Degradation mechanisms in InGaN laser diodes grown on bulk GaN crystals

We have investigated the aging processes in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals. The measured threshold current turned out to be a square root function of aging time, indicating the importance of diffusion for device degradation. The differential efficiency, in contrast, was roughly constant during these experiments. From these two observations we can conclude that the main reason for degradation is the diffusion-enhanced increase of nonradiative recombination within the active layer of the laser diode. Additionally, microscopic studies of the degraded structures did not reveal any new dislocations within the active area of the aged diodes, thus identifying point defects as a source of nonradiative processes.