UC Santa Barbara

Silicon photonics has over the past decade dramatically expanded in scale and importance and now plays a key role in optical communications for data centers, with many longer-term applications such as LIDAR, optical computing, and biomedical sensing. Monolithically integrated light sources based on III-V alloys grown directly on silicon have for decades been a goal in the field, but this has only recently become a commercially feasible approach after steady reductions in defect densities for III-V-on-Si epitaxy and the introduction of quantum dot (QD)-based active regions. This work focuses on improving the reliability of such InAs QD lasers on silicon by understanding their fundamental degradation mechanisms, particularly by studying the evolution and impacts of dislocations. Indium alloying of AlGaAs is demonstrated to halt most dislocation motion and dramatically slow all remaining dislocations via an alloy hardening effect. This leads to the most significant finding of this work: describing a formation mechanism for misfit dislocations around the active region of QD lasers and devising a solution. The misfit dislocations form, in part, due to dislocation pinning through the active region, so thin indium alloyed layers, termed trapping layers, are inserted to extend the pinning effect and displace the dislocations away from the active layers. This yields notable performance improvements but more importantly enhances the reliability of lasers by up to 100×. These trapping layers are later employed for defect reduction in a heterogeneous integration scheme for templated regrowth. The impacts of misfit and threading dislocations on QD luminescence beyond non-radiative recombination is also explored. The source of lingering gradual degradation in QD lasers is clarified through electroluminescence and TEM imaging of aged and unaged lasers. Degradation is spread uniformly across the laser and is caused by growth of non-visible point defects, some of which coalesce into observable dislocation loops. Trapping layers are also explored in quantum well (QW) lasers on silicon to enhance defect filtering and reliability, but it is expected that untrapped misfit dislocations and remaining threading dislocations will limit reliability of such devices. Finally, suggestions are made for future work to improve QD laser reliability by optimizing trapping layer performance and addressing point-defect-based degradation.