# Why is spectral sensivity of a photodiode expressed in A/W

Can someone explain me the meaning of the A/W unit of the photosensivity when reading a spectral response function of the wavelength characteristic of a photodiode?

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I'm not an expert but my guess is that it refers to the current (in Ampère) produced per Watt of light incident on the photodiode. –  Wouter Feb 25 '13 at 18:58
Is electronics.stackexchange.com a better home for this question? –  Qmechanic Feb 25 '13 at 19:02
@Wouter: If this question isn't moved, then you should turn your "guess-comment" into a "fact-answer". –  KDN Feb 25 '13 at 19:06
This looks like physics to me, being focused on the device-level. Electronics.stackexchange.com seems more like circuit-level. Sorry for the misplacing though, if it is indeed misplaced. Thanks Wouter for the answer. –  arminski42 Feb 25 '13 at 19:16
I wrote up an answer as @KDN suggested, since it's more clear than a comment. –  Wouter Feb 25 '13 at 19:39
The $A/W$ units refer to the current (in Ampère) produced per Watt of light incident on the photodiode. This current-production happens when the diode operates in the so-called photoconductive mode. Since your question wasn't on the inner workings of a photodiode, I won't expand on this, but Wikipedia contains some more information if desired.