dark current (physics)

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{{Short description|Weak electric current generated by photosensitive devices in pure darkness}}In physics and in electronic engineering, dark current is the relatively small electric current that flows through photosensitive devices such as a photomultiplier tube, photodiode, or charge-coupled device even when no photons enter the device; it consists of the charges generated in the detector when no outside radiation is entering the detector. It is referred to as reverse bias leakage current in non-optical devices and is present in all diodes. Physically, dark current is due to the random generation of electrons and holes within the depletion region of the device.{{Cite journal |last1=Allam |first1=J. |last2=Capasso |first2=F. |last3=Alavi |first3=K. |last4=Cho |first4=A.Y. |date=January 1987 |title=Near-single carrier-type multiplication in a multiple graded-well structure for a solid-state photomultiplier |url=https://ieeexplore.ieee.org/document/1487081 |journal=IEEE Electron Device Letters |volume=8 |issue=1 |pages=4–6 |doi=10.1109/EDL.1987.26531 |bibcode=1987IEDL....8....4A |issn=0741-3106|url-access=subscription }}

Dark current is one of the main sources for noise in image sensors such as charge-coupled devices. The pattern of different dark currents can result in a fixed-pattern noise; dark frame subtraction can remove an estimate of the mean fixed pattern, but there still remains a temporal noise, because the dark current itself has a shot noise.