Introduction high power pulsed laser directly to the

Introduction

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
growth.

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procedure

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

In the MOCVD step the pure gases are put into
a reactor and finally deposit a very thin layer of atoms onto a semiconductor
wafer. As an example PIn can be grown in a heated substrate which made up from trimethylindium
and phosphine. The initial molecular decompose in absence of oxygen. So the
atoms can connect to substrate surface and a new crystalline layer has been
appeared.

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
nitride.

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..

Application

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 micro wave heating to 4G cell site. There are many
companies have focus on the development and research of GaN Such as SAMSUNG and
MITSUBISHI ELECTRIC. Although there are some problems lie high density of
heterogeneous epitaxial defect the GaN still has a large market.