Abstract
In recent years, some methods or techniques that enhance light output power of LEDs have been published from many researches, including backside reflector 、surface roughness、flip chip、micro-structure array, and so on. In this thesis, we used DBR 、Al +DBR and Ag+DBR as backside reflector of GaN-based LEDs to enhance light output power. In addition, DBR can enhance the small-angle incident light particularly evident. Based on the characteristic, we can fabricate highly directional LEDs and increased the coupling light into a fiber. It can be applied to plastic optical fiber (POF) communication. In our experiment,we simulated the reflectivity of DBR、Al+DBR、Ag+DBR in blue region (460nm) first, check the high reflectivity in blue region, and then deposited these reflectors on glass. By measuring, the reflectivity of 6pairs DBR is 93%、Al+2.5pairs DBR is 95.04% and Ag+3pairs DBR is 97.71%, finally we deposited these reflectors on backside of device and analysis optical properties. LEDs with 6 pairs DBR on backside can enhance light output power about 38.7% at 50mA, LEDs with Al+2.5pairs DBR on backside can enhance light output power about 36% at 50mA, LEDs with Ag+3pairs DBR on backside can enhance light output power about 34.1% at 50mA. In the divergence angle measurement, the horizontal and vertical divergence angle of REF LED is 151.6°、144.6° respectively at 50mA, the horizontal and vertical divergence angle of LED with 6 pairs DBR is 123.6°、112.4° respectively at 50mA, the horizontal and vertical divergence angle of LED with Al+2.5pairs DBR is 125.9°、 119.1° respectively at 50mA, the horizontal and vertical divergence angle of LED with Ag+3pairs DBR is 127.3°、 119.2° respectively at 50mA. It was found that the LEDs with backside reflectors can reduce the divergence angle 25~32°.