Look at this data sheet, in the second page we have a graph for the spectral response.
Now, I have learned that photodiodes must be reverse-biased in order to get a decent signal from them, but then someone pointed out to me that all of the measurements in the data sheet are made at 0 volts, not at the reverse bias voltage, and so it would stand to reason that the spectral response was measured with 0 volts too.
Now, there must be a difference in the signal of a biased and an unbiased photodiode, right? A biased one produces a larger signal to the same amount of light intensity, right? That would mean that the spectral responses of biased and unbiased diodes are different.
Then the obvious question is, what is that difference? And for that matter, I would like to know all the properties of my photodiode at the voltage I'm going to use it at. How can I calculate those values?