Abstract
The degradation mechanism of mid-power GaN-based white LEDs were investigated by using the in-situ multi-functional accelerated aging tests. The changes of the luminous flux and the chromaticity shift during the stress time show some correlations. To quantitatively analyze the degradation behavior, a composite model considering the luminous flux increasing and decreasing mechanisms was proposed and the results agree well with the experiments in the entire aging time. Furthermore, different analytical technologies have been used to understand the cause of luminous flux degradation and chromaticity shift. The results show that the chromaticity shift was mainly due to the phosphors deterioration, while the serious degradation of luminous flux was the overall effects from the package, including the phosphors deterioration and oxidation of silicone encapsulant.
Highlights
With the development of luminous efficiency, GaN-based light emitting diodes (LEDs) have already been used in many kinds of applications, such as the display backlight, visible light communication and general illumination,[1,2,3] etc
The luminous flux degradation of mid-power GaN-based white LEDs were investigated by using the in-situ multi-functional accelerated aging tests
The decreasing behaviors of luminous flux are quite similar to the increase of the chromaticity difference, suggesting that the underlying mechanism for the luminous flux degradation are closely related to the chromaticity shift during the operation
Summary
With the development of luminous efficiency, GaN-based light emitting diodes (LEDs) have already been used in many kinds of applications, such as the display backlight, visible light communication and general illumination,[1,2,3] etc. How to evaluate the reliability effectively has drawn lots of attention.[4] It has been reported that, under high ambient temperature, the failure mechanism of GaN-based LEDs are mainly originated from LED chip and package during the operation,[3,5] including the defect generation/movement,[6] dopant diffusion,[7] electro-migration,[8] encapsulant yellowing,[9] delamination[10] and phosphors thermal quenching.[11]. The final exponential degradation data, lots of failure mechanisms occurred in the LEDs during the operation will be ignored. The luminous flux increased, became stable, and decreased exponentially. To understand the degradation behavior, a composite model considering both luminous flux increasing and decreasing mechanisms was proposed. The influence of different failure mechanisms to the luminous flux and chromaticity was discussed in details as well
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