Improved light extraction efficiency of AlGaN DUV light emitting diodes using Al/MgF₂-based highly reflective film

Abstract

AlGaN DUV light emitting diodes (DUV-LEDs) (275 nm emission) are safe, eco-friendly and smart alternatives for inactivating viruses and bacteria. However, DUV-LEDs suffer from the main bottleneck of low external quantum efficiencies, which are strongly associated with the low light extraction efficiency caused by the strong optical polarisation of Al-rich AlGaN. Optical simulation results show that the luminous intensity of DUV-LEDs was increased by 10% owing to the synergistic effect of the sidewalls and substrates. The optical power of DUV-LEDs was increased to 16.8%, the far-field pattern was expanded to 130 degrees and the emission intensity was more focus on the central region, proving that the highly reflective sidewalls and substrates could re-direct the sideways-travelling photons for extraction. Moreover, we also investigated the reflective mechanism of Al/MgF2 layers. Optimise refractive index distribution of Al/MgF2 layers could change the electric field intensity to improve the reflectivity. Meanwhile, the temperature of the sample after coating were significantly reduced by 7.33%. Thermal radiation benefits and the high stability of bonding interface are the main reasons to reduce the temperature of DUVLEDs after Al/MgF2 coating. The present strategy is proposed from the view of the chip fabrication, which is cost-effective, able to be manufactured at a large scale.