# Electronic Devices and Circuits Questions and Answers – Band Structure of an Open-Circuited p-n junction

This set of Electronic Devices and Circuits Questions and Answers for Experienced people focuses on “Band Structure of an Open-Circuited p-n junction”.

1. The conduction band edge in the p material is not at the same level to that of conduction band edge in the n material. Is it true or false?
a) True
b) False

Explanation: In a p-n junction diode, the energy levels of the p material and n material will not be at same level. They will be different. So, the conduction band edge as well as the valence band edge of the p material will not be same to that of the n material.

2. Which of the following equations represent the correct expression for the shift in the energy levels for the p-n junction?
a) Eo = Ecn – Ecp
b) Eo = Ecp – Ecn
c) Eo = Ecp + Ecn
d) Eo = -Ecp – Ecn

Explanation: The shift in the energy of the energy level will be the difference of the conduction band edge of the p material and conduction band edge of n material. In the energy level diagram, the conduction band edge of p material is higher than that of the n material.

3. Calculate the Eo given that Nd=1.5*1010cm-3, Na=1.5*1010cm-3 at temperature 300K?
a) 1.5*1010eV
b) 0.256eV
c) 0eV
d) 4.14*10-21eV

Explanation: Eo=kTln((Nd*Na)/(ni)2)
Substituting k=1.38*10-23/K, T=300k and the values ofNd,Naand ni,
We get
Eo=0eV.

4. In a p-n junction, the valence band edge of the p material is greater than which of the following band?
a) Conduction band edge of n material
b) Valence band edge of n material
c) Conduction band edge of p material
d) Fermi level of p material

Explanation: When the p-n junction is formed, the energy levels of the p- material go higher than the n material. That’s why the valence band of the p material will be greater than that of the n material.

5. Which of the following equations represent the correct expression for the band diagram of the p-n junction? (E1=difference between the fermi level of material and conduction band of n material and E2=difference between the conduction band of n material and fermi level of n material)
a) Ecn – E f = (1/2)*EG – E1
b) Ecn – E f = (1/2)*EG – E2
c) Ef – Ecp = (1/2)*EG – E1
d) Ecn – Ef = (1/2)*EG + E1

Explanation: From the energy band diagram of the p-n junction, the option ‘a’ satisfies that band diagram.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

6. Calculate the value of Eo when pno=104cm-3 and ppo=1016cm-3 at T=300K.
a) 1meV
b) 0.7meV
c) 0.7eV
d) 0.1meV

Explanation: Eo=kTln(ppo/pno)
Substituting the values, we get
Eo=0.7eV.

7. Calculate the value of Dp when µp=400cm/s and VT=25mV.
a) 1
b) 0.01
c) 0.1
d) 10

Explanation: Dp= µp*VT
=400*10-2*25*10-3
=0.1.

8. What is the value of kT at room temperature?
a) 0.0256eV
b) 0.25eV
c) 25eV
d) 0.0025eV

Explanation: kT=1.38*10-23*300K
=4.14*10-21/ (1.6*10-19)
=0.0256eV.

9. Is Vo depends only on the equilibrium concentrations. Is it true or false?
a) True
b) False

Explanation: Vo is the contact potential of the junction when the junction is in equilibrium. If, the junction is not in the equilibrium, Vo can’t be calculated.

10. Calculate Vo when ppo=1016cm-3, pno=104cm-3 and Vt=25mV.
a) 69V
b) 6.9V
c) 0.69V
d) 0.069V

Explanation: Vo=VT ln⁡(ppo/pno )
=25*10-3*ln(1016/104)
=0.69V.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

To practice all areas of Electronic Devices and Circuits for Experienced people, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]