Impact On The LED Efficiency By Periodic Micro-structures On The Chip Surface

The total reflection occurs when light of the active region emit to theinterface of GaN and air, and a part of photons are reflected back and can not exit,so that the extraction efficiency have been reduced.Several methods have beendemonstrated to be effective for enhancing light extraction of GaN-based LEDs,such as surface texturing, photonic crystal, and patterned sapphire substrates. Inaddition, the surface texturing has been reported to be useful.To improve the external quantum efficiency of the LED, we have fabricatedsome periodic micro-structure on the top of the LED by surface rougheningtechnology. The surface roughening technology can effectively improve theextraction efficiency of LED. Generally speaking,surface roughening on chipsurface by dry etching process or wet etching process. However, in this work weadopted a femtosecond laser process, which has a lot of advantages.This study mainly includes two parts: the simulation and the experiment. Inthe simulation, we have created a LED model in tracepro software and raytracing. The distribution of optical fields were observed. The simulation resultsshow that the light extraction efficiency of the LED can be increased by24.73%in theory. In the experiment, we fabricated micro-structures with periodic on thetop of the chip by femtosecond laser. The luminous flux of LED were measuredby using the integrating sphere. The experimental results show that the LEDluminous efficiency was increased by12.54%.These conclusions show that surface roughening technology can effectivelyimprove the light extraction efficiency of LED.