Test: Charge Densities in a Semiconductor Impurities - Electrical Engineering (EE) MCQ

The correct formula is n*p=ni².

n*p=(1.5*10¹⁰)²
n*15*10¹⁰=1.5*1.5*10¹⁰*10¹⁰
n=1.5*10⁹ electrons.

The n-type semiconductor has equal concentration of free electron and donor atoms.

The sum of the number of donors and the holes is equal to the sum of the number of the acceptors and the electrons.

The Fermi energy level changes as the electron and hole concentrations change because of the formula which defines the position of the Fermi level depending on the concentration of holes and electrons.

 n0=Nc*exp(-Eg/KT)=2.8*10¹⁹*exp(-0.25/0.0259)
=18*10¹⁶cm^-3.

For n-type, the Fermi energy level is greater than the intrinsic Fermi energy level because in an energy band, Fermi level of donors is always greater than that of the acceptors.

For an n-type semiconductor, the probability of f_F (E) decreases in the valence band. The probability of finding the electron in the conduction band is more.

The probability of finding the electron in the conduction band decreases for a p-type semiconductor because in a p-type semiconductor, the holes will be in conduction band rather than the electrons.

The intrinsic Fermi energy level always remains constant because it is an imaginary level taken to distinguish between the Fermi level of the types of semiconductor.