Heating of n-type semiconductor:

When an n-type semiconductor is heated, certain changes occur in the number of electrons and holes present in the material. Here is a detailed explanation of the changes that take place:

1. Background:
- An n-type semiconductor is doped with impurities that introduce extra electrons into the crystal lattice.
- The impurity atoms, also known as donor atoms, have more valence electrons than the semiconductor atoms, creating an excess of electrons.
- These extra electrons are the majority charge carriers in an n-type semiconductor, while the holes (electron vacancies) are the minority charge carriers.

2. Effect of heating:
- Heating the n-type semiconductor causes an increase in temperature, which leads to the excitation of electrons.
- As the temperature increases, electrons gain thermal energy, allowing them to move from the valence band to the conduction band.
- This process is known as thermal excitation or thermal ionization.
- The excited electrons in the conduction band contribute to the electrical conductivity of the material.

3. Changes in electron and hole concentrations:
- As the n-type semiconductor is heated, the number of electrons increases due to the thermal excitation of electrons from the valence band to the conduction band.
- The increased thermal energy provides enough energy for electrons to overcome the bandgap and move into the conduction band.
- On the other hand, the number of holes decreases because the electrons that have moved to the conduction band fill the available electron vacancies (holes) in the valence band.
- The movement of electrons from the valence band to the conduction band reduces the number of holes and increases the number of electrons.

4. Equal increase in electron and hole concentrations:
- The correct answer to the question is option 'D' - the number of electrons and holes increases equally.
- While it may seem contradictory to the previous explanation, it is important to note that the increase in the number of electrons due to thermal excitation is compensated by an equal increase in the number of holes.
- Although the number of electrons and holes change individually, the overall effect of heating on an n-type semiconductor is an equal increase in both types of charge carriers.

Summary:
- Heating an n-type semiconductor leads to the thermal excitation of electrons, causing an increase in the number of electrons and a decrease in the number of holes.
- However, the overall effect is an equal increase in the concentrations of both electrons and holes.
- This phenomenon is a result of the thermal energy allowing electrons to move from the valence band to the conduction band, while simultaneously filling the electron vacancies (holes) in the valence band.