# Question about the Fermi potential of NMOS and PMOS!!!

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#### leonken

##### Full Member level 3 fermi potential

Is the Fermi potential of NMOS the same as the Fermi potential of PMOS?
The Fermi potential of NMOS is a positive quantity. Is the Fermi potential of PMOS
is a negative quanatity?
Please tell me. Thanks

#### wchu01

##### Member level 3 fermi potential nmos

The fermi level for intrinsic silicon would be the intrinsic fermi level. With reference to this intrinsic level, should it be a n-type silicon the fermi level would be shifted up to the conduction band and for the p-type, the fermi level would be down to the valence band.

Equation:

(Fermi Energy) - (Intrinsic Energy) = kt In ((Donor Concentration)/(Intrinsic carrier concentration) -- (P-type)

(Intrinsic Energy ) - (Fermi Energy) = kt In ((Acceptor Concentration)/(Intrinsic carrier concentration) -- (N-type)

Hopefully this helps.

#### Sergiu_Q

##### Full Member level 3 fermi potential pmos

The Fermi energy, Ef, is the energy associated with a particle, which is in thermal equilibrium with the system of interest. The energy is strictly associated with the particle and does not consist even in part of heat or work. This same quantity is called the electro-chemical potential, µ in most thermodynamics texts .
Quasi-Fermi energies are introduced when the electrons and holes are clearly not in thermal equilibrium with each other. This occurs when an external voltage is applied to the device of interest. The quasi-Fermi energies are introduced based on the notion that even though the electrons and holes are not in thermal equilibrium with each other, they still are in thermal equilibrium with themselves and can still be described by a Fermi energy which is now different for the electrons and the holes. These Fermi energies are referred to as the electron and hole quasi-Fermi energies, Fn and Fp.
...but .... as you can see in the picture (Peltier coefficient for p-type (top curve) and n-type (bottom curve) silicon as a function of temperature) , the Peltier coefficient is positive for p-type silicon and negative for n-type silicon at low temperature. The semiconductor becomes intrinsic at high temperature. Given that the mobility of electrons is higher than that of holes, the Peltier coefficient of intrinsic silicon is negative.
The Peltier coefficient is the thermo-electric power in Volt/Kelvin and is noted with Π and is equal with T*P wher P is the thermo-electric power who have positive value for p and negatives for n

#### leonken

##### Full Member level 3 fermi energy kt

It means that the substrate material determines the quantity of Fermi potential .
For the same susbstrate the Fermi potential is the same for NMOS and PMOS.
Am I right?

#### Sergiu_Q

##### Full Member level 3 fermi potential in n type

almost the particle energy is given by the Fermi energy. if you have same substrate means your particle are in same system but with different values because of n and p

n= Nc exp [(Fn-Ec)/kT] and p= Nv exp[(Ev-Fn)/kT]

this subject is very complex and I hope I don't make to many mistakes

#### leonken

##### Full Member level 3 typical fermi potential values for nmos

And I have another question.
I am now designing a reference circuit.
How about the temperature performance or temperature coefficient of the Fermi potential?
thanks!

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