Semiconductor Electronics: Materials, Devices and Simple Circuits Test 25

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 25

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Question 1
1 / -0

Electric current is due to drift of electrons in

A
Metallic conductors

B
Semiconductors

C
Both (a) and (b) above

D
None of the above

Solution

Answer is A.
When an electric field is applied across the metallic conductors the randomly moving electrons are subjected to electrical forces along the direction of the field. Due to this field, the electrons do not give up their randomness of motion, but they will be shifting towards higher potential. That means the electrons will drift towards higher potential along with their random motions.
In semiconductors, in addition to electrons, the travelling vacancies in the valence-band electron population (called 'holes'), act as mobile positive charges and are treated as charge carriers. Electrons and holes are the charge carriers in semiconductors.
Hence, electric current is due to drift of electrons in metallic conductors.
Question 2
1 / -0

Semiconductor without any impurities are

A
Intrinsic Semiconductor

B
Extrinsic Semiconductor

C
Both (a) and (b)

D
None of these

Solution
Question 3
1 / -0

When a small quantity of donor impurity is added to pure semiconductor, then resulting semiconductor is

A
n - type

B
p-type

C
p-n-type

D
None of these

Solution
Question 4
1 / -0

Semi conductor in pure form is ........................... semiconductor.

A
Intrinsic

B
Extrinsic

C
Real

D
None of these

Solution
Question 5
1 / -0

A hole is :

A
a positively charged electron

B
an electron in valence band

C
an unfilled covalent bond

D
an excess electron in covalent bond

Solution

If an electron is excited into a higher state it leaves a hole in its old state.
An unfilled covalent bond is also reffered to be a hole as it is also created by removal of an electron from the bond.
Question 6
1 / -0

A semiconductor at $$0^{\circ}K$$ is

A
Unstable

B
Stable

C
Neutral

D
Forward biased

Solution
Question 7
1 / -0

In P-N junction diode offers high resistance in ................. condition.

A
Forward bias

B
Inverse bias

C
Reverse bias

D
None of these

Solution
Question 8
1 / -0

In a p-type semiconductor, the majority carries are

A
Electrons

B
Holes

C
-ve ions

D
+ve ions.

Solution
Question 9
1 / -0

The energy gap in a conductor at room temperature is ________ .

A
greater than that in a semiconductor.

B
less than that in a insulator.

C
greater than that in a insulator.

D
Both (A) and (B) are true.

Solution

The energy band gap is the energy difference between 2 bands i.e. valence band and the conduction band. In case of conductors, energy band gap is very small almost overlapping whereas, in case of insulators, the band gap is ∼6 eV. So. band gap of conductors is less than insulators.
Question 10
1 / -0

Diffusion current in a p-n junction is greater than the drift current in magnitude

A
if the junction is forward-biased

B
if the junction is reverse-biased

C
if the junction is unbiased

D
in no case

Solution

In case of forward bias, the corresponding charge density on the two sides will increase as a result of which diffusion current will increase since it depends on the charge density. Drift current will be less as the junction charge density will be less and hence low electric field is present in opposite direction (due to positive external voltage).