Impact ionization

For example, in semiconductors, an electron (or hole) with enough kinetic energy can knock a bound electron out of its bound state (in the valence band) and promote it to a state in the conduction band, creating an electron-hole pair.

If this occurs in a region of high electrical field then it can result in avalanche breakdown.

This process is exploited in avalanche diodes, by which a small optical signal is amplified before entering an external electronic circuit.

In an avalanche photodiode the original charge carrier is created by the absorption of a photon.

In some sense, impact ionization is the reverse process to Auger recombination.