Moss–Burstein effect

The Moss-Burstein effect, also known as the Burstein–Moss shift, is the phenomenon in which the apparent band gap of a semiconductor is increased as the absorption edge is pushed to higher energies as a result of some states close to the conduction band being populated.

[1][2] The effect occurs when the electron carrier concentration exceeds the conduction band edge density of states, which corresponds to degenerate doping in semiconductors.

In nominally doped semiconductors, the Fermi level lies between the conduction and valence bands.

For example, in n-doped semiconductor, as the doping concentration is increased, electrons populate states within the conduction band which pushes the Fermi level to higher energy.

Pauli's exclusion principle forbids excitation into these occupied states.