Enhancement of light extraction efficiency of blue-light-emitting diodes by moth-eye structure

Abstract

For high-performance light-emitting diodes (LEDs), the high light extraction efficiency obtained by surface texturing is currently indispensable. We have developed a new method of moth-eye structure fabrication based on low-energy electron-beam projection lithography (LEEPL). The moth-eye structure comprises periodic corns with a pitch of optical wavelength scale, and is known to have a very low optical reflectivity. Since the LEEPL technique has very high throughput ability for carrying out such submicron patterning, it is applicable to the mass production of highperformance LEDs. In this study, we aim to increase the light extraction efficiency of various nitride-based LEDs, including those fabrication on sapphire and SiC substrates. The influence of the pitch of the moth-eye structure on the light extraction is also clarified. The light extraction efficiencies of flip-chip blue LEDs fabricated on SiC and sapphire substrates are increased by factors of 3.7 and 3.2, respectively, when the moth-eye structure is applied on the back of the substrate.