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Optoelectronics: Dark current caused by Quantum fluctuations?

  1. Jun 17, 2013 #1
    Hello Physics Forums,

    This is my first time posting so apologies for any mistakes or misunderstand of forum etiquette here.

    I am having difficulty understanding a phenomenon known as "dark current"

    I've tried for a few hours to research it but most of what i find is very vague on the subject and still leaves me with many questions. There is very little information i can find in the way of explanations.

    I have a basic understand of semiconductor physics but i'm stumped at understanding exactly how dark current occurs in the physical sense.

    If anyone could shed some light on this for me, it would be greatly appreciated.

    Once again i apologise if i have posted in the wrong section or violated any forum regulations.

    Many thanks.
  2. jcsd
  3. Jun 17, 2013 #2


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    Staff: Mentor

    If your semiconductor has a non-zero temperature, there is thermal energy in it. Usually, this is not sufficient to produce an electron/hole pair, but sometimes enough energy is available for a single electron to bring it from the valence band to the conduction band.
    The electron energy levels are quantum mechanics, but the thermal fluctuations can be explained with classical physics.
  4. Jun 17, 2013 #3


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    It is a very broad question with no single answer.
    mfb's explanation is the simplest answer valid for semiconductor devices. However, you can get "dark current" in other types of devices as well, e.g. superconducting detectors (although there one should really talk about "dark counts" instead, since we are mostly NOT actually measuring a current) and in many cases these "extra" mechanisms are not fully understood. The most likely explanation is that it is a surface/interface effect caused by e.g. dangling bonds, oxides and impurities.
    Moreover, some of the mechanicsm causing these dark counts seems to be active even at very low temperatures; so it can not all be caused by thermal activation (i.e. it must be due to tunnelling).

    Hence, we can be sure that there is no single explanation for all dark currents. It is also likely that some of the dark current in semiconductor devices is NOT thermal, but is caused by the same mechanisms that is creating noise in other materials and devices as well.
    I believe that if one were to be able to fully explain dark currents in one type of device (such as semiconducting photon detectors), one would probably also get a better understanding of what is going on in e.g. superconducting qubits and ion traps.
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