High-efficiency 352 nm quaternary InAlGaN-based ultraviolet light-emitting diodes grown on GaN substrates

We demonstrated high-efficiency ultraviolet (UV) light-emitting diodes (LEDs) with an emission wavelength of 352 nm using a quaternary InAlGaN multiple-quantum-well (MQW) emitting region. GaN substrates were used in order to eliminate the effects of threading dislocations. Emission fluctuation due to In segregation was clearly observed even in a dislocation-free area by a cathode luminescence (CL) image of a quaternary InAlGaN MQW, which is considered to contribute to the achievement of a high-efficiency UV emission. 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 a top-emission geometry.