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

This study presents an optimized hybrid design integrating a distributed Bragg reflector (DBR) and a TiO2 nanocylinder metasurface to enhance light extraction efficiency (LEE) and beam directionality(narrow divergence angle) in light-emitting diodes (LEDs) based on gallium nitride (GaN).Parametric simulations were used to identify an optimal device architecture.The resulting structure comprises a single-period DBR,which has a thickness of TiO2(dTiO2) equal to forty-six nm and a thickness of SiO2 equal to seventy-sevsen nm,beneath a periodic array of TiO2 nanocylinders (radius is approximately seventy-one nm,height is approximately one handred and eighty-five nm).The DBR reflects guided modes to minimize internal optical losses,while the TiO2 metasurface employs Mie resonance to collimate the emitted light.As a result,the hybrid LED achieves a simulated LEE of 25.67 percent and a beam divergence angle of only 5.7 degree,representing a significant improvement in both efficiency and emission directionality over conventional designs.These findings demonstrate a viable strategy to overcome light trapping and broad angular emission in GaN LEDs,paving the way for high-brightness,highly directional GaN micro-LEDs for advanced display and optical communication applications.