Influence of light absorption on the performance characteristics of UV LEDs with emission between 239 and 217 nm

The development of ultraviolet AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) in the wavelength range between 239 and 217 nm is presented. The effects of aluminum composition in the MQW active region and of the underlying Al x Ga1−x N:Si current spreading layer on the emission characteristics and operating voltages are investigated. A strong reduction in output power is observed with decreasing emission wavelength which is partly attributed to light absorption within the underlying Al x Ga1−x N:Si. Additionally, a reduced carrier injection efficiency is identified as the root cause for the reduced emission power with decreasing emission wavelength. Emission powers at a dc current of 20 mA between 310 and 0.15 μW have been achieved for LEDs emitting between 239 and 217 nm. The maximum light output in pulsed mode operation of these LEDs ranged between 4.6 mW and 3.6 μW, respectively.