Physical mechanisms limiting the performance and the reliability of GaN-based LEDs

GaN-based optoelectronic devices are the market standard for light emission in the blue-green visible range, and the emission wavelengths are rapidly approaching the UV part of the electromagnetic spectrum. Given the complexity of their structure, composed of multiple quantum wells (MQWs), carrier blocking layers, nucleation layers, and strain relief structures for the reduction of the strain caused by the hetero-epitaxial growth, the analysis of the mechanisms influencing their performance is not straightforward, and often involves the use of computer-assisted simulations.The dynamics of the loss mechanisms may significantly change during the operation of the devices, resulting in the worsening of the overall optical and electrical properties. The generation of defects inside the active region, enhanced by the temperature and the bias level, affects the trap-assisted tunneling current components and the amount of non-radiative recombination. The diffusion of impurities/point defects, often originating from the p-side of the device, may lead to an increase in the non-radiative recombination components.The first part of this chapter describes the main processes that influence the optical and electrical behavior of the devices below and above the optical turn-on, along with their theoretical framework and a brief review of the literature on the topic. In the second part, we present a comprehensive analysis of diffusion-related degradation processes, based on previous literature reports. Finally, we present a discussion on the possible physical models able to explain experimental data on degradation of GaN-based optoelectronic devices.