Test: Fermi Level in a Semiconductor Having Impurities - Electrical Engineering (EE) MCQ

When the donor-type impurity is added to a crystal, first Nd states get filled because it is of the highest energy.

The correct position of the Fermi level is found with the formula in the ‘a’ option.

 When N_D=N_A, kTln(N_D/N_A )=0
So,
Ef=Ec.

whenever the temperature increases, the Fermi energy level tends to move at the centre of the energy gap.

When the temperature increases, there is an increase in the electron-hole pairs and all the donor atoms get ionized, so now the thermally generated electrons will be greater than the donor atoms.

The diagram A refers the most suitable energy level diagrams because Efp>Ef>Efi>Efp>Ev.

Quasi-fermi level is defined as the change in the level of the Fermi level when the excess chare carriers are added to the semiconductor.

When the Ef is in the middle of the energy level, it indicates the equal concentration of the holes and electrons.

=1.38*10^-23*300*ln(10¹³+10¹⁵/10¹³)
=0.2984 eV.

Using the same equation,

Substituting the respective values,
E_Fi – E_Fp=0.1792 eV.