| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 104 === In the light-emitting diodes (LEDs) technology, we usually use sapphire for the substrate. Due to the large lattice mismatch between GaN and Sapphire substrate, GaN will get compressive strain from substrate and exhibits lots of threading dislocations(TDs), decreasing the device efficiency. To solve these problems, patterned sapphire substrates (PSSs) is a common technology.
In this research, we fabricated a series of PSSs by our wet etching method and E-beam lithography system. After the epitaxy via MOCVD system, we use micro-PL, micro-Raman system and X-Ray diffraction system to measure the MQWs TDs density, Bulk TDs density, and Compressive stress. We find that the MQWs TDs can be reduced when the Bottom C-plane shape pinch off to special “Engel Beak” or “Benz mark” shapes. In the device level we use Electro Luminescence (EL) for measurement. Demonstrating that efficiency droop can be reduced when bottom shape pinch off as well. After our analysis, the decreasing of efficiency droop should be attributed to the decreasing of MQWs TDs Density. Besides, we proved that cubic arrangement is better than hexagonal arrangement in PSS design. A detailed research of epitaxial model will be discussed in this thesis.
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