Semiconductor Electronics : Materials, Devices and Simple Circuits Easy Questions and Answers | Page - 9

Semiconductor Electronics : Materials, Devices and Simple Circuits

A p-n photo diode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly

1. 10 × 10¹⁴ Hz
1. 5 ×10¹⁴ Hz
1. 1 × 10¹⁴ Hz
1. 20 × 10¹⁴ Hz

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E_g = 2.0 eV = 2 × 1.6 × 10^–19 J
E_g = hv
∴ v = E_g = 2 × 1.6 × 10^-19 J
h 6.62 × 10^-34 Js

= 0.4833 × 10¹⁵ s^-1 = 4.833 × 10¹⁴ Hz
≃ 5 × 10¹⁴

Correct Option: B

E_g = 2.0 eV = 2 × 1.6 × 10^–19 J
E_g = hv
∴ v = E_g = 2 × 1.6 × 10^-19 J
h 6.62 × 10^-34 Js

= 0.4833 × 10¹⁵ s^-1 = 4.833 × 10¹⁴ Hz
≃ 5 × 10¹⁴

For a cubic crystal structure which one of the following relations indicating indicating the cell characteristics is correct?

1. a ≠ b ≠ c and α = β = γ = 90°
1. a = b = c and α ≠ β ≠ γ = 90°
1. a = b = c and α = β = γ = 90°
1. a ≠ b ≠ c and α ≠ β and γ ≠ 90°

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For a cubic crystal,
a = b = c and α = β = γ = 90°

Correct Option: C

For a cubic crystal,
a = b = c and α = β = γ = 90°

Sodium has body centred packing. Distance between two nearest atoms is 3.7 Å. The lattice parameter is

1. 4.3 Å
1. 3.0 Å
1. 8.6 Å
1. 6.8 Å

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d = √3 a
2

3.7 = √3 a
2

a = 2 × 3.7 = 4.3 Å
√3

Correct Option: A

d = √3 a
2

3.7 = √3 a
2

a = 2 × 3.7 = 4.3 Å
√3

Choose the only false statement from the following

1. In conductors, the valence and conduction bands may overlap
1. Substances with energy gap of the order of 10 eV are insulators
1. The resistivity of a semiconductor increases with increase in temperature
1. The conductivity of a semiconductor increases with increase in temperature

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(a) is true as in case of conductors either the conduction & valence band overlap or conduction band is partially filled.
(b) is true as insulators have energy gap of the order of 5 to 10 eV.
(c) is false as resistivity (opposite of conductivity) decreases with increase in temperature.
(d) is true as with increase in temperature more and more electrons jump to the conduction band. So, conductivity increases.

Correct Option: C

(a) is true as in case of conductors either the conduction & valence band overlap or conduction band is partially filled.
(b) is true as insulators have energy gap of the order of 5 to 10 eV.
(c) is false as resistivity (opposite of conductivity) decreases with increase in temperature.
(d) is true as with increase in temperature more and more electrons jump to the conduction band. So, conductivity increases.

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (E_g)_C, (E_g)_Si and (E_g)_Ge respectively.
Which one of the following relationships is true in their case?

1. (E_g)_Si > (E_g)_Ge < (E_g)_C
1. (E_g)_C < (E_g)_Si
1. (E_g)_C = (E_g)_Si
1. (E_g)_C < (E_g)_Ge

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Due to strong electronegativity of carbon.

Correct Option: A

Due to strong electronegativity of carbon.