what is fermi level

The Fermi level is a thermodynamic quantity that measures the energy of the least tightly held electrons within a solid. It is a hypothetical energy level of an electron, such that at thermodynamic equilibrium, this energy level would have a 50% probability of being occupied at any given time. The Fermi level is the energy level which is occupied by the highest electron orbital at 0 Kelvin (absolute zero temperature) . It is a crucial factor in determining electrical properties of a solid, and its position in relation to the band energy levels is important in determining the conductivity of materials. The Fermi level is mainly used in discussing the solid-state physics of electrons in semiconductors, and a precise usage of this term is necessary to describe band diagrams in devices comprising different materials with different levels of doping. The Fermi level is also important in determining the thermal properties of solids. The Fermi level and Fermi energy are usually confusing terms and are often used interchangeably to refer to each other, although they are different at other temperatures.