Improvement of light-extraction efficiency of deep-UV LEDs using transparent p-AlGaN contact layer

We demonstrated deep-ultraviolet light-emitting diodes (DUV-LEDs) with emission wavelengths at around 285 nm using transparent p-AlGaN contact layer and reflective p-type electrode. The reflectivity of p-type electrode was increased from 30% to approximately 70% by introducing Ni(1nm)/Al metal layers. The external quantum efficiency (EQE) of the 288 nm LED was increased from 1.9% to 2.5% by replacing conventional p-GaN contact layer by transparent p-AlGaN contact layer. The increase of light extraction efficiency (LEE) was estimated to be by 1.5 times. We finally achieved EQE of 5% in DUV-LED by improving both of LEE and electron injection efficiency (EIE). The EQE of DUV-LED would be much increased by optimizing the device structure and by combining with other approaches.