Modeling of the impact of current crowding on catastrophic optical damage in 9xx-nm high power laser diodes

The process of catastrophic optical damage (COD) in 9xx-nm laser diodes is typically divided into three phases. In this work we model the first phase of COD by placing a localized additional heat source near the front facet corresponding to accumulated defects or misaligned optical feedback. We then compare two different multiphysical models to investigate thermal runaway, the second phase of COD. The first model considers only the carrier density within the quantum well coupled to a lateral-longitudinal optical model and a 3D thermal model. For this model, the temperature distribution converges within a few iteration steps without indication of thermal runaway and irrespective of the power of the additional heat source. The second model self-consistently computes the electrical and optical properties in the vertical-longitudinal plane and the 3D temperature distribution of the device. A critical power of the additional heat source is found above which the temperature distribution does not converge anymore and the maximum temperature increases to values above 1000 K. This strong temperature increase is accompanied by a thermally induced current crowding near the front facet and excessive carrier leakage from the quantum well. An analysis of the contributions of different heat sources shows that the nonradiative recombination in the waveguide and cladding layers exhibits the strongest changes during thermal runaway. The results of the two models indicate that the frequently proposed explanation of the feedback loop for thermal runaway consisting of a thermally induced bandgap shrinkage and increasing nonradiative recombination needs to be supplemented by thermally induced current crowding.