Dark current refers to the small amount of electric current that flows through a photodetector (such as a photodiode or a CCD—charge-coupled device) even when no photons are incident on the device. This current is a result of thermally generated charge carriers and can occur in various types of detectors.
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Dark current is charge produced in a detector without illumination, often by thermally excited carriers. Cooling reduces it, although cooling requirements also depend on the wavelength range and thermal background.