Enhanced forward emission by backside mirror design in micron-sized LEDs

Tiny InGaN micro-LEDs (µ-LEDs) play a pivotal role in emerging display technologies, particularly augmented reality (AR) applications. Achieving both a high internal quantum efficiency (IQE) and efficient light extraction efficiency (LEE) is essential. While wet chemical etching can recover the IQE after dry etching, it alters the pixel shape, impacting optical properties and reducing the LEE. In this study, we overcome this issue by fabricating 1 µm thin film-based µ-LED emitter arrays with a metallic backside mirror deposited on a patterned dielectric material around the µ-LED mesa. This concave mirror can be straightforwardly integrated into a thin film LED process chain and it redirects photons within the µ-LED structure, enhancing the LEE in forward direction. Electro-optical measurements show a 2.1-fold improvement in light output within the ±15◦ emission cone compared to µ-LEDs with vertical sidewalls. These findings hold significant implications for µ-LED projection displays, where maximizing the overall efficiency and directionality is critical.