Degradation of High-Brightness Green LEDs Submitted to Reverse Electrical Stress

This letter describes an extensive analysis of the reverse- bias degradation of green light-emitting diodes. The analysis consists in a wide set of stress tests carried out under different negative-bias levels. The results presented in this letter indicate the following: 1) Leakage current is strongly correlated to the presence of reverse-bias luminescence; 2) reverse current flows through preferential leakage paths and is due to a soft-breakdown mechanism that is possibly correlated to the presence of structural defects; 3) reverse-bias stress can induce an increase in the leakage current, with a corresponding decrease in the breakdown voltage of the samples; and 4) the degradation rate has a linear dependence on the (reverse) stress-current level, suggesting that degradation is induced by hot carriers. On the basis of the evidence collected in this letter, degradation can be ascribed to the generation/propagation of point defects due to the injection of highly accelerated carriers.