High-brightness LEDs have developed rapidly during the past five years. They are used in traffic lights, signs and specialty lighting and in new applications such as backlight units for LCDs, headlamps for cars and street lighting. The efficiencies of white light from high-brightness LEDs now have reached greater than 100 lm/W, while costs keep decreasing. The efficiency per cost of high-brightness LEDs has been doubling every two years, which will lead to even wider use in general lighting in the future.

A high-brightness LED is a solid-state light-emitting chip that emits in blue, green and red wavelengths. Typically, it consists of multiple quantum layers grown between p- and n-doped gallium nitride (GaN), which is grown on a lattice-matched substrate such as silicon carbide or sapphire. The substrate can be removed with a laser liftoff technique, and the GaN can be bonded to silicon. Direct-wire bonding or flip-chip bonding techniques are used to make electrical contacts to the chip...

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