Reliability issues in GaN-Based optoelectronic devices: from material to package

Gallium Nitride optoelectronic devices are expected to significantly penetrate the market, due to their intrinsically high efficiency and to their long expected lifetime. However, over the last few years, several authors have demonstrated that the lifetime of LEDs and lasers based on GaN can be shorter than expected: this is due to the existence of a number of physical mechanisms that can determine the degradation of the devices, when they are submitted to high current or high temperature stress conditions. With this presentation we give a complete description of the physical processes that limit the reliability of optoelectronic devices on Gallium Nitride. Based on a number of case studies, we describe in detail (i) the degradation of the active region of the devices due to the generation of point and extended defects; (ii) the electro-optical degradation of high power Light-Emitting Diodes related to the worsening of the properties of the ohmic contacts; (iii) the degradation of the facets of high power laser diodes; (iv) the degradation mechanisms of high power white LEDs due to the worsening of the optical properties of the package. The presented results provide important information on the weaknesses of state-of-the-art optoelectronic devices, including high power white LEDs, Blu-Ray laser diodes, and Deep-Ultraviolet Light-Emitting Diodes. Furthermore, presentation will provide hints for the design of procedures for reliability evaluation, based on the execution of accelerated stress tests, and on the combined electrical, optical and thermal characterization of LEDs and lasers. Results are compared with literature data throughout the presentation.