Analysis of diffusion involved in degradation of InGaN-based laser diodes

The gradual increase in threshold current in InGaN-based blue laser diodes (LDs) submitted to stress tests is generally attributed to diffusion-related phenomena. In fact, diffusion into active layers can increase the concentration of non-radiative recombination centers (NRCs). However, this hypothesis has not been verified yet for InGaN LDs. In this paper, we analyze the variation of the non-radiative recombination lifetime tau_nr in LDs submitted to stress tests: the analysis of tau_nr provides information on the density evolution of NRCs. Furthermore, we propose a novel model for the investigation of the degradation kinetics. This model assumes that the depth distribution of NRCs obeys to Fick´s diffusion equation. The obtained results suggest that the increase in 1/tau_nr can be correlated to a diffusion process. For the first time, we have estimated the value of the diffusion coefficient that is related to degradation, which is equal to 1.9times10^-19 cm²/sec. This value is very large if compared with the one obtained in bulk material. Therefore, we suggest that the diffusion process is driven by the presence of dislocations. The presented method for degradation analysis constitutes a powerful tool for the study of the degradation in InGaN-based LDs.