Examining Degradation Mechanisms in Strain-Relaxed AlGaN-Based UV-C Light-Emitting Diodes Using Raman Spectroscopy

This study delves into the degradation mechanism of AlGaN-based UV-C light-emitting diodes (LEDs) subjected to continuous current stress while maintaining a constant heat sink temperature over a 500-hour duration. Utilizing Raman spectroscopy, we observe the relaxation of strain at various stages of degradation. This is exemplified by the blue shift of the
${\text {E}_{{2}}}^{\text {H}}$
phonon peak from the P-GaN layer of AlGaN-based LEDs, measured from different orientations: back, front, and side views, throughout each degradation phase. Raman spectroscopy allows us to comprehensively explore the relaxation of stress specifically under the P-metal of the AlGaN-based UVC LEDs, while the N-metal remains unchanged. This comprehensive investigation sheds light on the intricate degradation mechanism of UV-C LEDs, providing valuable insights into their performance under prolonged stress conditions.