power semiconductor construction

[beenish fd]

can anyone tell me that in power applications, why semiconductor materials use an additional layer called epitaxial growth layer?what is the usage of this extra layer?

 

[mtwieg]

Epitaxial layers are useful when you want to have highly doped regions deep under the active device area. You start out with a normal wafer, then create those deep doping regions on the surface of the wafer. Then you grow the epitaxy on top of that. At that point you have undoped Si on top of a buried doped layer, which isn't feasible to achieve without epitaxy.

 

[beenish fd]

thank u sooo much.....

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next thing i want to no that, after adding epi layer how current will flow...

 

[mtwieg]

Depends on what specific device geometry you're building (DMOS, LDMOS, CMOS, bjt, igbt, etc).

 

[dick_freebird]

Your voltage standoff goes with distance, and inverse
to doping where your blocking depletion region will be.
You want a good low ohmic backside for current but
a lightly doped layer above, of high quality. An implant
that was capable of hammering the backside and broad
(tWafer-xDeplExtent) would (a) probably be impossible
to get - check out energies required for, say, a 20um
depth) and (b) really damage the intervening silicon.
Epi growth is well known art, clean and controllable
and about as defect free as the starting material and
equipment set.

 

[beenish fd]

And what is modulation conductivity?