Analysis of Diffusion-Related Gradual Degradation of InGaN-Based Laser Diodes

This report reveals that diffusion of hydrogen induces gradual degradation in InGaN-based laser diodes (LDs). The increase in nonradiative recombination centers (NRCs) in the LDs has been attributed to diffusion-related phenomena. Factors other than NRCs, such as the threshold carrier density $N_{th}$ , can increase threshold current $I_{th}$. Those factors, however, were not fully investigated. Moreover, the diffusant responsible for the degradation of the LDs has not been univocally identified yet. To separately evaluate the roles of NRCs and $N_{th}$ in increasing $I_{th}$, this report analyzes the stress-induced variation of nonradiative recombination lifetime $tau_{nr}$ and lasing wavelength $lambda_{l}$. It is revealed that the density of NRCs increases at the first stage of gradual degradation, followed by a rise in $N_{th}$. In addition, this report proposes a novel model for the time-variation of $1/tau_{nr}$ to investigate the diffusion-related degradation. By using this model, we extrapolate the value of the diffusion coefficient of diffusants involved in the degradation in InGaN-based LDs. The proposed analysis methods and obtained results are useful for understanding the physics of LD degradation.