Development of a novel chip structure for high-power light emitting diodes with heat-dissipation mirror substrates

• Main Authors: Chia-En Lee, 李佳恩
• Other Authors: Chung-Yuan KUNG
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/17642746804901643581

碩士 === 國立中興大學 === 電機工程學系 === 92 === High-efficiency light-emitting diodes (LEDs) are desired for many applications such as outdoor displays, automobile signals, and traffic indicators. It is well known that the AlGaInP LEDs lattice-matched GaAs substrates have the highest luminous efficiency in the yellow-to-red spectral region, and the GaN-based LEDs have the spectral region from green-to-blue. On the other hand, high power LEDs are usually driven on high current, the huge joule heating could contribute the early saturation trends of light output. Hence, in this thesis, the main purpose is to develop a novel chip structure for high-power light emitting diodes with heat dissipation mirror substrates. The LED device has not only the high reflective mirror but the high thermal dissipated metal substrate. Furthermore, the problem which was induced by metal dicing has also been avoided. The AlGaInP/mirror/Cu LEDs provide higher light output than original AlGaInP/GaAs LEDs due to the high reflective rate metal mirror. In the heat sink characteristic, It was found that the wavelength of the AlGaInP LED with Cu substrate exhibited only about 4 nm shift at 400 mA, corresponding to a ~40°C rising in the junction temperature. However, the junction temperature raised to 110 oC easily as the injection current at 400 mA for the AlGaInP/GaAs LED sample. This indicates that the device heating is more pronounced for the conventional AlGaInP LED with a GaAs substrate. Obviously, the metallic substrate provides a good thermal management. On the other hand, the GaN/mirror/Cu LEDs was developed by a combination of laser lift-off (LLO) and electroplating techniques. In particular, the I-V curves of the GaN/mirror/Cu and original GaN/sapphire LED samples are nearly the same. This suggests that the LLO and electroplating processes do not adversely affect the LED performance. The luminance intensity of the GaN/mirror/Cu LED is about 50% higher than that of the original GaN/sapphire sample. The output power of the GaN/mirror/Cu LED increases linearly with injection current up to 180 mA, while early saturation of the GaN/sapphire device occurs at 70 mA. These indicate that the joule heating is less pronounced for the GaN/mirror/Cu LED sample where the metallic substrate provides a good heat sink.