Abstract
Highly stress tests were carried out for GaN-based high power white LEDs with different structures, including traditional lateral, vertical as well as flip-chip LEDs. During the tests, all the electrical, optical and thermal properties were measured in-situ for each LED. The results show that for lateral LEDs, the structure property of LED epitaxial layer is still the key factor that influences the optical degradation behavior. With similar structure properties and leakage current, the failure mechanism will be similar and the activation energy is close to each other. In addition, it is shown that the vertical and flip-chip LEDs can improve the heat dissipation effectively, especially at high temperature. Compared the lifetimes of the LEDs with different structures at different stress temperatures, it can be found that the stress temperature play an important role for reliability evaluation. The optimized stress temperature can help to evaluate the reliability more efficiently. The study will give guidance for the future LED design with controllable lifetime.
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