Tag: semiconductors

Questions Related to semiconductors

Among the following, the wrong statement in the case of semiconductor is:

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

  1. Resistivity is in between that of a conductor and insulator.

  2. Temperature coefficient of resistance is negative.

  3. Doping increases conductivity.

  4. At absolute zero temperature, it behaves like a conductor.

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Correct Option: D
Explanation:

For semiconductor, as the temperature coefficient of resistance is negative, at absolute zero temperature, it behaves like an insulator.

At absolute zero, Si acts as

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

  1. non-metal

  2. metal

  3. insulator

  4. semiconductor

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Correct Option: C
Explanation:

The semiconductor (Si) has negative temperature coefficient of resistivity. At absolute zero temperature, its resistance becomes infinite and it act like an insulator.

What is the resistivity of a pure semiconductor at absolute zero ?

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

  1. Zero

  2. Infinity

  3. Same as that of conductors at room temperature

  4. Same as that of insulators at room temperature

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Correct Option: B
Explanation:

The electricity conductivity of a semiconductor at $0 K$ is zero. hence resistivity (= 1/electrical conductivity) is infinity.

Which one is the weakest type of bonding in solids ?

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

  1. Ionic

  2. Covalent

  3. Metallic

  4. Vander Wall's

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Correct Option: D
Explanation:

Vander Wall's force or bonding is the weakest exists between the two molecules of the solids.

The intrinsic semi conductor becomes an insulator at

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

  1. $0^{\circ}C$ 

  2. $0 K$

  3. $300 K$

  4. $-100^{\circ}C$

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Correct Option: B
Explanation:

At $0K (-273^{\circ}C)$ motion of free electron stop i.e., there is no electron in conduction band therefore at $0K$ intrinsic semiconductor becomes insulator.

Bands in solids are formed due to a group of closely spaced ________ .

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

  1. conductor bands

  2. valance bands

  3. energy levels

  4. solid bands

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Correct Option: C
Explanation:

Closely space energy levels combine to form an energy band in solids. This is because, the outer orbit of an atom in solids, are common to several neighboring atoms. Therefore, energy levels corresponding to outer orbit electrons spread up to form a band of energy called energy band.

The energy gap in glass at room temperature is :

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

  1. greater than that in a semiconductor

  2. less than that in a good conductor

  3. greater than that in a good conductor

  4. both (A) and (C) are true

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Correct Option: D
Explanation:

Glass is an insulator. The energy gap of an insulator is $\sim 6 eV$. Whereas for conductors, the energy gap is $\sim 0 eV$.
for semiconductors, energy gap $\sim 3 eV$.
So energy gap for glass is greater in conductors or a semiconductor.

A pure germanium crystal at absolute zero is :

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

  1. an insulator

  2. a good conductor

  3. a semiconductor

  4. none of the above

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Correct Option: A
Explanation:

A pure Ge crystal at absolute zero has electrons only in the valence band. No electron in the conduction band is there. So, it acts as an insulator at 0 Kelvin.

A pure semiconductor at absolute zero has :

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

  1. absence of electrons in the conduction band

  2. all the electrons occupying the valence band

  3. large ${E} _{g}$ value

  4. all of the above

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Correct Option: D

The band structure determines the _________ behaviour of a solid.

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

  1. chemical

  2. electrical

  3. mechanical

  4. molecular

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Correct Option: B
Explanation:

The band structure, i.e. valence band, conduction band and forbidden energy band (Eg) tells on the basis of the energy difference between valence and conduction band, that whether the given solid is a metal, insulator or a semiconductor. If the two bands overlap, then the solid is a conductor, i.e, it has high electrical conductivity. If Eg $\sim 6$ eV; then it is an insulator and has minimum electrical conductivity otherwise if Eg $\sim 3$ eV, it is a semiconductor whose electrical conductivity lies between conductor and insulator.