Realization of high-efficiency deep-UV LEDs using transparent p-AlGaN contact layer

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. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim