Understanding and Improving the Efficiency of LEDs with Quantum-Mechanical Calculations

Dr. Emmanouil Kioupakis (hosted by Li Yang), Department of Materials Science and Engineering, University of Michigan, Ann Arbor
April 24, 2017 at 4:00 pm
241 Compton
Event Description 

The group-III nitrides (GaN, InN, and AlN) are the key materials that enable the fabrication of LEDs in the ultraviolet and the short-wavelength part of the visible spectrum. Today, nitride LEDs are used in diverse applications ranging from cell phone and computer displays, indoor agriculture, and energy-efficient light bulbs. Their commercial success was recognized with the 2014 Nobel Prize in Physics. Despite their widespread adoption, the efficiency of nitride LEDs is low when they are designed to operate at high power (efficiency droop) or longer wavelengths (green-gap problem). In this talk, I will discuss how insights from atomistic quantum-mechanical calculations based on density functional and many-body perturbation theory can be applied to understand the origin of the efficiency-limiting mechanisms, and how to improve the performance of nitride LEDs. We identified the origin of the efficiency problems to be nonradiative Auger recombination and its interplay with the intrinsic polarization fields and alloy composition fluctuations of InGaN quantum wells. Our predictive calculations also suggest engineering solutions to improve the LED efficiency. I will discuss how extreme quantum confinement in atomically thin binary nitrides (GaN and InN) is a promising method to stabilize excitons at room temperature and realize efficient LEDs in the deep-ultraviolet and green part of the spectrum. I will also present our results for the design of BInGaN alloys that are lattice-matched to GaN for visible-light emission.

Coffee:  3:45 pm, 241 Compton