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AlGaN‐based deep‐ultraviolet light‐emitting diodes (DUV LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV LEDs is still much lower than that of blue LEDs due to the quite low light‐extraction efficiency (LEE). We are developing high LEE DUV LEDs by introducing a transparent contact layer and a highly reflective Ni/Al p‐type electrode. In this work, we investigate optimization of the Ni layer thickness of the highly reflective Ni/Al p‐type electrode for AlGaN DUV LEDs. We find that the reflectivity in the UV region becomes higher as the thickness of the Ni layer becomes smaller; however, the external quantum efficiency (EQE) is reduced if the Ni layer is too thin (<0.8 nm). As a result, we find that the most appropriate Ni thickness for the Ni/Al electrode is 0.9 nm. We fabricate 279 nm AlGaN quantum well (QW) DUV LEDs with the optimized electrodes and demonstrate an enhancement in EQE by a factor of 1.8 and a maximum EQE of 9% under bare wafer measurement conditions. We also demonstrate a high output power of 33 mW under an injection current of 100 mA. [ABSTRACT FROM AUTHOR]

AlGaN based deep‐ultraviolet light‐emitting diodes (DUV‐LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV‐LEDs is still much lower than that of blue LEDs due to a quite low light‐extraction efficiency (LEE). We improved the LEE of DUV‐LEDs by using a superlattice (SL) hole spreading p‐AlGaN contact layer, a dot matrix Ni/Au electrode and an Al reflector. DUV‐LED samples in which the SL p‐AlGaN contact layer has various period lengths, and forms two different p‐type electrodes, a conventional Ni/Au electrode and a dot matrix Ni/Au electrode with an Al reflector are fabricated. By comparing these LED samples, it is confirmed that contact layers with relatively longer periods are suitable both for vertical hole injection and lateral spreading of the holes. By increasing the Al content and recovering the transparency of the SL p‐AlGaN contact layer, the LEE is increased by up to a factor of 1.6. [ABSTRACT FROM AUTHOR]