| Summary: | 碩士 === 國立中興大學 === 材料工程學系所 === 94 === Group III nitride compound semiconductors have been widely used in optoelectronics and high-temperature electronic devices because of their wide band gap, chemical stability, and high temperature stability. These devices have been used extensively in various applications such as full color displays, back lighting in liquid-crystal displays, and exterior automotive lighting. Due to the poor electrical and thermal conductivity of the sapphire substrate, the GaN epilayer structure transferring to an electrically and thermally conducting substrate becomes an important issue in high power applications.
In this thesis, we fabricated the GaN LED structures and transferred to a copper (Cu) substrate by laser lift-off (LLO) process using two different methods; namely vertical-conducting (VC) and glue-bonding (GB) techniques. It was found that the luminous intensity of VC-LED can increase to about 2.1 times in magnitude as compared with that of the conventional GaN/sapphire LED at 500 mA, where the junction temperature can decrease by 56˚C at 300 mA. For the GB-LED, the luminous intensity also showed 2.5 times in magnitude better than that of the GaN/sapphire LED at 20mA. The enhanced output power could be attributed to the formation of an omni-directional reflector between GaN and Cu to improve the downward photons back to the surface effectively. The results indicate that the VC GaN/mirror/Cu LEDs are suitable for high power application while the GB GaN/mirror/Cu LEDs show an essential assistance in enhancing the light output power for low power devices.
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