The enhancement of the deflection effect in InGaN/GaN light-emitting diodes with an ellipsoidal air tunnel

This paper reports on the deflection effect of ellipsoidal air tunnel (EAT) array as an embedded deflector with low refractive index in InGaN/GaN light-emitting diodes (LEDs). Light extraction efficiency (LEE) for different height-to-width (h/w) ratios of air structure is analyzed by using an optical simulation program. Maximum LEE was obtained at a h/w ratio of 0.3, which corresponds to an ellipsoidal shape of the air structure. An LED structure with EAT array embedded between the sapphire substrate and the GaN epitaxial layer has been fabricated. The reflectance spectra measured over the entire visible spectral range showed reflectance modulations by the EAT structures. Moreover, the light-output power of the EAT-embedded LED was enhanced by 2.3 times compared to a conventional LED without EAT arrays. This could be attributed to the enhanced light deflection from EAT structures. (c) 2011 Elsevier Ltd. All rights reserved.