin AlGaN/AlN multiple quantum wells (MQWs), synthesized by plasma-assisted molecular-beam epitaxy, with thicknesses down to a single atomic layer (monolayer, ML). By tuning the well thickness and composition, the emission wavelength can be shifted from ∼370 nm (8 ML) to 235 nm (1 ML), with the internal quantum efficiency (IQE) increasing drastically for thinner wells. IQE values exceeding 50% are obtained at 235 nm for 1-ML-thick quantum wells, enabled by a sharp enhancement in in-plane carrier confinement. Polarization-resolved measurements reveal that transverse-electric (TE) emission dominates down to ∼260 nm, with a gradual transition to transverse-magnetic (TM) polarization at shorter wavelengths. A comparative analysis with Stranski–Krastanov quantum dots and nanowires shows that ultrathin MQWs provide the most promising performance for emission below 240 nm. These results open perspectives for the implementation of such nanostructures in high-efficiency solid-state and electron-beam-pumped light sources.