Published online by Cambridge University Press: 10 February 2011
To engineer high-quality InxGal-xP graded buffers on GaP substrates (InxGa1-xP/GaP), we have explored the evolution of microstructure and dislocation dynamics in these materials. We show that the primarily limiting factor in obtaining high-quality InxGa1-xP/GaP is a new defect microstructure that we call branch defects. Branch defects pin dislocations and result in dislocation pileups that cause an escalation in threading dislocation density with continued grading. The morphology of branch defects is dominated by growth temperature, which can be used to suppress the strength or density of branch defects. In the absence of branch defects, we observe nearly ideal dislocation dynamics that are controlled by the kinetics of dislocation glide. This new understanding results in two primary design rules for achieving high-quality materials: 1) control branch defects, and 2) maximize dislocation glide kinetics. Combining these design rules into optimization strategies, we develop and demonstrate processes based on single and multiple growth temperatures. With optimization, threading dislocation densities below 5 × 106 cm−2 are achieved out to x = 0.39 and a nearly steady-state relaxation process is recovered.