Semiconductor Electronics: Materials, Devices and Simple Circuits Test 33

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 33

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Question 1
1 / -0

What change could be seen when dopant atoms are added to an intrinsic semiconductor?

A
It will change the proton and hole carrier concentrations of the semiconductor

B
It will change the temperature of the semiconductor

C
It will change the electron and hole carrier concentrations of the semiconductor

D
It will decrease the formation of free electrons in the semiconductor

Solution

In an intrinsic semiconductor under thermal equilibrium the concentration of dopant affects the concentrations of electrons and holes.
That is,
$$n=p=n=n_{i}$$
where,
$$n\longrightarrow$$concentration of electrons.
$$p\longrightarrow$$concentration of holes.
$$n_{i}\longrightarrow$$Intrinsic concentration at given temperature.
So, when dopant atoms are added to an intrinsic semiconductor, it will change the electrons and holes carrier concentration of the semiconductor.
Question 2
1 / -0

Energy band gap between valence band and conduction band for insulator is:

A
Zero

B
greater than $$9\ eV$$

C
less than conductors

D
approximately $$1\ eV$$

Solution

An insulator does not have any electrons in its conduction band at room temperature. This implies that the energy of the electrons at room temperature is insufficient to jump from the valence band to the conduction band. Therefore, an insulator has significant band gap. The gap must be greater than 9eV.
Question 3
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Energy band gap between valence band and conduction band for conductor is:

A
more than semiconductors

B
Zero

C
more than insulators

D
None of these

Solution

A conductor always has electrons present in its conduction band irrespective of the temperature. This means that even when the electrons don't possess any energy, they lie in the conduction band. This is possible only if the energy gap between the valence band and conduction band is zero.
Question 4
1 / -0

Conductors are materials having an electrical conductivity :

A
greater than $$10^3$$ S/cm

B
between $$10^{-8}\ to \ 10^3$$ S/cm

C
equal to $$10^{-8}$$ S/cm

D
Zero

Solution

Conductors are the most conducting materials and hence have the highest conductivity or the least resistivity. Therefore, they have a conductivity of $$> 10^3$$ $$S/cm$$.
Insulators have the least conductivity i.e. $$< 10^{-8}$$ $$S/cm$$ whereas semiconductors have an electrical conductivity in between $$10^{-8}$$ and $$10^3$$ $$S/cm$$.
Question 5
1 / -0

The semiconductor diodes in which carriers are generated by photons (photo-excitation) are called devices.

A
thermo-optic

B
optical

C
optoelectronic

D
thermi-ionic

Solution

The junction diode or semiconductor diode which conducts when charge carriers are generated by photons i.e. light incident on it is known as optoelectronic function devices. Example: Photodiode, light emitter diode, solar cell.
Question 6
1 / -0

Energy band gap between valence band and conduction band for semiconductor is:

A
approximately 1 eV

B
less than conductors

C
equal to conductors

D
more than insulator

Solution

A semiconductor acts an insulator at very low temperatures and gradually begins conducting as the temperature increases. This means that as the temperature increases, the valence electrons gain enough energy to jump from the valence band to the conduction band. The band gap in semiconductor is very low, must be approximately 1eV.

Question 7

1 / -0

Match the following

a) p-type semiconductor	1) Pure semiconductor
b) Intrinsic semiconductor	2) Doped with impurity
c) Extrinsic semiconductor	3) majority carriers are electrons
d) n-type semiconductor	4) majority carriers are holes

a-3,b-2,c-4,d-1

a-1,b-2,c-4,d-3

a-4,b-1,c-2,d-3

a-2,b-1,c-4,d-3

Solution

p-type semiconductor is doped with trivalent impurities and hence has more holes than electrons.

n-type semiconductor is doped with pentavalent impurities and hence has more electrons than holes.

Intrinsic semiconductor is a pure semiconductor whereas an extrinsic semiconductor is made by doping an intrinsic semiconductor with impurities and so it has impurities in it.

Question 8
1 / -0

Semiconductors are materials having an electrical conductivity :

A
Less than insulators

B
between $$10^{-8}\ S/cm \ to \ 10^3\ S/cm$$

C
Equal to zero

D
Greater than $$10^3\ S/cm$$

Solution

Semiconductors are neither highly conducting nor highly insulating materials and hence have moderate conductivity. Therefore, their conductivity lies in between $$10^{-8}$$ and $$10^3$$ S/cm.
Insulators have the least conductivity i.e. $$< 10^{-8}$$ S/cm whereas conductors have the highest conductivity which is $$> 10^3$$ S/cm.
Question 9
1 / -0

The junction area is kept much larger in a solar cell

A
for solar radiation to be incident because we are interested in more power.

B
for solar radiation to be incident because we are interested in less power.

C
for solar radiation to be properly reflected from the junction.

D
None of these.

Solution

Solar cells are the devices that generate electricity when light falls on its material. It is a p-n junction diode which converts solar energy into electrical energy. Junction surface of these diodes is kept large so that large radiations are caught.
Question 10
1 / -0

Which of the following is a property of a Light Emitting Diode (LED)?

A
Low Threshold Voltage and High Reverse Breakdown Voltage

B
High Threshold Voltage and High Reverse Breakdown Voltage

C
High Threshold Voltage and Low Reverse Breakdown Voltage

D
Low Threshold Voltage and Low Reverse Breakdown Voltage

Solution

LED or Light Emitting Diode is a basic P-N junction diode operated when forward biased. It has very high threshold voltage and low reverse breakdown voltage(say $$5$$V)

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 33

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 33

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Question 1

It will change the proton and hole carrier concentrations of the semiconductor

It will change the temperature of the semiconductor

It will change the electron and hole carrier concentrations of the semiconductor

It will decrease the formation of free electrons in the semiconductor

Solution

Question 2

Zero

greater than $$9\ eV$$

less than conductors

approximately $$1\ eV$$

Solution

Question 3

more than semiconductors

Zero

more than insulators

None of these

Solution

Question 4

greater than $$10^3$$ S/cm

between $$10^{-8}\ to \ 10^3$$ S/cm

equal to $$10^{-8}$$ S/cm

Zero

Solution

Question 5

thermo-optic

optical

optoelectronic

thermi-ionic

Solution

Question 6

approximately 1 eV

less than conductors

equal to conductors

more than insulator

Solution

Question 7

a-3,b-2,c-4,d-1

a-1,b-2,c-4,d-3

a-4,b-1,c-2,d-3

a-2,b-1,c-4,d-3

Solution

Question 8

Less than insulators

between $$10^{-8}\ S/cm \ to \ 10^3\ S/cm$$

Equal to zero

Greater than $$10^3\ S/cm$$

Solution

Question 9

for solar radiation to be incident because we are interested in more power.

for solar radiation to be incident because we are interested in less power.

for solar radiation to be properly reflected from the junction.

None of these.

Solution

Question 10

Low Threshold Voltage and High Reverse Breakdown Voltage

High Threshold Voltage and High Reverse Breakdown Voltage

High Threshold Voltage and Low Reverse Breakdown Voltage

Low Threshold Voltage and Low Reverse Breakdown Voltage

Solution

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