Light-emitting diodes (LEDs) based on nitride semiconductors, such as GaN (gallium nitride), are capable of emitting a spectrum of light ranging from ultraviolet light to blue light and the application of a fluorescent substance enables them to emit white light. LEDs capable of generating high-output white light are used for vehicle lights and other applications.
Such LEDs have a semiconductor lamination containing at least an n-type semiconductor layer, an active layer for light emission, and p-type semiconductor layer. On the p-type semiconductor layer side of a layered semiconductor structure, a p-side transparent electrode and a reflector electrode are formed covering almost the entire light emitting region. On the n-type semiconductor layer side of the layered semiconductor structure, an n-side electrode is selectively formed. A part of the light emitted from the active layer is released directly from the n-type semiconductor layer. The rest is released from the n-type semiconductor layer after being reflected off the reflector electrode placed on the p-type semiconductor layer side.
When nitride-based semiconductors are used in a layered semiconductor structure, a growth substrate, for example, a sapphire substrate, is employed to enable such nitride-based semiconductors to grow. However, a sapphire substrate is poor in heat dissipation due to its low thermal conductivity, and is therefore unsuitable for high-output LED devices that draw large currents. In recent years, therefore, a method that, after growing nitride semiconductors grow over a sapphire or other growth substrate, secures those nitride semiconductors over a silicon or other support substrate with excellent heat dissipation, and peels the growth substrate off the semiconductor lamination by laser lift-off (for example, see Japanese Laid-open Patent Publication No. 2006-128710).
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