| Deep ultraviolet (UV) light emitting diodes (LEDs) with wavelength shorter than 300 nm have attracted enormous attention due to their potential applications in biomedical sensing and water and air purification. Compared with widely used mercuiry vapor lamps, the solid state deep UV LEDs have advantages in size, power consumption, spectral control and environmental safety. However, the first generation devices suffer from a premature degradation. The understanding of the degradation mechanisms is also very limited.; This work presents a thorough study of the degradation mechanisms of AlGaN-based multiple quantum wells (MQWs) deep UV LEDs. These degradation mechanisms have been identified via a study of Fabrication processes, elevated temperatures and electrical stresses. It is shown that the control of fabrication processes is crucial to improve the yield and UV inert materials are recommended for packaging processes. Self heating is found to accelerate the degradation of the electrical and optical properties of AlGaN-based MQWs deep UV LEDs. Under electrical stress, the devices exhibit two degradation modes: catastrophic and gradual degradation. The catastrophic degradation is found to relate to the growth defects and the surface morphology. Three factors are found to limit the lifetime of gradual degradation: junction temperature, current density and dislocation density. |
