Degradation Mechanisms of white LEDs for lighting applications

With this paper we give an overview on the degradation mechanisms that limit the reliability of white LEDs for lighting applications. During ageing, GaN-based LEDs can show a significant optical power decrease. By means of electrical and optical measurements, we show that LED degradation can be determined by the decrease in the efficiency of the blue semiconductor chip, and by the degradation of the package/phosphor system. The optical properties of the blue semiconductor chip can degrade due to the generation/propagation of defects within the active layer of the devices, induced by the flow of current through the quantum-well region. On the other hand, the phosphors and the package of the LEDs can degrade when devices are exposed to high temperature treatment. The results of this study provide information on the role of current and temperature in determining device degradation, and indicate that the operating conditions of the devices must be carefully optimized in order to achieve long LED lifetime.