Kinetically limited misfit dislocations formed during post-growth cooling in III–V lasers on silicon

Abstract

Misfit dislocations (MDs) classically form at interfaces when an epitaxially strained film exceeds a critical thickness. We show that metastable MDs also form between layers nominally below critical thickness with respect to each other when externally driven threading dislocations (TDs) have significant dissimilarities in dislocation mobility in these layers controlled by glide kinetics. The InAs quantum dot laser on silicon presents a technologically important case for this phenomenon where TDs are pinned by indium-containing regions but glide in GaAs or AlGaAs cladding regions driven by thermal expansion mismatch strain with silicon during sample cool down following growth. This generates long MDs adjacent to the active region that is responsible for gradual degradation in performance. We calculate the driving force for MD formation and its dynamics in model structures, building up to full lasers, and describe the design of intentionally introduced indium-containing trapping layers that displace the MDs away from the active region, which is key to long laser lifetime. We show that factors controlling dislocation glide kinetics: doping, indium alloying, and dislocation core character have a strong influence on the final structure of defects. Yet, the introduction of indium must be done with care, illustrated using two cases where indium is not useful to overall device defect engineering.