Introduction of conduction band of GaN is

Introduction    GaN(gallium nitride) is a typical third generation materials of wide band gapsemiconductors in Material field. Compared with formal semiconductor materials,GaN (gallium nitride) has a higher frequency, higher power, and higher densityfor making integrated electronics. What’s more, the strong radiation resistanceability for GaN (gallium nitride) could also make great contributions inmicrowave power devices filed. Properties for GaN(gallium nitride)  GaN (Gallium nitride) is very hard and stable chemical compound and it’smelting point is about 2000K.

Generally, the atomic structure for GaN (galliumnitride) is closed-packed hexagonal structure and that results in relativelylow symmetry of lattice and strong piezoelectricity and ferroelectricity.   GaN (Gallium nitride) is regard as wide band gap semiconductor. The bandgap is 3.4 eV and thermal conductivity is 1.3 W/cm*K.

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This two factors lead tothe GaN (Gallium nitride) has a high working temperature and breakdown voltageand a strong ability of radiation resistance. The bottom of conduction band ofGaN is at ? position which makes a huge energy difference with other with othervalley to resist the scattering between different valleys. As a result, GaN hasa very high saturated drift velocity of electrons.  Generally, wide-band gap semiconductors materials have band gaps in therange of 2-4 eV, whereas typical semiconductors have band gaps in the range of1-1.5 eV. Higher energy of band gap makes it suitable for working in a hightemperature. Wide band gap semiconductors are associated with a high voltage.

This is due to a large electric filed to generate carries through impactmechanism.  However, GaN also has itsshortcomings. Because of it structure of energy bond, the electron mobility isrelatively low while the charge carriers have a high valuable mass.

 Preparation for GaN(gallium nitride) Thepreparation of GaN (gallium nitride) includes four main steps: metalorganicchemical vapor deposition, hydride vapor phase epitaxy, separation and secondgrowth.In theMOCVD step, ultra-pure gases are transferred into a reactor and finally resultin a deposition of a very thin layer of atoms onto a semiconductor wafer. Forinstance, Pin can be grown in a heated substrate by trimethylindium andphosphine.The precursormolecular decomposition happens in the absence of oxygen. As to the equipment,the reaction chamber is the main body that is composed by reactor walls, liner,susceptor, gas injection units and temperature control units.Besides, twotemperature should be carefully noticed when we heat the substrate. One isaround 823K and another is around 1273K. In the lowtemperature 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 HVPE makes the GaN (gallium nitrate) grow continually.

The hydrogenchloride is reacted at a certain temperature while the group (III) metal producinggaseous 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 thannatural separation which uses high power pulsed laser directly to the surface. Application    One ofthe typical application for GaN (gallium nitride) is power devices.

ComparedGaN (gallium nitride) with other materials, it has relatively small volume andhigh efficiency to transport. Nowadays, as the popularization of 4G cell siteand wireless power, the potential market could be expected too. Conclusion    Besidesfrom the strong ability for GaN (gallium nitride) to transport information, thehigh luminous efficiency of GaN (gallium nitride) also could be applied to theLED.

For instance, many companies have put their eye on the research andexploitation on GaN (gallium nitride) materials, like Samsung, Mitsubishi etc.   Accordingto the graph mentioned on the slides, it can easily show us the promisingfuture of GaN (gallium nitride), the statistics also show that the total valuein US in 2015 has arrived at 298 million Dollars, and many of the cost isconcentrated on wireless infrastructure. 


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