Effects of Electro-Thermal stress on AlGaN deep-ultraviolet LEDs

In this work we will study the degradation of Deep Ultra Violet (DUV) Light emitting Diodes (LEDs) subjected to electro-thermal stress. Several LEDs emitting at 310nm have been aged at temperatures varying from RT to 70°C (corresponding TJ = 53-97°C) and current levels from 0 to 30mA. In particular the stress induces (i) a decrease in the non-radiative lifetime in the LED active region, (ii) an increase in generation/recombination currents, (iii) an increase of the device series resistance, (iv) a decrease in the junction capacitance. Results show that degradation modes are both gradual and catastrophical. The current level has a strong effect in the gradual degradation while temperature only has a modest impact on degradation kinetic. The catastrophical degradation is instead related to localized overstress at mesa edges where conductive paths are generated during degradation.