| Summary: | 碩士 === 國立中興大學 === 精密工程學系所 === 95 === The effect of backside aluminum (Al) reflectors on the performance of GaN light-emitting diodes (LEDs) was investigated in this thesis. For a typical chip process line, the backside Al coating on a sapphire substrate can enhance the external quantum efficiency except the poor adhesion problem. After the chip dicing process, the Al films can be peeled off by the blue tape easily. Therefore, it is necessary to insert a proper adhesive layer between Al and sapphire or incorporating an additional cleaning process. However, the adhesive layer such as Ti or Cr will sacrifice the reflectivity of the backside mirror. In this study, various backside mirror structures (e.g. Ni/Al, Ti/Al, Cr/Al, and SiO2/Al) for the GaN/sapphire green LEDs were attempted. However, the SiO2 interlayer can not solve the adhesion problem in our experiments.
It was found that a comprise should be made between the metallic interlayer thickness and output power. As compared with the original GaN LED without a backside mirror, the samples with the backside Ni/Al, Ti/Al and Cr/Al reflectors show 23.7, 28.6 and 20.8% improvement in output power, respectively. On the other hand, the adhesion between Al and sapphire is found to be greatly improved and the peeling ratio can be reduced to 0.1% by incorporating a plasma clean process before the Al evaporation. It provides not only higher adhesion property but also the best LED performance (44% enhancement in luminance intensity).
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