Engineering Questions with Answers - Multiple Choice Questions
MCQs on Charge Densities in a Semiconductor impurities
1 - Question
Is n/p=ni2 is a correct formula?
a) True
b) False
View Answer
Answer: b
Explanation: The correct formula is n*p=ni2.
2 - Question
Calculate the number of electrons is the number of holes are 15*1010?
a) 15*1010
b) 1.5*108
c) 1.5*109
d) 1.5*1010
View Answer
Answer: c
Explanation: n*p=(1.5*1010)2
n*15*1010=1.5*1.5*1010*1010
n=1.5*109 electrons.
3 - Question
For which type of material, the number of free electron concentration is equal to the number of donor atoms?
a) P type semiconductor
b) Metal
c) N-type semiconductor
d) Insulator
View Answer
Answer: c
Explanation: The n-type semiconductor has equal concentration of free electron and donor atoms.
Explanation: The n-type semiconductor has equal concentration of free electron and donor atoms.
4 - Question
Identify the correct condition for a semiconductor to be electrically neutral.
a) Nd+p=Na+n
b) Nd-p=Na+n
c) Nd+p=Na-n
d) Nd-p=Na-n
View Answer
Answer: a
Explanation: The sum of the number of donors and the holes is equal to the sum of the number of the acceptors and the electrons.
5 - Question
Do the Fermi energy level changes in a semiconductor?
a) True
b) False
View Answer
Answer: a
Explanation: 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.
6 - Question
Consider a silicon wafer having Nc=2.8*1019cm-3 and the Fermi energy is .25eV below the conduction band. Calculate the equilibrium concentrations of electrons at T=300K?
a) 18*1016cm-3
b) 1.8*1016cm-3
c) 1.8*1014cm-3
d) 180*1016cm-3
View Answer
Answer: a
Explanation: n0=Nc*exp(-Eg/KT)=2.8*1019*exp(-0.25/0.0259)
=18*1016cm-3.
7 - Question
If Ef>Efi, then what is the type of the semiconductor?
a) n-type
b) P-type
c) Elemental
d) Compound
View Answer
Answer: a
Explanation: 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.
8 - Question
The 1-fF (E) increases in which of the following band for n type semiconductor?
a) Conduction band
b) Donor band
c) Acceptor band
d) Valence band
View Answer
Answer: d
Explanation: For an n-type semiconductor, the probability of fF (E) decreases in the valence band. The probability of finding the electron in the conduction band is more.
9 - Question
The fF (E) decreases in which of the following band for p-type semiconductor?
a) Conduction band
b) Donor band
c) Acceptor band
d) Valence band
View Answer
Answer: a
Explanation: 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.
10 - Question
Do the intrinsic Fermi energy level changes with the addition of dopants and acceptors?
a) True
b) False
View Answer
Answer: b
Explanation: 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.