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

这项研究的目的是通过计算研究i)III-氮化物固态照明(SSL)设备中的效率下降和颜色退化是如何受到晶体原子性、内置结构场以及电荷和声子传输过程的复杂相互作用的影响的，以及ii)如何在纳米尺度上调节基本物理性质来创建转变的解决方案路径。多尺度数值方法主要建立在i)用于获得结构弛豫和声子模的大规模并行分子动力学程序，ii)原子紧束缚模型来计算激子和光谱，以及iii)量子校正的三维蒙特卡罗输运求解器。我们将使用从头算方法和现有的实验数据进行参数化和模型能带结构计算。智能优点：这项研究在连续体系统和从头算材料建模范例之间架起了一座桥梁，并将通过模拟包含1亿个原子的实际大小的器件来提出设计优化路线，这些器件随后可以被实验者用来制造器件。该模拟器将利用计算能力和评估千万亿级集群的可靠性，使用新的、节省内存的快速算法，并融入最先进的软件设计方法。广泛的影响：到2025年，SSL有潜力减少50%的照明用电量，每年减少约2800万吨的碳排放，并使普通照明、交通、通信、汽车、成像、农业和医药受益。SSL将给半导体市场带来革命性的变化，并可以重新确立美国制造业的领导地位。该模拟器和教程的免费版本将部署在nanHUB.org上。研究结果将纳入本科生和研究生课程。

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.