Intrinsic Semiconductors

A semiconductor is a material whose electrical conductivity falls between that of a conductor and an insulator. The semiconductor is classified into intrinsic and extrinsic semiconductor based on their level of purity. Here in this article, let us learn more about intrinsic semiconductors.

What are Intrinsic Semiconductors?

The semiconductors that are chemically pure, that is, free from any impurities are termed as intrinsic semiconductors. This means the holes or vacancies in the valence band are not provided by any “foreign” atom that acts as an impurity. They are also termed as undoped semiconductors or i-type semiconductors. Silicon and germanium are the examples of i-type semiconductors. As we know, these elements belong to the IVth Group of the periodic table and their atomic numbers are 14 and 32, and thus the electronic configuration

Intrinsic semiconductors

Silicon-1s2 2s22p6 3s2 3p2

Germanium- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2

We notice here that both the elements have four electrons in their outermost shell or valence shell. As the temperature of the semiconductor is increased, the electrons gain more thermal energy and thus break free from their shell. The process of ionization of the atoms in the crystal lattice creates a vacancy in the bond between the atoms. The position from which the electron gets dislodged has a hole which is equivalent to an effective positive charge. The hole is then occupied by a free electron, as a result of which the latter vacant position becomes a hole and the former becomes a neutral position. This way the hole or the effective positive charge is transferred from one position to another. In an intrinsic semiconductor, the number of free electrons is equal to the number of holes. Mathematically,

Intrinsic Semiconductor

Here, the ni gives the number of total intrinsic carrier concentration which is equal to the total number of holes or the total number of electrons.

When the temperature of an intrinsic semiconductor is T=0K, it behaves like an insulator. When the temperature is increased further, (T>0), the electrons get excited and move from the valence band to the conduction band. These electrons occupy the conduction band partially, leaving a correspondingly equal number of holes in the valence band.

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Intrinsic Semiconductor Important Questions

Q1. What are intrinsic semiconductors?

Ans: Intrinsic semiconductors are those made from the purest form of semiconductor material.

Q2. What is used by the intrinsic semiconductors for conduction at room temperature?

Ans: Electrons and holes are used.

Q3. How does the intrinsic semiconductor behave at absolute zero?

Ans: At absolute zero, the intrinsic semiconductor behaves like an insulator.

Q4. Name the doping elements used for converting intrinsic semiconductor.

Ans: Following are the doping elements used for converting intrinsic semiconductor:

  • Phosphorous
  • Arsenic
  • Antimony

Q5. What is the temperature coefficient of an intrinsic semiconductor?

Ans: The temperature coefficient of an intrinsic semiconductor is negative.

Q6. What happens when an intrinsic semiconductor is doped with trivalent impurity?

Ans: When a trivalent impurity is doped with an intrinsic semiconductor, a p-type semiconductor is obtained.

Q7. What is the Hall coefficient value for insulator?

Ans: Zero.

Q8. What is the Hall coefficient value for p-type semiconductor?

Ans: It is always positive.

Q9. What is the electrical conductivity value for insulator?

Ans: For insulators, the electrical conductivity value is less than 1*106 mho/m.

Q10. Why n-p-n transistors are preferred over p-n-p transistors?

Ans: The mobility of electrons is higher than the mobility of holes in the n-p-n transistor when compared to p-n-p transistor.

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Number of secondary electrons emitted per number of primary electrons depends on [RPET 2000]