Dark current (physics)

As dark current is defined as

• The spontaneous formation of free charge carriers by heat in a photosensitive semiconductor such as a CCD image sensor, a photodiode or a photoresistor
• Triggering of electrons from the photocathode of a photomultiplier tube or a photocell by the thermal motion of the material.

Due to the third law of thermodynamics to move the atoms or molecules that make up a light-sensitive detector. Through inelastic collisions carriers can be triggered in the detector, even if it is not exposed. These thermally induced conductivity in devices that use the internal photoelectric effect, or thermally emitted electrons at the photocathode ( external photoelectric effect) generate the dark current.

The effect can be reduced by lowering the temperature of the photoreceptor. Photoreceiver for the mid-infrared to be cooled in principle (for example, with liquid nitrogen).

Systematic caused by the dark current noise on digital images can be subsequently partially removed by image processing on the computer or in the camera. The dark current varies per se ( apart from external factors such as chip temperature, etc. ) due to the Poisson statistics also, this actual noise can not be removed in this way, but at CCDs, for example, in general, very small compared to the noise of the actual signal.

Sensory Physiology

The sensory physiology of the dark current refers to the flow of sodium ions in the dark. In the dark, in the resting state of the sensory cell, the Na channels in the membrane of the photoreceptor are open. The dark current depolarizes the membrane potential to about -30 mV to -40 mV.

• Electricity