Optical characteristics of thin film-based InGaN micro-LED arrays: a study on size effect and far field behavior

Micro -light emitting diodes ( mu -LEDs) are considered the key enabler for various highresolution micro -display applications such as augmented reality, smartphones or head -up displays. Within this study we fabricated nitride -based mu -LED arrays in a thin film chip architecture with lateral pixel sizes down to 1 mu m. A metal mirror on the p -side enhances the light outcoupling via the n -side after removal of the epitaxial growth substrate. Mounted devices with pixel sizes ranging from 1 x 1 to 8 x 8 mu m 2 were electro-optically characterized within an integrating sphere and in a goniometer system. We measure increased external quantum efficiencies on smaller devices due to a higher light extraction efficiency (LEE) as predicted by wave optical simulations. Besides this size dependence of the LEE, also the far field properties show a substantial change with pixel size. In addition, we compared mu -LEDs with 40 nm and 80 nm thick aluminium oxide around the pixel mesa. Considerably different far field patterns were observed which indicate the sensitivity of optical properties to any design changes for tiny mu -LEDs. The experimentally obtained radiation behavior could be reasonably predicted by finite -difference time -domain simulations. This clearly reveals the importance of understanding and modeling wave optical effects inside mu -LED devices and the resulting impact on their optical performance. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement