High-Efficiency UV LEDs using Quaternary InAlGaN

High-efficiency ultraviolet (UV) light sources are very attractive for application to white lighting, high-density memories, medical fields, etc. We have demonstrated that 300-370 nm UV emission is considerably enhanced by the introduction of several percent of In into AlGaN due to an In-segregation effect. We fabricated 310 nm band UV LEDs with quaternary InAlGaN emitting layers on sapphire substrate and obtained sub-milliwatt output power. We also fabricated 350 nm band InAlGaN-based quantum-well (QW) LEDs on GaN substrates in order to eliminate the effects of threading dislocations. The maximum UV output power obtained was as high as 7.4 mW under room temperature (RT) CW operation. The maximum external quantum efficiency (EQE) was 1.1% with an injection current of 50 mA, which is the highest EQE ever obtained for 350 nm band UV LEDs with top-emission geometry.