Analysis of the degradation processes of commercial LEDs and lifetime-related modelling

The purpose of this thesis is to perform aging tests on commercial LEDs in order to collect and process degradation data and extract the main degradation mechanisms involved. The devices under test are employed in different fields, such as automotive, home and urban lighting systems, as well as horticulture environments. In these scenarios, the possibility to estimate the overall lifetime of the devices based on the environmental conditions is crucial in terms of both economic and safety related reasons. The classification of a set of degradation parameters will eventually serve artificial intelligence algorithms to produce accurate predictions. After the identification of the stress conditions for each LED (i.e., current and ambient temperature), a series of stress tests were conducted. Tests were divided into steps, each one resulting in a characterization phase with the aim to keep monitored the electrical and optical characteristics. All data, except for the one related to temperature, were extrapolated from the IV and the LI curves, along with the PSD profiles which were collected with a time step dependent on the degradation observed. From the temperature standpoint, an estimate of the junction temperature was performed by means of pulsed thermal maps at the beginning of each stress test. Finally, the degradation metrics were expressed as a function of the stress conditions and were related to physical degradation processes of LEDs.