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I've been reading the particle detector section of the PDG and in point 33.2.3 they talk about Solid-state photon detectors. They say there that Silicon Photodiodes are simply a "reverse-biased p-n junction", and somewhere else I also read that semiconductors used as radiation detectors are usually inverse polarized, what is the reason for that?

Maybe too naive but, what is the difference between the Silicon photodiodes they talk about in this section (90% quantum efficiency) and the Silicon photomultipliers (SiPM) that are being used more and more in particle and astroparticle physics?

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    $\begingroup$ I think inversely polarised just means reverse biased. Can you provide some links as to where you've seen the phrase inversely polarised used? $\endgroup$
    – John Rennie
    Commented May 5, 2018 at 5:31

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In a reverse biased junction no current is running, apart from some leakage. The reason is that there is a depletion zone without charge carriers. If a photon is absorbed in the depletion zone it may create a hole and an electron, so for a brief time a current peak is detected. Count the current peaks and you have counted the photons.

https://en.wikipedia.org/wiki/Photodiode

For the difference with a SiPM see also https://en.wikipedia.org/wiki/Silicon_photomultiplier

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  • $\begingroup$ And if you reverse bias it, the depletion layer gets thicker so the probability of a photon being absorbed in the depletion layer increases. $\endgroup$
    – Jon Custer
    Commented May 7, 2018 at 13:28

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