High-reflectivity electrode boosts DUV LED efficiency
WHU team shows enhanced performance of AlGaN-based DUV flip-chip LED using Ni/Rh/Ni/Au p-type electrode
Researchers from Wuhan University in China have reported a thermally stable and high-reflectivity Ni/Rh/Ni/Au p-type electrode for improving the efficiency of 275-nm deep-ultraviolet flip-chip LEDs (DUV FCLEDs).
“We reveal that Rh can suppress the aggregation of underlying Ni film, and thus the reflectivity of Ni/Rh/Ni/Au electrodes remains almost constant after annealing.” said Shengjun Zhou, a professor at Wuhan University who directed the research.
AlGaN-based DUV FCLEDs have garnered considerable attention due to their diverse range of applications. However, as approximately 50% of photons propagate downward, high-efficiency DUV FCLEDs must be developed with high-reflectivity electrodes that reflect photons upward. Therefore, the typical thick p-GaN and Ni/Au electrode are not suitable for DUV FCLEDs due to the severe absorption of DUV light. In addition, the problem of reflectivity degradation of Ni/Au electrodes after annealing also limits their application in DUV FCLEDs.
To address these issues, the researchers introduce an optimized combination of a Ni/Rh/Ni/Au p-type electrode and a thin p-GaN layer to improve the efficiency of DUV FCLEDs.
The proposed Ni/Rh/Ni/Au p-type electrode shows high thermal stability as a result of the suppression of underlying Ni agglomeration by the Rh layer at high-temperature annealing, according to the researchers. Besides, due to the higher reflectivity of the Ni/Rh/Ni/Au electrode and its lower specific contact resistivity formed with p-GaN, the external quantum efficiency and wall-plug efficiency of a DUV FCLED with Ni/Rh/Ni/Au electrode are increased by 13.94 percent and 17.30 percent in comparison with the one with Ni/Au electrode at an injection current of 100 mA.
The Ni/Rh/Ni/Au electrode effectively solves the long-standing dilemma of efficiency degradation of DUV FCLEDs with a Ni/Au electrode after high-temperature annealing, and promotes the development and application of AlGaN-based high-power DUV LEDs.
Reference
'Improved efficiency of AlGaN-based flip-chip deep-ultraviolet LEDs using Ni/Rh/Ni/Au p-type electrode' by Zhefu Liao et al; Optics Letters 2023, 48(16), 4229
