Abstract
This paper investigates the mechanisms that limit the efficiency and the reliability of InGaN-based LEDs, by presenting an analysis carried out on devices having two quantum wells that emit at different wavelengths (405 nm and 495 nm). A color-coded test structure was designed in order to easily quantify the optical characteristics of both quantum wells, and to describe in detail the stress dynamics as a function of In-content and of the position of the quantum wells.The attention was focused on: (i) electrical degradation induced by constant current stress at high temperature, that was found to be related to a diffusion process; (ii) degradation of the optical parameters, which was dominantly ascribed to an increase in SRH recombination and to a decreased carrier injection efficiency; (iii) effect of indium content and carrier distribution on the efficiency and reliability of the devices. The results strongly suggest that the internal quantum efficiency is limited by a low injection efficiency and by the quantum confinement Stark effect. In addition, the results on optical degradation highlight the presence of different mechanisms that contribute to the degradation: the role of Shockley-Read-Hall recombination, carrier escape and Auger processes are discussed.
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