Biomimetic overlayer inspired by firefly for LED light-extraction efficiency improvement

In this poster, the design, fabrication and characterization of a bioinspired overlayer deposited on a GaN LED are described. The layer design is inspired by the microstructure found in the firefly Photuris sp. The actual dimensions and material composition have been optimized to take into account the high refractive index of the GaN diode stack. This two-dimensional pattern contrasts other designs by its unusual profile, its larger dimensions and the fact that it can be tailored to an existing diode design rather than requiring a complete redesign of the diode geometry. With rigorous coupled-wave analysis (RCWA) simulations, the optimal ratio between the period and height of the bio-inspired structures is calculated [1]. The optimal geometry for this structure is changed in comparison to the firefly, but still remain micrometrical and simple without multiple depositions, colloids etc. like in the reproduction of butterfly wings structures found on the Papilio Blumei for instance [2]. In the case of the firefly microstructure fabrication, the use of standard optical lithography is well suited. The gain of light extraction reaches values up to 55% with respect to the reference unprocessed LED.