Introduction high-power devices and high Frequency microwave

Introduction The history for human lighting is from candles to lamps. Nowadays the most popular lighting way is LED has been made from GaN. This study has made great breakthrough in 1989.It has wide direct bandgap, strong atomic bonds, high thermal conductivity, good chemical stability (almost no acid corrosion) and other properties and strong anti-radiation ability. It has a broad prospects in optoelectronics, high-temperature high-power devices and high Frequency microwave device applications.  PropertiesGaN is very hard and stable chemical compound and it’s melting point is about 2000K. Generally, the atomic structure for GaN is closed-packed hexagonal structure and that results in relatively low symmetry of lattice and strong piezoelectricity and ferroelectricity. This describes when the lattice suffers from certain direction pressure or tension, the vertical surface of the coming force will obtain equal quantity inverse charges at two sides. The Ferroelectricity describes the spontaneous polarization when the structure of lattice don’t have a center of symmetry that makes the gravity which is the center of charges don’t coincide together leading to the electric moment and is not equal to 0. The two factors lead to very strong piezoelectric polarization and spontaneous polarization, totally it generates 5(MV/cm) which’s called breakdown electric energy. PreparationThe preparation of GaN (gallium nitride) includes four main steps: metalorganic chemical vapor deposition, hydride vapor phase epitaxy, separation and second growth.In the MOCVD step, pure gases are transferred into a reactor and finally deposit to a very thin layer of atoms onto a semiconductor wafer. For instance, PIn can be grown in a heated substrate which made up from trimethylindium and phosphine.The initial molecular decomposition in the condition without oxygen. As to the MOCVD machine, the reaction chamber is the main body that is composed by reactor walls, liner, susceptor, gas injection units and temperature control units.Besides, two temperature should be paid attention when we heat the substrate. One is around 550? and another is around 1000? In the low temperature condition, there will be a buffer layer growing firstly. However, in the high temperature, GaN (gallium nitrate) will grow directly.  So the temperature should be controlled.The hydride vapor phase epitaxy (HVPE) makes the GaN continue growing . The hydrogen chloride is reacted at elevated temperature while the group (III) metal producing gaseous metal chlorides and then it will react with ammonia to produce group (III) metal nitride.As to the separation part, the technique of laser lift-off is better than natural separation which uses high power pulsed laser directly to the surface. The energy of light is between Esubstrate and EGaN. ApplicationsOne of the typical application for GaN is power devices. Compared GaN with other materials, it has relatively small volume and high efficiency to transport. Nowadays, as the popularization of 4G cell site and wireless power, the potential market could be expected too.Besides from the strong ability for GaN to transport information, the high color rendeing index and luminous efficiency of GaN also could be applied to the LED.For instance, many companies have put their eye on the research and exploitation on GaN materials, like Samsung, Mitsubishi etc.Although there are some problems such as the high density of heterogeneous epitaxial defect, the GaN semiconductor materials have had enough market competitiveness. The red LED consist of the In GaN, AlGaP and AlGaAs produce the High-brightness panchromatic display. The three primary colors mixed white light source also opens up new applications.  ConclusionGaN can be used in different areas such as consumer( air conditioner, washing machine), datacenter( UPS, cellular base stations), industrial( motor, pump), space( aviation power modules, power switching modules), transportation( EV traction inverter, on-board battery charger). It you want, you can find the trace of GaN everywhere.


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