What is a MOSFET but a plain old block of silicon with some terminals printed on it.  I start here with the most basic of components. Here are the relevant points:

  •  I want to think about N channel MOSFET so I start with P type material doped at Na=10^16 cm^-3
  • Area = A = 1cm x 1cm 
  • Length = 429cm   I chose this because mobility of Boron doping @10^16 = 429cm^2 / V*S

Line of reasoning

  • Apply 1 volt
  • In 1 second the carriers travel 429cm and thus all the charge in the entire block is swept out and totally replaced. 
  • Calculate R=V/I 
  • Compare with value calculated from the page below

Ncarriersinblock = L*A*Na

Qtotalinblock = qL*A*Na

Qtotalinblock = 1.6*10^16 * 429 * (1 * 1) * (1 *10^16) = 0.686 Coulomb

but this is the amount of charge swept out in 1 second from the silicon bar so 

I = 0.686 Ampere

Remember 1 volt was applied to get the 429cm/second carrier velocity and thus

R = 1/0.686= 1.45 Ampere   Which agrees with the calculated value from the first web link reference below.

 

Research Links

Categories: MOSFET Basics

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