Anderson's rule

Anderson's rule is used for the construction of energy band diagrams of the heterojunction between two semiconductor materials.

in solid state physics) gives the energy difference between the lower edge of the conduction band and the vacuum level of the semiconductor.

Each semiconductor has different electron affinity and band gap values.

For semiconductor alloys it may be necessary to use Vegard's law to calculate these values.

Much like with the Schottky–Mott rule, Anderson's rule ignores the real chemical bonding effects that occur with a small or nonexistent vacuum separation: interface states which may have a very large electrical polarization and defect states, dislocations and other perturbations caused by imperfect crystal lattice matches.

To try to improve the accuracy of Anderson's rule, various models have been proposed.

[citation needed] Tersoff[5] proposed the presence of a dipole layer due to induced gap states, by analogy to the metal-induced gap states in a metal–semiconductor junction.

Band diagrams for a straddling-gap type heterojunction, as understood by Anderson's rule. The junction alignment at equilibrium (bottom) is predicted based on a hypothetical flat-vacuum alignment (top).