N-contacts degradation analysis of white flip chip LEDs during reliability tests

Current and temperature aging have been conducted on flip chip high power light emitting diodes (LEDs) with Al-Ni-Ti-Au n-contacts. Electrical and optical characteristics have been monitored during aging and a forward voltage increase has been observed. In order to understand this behavior, cross sections have been made on representative aged samples. For LEDs with a forward voltage shift, in the n-contact area, Au-Al inter-diffusion leading to a possible formation of Au-Al intermetallic compounds has been observed. We propose here to analyze the failure modes; the related failure mechanism(s) and consequences on LED flip chip reliability.