Enhanced Light Extraction Efficiency of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Incorporating High-Reflective n-Type Electrode Made of Cr/Al

Mercury-free semiconductor deep ultraviolet light-emitting diodes (DUV-LEDs) still suffer from low power efficiencies due to extremely poor light extraction efficiency. In this paper, a high-reflective electrode is proposed and carefully optimized for making an ohmic contact with the n-type AlGaN layer in the DUV-LEDs (~280 nm). The electrode is made of Cr/120-nm Al metal stack with a different thickness of the Cr layer in a range of 1-20 nm followed by the complete LED fabrication process. We found that the DUV-LED with a 1-nm Cr/120-nm Al electrode obtains maximum light output power and the highest external quantum efficiency, showing an enhancement factor of 40.9% and 25.4%, respectively, in comparison to a conventional LED with an electrode made of 20-nm Cr/120-nm Al. This enhancement is mainly attributed to a higher UV reflectivity of the 1-nm Cr/120-nm Al electrode. Furthermore, a better ohmic contact was achieved in such electrode due to the formation of higher quality Al-Cr and Cr-N alloys in such metal/n-AlGaN junction.