Accurate measurement and influence on device reliability of defect density of a light-emitting diode

A method of accurately measuring the defect density of a high-power light-emitting diode (LED) is proposed. The method is based on measuring the number of emitting photons in the magnitude of 105 under the injection current as weak as nA and calculating the non-radiative recombination coefficient which is related to defect density. Defect density is obtained with the self-developed measurement system, and it is demonstrated that defect density has an important influence on LED optical properties like luminous flux and internal quantum efficiency (IQE). At the same time, a batch of GaN-based LEDs with the chip size of 1 mm × 1 mm are selected to conduct the accelerated aging tests lasting for 1000 hours. The results show that defect density exhibits a greater variation and is more sensitive to LED reliability than luminous flux during aging tests. Based on these results, it is concluded that for the GaN-based LED with a chip size of 1mm × 1mm, if its defect density is over 1017/cm3, the LED device performance suffers a serious deterioration, and finally fails.