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SUMMARY Deep-ultraviolet (DUV) light-emitting diodes (LEDs) are in demand for a wide variety of potential applications, such as sterilization, water and air purification, medical uses, and so on. We have demonstrated 222-351 nm AlGaN and quaternary InAlGaN-based DUV-LEDs by developing a low threading dislocation density (TDD) AlN crystal. We achieved an external quantum efficiency (EQE) of about 4% and an output power greater than 30 mW in DUV-LEDs for use in sterilization applications by developing new crystal growth techniques. [ABSTRACT FROM AUTHOR]

We demonstrated high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs) by improving light-extraction efficiency (LEE) by using a transparent p-AlGaN contact layer and a highly-reflective p-type electrode. We fabricated DUV-LEDs with emission wavelengths between 265-288 nm using p-AlGaN contact layers with compositional wavelength at around 275 nm. The reflectivity of p-type electrode was increased to be approximately 70% by introducing Ni(1nm)/Al layers. The external quantum efficiency (EQE) of the 287 nm LED was increased from 2% to 5.5% by replacing conventional p-GaN contact layer by transparent p-AlGaN contact layer. The increase of LEE was estimated to be by approximately more than 1.7 times. The use of transparent p-AlGaN contact layer is considered to be basic and quite important technique in order to obtain high LEE in DUV LEDs. The EQE of DUV-LED would be much increased by optimizing the device structure and by combining with other approaches to improve LEE. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]