Multiphysics modeling of feedback-induced catastrophic optical damage in 9xx-nm high-power laser diodes

In this work, we use a multiphysics model of an external-cavity laser diode to study the influence of misaligned external optical feedback on the COD level of the device. The model solves the drift-diffusion equations for the electrical transport in the vertical-longitudinal plane self-consistently with a wave-optical model (including semiconductor chip and external resonator) and a 3D thermal model of chip and submount. A vertical misalignment of the FAC lens in an external resonator configuration consisting only of the FAC lens and feedback mirror leads to strongly reduced COD levels within the simulation if the feedback radiation hits the metal layers on the p-side of the device. The absorbed feedback radiation is the initial driver for the COD, whereas vertical leakage currents lead to ever increasing temperatures during thermal runaway. Experimental data of pulsed COD tests confirm the simulation results qualitatively. The minimum absorbed optical feedback power leading to COD depends on the operating point of the device. It increases with increasing external reflectivity due to the onset of COD at lower currents and corresponding lower internal optical power densities. For a low external reflectivity the output power is limited by thermal rollover instead of COD. The surface recombination velocity as the parameter quantifying the facet passivation quality has only a minor influence on the COD level in the simulation as for a low surface recombination velocity (high facet quality) the carriers can still recombine nonradiatively in the bulk layers due to the vertical leakage currents.