LED 봉지재의 다양한 굴절률 및 기하학적 구조에 따른 광출력 특성 연구

Abstract

In this research we performed the simulations and experiments for LEDs？ light extraction with the variation of the refractive index and the geometrical structure of the encapsulants. We used XEUS？LEWWH77AAB LED (LG Innotek, Korea) for our research, which consisted of a GaN-based LED chips with 410 nm and 460 nm emission wavelength, respectively and the Ag reflector cup within an polyphthalamide (PPA) chip carrier. We conducted the fabrication of LED encapsulants onto LED using the dispenser system with a fine tuning and successfully fabricated the various refractive index and the geometrical structure of the encapsulants. The output power of the fabricated LEDs were measured using the conventional integrating sphere. It was shown that the light output power increases with the refractive index of encapsulant materials in the case of spherical geometry encapsulant while the light output power decreases with the refractive index of encapsulant materials in the case of with flat geometry encapsulant. We used LightTools software (Optical Research Associates, Pasadena, CA, U.S.A.) for the ray tracing simulation on our study and showed that the ray tracing simulations results are consistent with the experimentally measured results. The light extraction efficiency increased with the refractive index for every radius curvature value of encapsulant R, except with R=infinite (flat geometry). In addition, the light extraction rapidly increased with the sidewall angle in the case of the flat geometry at a given refractive index of the encapsulant while it is not affected by sidewall angle being kept in a constant in the case of the spherical geometry.