We report on the degradation dynamics and mechanisms of commercially available green high-power light-emitting diodes (LEDs) with a peak wavelength of 522 nm. The stress tests were carried out for up to 8800 hours with forward currents ranging from 350 mA to 1000 mA at junction temperatures between 86 C and 155 C. Two complementary test designs were used to isolate temperature- and current-driven effects. The results of the accelerated tests reveal the following key findings: 1.) A square-root-time-dependent loss in the quantum wells caused by the generation of point defects, leading to up to 90 % flux reduction within the first 500 hours at low forward currents. 2.) A logarithmic decay governed by defect-induced carrier-injection loss, evident above I_EQE,max and accompanied by a spectral red shift. 3.) A temperature-activated blue shift with an activation energy of E_a =0.23 eV, indicating the coexistence of competing degradation mechanisms. The interplay between different mechanisms results in an enhanced device lifetime at higher stress temperatures and stands in contrast to previous findings reported in the literature. 4.) The isothermal stress test indicates a cubic acceleration of degradation with carrier density, implicating Auger-Meitner-generated hot electrons in defect formation. These insights provide guidance for mitigating reliability issues of green high-power LEDs in future devices.

This review is aimed at providing an overview of the technologies of currently-available UVC LEDs, on the challenges that these devices have to face, and on the peculiar features that these modern solid-state emitters exhibit. In particular, this paper is aimed at serving as a bridge between device developers and system manufacturers, by increasing awareness of the differences, both in terms of reliability and operation, that AlGaN-based UVC LEDs show with respect to their visible InGaN/GaN-based counterparts. In this view, this work reports performance and lifetime figures of both commercially-available and research-grade LEDs, showing their limitations in terms of temperature- and current-dependency of the emission spectrum. Both catastrophic and gradual processes that lead to device degradation are discussed, with a particular focus on the kinetics that device properties exhibit during prolonged operation. Moreover, also package-related degradation processes are investigated, which stand-out due to the peculiar structures and materials required to sustain both high-energy UV photons and high localized self-heating, while maximizing the optical efficiency of the LEDs. Ultimately, the data reported within this paper should help the final user in predicting and mitigating degradation effects, while also serving as a reference to manufacturers for the improvement of next generation devices.

We report on the degradation mechanisms and dynamics of silicone encapsulated ultraviolet A (UV-A) high-power light-emitting diodes (LEDs), with a peak wavelength of 365nm. The stress tests were carried out for a period of 8665 hours with forward currents between 350mA and 700mA and junction temperatures up to 132°C. Depending on stress condition, a significant decrease in optical power could be observed, being accelerated with higher operating conditions. Devices stressed at a case temperature of 55 °C indicate a decrease in radiant flux between 10-40% varying with measurement current, whereas samples stressed at higher case temperatures exhibit crack formation in the silicone encapsulant accompanied by electromigration shorting the active region. The analyzed current and temperature dependency of the degradation mechanisms allows to propose a degradation model to determine the device lifetime at different operating parameters. Additional stress test data collected at different aging conditions is used to validate the model's lifetime predictions.