DARK CURRENT:

dark current is the relatively small electric current that flows through photosensitive devices such as a photomultiplier tube, photo diode, or charge coupled device even when no photons are entering 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.