Nano-structured micro-LEDs

Light-matter interactions at scales much smaller than the wavelength of the light opens new possibilities to control light. This field is called nano-photonics and enables improvements and new applications in micro-LEDs that are not possible with classical optics and current micro-structuring methods.Micro-LEDs have 3 challenges that can be “overcome” by making use of wafer-scale sub- 100nm patterns with single nm reproducibility. First, by making use of templated growth a full RGR LED system can be made on one substrate. For high resolution displays, the recombination process is not required anymore. Second, the light generated in the high refractive index semiconductor needs to be couple to air-modes. In macroscopic LEDs this is achieved by micro-patterns, light re-direction and recycling. This method is not possible to use in micro-LEDs as the micro-patterns are the size of the LED size. Photonic crystals can extract the light and also shape the extraction to either beam-like or bat-wing, compared to Lambertian in conventional LEDs. This creates directly more usable light by the enhanced out-coupling and directionality. Last, depending on the application, LED size and use of photonic crystals ,additional beam shaping might be required. The fast growing field and adoption of meta-lenses can help to keep the whole optical system efficient and compact. Metalenses function by precisely positioning nano-resonators that control the phase of the light and thereby can shape the wave-front and the (freeform) lens. These are robust, flat, thin (lens < 1micron) and therefore allow for easier integration. All the above mentioned applications of nano-photonics require feature sizes below 50nm with 1-5nm absolute size control to achieve the desired functions. The patterning method that can achieve this in a cost efficiency production method is based on nanoimprinting to form inorganic hard masks or functional devices. In the contribution the technology and nano-photonic applications will be discussed.