SEMICONDUCTORS

Electronic Devices Semiconductor Electronics:

Very Short Answer Questions

1. What is intrinsic semiconductor?

2. What is an extrinsic semiconductor?
3. How does the conductance of a semiconducting material change with rise in temperature?
4. What is the order of energy gap in a semiconductor?
5. How does the conductivity of a semiconductor change with temperature?
6. What is the Fermi Level?
7. What is doping?
8. What type of impurity is added to obtain n-type semiconductor?
9. What type of impurity is added to obtain p-type semiconductor?
10. How does the energy gap in an intrinsic semiconductor vary, when doped with pentavalent impurity?
11. What is meant by the term doping of an intrinsic semiconductor? How does it affect the conductivity of a
semiconductor?
12. How resistance varies in semiconductor with temperature?
13. What type of charge carriers are there in a p-type semiconductor?
14. What type of charge carriers are in n-type semiconductor?
15. Draw the energy band diagram for semiconductor.
16. Draw energy band diagram for a extrinsic semiconductor.
17. Doping of arsenic in silicon leads to which type of semiconductor?
18. What is the effect of rise in temperature on the conductivity of copper and silicon
19. Why is a semiconductor damaged by a strong electric field?
20. What is P-type semiconductor?
21. Why germanium is preferred over silicon for making semiconductor devices?

Short Answer Questions

1. Distinguish between a metal and an insulator on the basis of energy bands.

Or
Explain the behaviour of metals, insulators and semiconductors on the basis of energy bands in solid.
2. What is intrinsic semiconductor? Why the conductivity of intrinsic semiconductor increases with rise of
temperature?
3. Distinguish between intrinsic semiconductor and extrinsic semiconductor.
4. Distinguish between n-type and p-type semiconductors on the basis of energy band diagram.
5. What is an intrinsic semiconductor? How can you convert an intrinsic semiconductor into N-type extrinsic
semiconductor?
6. Differentiate between P-type and N-type semiconductor.
Or
Give any three points of difference between P-type and N-type semiconductor. (P.S.E.B. 2004)

7. How does the resistance of (i) good conductor, (ii) semiconductor change with rise of temperature
8. Compare N-type and P-type semiconductors.
9. How is a p-type semiconductor formed? Name major charge carriers in it? Draw energy band diagram of a a
p-type semiconductor?
10. The ratio of number density of free electrons to holes /n for two different materials A & B are equal to one or
less than one respectively. Name the type of semiconductors to which A and B belong. Draw energy level
diagrams for A & B.
11. Derive an expression for conductivity in case of intrinsic semiconductor
12. What is semiconductor? What do you mean by n-type and p-type semiconductor?
 13. What do you mean by 'hole' in a semi- conductor? Write its three characteristics
14. Distinguish between conductor, insulator and semiconductor on the basis of their energy bands.
15. Distinguish between n-type and p-type semiconductor on the basis of energy diagram.
16. What is doping? Why is it done

Long Answer Questions

1. Distinguish between metals, insulators and semiconductors on the basis of energy band diagrams. Indicate
against each of the following if it is a conductor, a semiconductor or an insulator.
2. Explain the formation of energy bands in solids. On the basis of energy bands, distinguish between (i) a
metal (ii) insulator and (iii) a semiconductor
3. How are energy bands formed in solids? Explain the behavoiur of metals, insulators and semiconductors on
the basis of energy bands in solids.
4. Distinguish between conductors, semi- conductors and insulators on the basis of band theory of solids.
5. Explain how an intrinsic semiconductor can be converted into (i) n-type and (ii) p-type semiconductor? Give
one example of each and their energy band diagram.
6. Using the concept of electron current and hole current, derive expression for conductivity of semiconductor.
7. Derive the expression for current through a semi conductor. Obtain expressions for electrical resistivity and
conductivity of a semiconductor.
8. Describe how N-type and P-type semiconductors are formed. Name the dopant and majority carrier in each
type of semiconductors you describe.
9. What do you mean by Doping? State the necessary conditions for doping ? What are the various methods o
doping ?
10. Explain the formation of energy bands in solids. Draw energy band diagrams for (i) a conductor, (il) an
intrinsic semiconductor.

