Since the luminescence efficiency of GaAsP red light-emitting diodes (L ED) has reached 1 lm/W by the nitrogen doping process in 1968, LED research has been rapidly developed. In 1985, liquid phase epitaxy was used to make the luminescence intensity of Al GaAs LEDs exceed 1 cd for the first time. The study of InGaAlP quaternary materials in the early 1990s not only greatly improved the efficiency of LEDs, but also extended the spectrum of high-brightness LEDs from red to yellow and yellow-green. In the mid-1990s, Nakamura et al. successfully prepared high-intensity InGaN/Al GaN double heterojunction blue LEDs and InGaN quantum well structure UV LEDs by MOCVD. The emergence of GaN-based blue LEDs and their rapid increase in efficiency have enabled LEDs to form a complete three-primary luminescence system and enable the development of white light L ED. There are two main technical ways to realize white LED: one is to use white, red, green and blue to produce white light; the other is to realize white light by means of phosphor conversion. As the power and efficiency of white LEDs continue to increase, LEDs are moving from the field of indications and displays to the field of lighting, and will become the fourth generation of illumination sources after incandescent, fluorescent and HID.
Although high-power white LEDs are currently the research hotspots, there are still problems such as insufficient luminous efficiency, poor uniformity of spatial chromaticity, and high cost for illumination. In addition, although LEDs are recognized as high-reliability semiconductor products, reports on life test data for high-power LEDs are still insufficient. In this paper, the attenuation characteristics of the light output of GaN-based high-power white LEDs with phosphors are discussed, and the failure of LEDs during aging is analyzed. In addition, in order to avoid the influence of phosphor on the attenuation characteristics of LED light output, the aging test of high-power blue light L ED was carried out, and the failure mechanism of high-power blue light L ED was analyzed.
The method of realizing white light by phosphor conversion is based on blue light emitted by a GaN-based LED with a peak wavelength of 450-470 nm, wherein a part of blue light is emitted through the phosphor and another part is excited by the phosphor, so that the peak of the phosphor is emitted. The yellow-green light of 560-580 nm, the blue light emitted by the light and the yellow-green light emitted by the phosphor constitute white light.
Four sets of high-power white LEDs were prepared by commercial GaN-based high-power blue light-emitting chips manufactured by different manufacturers. The life test was carried out by using the aging test device designed by ourselves. In order to eliminate the effect of phosphor on the attenuation characteristics of L ED light output, high-power blue light-emitting diodes were fabricated using the same batch of chips as the associated white LEDs. Finally, the anti-static protection measures are used to improve the life test of high-power LEDs.
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