IntroductionThe history for human lighting is from candlesto lamps. But nowadays the most popular lights is LED. GaN(gallium nitrate) isone of the main source to product LED. The compound has been studied for about30 years.
In 1989 the Japanese scientist isamu akasaki successfully made bluelight emitting diode(LED) from GaNand he created the new measures for GaNgrowth.procedureThe preparation of GaN has four main steps (metalorganicchemical vapor deposition, hydride vapor phase epitaxy, separate and secondgrowth)In the MOCVD step ultra-pure gases areinjected into a reactor and finally deposit a very thin layer of atoms onto asemiconductor wafer. For example PIn can be grown in a heated substrate whichmade up by trimethylindium and phosphine. The precursor molecular decompose inabsence of oxygen. So the atoms connect to substrate surface and a newcrystalline layer as been grown.
In the machine of MOCVD, the reaction chamber isthe main body which composed by reactor walls, liner, susceptor, gas injectionunits and temperature control units.There are two main temperature shouldbe paid attention when heated substrate. One is around 550cetigrade and another is just above 1000centigrade. Inthe low temperature condition there will be a buffer layer growing firstlywhile in the high temperature gallium nitrate will grow directly.
So in themass production the temperature should be controlled very well. The MOCVDprocess has a controllable growth rate and great crystal quality.The hydridevapor phase epitaxy(HVPE) makes the gallium nitrate continue growing. The hydrogenchloride is reacted at elevated temperature with group(III) metal to producegaseous metal chlorides.
Then it will react with ammonia to produce group(III)metalnitride.In theseparate ways, laser lift-off is better than natural separate. It use highpower pulsed laser directly to the surface.
The energy of light is between Esubstrateand EGaN..ApplicationThe GaN can be used as power devicesbecause of its high dielectric strength and high efficient. Today GaN has been usedamount a large area from