Fundamental Studies of Efficiency Droop in III-Nitride Solid-State Lighting Devices

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The objective of this research is to computationally investigate i) how efficiency droop and color degradation in III-nitride solid-state lighting (SSL) devices are governed by an intricate interplay of crystal atomicity, built-in structural fields, and charge and phonon transport processes, and ii) how tuning the basic physical properties at nanoscale can create transformative solution paths. The multiscale numerical approach is built primarily upon i) a massively parallel molecular dynamics code for obtaining structural relaxation and phonon modes, ii) atomistic tight-binding models to calculate exciton and optical spectra, and iii) a quantum-corrected 3-D Monte Carlo transport solver. ab initio methods and available experimental data will be used for parameterization and model bandstructure calculations.Intellectual Merit: The research bridges the gap between continuum system and ab initio material modeling paradigms and will suggest design optimization routes by simulating realistically-sized devices containing 100 million atoms, which can subsequently be used by experimentalists to manufacture the device. The simulator will exploit computing capability and assess reliability of petascale clusters, use novel, memory-miserly, and fast algorithms, and incorporate state-of-the-art software design approaches.Broader Impact: SSL has the potential, by 2025, to decrease electricity consumed by lighting by 50%, cut ~28 million metric tons of carbon emission annually, and benefit general illumination, transportation, communication, automobiles, imaging, agriculture, and medicine. SSL will revolutionize semiconductor market and can reestablish U.S. manufacturing leadership. A free version of the simulator and tutorials will be deployed on nanoHUB.org. Findings of the research will be integrated into both undergraduate and graduate courses.