I'm trying to get a reading off an InAs photodiode.
To do it i'm using an transimpedance amplifier with the PD in photovoltaic mode.
Now, with a silicon PD everything works fine, with Rf up to GΩ range.
But the InAs PD produce a varying current of about 50µA, whether it's lit or not.
This current keeps changing, from the light level and/or temperature.
My best guess is that this is caused by low shunt resistance - R0 is ~10^11Ω range for silicon, but only about 400Ω for the InAs one:
I've tried to compensate for that current by routing it away:
But that does not do a lot, since the current is extremely variable - shining the light on the PD apparently causes the photocurrent to go up, while the parasitic one goes down, so the reading rises for a moment and then rapidly falls out of range.
So, the questions are:
-Is such behaviour explained by the low shunt resistance and it's high temperature sensitivity, or there is something else at work?
-How do i compensate for that properly?
Summarily, how do you get high-sensitivity readings off an InAs photodiode?
It should be useful well into pA range, according to the descriptions.