Fermi Level
The thermodynamic Fermi-Dirac chemical potential representing the energy level at which the probability of electron occupancy is exactly 50% at finite temperature.
Governing formula
f(E) = 1 / (e^((E - E_F) / (k_B T)) + 1)
SI unit
eV (Chemical Potential)
In depth
At absolute zero (0 K), all electronic states below the Fermi level E_F are completely filled (f(E)=1) and all states above are empty (f(E)=0). The position of E_F relative to band edges determines whether a solid is a metal, n-type semiconductor, or p-type semiconductor.
Examples in the real world
The Fermi level resting inside the bandgap near the conduction band in n-type doped silicon.