Analysis of Dark Stain on Chip Surface of High-Power LED

In the process of aging or in service of some high power blue LEDs, dark stain may occur on the LED chip surface, which cast a shadow over the chip and thus led to the losing of luminous flux. In the degraded samples, it was found that firstly the dark stain was formed on the chip surface equably, and then the color of this stain gradually darken with time. In this paper, this kind of dark stain was detected and analyzed. The morphology of the dark stain and the elements contained in it were measured by scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (EDAX), respectively. A large mount of oxygen and carbon were found in the black zones, which implied that some chemical reactions occurred on the interface. After we removed the black materials off the chip surface, the quantity of luminous flux evidently increased. The origin of oxygen and the possible reason of the dark stain were also discussed