Improvement in heat dissipation capability of GaN-based light-emitting diodes

Recently, high brightness GaN-based light emitting diodes (LEDs) have attracted a lot of interest owing to their excellent device characteristics. The GaN-based LEDs are widely used for a variety of applications such as general lighting, liquid crystal display and traffic signal. In order to achieve high performance of these devices, it is urgently required to enhance the optoelectronic properties of LEDs. It is well-known that the poor heat dissipation of sapphire substrate is the main limitation to fabricate the high-efficiency LEDs. For a conventional LED, the heat is easily accumulated in the device, resulting in the performance deterioration. In this chapter, the improvement heat dissipation of GaN-based LEDs is proposed and discussed. In this chapter, we have proposed several techniques including the employment of cupshaped copper-diamond heat spreader, the combination of beveled sapphire and cup-shaped copper sheet, and the addition of diamond like carbon layer into LED structure. To develop these techniques, many methods consisting of copper electroplating, chemical mechanical polishing, metal mirror coating, wafer bonding, laser lift-off, and so on. After fabricating the LEDs by using these techniques, the surface temperature, thermal resistance, and light output power of LED devices are investigated in detail. With the aids of above-mentioned techniques, the results reveal that not only the heat dissipation but also the light extraction of LEDs can be improved efficiently.