Investigation of nonlinear power degradation and progressive recovery behavior in GaN-based violet laser diodes

Nonlinear degradation behavior in semiconductor laser diodes (LDs) is critical for understanding the reliability limitations after long-term operation. Here, we have investigated an observed nonlinear power degradation and a subsequent progressive recovery behavior of GaN-based violet LDs during constant-current aging. The aged devices exhibit a pronounced increase in threshold current and reduced optical output, accompanied by a reduced radiative efficiency at low injection levels. Electrical measurements, below-threshold electroluminescence (EL) spectroscopy, and scanning electron microscopy (SEM)/cathodoluminescence (CL) micrograph analyses reveal that the degradation is highly localized beneath the ridge waveguide, where enhanced defect-assisted recombination and carrier transport nonuniformity occur. Based on these results, a localized defect-assisted transport evolution model is proposed, suggesting that the formation of defect-induced shunt channels may cause carrier leakage and trigger the nonlinear output power degradation, while their dynamic reconstruction may contribute to the subsequent progressive recovery behavior. This discovery provides experimental insight into nonlinear degradation mechanisms in high-power GaN-based violet LDs.