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 wide set of stress tests under different driving conditions. During stress, the optical and electrical characteristics of the samples have been continuously monitored, with the aim of determining the physical mechanisms responsible for degradation and the dependence of the degradation rate on the driving conditions. The results reported in this paper demonstrate that: (i) constant current stress determines the increase of the threshold current of the devices, that is 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. The results described in this paper indicate that the degradation kinetics are mostly determined by the stress current level used during operation: optical field and temperature are thought to play only a minor role in determining the degradation rate. Furthermore, the strong correlation between the threshold current increase and the sub-threshold emission decrease suggests that degradation can be ascribed to the increase of the non-radiative recombination rate in the active region of the devices.