# Why isn't the saturation current of a photodiode the same as its short circuit current?

The formula I see everywhere is:

$$I_{sat} = \frac{V_{bias}}{R_L}$$

But this seems incomplete for the following reason:

The larger the resistance is the smaller the saturation current, it stands to reason then that if it was zero, we would have the greatest current the device can physically produce, but if you see the short circuit current of any photodiode like this one (second table in the data sheet) it will be very low, microamperes in this case, instead of microamperes as one would expect.

How then can I calculate the highest saturation current of a photodiode and how is it different from the saturation current?

• Where specifically do you see that formula? – Andy aka Feb 1 '19 at 12:58
• For instance at chapter 2.3.5 of "Optoelectronic Sensors" by Didier Decoster and Joseph Harari imgur.com/a/7QB8O95 Also, in this Thorlabs guide thorlabs.com/images/TabImages/Photodetector_Lab.pdf – Fernando Franco Félix Feb 1 '19 at 13:40
• Your formula for Isat clearly doesn't apply when the photodiode is used in photovoltaic mode. – The Photon Feb 1 '19 at 16:22
• On what page of that thorlabs document did you see the formula in your question? – Andy aka Feb 1 '19 at 17:17