Evaluation of GaN-based blue light emitting diodes based on temperature/humidity accelerated tests

The degradation of high power GaN-based blue light-emitting diodes (LEDs) was investigated by considering the electrical, optical and electroluminescence spectrum aging characteristics. The LED samples are stressed at the condition of 85°C and 85% RH using an injection current of 1000 mA. Optical output power decreases to 80% of initial value after 1000 hours of temperature/humidity accelerated tests. Changes in the series resistance can be observed from the current-voltage characteristics during the stress tests. The increase of nonradiative paths and discoloration of encapsulation materials are possibly responsible for the degradation of optical output power. The mechanisms of increasing nonradiative recombination paths may be related to the generation of defects in the active region due to the high injection current and the increase of LED chip temperature. The influence of degradation on the electroluminescence spectrum has also been analyzed. The peak position of electroluminescence spectrum under the same current showed a redshift after the temperature/humidity accelerated tests, indicating a decreased band gap. The particular humidity effects on the degradation of blue LED are investigated, and the luminous flux of the packaged blue LEDs decreased with the increasing stress time due to the prolonged humidity test.