High-Efficiency Top-Emitting AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

Top-emitting structures offer significant advantages for light-emitting diodes (LEDs), simplifying fabrication processes and reducing production costs compared to bottom-emitting structures that extract light through the substrate. However, previously reported AlGaN-based deep-ultraviolet LEDs (DUV-LEDs) have exclusively relied on bottom-emitting designs, primarily because of the lack of suitable p-electrode materials with high DUV transparency. In this work, we demonstrate top-emitting DUV LEDs emitting at 275 nm using microscale concentric-ring p-electrodes with a ring-shaped mesa. This design provides high light extraction while maintaining high electrical and current-injection efficiencies. In addition, we incorporate HfO2 truncated cone nanostructures at electrode openings to further enhance light extraction by enlarging the escape cone. As a result, we achieve a wall-plug efficiency of 6.5%, which is approximately 35% higher than that of conventional bottom-emitting flip-chip DUV-LEDs. Despite using a microring p-electrode with high light extraction, the device maintains a high electrical efficiency of 85%.