Tag: semiconductors

Questions Related to semiconductors

In insulators (CB is conduction band and VB is valence band)

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. VB is partially filled with electrons

  2. CB is partially filled with electrons

  3. CB is empty and VB is filled with electrons

  4. CB is filled with electrons and VB is empty

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Correct Option: C
Explanation:

In insulators conduction band is empty and valence band is filled with electrons.

The energy gap in a semiconductor 

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. Increases with temperature

  2. Does not change with temperature

  3. Decreases with temperature

  4. Is zero

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Correct Option: C
Explanation:

The energy bandgap of semiconductors tends to decrease as the temperature is increased.  the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. This effect is quantified by the linear expansion coefficient of a material. An increased interatomic spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap. A direct modulation of the interatomic distance, such as by applying high compressive (tensile) stress, also causes an increase (decrease) of the bandgap.

The variance of energy gap with temperature is given by
$E _g(T)=E _g(0)-\dfrac{\alpha T^2}{T+\beta}$

When the band gap for a semiconductor is low 

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. conductivity of that material is low

  2. conductivity of that material is high

  3. the resistance of that material is high

  4. none of the above

Show answer
Correct Option: B
Explanation:

When the band gap for a semiconductor is low, it means it is easy for the valance electrons to jump into conduction band i.e. less energy is required for the electrons to enter into conduction band. Hence, the resistance of the material is low and conductivity is high.

Which of the following has least band gap energy at $273K$.

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. InSb

  2. InAs

  3. InP

  4. GaSb

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Correct Option: A
Explanation:

The energy gaps of the given semiconductors at $273K$ are given:

   $InSb=0.16eV$ (Indium antimonide),
   $InAs=0.33eV$ (Indium arsenide),
   $InP=1.29eV$ (Indium phosphide),
  $GaSb=0.67eV$ (Galiumium antimonide),
It is clear that $InSb$ has the least energy gap.

What is the optimum band gap energy for a material to be considered as a semiconductor?

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. greater than $6eV$

  2. less than $6eV$

  3. $0eV$

  4. $0.5-3eV$

Show answer
Correct Option: D
Explanation:

Semiconductor materials have low but finite band gap energy, due to which there is an easy jump of electron from valence band to conduction band upon provision of external thermal energy.

The typical range of band gap energy for a semiconductor material is $0.5eV-3eV$.

Choose the correct statement(s):

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. Band gap of a semiconductor increases as temperature increases.

  2. Band gap of a semiconductor decreases as the temperature increases.

  3. Band gap of a semiconductor is independent of temperature.

  4. Bandgap of a semiconductor decreases till critical temperature and increases after that. 

Show answer
Correct Option: B
Explanation:

The energy bandgap of semiconductors tends to decrease as the temperature is increased. This behaviour can be understood if one considers that the interatomic spacing increases when the amplitude of the atomic vibrations increases due to the increased thermal energy. This effect is quantified by the linear expansion coefficient of a material. An increased interatomic spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap. 

This is the reason behind the decrease in resistance of semiconductor materials by increasing temperature.

Which among  the following having highest band gap ?

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. Diamond

  2. Silicon

  3. Germanium

  4. Gallium nitride

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Correct Option: A
Explanation:

The energy gaps of the given materials are given:

   Diamond $=6eV$  (insulator)
   Silicon $=1.1eVeV$  (semiconductor)
   Germanium $=0.6eV$  (semiconductor)
   Gallium nitride $=3.4eV$  (semiconductor)

What is the energy band gap of silicon and germanium respectively in $eV$  ?

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. $1.1, 0.7$

  2. $0.7, 1.1$

  3. $-0.7, -1.1$

  4. $-1.1, -0.7$

Show answer
Correct Option: A
Explanation:

A band gap, also called an energy band, is an energy range in a solid where no electron states can exist. It generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. The energy band gaps of silicon and germanium are $1.1eV $ and $0.7eV$ respectively.

Which of the following statement(s) is/are correct

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. If the band gap becomes much more higher for a semiconductor then electrons from lower energy state can't move to higher energy state

  2. Lesser the band gap lesser is the conduction

  3. Lesser the band gap higher is the conduction

  4. none of the above

Show answer
Correct Option: A,C
Explanation:

When the band gap for a semiconductor is low, it means it is easy for the valance electrons to jump into conduction band i.e. less energy is required for the electrons to enter into conduction band. Hence, the resistance of the material is low and conductivity is high i.e. lesser the band gap higher is the conduction.

When the band gap becomes much higher for a semiconductor then electrons can't move to higher energy state from lower energy state.

At what temperature semiconductors behaves as an ideal insulator?

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. 273.15 $^\circ C$

  2. -459.67 $^\circ\ F$

  3. -273 $^\circ\ F$

  4. Room temperature

Show answer
Correct Option: B
Explanation:

Semi-conductors behaves as an ideal insulator at absolute zero temperature($0K$) which is 0 Kelvin. Because at the absolute zero temperature the electrons in the valence band of semi-conductors do not posses enough thermal energy to overcome forbidden energy gap. so semi-conductors stop conducting and behaves as an insulator.

But  $0K=-459.67F$   
Hence correct answer is   $-459.67F$.