Bragg Reflector For High-brightness Light-emitting Diodes Study

The InGaAlP LEDs(light emitting diodes) have become new attractive light sources with superiority in high reliability, high brightness, long life and high energy efficiency and have extensively been used for information displaying, traffic signal lights and even lighting in the future for its broader spectral radiation bandwidth and wider half-intensity angle compared with laser. Development of applied areas and markets has led to heavy research and development in LED for even higher brightness. The reason for higher internal efficiency but lower brightness is its poor external efficiency. In this thesis, the effects of the current spreading layer and DBR on LED's external efficiency have been analyzed theoretically and manufactured experimentally, and great progress has been obtained.1. The ways to increase LED's external efficiency were compared with each other. The factors that have contribution to the external efficiency including the current spreading layers with different materials, the thickness, growth quality, doping and working current have been analyzed based on the current spreading model. And the key to improve external efficiency was qualified GaP layer with reasonable doping and thickness.2. The DBRs composed of different materials were compared with each other and the relations between DBR optical properties and Al composition have been discussed. A model of the effect of different DBR types on the external efficiency was proposed.3. The factors that have effects on the uniformity and repeatability of DBRs' thickness and compositions were analyzed. The results indicated that the repeatability was determined by the system's stability and control precision, the uniformity was determined by the stability and uniformity of flow and temperature distribution.4. 10-AlAs/Al0.491Ga0.509 As DBRs were manufactured and high reflectivity and bandwidth were measured.5 X-ray double-crystal diffraction used in DBR analysis was summarized. By means of an agreement between theoretical and experimental diffraction profiles based on kinematical theoretical model, the effects of compositions and thickness variations, interface roughness and strain on rocking curve were discussed for the improvement of material growth process.