Enhanced light extraction efficiency via double nano-pattern arrays for high-efficiency deep UV LEDs

Abstract

This work reports on the packaging structure of double-layer nano-pattern arrays (NPAs) for AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs), which can significantly enhance the light extraction efficiency (LEE), a major device performance bottleneck. The double-layer NPAs were fabricated on the surface of the flip-chip DUV LED by etching sapphire and coating the fluoropolymer resin, which can alleviate the total internal reflection (TIR) at the top interfaces and enhance light extraction on sidewalls, leading to the great improvement of both TE and TM-polarized light. As a result, the 273 nm DUV LED with double-layer NPAs realized 28.3% enhancement in light output power (LOP) compared with the reference device without the NPA at large current of 100 mA. High peak external quantum efficiency (EQE) and wall-plug efficiency (WPE) of 5.19% and 4.38% were demonstrated, respectively. Combined with the finite element analysis (FEA), it is further confirmed that the double-layer NPAs have higher external coupling efficiency to enhance LEE. The proposed LEE enhancement strategy comes from the combination of nanostructured materials and packaging technology, which is cost-effective and meets mass production, providing efficient value in practical applications of UV devices.