Tag: semiconductors

Quizzes (4) Questions (79)

Questions Related to semiconductors

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

At absolute zero, a semiconductor is an insulator because _________.

  1. No electron is present in the conduction band

  2. All electrons occupy the valence band

  3. The value of $E _G$ is large

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At absolute zero, the band gap in a semiconductor is of order $\sim 3eV$. The electrons in the valence band do not have sufficient energy to jump to the conduction band and hence semiconductor, behaves as an insulator at 0K.

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

With rise in temperature the resistance of germanium,

  1. increases

  2. decreases

  3. remains the same

  4. first increases then decreases
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

germanium is a semiconductor and as we know  when a semiconductor is heated, electron-hole pair is generated in it which increases its conductivity as the number of charge carriers are increasing.
Now, as conductivity increases resistance decreases because both are opposite of each other.

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

The energy bands are present only when the substance is present in the solid state.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is because in a solid, there are several atoms placed closely together. The energy levels of inner orbit electrons of an atom are not influenced by the neighboring atoms as these electrons are tightly bound to their parent nucleus.
However, energy levels of outer orbit electrons of an atom are altered as these are influenced by the neighboring atoms. Therefore, the energy levels corresponding to outer shell electrons are spread up to form a band of energy. Therefore, the closely spaced energy levels of atoms in the solid combine to form an energy band.

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

The energy gap $E _G$ of a semi-conductor decreases with rise in temperature.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the temperature is increased, the thermal energy to the electron within the semiconductor material also increases. Therefore, now lower energy is required to break the bond. This reduction in Bond energy also reduces the band gap. So, the band gap of a semiconductor decreases with increasing temperature.

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

With rise in temperature, resistance of a semiconductor material (germanium or silicon)

  1. increases

  2. decreases

  3. remains the same

  4. first increases then decreases
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

With rise in temperature, the number of charge carriers (holes and electrons) increases in the case of a semiconductor dominating the effect of decreasing relaxation time, increasing collision frequency.
So, as a whole the resistance of the material decreases with rise in temperature.

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

State whether True or False :

A semiconductor at absolute zero become a insulator.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The conductivity and non-conductivity of material are dependent on the motion of electrons. If the motion is happening it is conductor.

Now, at absolute zero, the temperature is so low that it stops the motion of the electrons. Thus making it a complete insulator.
$\Rightarrow$  Statement (A) is the correct answer.

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

What is forbidden energy gap(Eg) or band gap?

  1. Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and within conduction band

  2. Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and valence band.

  3. when there is no energy

  4. conduction band
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and valence band.

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

Give band gap Eg value for conductor, insulator and semiconductor?

  1. Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 8eV$.

  2. Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.

  3. Conductor$<2MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.

  4. Conductor$<1MeV$, insulation $\ge 7eV$, semiconductor $\approx 1eV$.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.