Dark count or Dark Current is one of the most important CCD specifications, :: Computer Science

forbidding count or muddy Current is one of the most important CCD specifications, along with resolution, quantum efficiency and preventative figure. gamy count or Dark Current is one of the most important CCDspecifications, along with resolution, quantum efficiency and noisefigure. Dark current causes an output to come without the previousintroduction of an input. This is caused by the thermal coevals andthen diffusion of vote out. This Dark Current is generated at differentlocations in the CCD, but the cause of this charge generation isbasically the same in all locations. This is because all cases are todo with irregularities in the fundamental crystal structure of thesilicon present in CCDs. Examples of these irregularities includemetal impurities such as gold, copper or iron, and crystal defectssuch as dislocations and stacking faults, all of which are known to bethermal generation sites of charge carriers in silicon. THE BESTEXAMPLE OF WHERE THIS DARK Current push aside b e located is at the SiliconOxide to silicon interface of the MOS capacitor (which is the importantbuilding block of a CCD) . This is due to the fact that this is wherethe largest irregularity in the silicon crystal structure occurs.However, it can also be located in the in the bulk of the silicon bothinside and outside the depletion layer, which is defined by the CCDpotential wells.To give an example of the amount of Dark Current, which is induced AKodak KAF-0400 and KAF-1600 sensor is specified to have a Dark Currentof 50 electrons being induced per second at 25 degrees c. Taking aone-minute exposure at this temperature would generate 3000 electronsof thermally induced charge, which is calculated by 60secs times 50electrons.In theory the average Dark Current value can be subtracted from theoutput value to provide the signal due to photoelectrons. However inreality there are fluctuations in the Dark Current called Dark noise,and this cannot be accounted for in the same way. Noise occurs indifferent forms such as shot noise and trapping noise which bothappear in the CCD channel. It also occurs at the input and outputstages as KTC noise, but my main focus shall be on shot noise as it isclosely associated with Dark Current.We know that the generation of Dark Current is a totally randomprocess, due to the fact that the generation sites are randomlydistributed and perhaps more importantly, the Dark Current generationprocess is random as a function of time. The number of electronsgenerated and then collected in a charge packet travelling through the