1 electron = 1 photon?

Started Apr 12, 2013 | Discussions thread
cpw Regular Member • Posts: 313
Re: 1 electron = 1 photon?

Jack Hogan wrote:

gvk wrote:

There is a good summary of the photoelectric effect in silicon in Chapter 2 of Janesick's book on photon transfer. From the band gap IR cutoff at 1.0868 um to 400 nm, covering near IR through visible spectrum, only a single conduction band electron is generated per photon absorbed. For photon energy greater than 3.1 eV (< 400 nm wavelength), the photoelectron produced can have enough energy to free additional electrons by collisions; 3.1eV is more than twice the Si band gap due to the momentum conservation condition with non-direct band gap semiconductor materials mentioned earlier in this thread. For photon energy above 10 eV, the average number of electrons generated by a single photon (quantum yield) is given by the photon energy (h nu) / 3.65 eV, where 3.65 eV is the energy required to generate an electon-hole pair in Si. Hard X-ray photons, above about 10 keV, have small collision cross sections with low probability for interaction with Si.

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Very good explanation, Gerry, it fits well with my gut feeling (which is not always a good thing :-)).  Janesick's book has come up in a number of discussions, I am going to have to get me a copy.

So, as it pertains to sensors in widely available modern DSLRs, can we assume that in practice multiple electron generation happens very seldom?

Yes hi Jack,

Yes very seldom for Vis light.  To give you an idea of order of magnitudes involved, continuing along Gerry's thoughts, p. 18 of Janesick's book shows a graph of a quantum yield measurement he did on a CCD, which is monotonically increasing from about 1.005 @ 500 nm, to 1.01 @ 400 nm, to about 1.06 at 280 nm, so probabilities are low for modern Dslrs (these numbers would probably vary from sensor to sensor, but this at least gives you an idea).

Yes, I agree about Janesick's works, which I have regularly highly recommended over the years


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