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AlGaN‐based deep ultraviolet light‐emitting diodes (DUV LEDs) are featured with small size, DC driving, no environmental contamination etc., and they are now emerging as the excellent solid‐state light source to replace the conventional mercury based light tubes. Nevertheless, the DUV LEDs are currently affected by the poor external quantum efficiency (EQE), which is caused by the low internal quantum efficiency (IQE) and the very unsatisfying light extraction efficiency (LEE). In this work, the authors disclose the underlying mechanism for the low EQE and summarize the technologies that have been adopted so far for enhancing the EQE. This paper comprehensively reviews III–V nitride based deep ultraviolet light‐emitting diodes (DUV LEDs), which are suffering from the low external quantum efficiency (EQE). This article conducts an in‐depth investigation on the issues that DUV LEDs are encountering now. The strategies that are taken by the research community to improve the EQE are summarized and analyzed. [ABSTRACT FROM AUTHOR]