.SiC BJT problem

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aina

Joined Aug 22, 2011
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I am working on the the tcad simulation of Silicon Carbide BJT. While working i have to apply different physics models ondifferent regions. Can anybody tell me the Physics Process happening in the collecter i.e, drift , electric field etc
 

Wendy

Joined Mar 24, 2008
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Last I heard a BJT (bipolar junction transistor) uses silicon or germanium with a several very light doping agents. Carbide might be the doping agent, but I'm a little leary of the assertion. Have any references?
 

Wendy

Joined Mar 24, 2008
22,164
OK, the key is the pure material (silicon or germanium) and the light doping impurities. I don't remember the elements used off the top of my head, but it is less than 1 part per million, one creates a positive biased material, the other negative.

This creates a material (basically silicon) with a surplus of electrons on one side, and a deficit of electrons on the other, which creates the classic PN junction diodes use. A transistor is a PNP or NPN junction, 3 layers.

You can't actually isolate the collector from the rest of the transistor. By adding or removing electrons on the base material you electrically bring the emitter closer to the collector, and it starts to conduct. The more electrons (or less, depending on type of transistor) the more conductive the base becomes and allows flow between the collector and emitter. I am sure my explanation is wrong in the particulars, a better one can be found here...

http://www.allaboutcircuits.com/vol_3/chpt_2/8.html

Thing is, a lot of this is quantum effects, so some counter intuitive stuff comes along with it. The BE (base emitter) when conducting current drops a diode type voltage, for silicon this is around 0.6 or more volts. If the transistor is saturated, another way of saying fully on, the CE (collector emitter) can drop less than 0.1 volts. The base and the collector don't interact much, both are interacting with the emitter.

If you want something that involves electric fields that would be more in the FET type transistors. FETs, and their cousins, MOSFETs, are totally different that BJTs, and have a totally different theory of operation.
 
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