Avalanche photodiode

Avalanche photodiodes (APDs) are photodetectors that can be regarded as the semiconductor analog to photomultipliers. By applying a high reverse bias voltage, APDs show an internal gain effect due to impact ionization. The higher the reverse voltage the higher the gain. Avalanche photodiodes therefore are more sensitive compared to other semiconductor photodiodes.

If very high gain is needed (10⁵ to 10⁶) an reverse voltage above the APDs breakdown voltage can be applied if the current is limiteted to below the APDs latching current (Geiger mode). This is in particular useful for single photon detection.

A typical application for APDs are laser range finders.

Also APD arrays are commercial available.