Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector

AlGaN based deep-ultraviolet light-emitting diodes (DUV-LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV-LEDs is still much lower than that of blue LEDs due to a quite low light-extraction efficiency (LEE). We improved the LEE of DUV-LEDs by using a superlattice (SL) hole spreading p-AlGaN contact layer, a dot matrix Ni/Au electrode and an Al reflector. DUV-LED samples in which the SL p-AlGaN contact layer has various period lengths, and forms two different p-type electrodes, a conventional Ni/Au electrode and a dot matrix Ni/Au electrode with an Al reflector are fabricated. By comparing these LED samples, it is confirmed that contact layers with relatively longer periods are suitable both for vertical hole injection and lateral spreading of the holes. By increasing the Al content and recovering the transparency of the SL p-AlGaN contact layer, the LEE is increased by up to a factor of 1.6.