Question

What is Fermi energy level? What is its position in case of an intrinsic semiconductor?

Answer 1

Hint: The energy corresponding to the highest energy level in the conduction band at absolute zero is termed as Fermi energy level. The word intrinsic means natural, so it would define natural semiconductor which does not have any impurities added to them.

Complete answer:
The highest energy level in the conduction band filled up with electrons at absolute is called Fermi level and the energy corresponding to the Fermi level is called Fermi energy. In other words, it can also be defined as the probability by which electrons occupy energy levels in the valence band and conduction band.
Semiconductors are solid substances that have a conductivity between an insulator and of most metals. This change in conductivity is either due to the addition of an impurity or due to a change in temperature. Semiconductors are materials that have a very small forbidden energy gap that is the energy gap between the conduction and valence bands.
The pure semiconducting tetravalent crystals are called the intrinsic semiconductors. Their electric conductivity is very low in comparison to extrinsic semiconductors, which are semiconductor materials doped with impurities.
At 0K, the valence band of an intrinsic type semiconductor is completely filled with electrons, while the conduction band is empty. Additionally, the number of holes in the valence band is always equal to the number of electrons in the conduction band, as there is no excess amount of charge doped on the semiconductor. Thus the Fermi energy level is amidst the conduction band and the valance band because the probability of occupation of energy levels is the same at both ends
Therefore, the Fermi energy levels for an intrinsic semiconductor must lie exactly in the middle of the forbidden energy gap.

Note: Intrinsic semiconductors are not used to make electronic devices because of their low electric conductivity and thus lower efficiency. The conduction of intrinsic semiconductors is temperature dependent, which is not a physical quantity that is kept high for any electronic device, due to high energy loss.