Towards high reliability GaN LEDs: Understanding the physical origin of gradual and catastrophic failure

This paper reviews the most relevant mechanisms responsible for the gradual and catastrophic failure of InGaN-based light emitting diodes, for application in general lighting. Based on recent results obtained on state-of-the-art LEDs and lamps, we discuss the following: (i) the lifetime of 800 lm retrofit lamps is still limited by the early degradation of the InGaN-LEDs, of the plastic encapsulant/reflectors, and of the driving circuitry. High temperatures and/or poor thermal management can significantly reduce the lifetime of the lamps in real-life applications. (ii) mid-power LEDs, that represent a low-cost widely adopted alternative to power devices, can suffer from both chip and package degradation, that result in a significant decrease in optical power and shift in the chromatic properties. (iii) Electrical overstress (EOS) can result in the sudden failure of power LEDs; failure can be due to the fusion of the bonding wires, to the degradation of the metal lines, or to the cracking of the semiconductor material. The results presented within this paper provide an update on the state-of-the-art of LED reliability.