질화갈륨 기반 다각형 발광다이오드의 광추출 효율 향상

Abstract

GaN based LEDs have gradually replaced traditional light sources in various applications including backlight display units, traffic signals, automotive lighting, architectural lighting, and general lighting. However, improvements to the external quantum efficiency (EQE) are required for these various application. The EQE of LED is correlated to the internal quantum efficiency (IQE) and the light extraction efficiency (LEE). Although the IQE of GaN-based LEDs has reached more than 80% due to the rapid development of growth techniques for high-quality epi-layers, the LEE of the LEDs is still low because of the large refractive index difference between the GaN (nGaN=2.5) and air (nair=1). Herein, various polygon shaped(triangle, parallelogram, pentagon, hexagon, circle shaped) LEDs are compared with those of a traditional quadrangular LED to enhance LEE of LED. To estimate the enhancement of LEE, we simulated the various shaped LEDs with ray-trace simulation tools. In addition, to measure the total amount of photons emitted from LEDs in all directions, the various polygon LEDs were encapsulated and packaged with To-can. Their optical output power of polygonal shaped LED is significantly improved, compared to that of traditional quadrangular LED due to increase in LEE along to lateral direction.