Highly Efficient Photon-Blocking Layer for AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

The light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) is severely constrained by pronounced ultraviolet absorption in the p-GaN contact layer. Drawing inspiration from the electron-blocking layer (EBL) principle and total internal reflection (TIR)-mediated light-blocking via refractive index engineering, we propose and demonstrate a photon-blocking layer (PBL). This PBL effectively suppresses photon propagation into the p-GaN layer via TIR, thereby mitigating photon loss and enhancing LEE. Monte Carlo ray-tracing simulations confirm that incorporating a thin hexagonal boron nitride (hBN) layer as the PBL in 280 nm AlGaN DUV LEDs reduces the fraction of emitted light entering the p-GaN layer from 62.4 to 25.7% for transverse electric (TE)-polarized light and from 45.9 to 7.8% for transverse magnetic (TM)-polarized light. Correspondingly, the total LEE is enhanced by 1.37- and 1.91-fold for TE- and TM-polarized light, respectively, with these enhancements further elevated to 1.81- and 2.48-fold upon integration with inclined sidewalls. Strategies aimed at further enhancing PBL efficacy and LEE are systematically analyzed using an analytical model of light extraction mechanisms. Importantly, our findings demonstrate that integrating a PBL with a thick p-GaN layer offers a promising route to mitigate the long-standing trade-off between light extraction and electrical performance in AlGaN DUV LEDs.