Masafumi Jo

Masafumi Jo

Laboratory for Advanced Brain Signal Processing, RIKEN Brain Science Institute, Japan

Title: Recent progress of AlGaN-based deep-ultraviolet light-emitting diodes


Masafumi Jo has received his PhD from the University of Tokyo in 2003. He is the Researcher of Quantum Optodevice Laboratory at RIKEN. He has worked on fabricating nano-structured solid-state light sources.


AlGaN deep ultraviolet light-emitting diodes (DUV-LEDs) and laser diodes (LDs) are attracting a great deal of attention, since they have the potential to be used in a wide variety of applications, such as for sterilization, water purification, UV curing and in the Medical and Biochemistry fields and so on. As a result of recent developments in AlGaN DUV LEDs, high internal quantum efficiencies (IQE) of more than 60-70% have been achieved by reducing the threading dislocation density (TDD) of the AlN, by improving the crystal growth technique and/or by the introduction of AlN single crystal wafers. However, the wall-plug efficiency (WPE) of AlGaN DUV-LEDs still remains at several percent. The first target for the efficiency of AlGaN DUV-LEDs is to go beyond an efficiency of 20%, which would make them comparable to mercury lamps. In this work, we demonstrate an external quantum efficiency (EQE) of over 20% in an AlGaN DUV-LED by a significant improvement of light extraction efficiency (LEE). In order to increase LEE of DUV LEDs, we introduced a transparent p-AlGaN contact layer, a highly reflective p-type electrode and AlN template buffer fabricated on patterned sapphire substrate (PSS). By introducing transparent p-AlGaN contact layer and reflective electrode, LEE was enhanced by approximately 3 times. We also tried to increase wall plug efficiency (WPE) by reducing the applying voltage that was increased by increasing p-AlGaN contact resistance. By optimizing p-AlGaN layer structures, we have succeeded in reducing the operating voltage of DUV LED and obtained record WPE of 9.6%.