Enhanced conversion efficiency and tailored radiation patterns assisted by photonic-crystal light-extractors in compact MQW based color-converters for μLED applications
26 January 2022 • 2:20 PM - 2:40 PM PST | Room 154 (Upper Mezzanine South)
State-of-the-art RGB microdisplays use quantum-dot color converters (CC), which suffer from photostability issues and low blue-light absorption. Inorganic MQW based CC offer higher blue-light absorption and better photostability. However, their practical use for microdisplays has not been implemented yet because of their low light extraction efficiency (LEE) inherent to their high refractive indices. In this paper, we investigate the use of photonic crystals (PhC) with different optogeometrical parameters to fully optimize AlGaInP/InGaP MQW CC for blue-to-red and green-to-red color conversions in microdisplays. A 600nm-thick CC was successfully bonded on a transparent substrate using oxide-mediated molecular bonding. By using optimized photonic-crystal designs, we obtained a large LEE enhancement (x 9) within ultra-short extraction lengths (~2μm), which shows quasi-perfect light outcoupling and compatibility with pixel lateral sizes under 5μm. Experimental results are in agreement with 3D-FDTD simulations, showing that those unique characteristics are paired with highly directional emission. A phenomenological model derived from the standard coupled-mode theory has been proposed and used to determine the mean coupling strengths between the guided Bloch modes and radiated modes. We believe that the design guidelines set in this work could pave the way for the use of inorganic MQW CC to achieve monolithic integration for full-color microdisplay applications.
Univ. Grenoble Alpes, CEA, LETI, CEA-Grenoble (France), Univ. Lyon, (France), Institut des Nanotechnologies de Lyon-INL, CNRS, Ecole Centrale de Lyon (France)
Amade NDIAYE received the M.Sc. degree in the fields of electrical engineering and Photonics from CentraleSupélec and Université de Lorraine, France, in 2019. He is currently pursuing his Ph.D. degree in Applied Physics / Photonics at CEA LETI in Grenoble and the Institut des Nanotechnologies in Lyon . His research comprises the design, simulation, modelling, fabrication and characterization of high efficiency optoelectronic emissive devices, with a current focus on the study and development of high-efficiency MQW-based color-converters for RGB microdisplays.