I'm searching a few PiN Diode. But the I-V characteristics are quite different. I cannot understand why the photo current's lowest level is not 0V. and the reason of Shift. Thank you for answer
One may think of photodiode when at 0V external as effectively being reverse biased to about 0.6V (about half bandgap, for higher precision one needs to take into acount ratio of logarithm of doping concentration and doping profile). Reverse biasing means wider depletion region so more of rather penetrating red photons can be captured in depletion region and contribute to photocurrent.