Tag: semiconductors

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Questions Related to semiconductors

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

What is an energy gap?

  1. the space between two orbital shells

  2. the energy equal to the energy acquired by an electron passing a $1 V$ electric field

  3. the energy band in which electrons can move freely

  4. an energy level at which an electron can exist
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  1. Orbiting electrons contains energy and are confirmed to definite energy levels.
    2. The various shells in an atom represent these levels.
    3. Therefore, to move an electron from the lower shell to a higher shell a certain amount of energy is required.
    3. Below the conduction band is the forbidden band or energy gap, electrons are never found in this band, but may travel back and forth through it, provided they do not come to rest in the band.
    4. As the electrons can also lose energy as well as receive it when an electron loses energy it moves to a lower shell.
    5. And supplying more energy than is needed will only cause the electron to move to the next higher shell.
    6. It means that an energy gap is the spacing between two orbital shells.
Multiple choice physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

 Fermi energy level for $p-type$ extrinsic semiconductors lies 

  1. At middle of the band gap

  2. Close to conduction band

  3. Close to valence band

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In case of a p-type semiconductor, the number of holes in valence band is grater then number of electrons in conduction band. hence, the probability of occupation of energy levels by the holes in valence band is greater than probability of occupation of energy levels by electrons in conduction band. This probability of occupation of energy levels is represented in terms of Fermi level.

$\therefore $ female level in p-type semiconductor lies does to valence band.

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

Energy gap of conductor is

  1. $0 \ eV$

  2. $1 \ eV$

  3. $2 \ eV$

  4. $3 \ eV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The range of energy of the valence electrons of an atom is known as valence band. The range of energy in which an electron must exist in order to participate in the conduction of electricity is known as conduction band. The difference between the valence band and conduction band is known as band gap or energy gap. In conductors, the valence band overlaps with the conduction band. Which means, electrons are already ready for conduction and energy gap in a conductor is zero.

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

Fermi energy level for intrinsic semiconductors lies 

  1. At middle of the band gap

  2. Close to valence band

  3. Close to conduction band

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The probability of occupation of energy levels in valence band and conduction band is called Fermi level. As the temperature increases free electrons and holes gets generated. In intrinsic semiconductor, the number of holes in valence band is equal to the number of electrons in the conduction band. Hence, the probability of occupation of energy levels in conduction band and valence band are equal. Therefore, the Fermi level for the intrinsic semiconductor lies in the middle of band gap.

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

Energy gap of semiconductor is approx

  1. $1 eV$

  2. $0 \ eV$

  3. $6-7 eV$

  4. $> 8\ eV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The energy gap of a semiconductor lies in between insulators and conductors. In case of conductors, band gap Eg $\sim 0$ eV. Whereas in case of insulators, Eg $\sim 3-4$ eV. So, Band gap in case of a semiconductor is of order $\sim 1$ eV.

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

The level formed due to impurity atom, in the forbidden energy gap, very near to the valence band in a P-type semiconductor is called

  1. an acceptor level

  2. a donor level

  3. a conduction level

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The level formed due to impurity atom, in the forbidden energy gap, very near to the valency band in a p-type semiconductor is called an acceptor level.

The level formed due to impurity atom, in the forbidden energy gap, very near to the conduction band in a p-type semiconductor is called a donor level.
Therefore option $A$ is correct.

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

The band gaps of a conductor, semiconductor and insulator are respectively ${Eg} _{1}, {Eg} _{2}$ and ${Eg} _{3}$. The relationship between them can be given as.

  1. ${ Eg } _{ 1 }={ Eg } _{ 2 }={ Eg } _{ 3 }$

  2. ${ Eg } _{ 1 }<{ Eg } _{ 2 }<{ Eg } _{ 3 }$

  3. ${ Eg } _{ 1 }>{ Eg } _{ 2 }>{ Eg } _{ 3 }$

  4. ${ Eg } _{ 1 }<{ Eg } _{ 2 }>{ Eg } _{ 3 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Band gap of the insulator is largest as it restricts the flow of electrons through it. So, $E _{g _{3}} > E _{g _{2}} > E _{g _{1}}$.