Intrinsic semiconductors-conductivity

Fermi level in intrinsic semiconductors

Fermi level is defined as the energy level separating the filled states from the empty states at 0 K. It is also the highest filled energy level in a metal. This definition needs to be modified for a semiconductor since these have an energy gap between the filled states (valence band) and empty states (conduction band). The expression for the carrier concentration (n or p) in

In metals the Fermi level separates the filled and empty states. This is because metals have partially filled energy bands and the Fermi level lies within the band. This definition cannot be used for semiconductors. Another definition is that Fermi level defines the average energy required to remove an electron from the material. This is called the work function, denoted by φ, and is the energy difference between the Fermi level and the vacuum level. This definition can also used for semiconductors, with the realization that electrons in the CB and the holes in the VB are linked. So the Fermi level, defines the average potential energy per electron for electrical work. If an external electric field is applied the Fermi level in the material will no longer be uniform. This will be important when considering junctions formed between different semiconductors and between semiconductors and metals.

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