ENHANCED LIGHT EXTRACTION FROM LIGHT EMITTING DIODES UTILIZING A NANOPARTICLE META-GRID

Light extraction efficiency of existing semiconductor light emitting devices can be increased significantly by introducing a nanoparticle 'meta-grid' on top of a conventional light emitting diode (LED) chip, within its usual encapsulating packaging or casing. The 'meta-grid' is essentially a monolayer or a 2D array of sub-wavelength metallic nanoparticles (NPs) with sub-wavelength inter-particle separation. The local dielectric environment around the NPs and within the gaps between the NPs could be the same as the encapsulant, or any other optically transparent material with refractive index close to that of the encapsulant. Upon optical excitation, the collective oscillations of conduction electrons, or surface plasmon, of the metallic NPs give rise to localized surface plasmon resonances. When placed on top of the LED chip, which acts as a high refractive index substrate for the NPs, these NPs can couple strongly to the light emitted by the chip, acting as efficient resonant plasmonic antennae or scatterers for light. The plasmon-mediated light coupling can by optimized by tuning the composition, size, and shape of the NPs, their inter-particle gaps and their distance from the LED chip surface. By virtue of the localized-surface-plasmon-enhanced light transmission through the optimized NP 'meta-grid', the efficiency of extraction of the light generated by the semiconductor LED chip into its encapsulating casing can be significantly improved.