Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light-emitting diodes

In this paper, recent advances in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) are demonstrated. 220–350-nm-band DUV LEDs have been realized by developing crystal growth techniques for wide-bandgap AlN and AlGaN semiconductors. Significant increases in internal quantum efficiency (IQE) have been achieved for AlGaN DUV emissions by developing low-threading-dislocation-density (TDD) AlN buffer layers grown on sapphire substrates. The electron injection efficiency (EIE) of the LEDs was also significantly increased by introducing a multiquantum barrier (MQB). We also discuss light extraction efficiency (LEE), which is the most important parameter for achieving high-efficiency DUV LEDs. We succeeded in improving LEE by developing a transparent p-AlGaN contact layer. The maximum external quantum efficiency (EQE) obtained was 7% for a 279 nm DUV LED. EQE could be increased by up to several tens of percent through the improvement of LEE by utilizing transparent contact layers and photonic nanostructures in the near future.