<title>Engineering high-quality InxGa1-xP graded composition buffers on GaP for transparent substrate light-emitting diodes</title>

Abstract

We present the development of high-quality In x Ga 1-x P graded buffers on GaP substrates (In x Ga 1-x P/GaP) for use in epitaxial transparent-substrate light-emitting diodes (ETS-LEDs). The evolution of microstructure and dislocation dynamics of these materials has been explored as a function of growth conditions. The primarily limiting factor in obtaining high-quality In x Ga 1-x P/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 control the strength and 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 5×10 6 cm -2 are achieved out to x = 0.39 and a nearly steady-state relaxation process is recovered. Having controlled the severe material degradation with continued grading that stopped earlier In x Ga 1-x P/GaP efforts, we describe the basic device design and process for ETS-LEDs. The ETS-LED technology promises significantly reduced processing requirements, higher yield, lower cost, and enhanced design flexibility over existing LED technologies.