Analysis of the role of current in the degradation of InGaN-based laser diodes

This paper presents an analysis of the role of current in the long-term degradation of InGaN-based laser diodes (LDs). The analysis has been carried out by means of a set of stress tests under different driving conditions. The novelty of this work with respect to our previous preliminary reports [1] is that (i) we have investigated for the first time the important effect of low stress current levels (down to 200 μA) on the LDs stability, demonstrating the significant role of current as a driving force for devices degradation, and (ii) that we have analyzed the long-term degradation kinetics of the LDs (up to 1000 h). Thanks to the new findings reported in this paper, we demonstrate that: (i) stress determines the increase of the threshold current of the devices, well related to the decrease of the sub-threshold emission; (ii) stress induces the increase of the reverse current of the devices, but does not affect their forward-bias characteristics; (iii) degradation rate has an almost linear dependence on stress current level; (iv) degradation takes place also below lasing threshold and for very low stress current levels, i.e. with very limited optical field levels. On the basis of the evidences presented within this work, degradation is attributed to the increase of the nonradiative recombination rate. Furthermore, it is shown that degradation rate has a linear dependence on the stress current level, while the optical field is suggested not to play a significant role in determining threshold current increase.