Unlocking Brighter MicroLEDs: Advances in Light Extraction Efficiency

MicroLEDs offer tremendous promise for next-generation displays and lighting, but maximizing their light output remains a key challenge. Recent innovations in photonic nanostructures, novel geometries, and manufacturing methods are poised to significantly boost microLED brightness and efficiency.

MicroLEDs integrate microscopic LEDs onto a unified array substrate, eliminating individual packaging. The technology enables unparalleled image quality, response times, reliability and efficiency compared to existing displays.

However, a fundamental issue hampering microLED performance is inadequate light extraction. Due to the high refractive index contrast between GaN-based devices and air, over 70% of light can remain trapped in waveguided modes. New techniques to extract this wasted light are critical.

Let's explore some of the most exciting advances in enhancing microLED light extraction efficiency:

1. Photonic Nanostructures

Specialized nanoscale optical structures engineered onto microLED surfaces provide new light escape pathways. Examples include:

Dielectric Photonic Crystals

Periodic dielectric nanopatterns surrounding microLEDs are designed to concentrate and redirect photons. By tailoring the photonic density of states, directional light enhancement over 130% has been demonstrated.

Plasmonic Arrays

Resonant metallic nanostructures integrated directly on top of microLED multiple quantum wells can couple with trapped waveguided light via plasmonic interactions. Through near-field oscillations, plasmons scatter photons upwards extracting additional output.

Microlens Arrays

Wafer-scale microlens layers mounted over microLED arrays angularly constrain the output beam for enhanced light extraction. Condenser-like effects maximize external quantum efficiency with collimated high-intensity emission.

2. Novel Device Geometries

By altering microLED shape and layout, more external outcoupling paths are possible to overcome substrate losses. Examples include:

Horizontal Nanowire Arrays

Moving to horizontal nanowire LED orientations eliminates vertical waveguide effects inherent to planar geometries. Without transverse guiding layers, photons emit radially without trapping.

3D Pyramid Layouts

MicroLEDs are shaped into 3D pyramids with angled sidewall facets. This provides multiple outcoupling surfaces to redirect internally reflected light. Efficiency gains over 55% have been demonstrated with pyramidal shaping.

Curved Device Surfaces

Instead of a flat emissive layer, microLEDs are fabricated on curved surfaces to match focal fields. This minimizes coupling losses into the substrate by radially extracting photons.

3. Advanced Manufacturing Techniques

New microLED production techniques further aid efficiency by preserving delicate photonic nanostructures:

Laser Lift-Off Printing

A scanned laser release process gently lifts microLED devices off the original growth wafer while retaining nanostructured enhancements on the emitter surface.

Grayscale Lithography

Varying ultraviolet light exposure during microlens photoresist development enables smooth 3D shaping. The resulting tailored lens profiles significantly improve collimation and extraction efficiency.

Large Area Nanoimprinting

High-throughput nanopatterning of large-area wafers is achieved with nanoimprint lithography. This facilitates low-cost, reliable fabrication of optimized photonic nanostructures over microLED arrays.

Conclusion

As these light extraction advances continue, microLEDs are getting brighter. With the aid of photonic engineering, microLED walls are no longer barriers but rather gateways for producing highly efficient, vivid displays and lighting. Unlocking the trapped light in high-performing microLEDs makes their widespread adoption across consumer and industrial applications much more viable.