In recent years, optical devices, such as light-emitting diodes (LED), laser diodes, and UV photo-detectors have increasingly been used. Group-III nitride compounds, such as gallium nitride (GaN) and their related alloys, have been known suitable for the formation of the optical devices. The large bandgap and high electron saturation velocity of the group-III nitride compounds also make them excellent candidates for applications in high-temperatures and high-speed power electronics.
Due to the high equilibrium pressure of nitrogen at typical growth temperatures, it is extremely difficult to obtain GaN bulk crystals. Therefore, GaN layers and the respective LEDs are often formed on other substrates that match the characteristics of GaN. Sapphire (Al2O3) is a commonly used substrate material. FIG. 1 illustrates a cross-sectional view of an LED package component. LED 2, which includes a plurality of GaN-based layers formed on sapphire substrate 4. Sapphire substrate 4 is further mounted on lead frame 6. Electrodes 8 and 10 electrically connect LED 2 onto lead frame 6 through gold wires 12.
Sapphire has a low thermal conductivity. Accordingly, the heat generated by LED 2 cannot be dissipated efficiently through sapphire substrate 4. Instead, the heat is mostly dissipated through the top end of LED 2 and through gold wires 12. However, the necessary length of gold wires 12 to extend to lead frame 6 renders the heat-dissipating efficiency low. In addition, electrode 10 occupies chip area and reduces the total chip area available for LED light output.