Fabrication and characteristics of thin-film InGaN-GaN light-emitting diodes with TiO_2/SiO_2 omnidirectional reflectors

摘要

In this paper, a novel GaN-based thin-film vertical injection light-emitting diode (LED) structure with a TiO_2 and SiO_2 omnidirectional reflector (ODR) and an n-GaN rough surface is designed and fabricated. The designed ODR, consisting of alternating TiO_2 and SiO_2, layers possesses a complete photonic band gap within the blue region of interest. The arrays of the conducting channels are integrated into the TiO_2/SiO_2 ODR structure for vertically spreading the current. Assisted by the laser lift-off and photo-enhanced chemically etched surface roughening process, the light output power and the external quantum efficiency of our thin-film LED with a TiO_2/SiO_2 ODR (at a driving current of 350 mA and with chip size of 1 mm x 1 mm) reached 330 mW and 26.7%, increased by 18% and 16%, respectively, compared with the results from the thin-film LED with an Al mirror. By examining the radiation patterns of the LEDs, the optical output power mainly increased within the 120 deg cone due to the higher reflectance of the TiO_2/SiO_2 ODR within the blue regime.