The degradation behaviors of high power GaN-based vertical blue LEDs on Si substrates were measured using in-situ accelerated life test. The results show that the dominant failure mechanism would be different during the operation. Besides that, the corresponding associated failure mechanisms were investigated systematically by using different analysis technologies, such as Scan Electron Microscopy, Reflectivity spectroscopy, Transient Thermal Analysis, Raman Spectra, etc. It is shown that initially, the failure modes were mainly originated from the semiconductor die and interconnect, while afterwards, the following serious deterioration of the radiant fluxes was attributed to the package. The interface material and quality, such as die attach and frame, play an important role in determining the thermal performance and reliability. In addition, the heating effect during the operation will also release the compressive strain in the chip. These findings will help to improve the reliability of GaN-based LEDs, especially for the LEDs with vertical structure.

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By modulating the indium composition in the quantum barriers of InGaN-based LEDs, the influence of electron distribution, electron overflow and Auger recombination on the external quantum efficiency (EQE) and droop effect have been investigated. Experimental results as well as numerical simulations reveal that the electron distribution is the key factor to influence both the peak efficiency and droop effect. The results show that the high electron concentration in the individual quantum well can stimulate the Auger recombination and lead to the droop effect instead of the total effective electron concentration, which is more related to the external quantum efficiency. If we modulate the indium composition in the quantum barriers of the InGaN-based LEDs, a uniform electron distribution can be achieved, which can not only enhance the EQE but also avoid the Auger recombination and improve the droop effect.