In-situ monitoring on junction temperature for degradation analysis of light-emitting diodes

A precise monitoring on the junction temperature of the light-emitting diode (LED) packages during a lifetime tests is very helpful to make a diagnosis of their quality change and to analyse the optical degradation. We proposed a new model for internal quantum efficiency (IQE) of the LED packages as a function of the junction temperature and developed an in-situ IQE measurement system for an investigation of the optical degradation mechanism in the LED packages. A lifetime test for 2,500 hours had been carried out with in-situ monitoring on the relative optical power and the sub-threshold leakage current. In addition, we had measured the junction temperature and the IQE as a tool for the degradation analysis of the LED packages. No change in the IQE and the leakage current throughout the lifetime test has been observed although there was a 10% optical degradation of the LED package.