Photocurrent is the current that flows through a photosensitive device, such as a photodiode

Photodiode

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....

, as the result of exposure to radiant power.

The photocurrent may occur as a result of the photoelectric, photoemissive, or photovoltaic effect

Photovoltaic effect

The photovoltaic effect is the creation of voltage or electric current in a material upon exposure to light. Though the photovoltaic effect is directly related to the photoelectric effect, they are different processes. In the photoelectric effect, electrons are ejected from a material's surface...

.

The photocurrent may be enhanced by internal gain

Gain

In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...

 caused by interaction among ions and photons under the influence of applied fields, such as occurs in an avalanche photodiode

Avalanche photodiode

An avalanche photodiode is a highly sensitive semiconductor electronic device that exploits the photoelectric effect to convert light to electricity. APDs can be thought of as photodetectors that provide a built-in first stage of gain through avalanche multiplication. From a functional standpoint,...

(APD).