The history for human lighting is from candles
to lamps. But nowadays the most popular lights is LED. GaN(gallium nitrate) is
one of the main source to product LED. The compound has been studied for about
30 years. In 1989 the Japanese scientist isamu akasaki successfully made blue
light emitting diode(LED) from GaNand he created the new measures for GaN


The preparation of GaN has four main steps (metalorganic
chemical vapor deposition, hydride vapor phase epitaxy, separate and second

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In the MOCVD step ultra-pure gases are
injected into a reactor and finally deposit a very thin layer of atoms onto a
semiconductor wafer. For example PIn can be grown in a heated substrate which
made up by trimethylindium and phosphine. The precursor molecular decompose in
absence of oxygen. So the atoms connect to substrate surface and a new
crystalline layer as been grown.

In the machine of MOCVD, the reaction chamber is
the main body which composed by reactor walls, liner, susceptor, gas injection
units and temperature control units.

There are two main temperature should
be paid attention when heated substrate. One is around 550cetigrade and another is just above 1000centigrade. In
the low temperature condition there will be a buffer layer growing firstly
while in the high temperature gallium nitrate will grow directly. So in the
mass production the temperature should be controlled very well. The MOCVD
process has a controllable growth rate and great crystal quality.

The hydride
vapor phase epitaxy(HVPE) makes the gallium nitrate continue growing. The hydrogen
chloride is reacted at elevated temperature with group(III) metal to produce
gaseous metal chlorides. Then it will react with ammonia to produce group(III)metal

In the
separate ways, laser lift-off is better than natural separate. It use high
power pulsed laser directly to the surface. The energy of light is between Esubstrate
and EGaN..


The GaN can be used as power devices
because of its high dielectric strength and high efficient. Today GaN has been used
amount a large area from



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