Dark current

Dark current is electrical current produced by a photosensitive device in the absence of intended illumination. It arises from thermally generated charge carriers, leakage paths, or other non-signal sources.

Thermal generation: The creation of mobile charge carriers by thermal energy in a material. Thermally generated carriers can cross a detector even when no light is present.
Image sensor: A device that converts an optical image into electrical signals for recording or processing. Dark current appears as a baseline signal in the sensor's pixels.
Photocurrent: Electrical current generated when absorbed photons create mobile charge carriers in a photosensitive device. Photocurrent is the intended light-dependent signal; dark current persists without it.
Dark current doubling temperature: An approximate temperature interval over which a detector's dark current doubles. This rule of thumb explains why modest cooling can substantially reduce the unwanted signal.
Arrhenius equation: An equation describing how a rate depends exponentially on temperature through an activation energy. Temperature-dependent dark-current measurements often use Arrhenius behavior to infer activation energies.
Shockley–Read–Hall recombination: A semiconductor process in which defects mediate the recombination or generation of electrons and holes. Defect-mediated generation is a major source of current in depleted photodiode regions.
Charge-coupled device: An image sensor that transfers accumulated electrical charge through a sequence of semiconductor wells. Charge accumulates during exposure, making its dark signal especially relevant for long integrations.
Read noise: Random variation added when an electronic system measures and converts a sensor's stored signal. Read noise arises during measurement, whereas dark current accumulates charge during exposure.
Dark-current shot noise: The statistical noise produced by the discrete charge carriers that make up dark current. Longer exposure increases accumulated dark charge and its irreducible shot noise.
Activation energy: The energy barrier that a process must overcome to occur at an appreciable rate. Different dark-current mechanisms can have different activation energies and temperature responses.

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