A common model used to represent a photo-diode is shown below:
It is then said that the current through Rsp (series resistance) is ip+id, where ip is the current proportional to the incident luminous flux and id the dark current (constant at a given temperature).
My question is: In the model it is always shown a diode Dp, that accounts for the rectifying effect of the junction. But it can't be an ideal diode, otherwise ip+idwould flow through it and not through Rps. What is the role of this diode in the model and how does it affect the current through Rsp?