Transfer Function of Photodiode
Your model seems reasonable, although for most photodiodes Rs and Cp will be very small while Ri will be very large.  If the leads on the diode are kept short, usually Ls will be small as well.  The reduces to current source driving an RC filter with time constant Rl*Ci, thus a typical photodiode looks like a first order low pass filter.
Note that Rl (the load resistance) is an external resistor in the read out circuit.  Thus you can adjust the bandwidth of a photodiode by using a larger or smaller load resistor, at least up until the point where Rl gets large enough that Ri is no longer negligible or small enough that Ls cannot be neglected.