IMPROVING LED EXTRACTION EFFICIENCY THROUGH SURFACE PATTERNING

摘要

We investigate improvement in performance attainable by etching Photonic Crystals and Photonic Quasicrystals (PQC) into the top emitting surface of LEDs (PQC-LEDs). We describe the physical mechanisms of extraction enhancement through ordered surface patterning and investigate benefits in terms of total extraction enhancement, beam directionality, and far field beam quality. We show that a great variety of far field beam profiles tailored for' specific applications such as projection TV light engines and direct flat panel display illumination can be obtained simply by adjusting geometric design parameters. Our results show that PQC-LEDs can provide around 50% improvement in extraction enhancement and coupling efficiency for applications requiring non Lambertian beam shapes when etched into standard epitaxy wafers in comparison to "state of the art" surface roughened GaN LED devices. We also show that by tailoring the epi-structure to complement the properties of the PQC, extraction as well as directional light coupling enhancements can be improved by a factor of 9 amounting to a total coupling enhancement of around 78%.