Basic question about doping in CMOS

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Simon-circuit

Joined Sep 12, 2016
3
The following picture shows a cross sectional view of a CMOS,in which, the channel of NMOS is P type, S/D is n+ type, while the channel of PMOS is N type, S/D is p+ type. Why is that? Is it feasible to dope the channel of NMOS with phosphorous (N type)? Thanks~
 

Bordodynov

Joined May 20, 2015
3,177
Generally everywhere Silicon, where impurities can be less than a millionth part (in the channel area). In the open channel of the n-channel transistor is not Phosphorus, but an excess of electrons. Sometimes the channel region of the n-channel transistor is additionally ligated by Bohr (ion doping).
 

WBahn

Joined Mar 31, 2012
29,976
If the channel were N-type and it is between two N-type S/D regions, the wouldn't you have a conducting channel between source and drain even with no applied gate potential?

Consider what happens in the case of the NMOS transistor as a positive voltage is applied to the gate.

You might look at the difference between depletion mode and enhancement mode MOSFETs.

http://www.rfwireless-world.com/Terminology/Depletion-MOSFET-vs-Enhancement-MOSFET.html
 
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