Enhanced Light Extraction and Beam Focusing in GaN LEDs Using Hybrid Metasurface-Distributed Bragg Reflector Structures

This study presents an optimized hybrid design integrating TiO₂ nanocylinder metasurfaces with Distributed Bragg Reflectors (DBRs) to simultaneously enhance light extraction efficiency (LEE) and beam collimation in GaN-based light-emitting diodes (LEDs). Through systematic theoretical modeling and numerical simulations using COMSOL and Finite-Difference Time-Domain (FDTD) methods, we investigate the impact of DBR layer count and metasurface geometry—including nanocylinder radius, height, and periodicity—on optical performance. The optimized structure achieves a narrow divergence angle of 5.7° alongside an LEE of 25.67%, demonstrating competitive performance compared to existing technologies. The DBR enhances reflectivity to minimize trapped light, while the TiO₂ metasurface leverages Mie resonance for precise beam control. Parametric studies reveal that a single-layer DBR (46 nm TiO₂/77 nm SiO₂) combined with a nanocylinder metasurface (radius = 71 nm, height = 185 nm, periodicity = 222 nm) optimally balances efficiency and directionality. Far-field analysis confirms strong main lobe intensity (0.00752 V/m) with suppressed sidelobes, ensuring high-directionality emission. Compared to prior works, our design achieves superior beam collimation without significant LEE trade-offs, addressing key challenges in LED performance such as photon recycling losses and angular dispersion. These findings provide a practical framework for advancing highbrightness, directional LEDs in applications like micro-displays, LiDAR, and optical communications. Future work will explore broadband optimization and polarization control to further enhance performance.