Growth and characterization of quaternary AlGaInN layers and performance of AlGaInN-based ultraviolet light-emitting diodes

We report the growth and the characterization of both quaternary AlGaInN bulk layers and AlGaInN/InGaN multiple-quantum-well (MQW) layers grown by using metal-organic chemical vapor deposition for high-efficiency ultraviolet light-emitting diodes (UV LEDs). Inclusion of a small fraction of indium in the AlGaInN layer was found to reduce the number of structural defects and the strain in the layer. From the intensities of temperature-dependent photoluminescence and time-resolved photoluminescence, the internal quantum efficiency at 300 K was obtained as 60% for the sample grown with a quaternary AlGaInN barrier in the MQWs and 25% for the sample with a ternary AlGaN barrier. The dominant optical transition in the AlGaInN/InGaN MQWs was considered to be caused by localized exciton recombination and reduction of the strain in the MQW stack, with indium incorporation in the barriers, resulting in the longest decay lifetime from quaternary AlGaInN alloys. We measured the optical output power from the UV LED device grown with quaternary AlGaInN barriers. The LEDs reached a maximum output power of 50.6 mW and a wall-plug efficiency of 2.99% under an input current level of 400 mA.