Question

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

Answer 1

Hint The highest energy level occupied by an electron in an atom at absolute temperature or zero Kelvin is called its Fermi energy level. Intrinsic semiconductors are semiconductors that are not doped externally. It has charge carriers that are inherent to the material.

Complete Step by step solution
Fermi energy is energy defined at absolute zero temperature. It refers to the difference in energy levels occupied by an electron when it is at its highest energy level and the lowest energy level at absolute zero temperature when the electrons are non-interacting. This definition allows us to define it as the probability by which electrons occupy the conduction band or the valence band.
Semiconductors are generally defined as materials which have conductivity more than insulators but less than conductors. There can be two types of semiconductors depending on the composition of the material. Intrinsic semiconductors are semiconductors that are pure elements. Examples are silicon or germanium. Extrinsic semiconductors are compound semiconductors that have more than one element in its composition. Examples are gallium arsenide, cadmium selenide, etc.
As no external dopants are added to increase the conductivity in intrinsic semiconductors, the conductivity is very low compared to extrinsic type semiconductor. The valence band in an intrinsic semiconductor will be completely filled, with no electrons in the conduction band at absolute zero temperature. The number of holes in the conduction band will be equal to the number of holes in the valence band as the semiconductor is not doped additionally. Hence, the Fermi energy level of an intrinsic type semiconductor will lie at the exact midpoint between the conduction band and the valence band.

Note
Do not confuse Fermi energy with a Fermi energy level as it is a very commonly made mistake. Fermi energy is only defined at zero Kelvin; whereas Fermi energy level can be defined at any temperatures. Intrinsic type semiconductors are not commonly used due to their low conductivity compared to extrinsic type semiconductors.