Comparative study of aging-induced optical and electrical degradation and dynamic stability in GaN-on-sapphire and GaN-on-GaN micro-LEDs

The aging behavior of GaN-based micro-light-emitting diodes (micro-LEDs) is strongly influenced by substrate material and device structures, yet systematic comparisons remain limited. In this work, we compared the aging-induced optical and electrical degradation of horizontal GaN-on-sapphire and GaN-on-GaN micro-LEDs under ultra-high current-density stress. The GaN-on-sapphire devices exhibit significant full width at half maximum (FWHM) broadening, peak wavelength shifts, reduced optical power, increased reverse leakage current, and elevated series resistance after aging, indicating enhanced defect-assisted recombination as well as increased carrier scattering and trapping. In contrast, GaN-on-GaN micro-LEDs show markedly improved stability in optical and electrical characteristics. Further frequency-dependent and voltage-dependent electrical analyses reveal substrate-dependent defect evolution during aging. Furthermore, step-current-density stress tests demonstrate superior dynamic voltage stability in GaN-on-GaN micro-LEDs, especially in vertical structures. These findings underscore the importance of GaN substrates and current transport geometry for improving micro-LED aging reliability.