Quantitative Multi-Scale, Multi-Physics Quantum Transport Modeling of GaN-Based Light Emitting Diodes

The performance of nitride-based light emitting diodes is determined by carrier transport through multi-quantum-well structures. These structures divide the device into spatial regions of high carrier density, such as n-GaN/p-GaN contacts and InGaN quantum wells, separated by barriers with low carrier density. Wells and barriers are coupled to each other via tunneling and thermionic emission. Understanding of the quantum mechanics-dominated carrier flow is critical to the design and optimization of light-emitting diodes (LEDs). In this work a multi-scale quantum transport model, which treats high densities regions as local charge reservoirs, where each reservoir serves as carrier injector/receptor to the next/previous reservoir is presented. Each region is coupled to its neighbors through coherent quantum transport. The non-equilibrium Green's function (NEGF) formalism is used to compute the dynamics (states) and the kinetics (filling of states) of the entire device. Electrons are represented in multi-band tight-binding Hamiltonians. The I-V characteristics produced from this model agree quantitatively with experimental data. Carrier temperatures are found to be about 60K above room temperature and the quantum well closest to the p-side emits the most light, in agreement with experiments. Auger recombination is identified to be a much more significant contributor to the LED efficiency droop than carrier leakage.