Numerical

1. A semiconductor has the electron concentration 0.45X 10^{12}m^{-3 and hole concentration 5X10^{20}m^{-3}
Find its conductivity. Given electron mobility 0.135~m^{2}V^{-1}s^{-1} and hole mobility 0.48 m² V-1s-1.

2. A semiconductor has the electron concentration f~8X10^{13}cm^{-3} and hole concentration X10^{12}cm^{-3} Is
this semiconductor P-type or N-type? Also calculate the resistivity of this semiconductor. Given: Electron mobility
=24000~cm^{2} V-1 s-¹ and hole mobility = 200 cm² v^{-1}s^{-1}
[Ans. N-type, 3-3 × 10-2 mho m^{-1}]

Very Short Answer Questions

1. What is p-n junction diode ?

2. What causes depletion region in a p-n junction?
3. In the given diagram, is the diode D forward or reversed biased?
4. Which type of biasing gives a semiconductor diode very high resistance ?
5. When the voltage drop across a p-n junction diode is increased from 0.65 V to 0.70 V, the charge in the
diode current is 5 mA. What is the dynamic resistance of the diode?
6. Draw a circuit diagram for the use of a p- n junction diode as a full wave rectifier.
7. How does the junction width change when p-n junction is forward biased?
8. What is a rectifier ?
9. Give the threshold voltage for a (i) silicon diode (ii) germanium diode.
10. Draw a p-n junction with reverse bias.
 11. Draw the circuit of a PN junction with forward bias.
12. What is depletion region in a p-n junction?
13. How is a p-n junction diode formed?
14. What do you mean by forward biasing and reverse biasing of a p-n junction diode?
15. Draw a labelled voltage-current curve for a junction diode and explain it briefly.
Or
Draw the characteristics of a p-n junction diode.
16. Draw a circuit diagram for p-n junction diode in forward bias. Sketch the voltage versus current graph for the
same.
17. Distinguish clearly between forward biasing and reverse biasing of junction diode.
18. What is a rectifier? On what principle does it works?
Or
What do you mean by rectification? Draw a neat and labelled circuit diagram to show how junction
diode acts as a half wave rectifier.
19. Discuss the action of a p-n junction diode in (i) forward bias arrangement, (ii) reverse bias arrangement.
20. What are the advantages and disadvantages of semiconductor devices over vacuum tubes?

Long Answer Questions

1. Explain the formation of potential barrier and depletion region in a p-n junction.
2. What is a p-n junction diode? Explain with the help of a diagram, how depletion region is formed near the
junction ? Explain also what happens to this layer when the junction is
i) forward biased and (ii) reversed biased.
Or
What is p-n junction diode ? With the help of a diagram, explain the formation of potential barrier and depletion
region in it. On what factors, does the magnitude of potential barrier of p-r junction diode depend ?
3. Define the terms 'potential barrier' and 'depletion region' for a p-n junction. Explain with the help of a circuit
diagram, the use of a p-n junction as a full wave rectifier. Draw the input and output wave diagram.
4. Explain the formation of a p-n junction and effect of forward and reverse bias on it.
5. What is a p-n junction diode? Define the term 'dynamic resistance' for the junction diode. With the help of a
circuit diagram explain the working of a p-n junction diode as a full wave rectifier.
6. Define the terms 'potential barrier' and 'depletion region' for a p-n junction diode. State how the thickness of
depletion region. will change when the p-n junction diode is (a) forward biased (b) reverse biased.
7. What is rectification ? How can a diode valve be used as a half wave rectifier?
Or
What is rectification? With the help of necessary circuit diagram, give working of a diode as a half
wave rectifier.
8. What is a p-n junction? Discuss its action in forward bias and reverse bias arrangement.
9. Explain the forward and reverse bias characteristics of a p-n junction. Draw the rectifier. Circuit diagram of a
p-n diode as a full wave
10. Explain full wave rectifier function of diode with diagram?
11. How is a junction diode formed? Discuss the working of a junction diode as a rectifier ?
Or
Discuss the use of a p-n junction diode as a full wave rectifier.
12. Explain the use of a p-n junction diode as a rectifier. Draw the circuit diagram of a full wave rectifier and
explain its working. Draw the input and output waveform.
13. What is a p-n junction diode ? Draw its characteristic curves with the help of a circuit diagram explain the
working of a p-n junction diode as a full wave rectifier. Draw the input and output waveform.