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I am currently studying about photodiodes and came across this fact that photodiodes take quite a bit of time to come out of the saturation. What really happens during this time (after it is saturated and time it takes to come out of saturation)?

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  • \$\begingroup\$ Do you have a link or some reference. By saturation I assume you mean very high light intensity. I've seen some weird few micro second stuff in PD's, but nothing that last's for milliseconds (let alone seconds.) Or are you talking about CdS LDR's? \$\endgroup\$ – George Herold Oct 14 '14 at 13:09
  • \$\begingroup\$ yes, even if it is microseconds of time then why would it take that much of time. I could be wrong on my approximation on how much time it takes to come out of saturation. Currently, I don't have any good reference I can share. \$\endgroup\$ – dr3patel Oct 14 '14 at 16:48
  • \$\begingroup\$ Well you are the one who came across the fact that the recovery from saturation takes time. I haven't looked at it. The one weird ~10us thing I say had to do with edge effects. There were these long tails in the step response, that was due to carriers created in the (presumably) un-doped edge regions diffusing into the active region. \$\endgroup\$ – George Herold Oct 14 '14 at 17:15
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You know that when you accelerate a car and then "disengage" the motor, the car does not stop immediately. likewise, when a photodiode is "excited," it will take some time to "loose" the excitation energy and return to its previous state.

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  • \$\begingroup\$ Huh, have you used any photodiodes? Most of them have response times in the ~10 ns range. Maybe 100's of ns for the big ones. (This assumes the PD is reverse biased.) Here's a zippy one, osram-os.com/Graphics/XPic3/00118355_0.pdf If you look at the current with a big resistor you'll see an RC time (C is PD capacitance), but that's a circuit thing and not a function of the PD. \$\endgroup\$ – George Herold Oct 21 '14 at 18:19

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