Semiconductor Electronics Materials Devices & Simple Circuits

Previous Years' CBSE Board Questions

14.2 Classification of Metals. Conductors and Semiconductors

MCQ

1. The energy required by an electron to jump the forbidden band in silicon at room temperature is about
2. 0.01 eV (b) 0.05 eV
3. 0.7 eV (d) 1.1 eV

V5A (1 mark)

2 The ____, a property of materials C, Si and Ge depends upon the energy gap between their conduction and valence bands. (2020)

SAI (2 marks)

1. What is meant by energy band gap in a solid? Draw the energy band diagrams for a conductor, an insulator and a semiconductor. (Term II 2021-22)
2. in the conduction band.
3. Distinguish between a metal and an insulator on the basis of energy band diagrams. (Foreign 2014)

SAII (3 marks)

1. Draw a plot showing the variation of resistivity of a (i) conductor and (ii) semiconductor, with the increase in temperature. (2/3, Delhi 2014C)
2. Write any two distinguishing features between conductors, semiconductors and insulators on the basis of energy band diagrams. (AI 2014) R

14.3 Intrinsic Semiconductor

MCQ

1. Assertion (A): The resistance of an intrinsic semiconductor decreases with increases in its temperature.

Reason (R): The number of conduction electrons as well as hole increase in an intrinsic semiconductor with rise in its temperature.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A)
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the

density of holes but the crystal maintains an overall

charge neutrality.

Reason (R): The charge of electrons donated by

donor atoms is just equal and opposite to that of the

ionised donor.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.
4. Assertion (A) is false and Reason (R) is also false. (2023)

In an n-type semiconductor, the donor energy level lies (a)

1. just below the conduction band.
2. just above the valance band.

When the temperature of an n-type semiconductor

is increased, then the

1. number of free electrons increases while that of the holes decreases.
2. number of holes increases while that of the free electrons decreases.
3. number of free electrons and holes remains unchanged.
4. number of both the free electrons and the holes increase equally. (2020 C)

SAI (2 marks)

Name the extrinsic semiconductors formed when

a pure germanium is doped with (i) a trivalent and

(ii) pentavalent impurity. Draw the energy band

diagrams of extrinsic semiconductors so formed.

(Term II 2021-22)

1. What is meant by doping of an instrinsic semiconductor? Name the two types of atoms used for doping of Ge/Si. (Term II 2021-22)
2. Distinguish between 'intrinsic' and 'extrinsic' semiconductors. (Delhi 2015) R

Assertion (A)

1. Assertion (A) is true, but Reason (R) is False.
2. Assertion (A) is false, but Reason (R) is true.

(2023)

14.4 Extrinsic Semiconductor

MCQ

Assertion (A): In 'n' type semiconductor, number density of electrons is greater than the number

these energy levels play in conduction and valence bands. (Al 2019, Al 2015 C) [II]

D 100 Ω

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1. (i) Distinguish between n-type and semiconductors on the basis of energy band diagrams.

1. Compare their conductivities at absolute zero temperature and at room temperature.

(Delhi 2015C)

0.5 V

(a) Forward biasing, 0 A (b) Reverse biasing, 0 A (c)

14.5 p-n Junction

SA II (3 marks)

At equilibrium, in a p-n junction diode the net current is (a)

1. Explain the formation of a p-n junction.
2. Can we take one slab of p-type semiconductor and physically join it to another n-type semiconductor to get a p-n junction? Explain

(2022 C)

(2020)

1. Answer the following, giving reason:
2. The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased.
3. Doping of intrinsic semiconductors is a necessity for making electronic devices.

(Term II 2021-22)

1. Write the two processes that take place in the formation of a p-n junction. Explain with the help of a diagram, the formation of depletion region and barrier potential in a p-n junction. (Delhi 2017)

OR Explain with the help of the diagram the formation of depletion region and barrier potential in a p-n junction. (2/3, Al 2016) OR Write briefly the important processes that occur during the formation of p-n junction. With the help of necessary diagrams, explain the term barrier potential. (Foreign 2015)

SAII (3 marks)

14. Draw the energy band diagram of (i) n-type, and

(ii) p-type semiconductors at temperatures T > 0 K.

In the case of n-type Si-semiconductor, the donor

energy level is slightly below the bottom of

conduction band whereas in p-type semiconductor,

the acceptor energy level is slightly above the top of

valence band. Explain, giving examples, what role do

14.6 Semiconductor Diode

MCO

The threshold voltage for a

p-n junction diode used in

the circuit is 0.7 V. The type

of biasing and current in the

circuit are

1. due to drift of minority charge carriers.
2. zero as diffusion and drift currents are equal and opposite.
3. zero as no charge carriers cross the junction.

VSA (1 mark)

In an unbiased p-n junction diode, the p-side of the

junction is at _____ potential as compared to that

on the n-side of the junction. (2020)

How does an increase in doping concentration

affect the width of depletion layer of a p-n junction

diode? (2020) (Ap)

SAI (2 marks)

25. Explain the formation of the barrier potential in a

1. n junction. (Term II 2021-22) U

1. With the help of the circuit diagram, explain the working of a silicon p-n junction diode in forward biasing and draw its I-V characteristics. (2020 C)
2. Explain the term 'depletion layer' and 'potential barrier' in a p-n junction diode. How are the (a) width of depletion layer, and (b) value of potential barrier affected when the p-n junction is forward biased? (2020)
3. Draw V-I characteristics of a p-n junction diode. Explain, why the current under reverse bias is almost