Electron-multiplying CCD

An Electron multiplying charge-coupled device (English, EMCCD, also known as L3CCD and impactron CCD) is a CCD (charge- coupled device), in which an amplifier distance between the shift register and the output amplifier is implemented. The amplifier range is composed of a large number of charge-coupled shift register. In each shift register, the number of electron- impact ionization by the effect can be similarly increased by an avalanche diode. The probability of impact ionization in each stage is small (P <2%), but as the number of stages n is large ( typically> 500 ), the overall gain may assume large values ​​g = (1 P ) N: an electron in the input generates thousands of electrons at the output. The gain response of multiplication register with many levels and a high overall gain can be well approximated by the following stochastic equation:

Where P ( n) is the probability of the n output electron at m input electrons and a total gain of G.

The input noise of evaluation circuits of CCDs usually has a level of a few tens of electrons, the signal from EMCCDs is in contrast to normal CCDs significantly higher. In this way, a image sensor with negligible readout noise. Even single photons can be detected.

EMCCDs have a similarly high, sometimes greater sensitivity than an intensified charge-coupled device ( ICCD ). In both, however, fluctuates due to the stochastic amplification process, the reinforcement; the exact gain of a pixel charge varies from time to time. At high gains ( > 30) of this variation has the same effect with respect to the signal -to-noise ratio as a halving of the quantum efficiency. At low light intensities ( where sensitivity is most important ), however, outweighs the advantage obtained by the lower readout noise. In particular, in applications in which it can be assumed that a pixel contains a maximum of one electron in an exposure, they can be reliably detected. By repeated recordings, the number of photons can be determined very accurately in this way.

Applications

EMCCDs example, be used in night vision devices, in astronomical observation and fluorescence microscopy.

They displace there because of their lower price ICCDs which, however, have the advantage of fast electronic control of the exposure time.