III-Nitride Light-Emitting Diodes for Solid-State Lighting – Hongping Zhao

Date: Mon. March 12th, 2012, 12:30 pm-1:30 pm
Location: Rockefeller 221

Energy efficiency and renewable energy technologies have significant importance for achieving sustainable energy systems in modern society. Lighting accounts for more than 22% of the total electrical energy usage in US, and technologies based on solid state lighting (SSL) utilizing semiconductor-based material has tremendous promise to replace the existing lighting devices. As compared to traditional incandescent and fluorescent lamps, SSL is more energy-efficient, reliable, and environmentally-friendly. Once widely used, SSL could lead to the decrease of worldwide electricity consumption for lighting by >50% and reduces total electricity consumption by >10%. The U.S. Department of Energy describes SSL as a pivotal emerging technology that promises to fundamentally alter lighting in the future. Rapid progress in SSL research and development has resulted in the advent of light emitting diodes (LEDs) for general lighting applications. Two major challenges for current state-of-art III-nitride based LEDs are green issue in InGaN quantum well light-emitting diodes, and efficiency’efficiency droop’ issue in III-nitride LEDs resulting in output power quenching at high current injection.
In this talk, I will discuss our novel approaches to address the major issues related to state-of-the-art nitride LEDs, in particular related to 1) engineering of InGaN nanostructure active layers for achieving high internal quantum efficiency and minimal efficiency droop in nitride LEDs, and 2) the use of surface plasmon approach for increasing the radiative efficiency in nitride LEDs. Specifically, I will present the following topics: 1) novel InGaN-based quantum well structures with enhanced matrix element for achieving high radiative efficiency, 2) the use of lattice-matched InGaN-AlInN QW-barrier structure for suppressing the efficiency-droop in nitride LEDs, and 3) the use of surface plasmon dispersion engineering to achieve wide-spectrum tuning of the Purcell peak enhancement of the radiative recombination rate for InGaN quantum well LEDs.