Investigation of Light-Extraction Efficiency of Flip-Chip AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes Adopting AlGaN Metasurface

Abstract

Herein, we investigate the influence of an AlGaN metasurface on AlGaN-based deep-ultraviolet light-emitting diodes' lightextraction efficiency by utilizing the 3D finite-difference time-domain method. As the first step in this study, we optimize an AlGaN metasurface to maximize the transmittance from LED to air. Then, six different flip-chip structures' light-extraction efficiencies are compared with each other to judge the usefulness of the metasurface's adoption on AlGaN-based LED. Considered structures are classified into two categories, with and without inclined sidewall, respectively. Each classified structure is subdivided again by three factors: flat interface, roughed cones, and metasurface on n-AlGaN. Extracted results show that the combination of inclined sidewall and the AlGaN metasurface shows synergetic results positively increasing light-extraction efficiency.

Planar Compound Eye Lens for Enhanced Light Extraction Efficiency in AlGaN‐Based Deep Ultraviolet LEDs

“…The LEEs of DUV‐LED with unstructured plate are 3.34% and 0.48% for TE and TM modes, fitting well with the previous works. [ 36,39 ] By etching optimized PCEL on the n‐AlGaN surface, the LEEs rise to 9.37% and 2.1% respectively for the TE and TM modes, indicating the corresponding improvement as 181% and 337%, respectively. As expected, the LEEs of PCEL are quite similar with Meta‐I, especially for the TE mode (the deviation is 1.7%), indicating the superiority of functional reconfiguration by metasurface.…”

“…The frequently used flip-chip LED structure [36,37] is adopted to investigate the LEE enhancement, as shown in Figure 4a. As the TIR exists extensively at the interface between the dielectrics with different refractive indices, the substrate-free AlGaN-based structure with thin epitaxial layers is selected to accelerate the simulation process.…”

“…And, their corresponding refractive indices are set as 2.6 and 2.9, respectively. [36] Owing to the periodic structure of the biomimetic structures, several units of compound eye can be picked to economize time of computation in the LEE simulation. [37,38] Boundary configuration in the LEE simulation was adopted: perfect mirror for lateral dimension and perfectly matched layer (PML) for vertical dimension respectively, as shown in Figure 4b.…”

Investigation on external quantum efficiency droops and inactivation efficiencies of AlGaN-based ultraviolet-c LEDs at 265–285 nm

“…Although the quantum barrier and electron barrier layer (EBL) can effectively confine carriers in the active region, there are still a part of energetic carriers escaping from multiple quantum wells (MQWs) to p-doped layer in the form of thermionic overflow or defect-related tunneling process [12][13][14]. In addition, previous works also reported that a variety of factors, such as extended dislocations (EDs), quantum confined stark effect, carrier delocalization, and Auger recombination, also affected the efficiency droops of AlGaN-based UVC-LEDs [15][16][17].…”

Light Guide Layer Thickness Optimization for Enhancement of the Light Extraction Efficiency of Ultraviolet Light–Emitting Diodes

“…Yang Peng employed this encapsulation material doped with fluoropolymer on an aluminum nitride substrate to enhance the LEE of a chip-on-board encapsulation structure [ 28 ]. Joosun Yun and Hideki Hirayama proposed different wafer structures in a comparative study with six different flip-chip structures, obtaining an AlGaN meta-surface for improved LEE [ 29 ].…”